Java from a Parallel Universe

Jan Ouwens





| EqualsVerifier

jqno | jqno.nl


#jspring    #paralleljava

#1

#10

#1024579 23508726

#1024579 2350x1042

#1024579 2350x10∞

Let me

help you

Language of the Year

Language of the Year


Parallel Java

Language of the Year


Parallel Java

Java for parallel computing and multi-threading

Language of the Year


Parallel Java

Java for parallel computing and multi-threading

Language of the Year


Parallel Java

Java from a Parallel Universe

Language of the Year


Parallel Java

Java without annotations

Annotations

What are they?


@Override
public int hashCode() { ... }

@Test
public void something() { ... }

@JsonTypeInfo(
  use = JsonTypeInfo.Id.NAME,
  include = JsonTypeInfo.As.PROPERTY,
  property = "type")
@JsonSubTypes({
  @Type(value = SubA.class, name = "SubA")
})
public class Something { ... }

What are they?


@Override
public int hashCode() { ... }

@Test
public void something() { ... }

@JsonTypeInfo(
  use = JsonTypeInfo.Id.NAME,
  include = JsonTypeInfo.As.PROPERTY,
  property = "type")
@JsonSubTypes({
  @Type(value = SubA.class, name = "SubA")
})
public class Something { ... }

Why?

Why?

C# had them

¯\_(ツ)_/¯


  • 2002 → C#
  • 2004 → Java
  • never → Parallel Java

Why?

Add metadata

@Override

@Deprecated

@SuppressWarnings("deprecation")

@Nonnull

Why?

Remove external configuration (xml)

@Inject

@Autowired

@Bean

Why?

Generate code

@Entity

@Data(staticConstructor = "of")

Why?

Modify runtime behavior

@Test

@Transaction(isolation = Isolation.SERIALIZABLE)

@GetMethod(value = "/endpoint/{id}",
    produces = MediaType.APPLICATION_JSON_VALUE)

How?

  • Reflection
  • Code generation

Magic

Dark     magic

The problem

The problems

The problems

Checked at runtime

The problems

The problems

Weakly typed

The problems

Weakly typed

@Autowired @Bean
@Column(name = "id")
@PostMapping("/endpoint/new")
@Test
public void waitwhat() { ... }

The problems

Stringly typed

The problems

Stringly typed

@PreAuthorize("isFullyAuthenticated")

The problems

Stringly typed

@PreAuthorize("isFullyAuthenticated()")

The problems

Discoverability

The problems

Discoverability

The problems

Debugability

The problems

Debugability


java.lang.IllegalArgumentException: Cannot find cache named 'vets' for Builder[public abstract java.util.Collection com.example.petclinic.vet.VetRepository.findAll() throws org.springframework.dao.DataAccessException] caches=[vets] | key='' | keyGenerator='' | cacheManager='' | cacheResolver='' | condition='' | unless='' | sync='false'
    at org.springframework.cache.interceptor.AbstractCacheResolver.resolveCaches(AbstractCacheResolver.java:92) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.cache.interceptor.CacheAspectSupport.getCaches(CacheAspectSupport.java:252) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.cache.interceptor.CacheAspectSupport$CacheOperationContext.(CacheAspectSupport.java:707) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.cache.interceptor.CacheAspectSupport.getOperationContext(CacheAspectSupport.java:265) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.cache.interceptor.CacheAspectSupport$CacheOperationContexts.(CacheAspectSupport.java:598) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.cache.interceptor.CacheAspectSupport.execute(CacheAspectSupport.java:345) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.cache.interceptor.CacheInterceptor.invoke(CacheInterceptor.java:61) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212) ~[spring-aop-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at com.sun.proxy.$Proxy133.findAll(Unknown Source) ~[na:na]
    at com.example.petclinic.vet.VetController.showVetList(VetController.java:44) ~[classes/:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:189) ~[spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:800) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1038) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:897) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) ~[tomcat-embed-core-9.0.16.jar:9.0.16]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.16.jar:9.0.16]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.16.jar:9.0.16]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.16.jar:9.0.16]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.16.jar:9.0.16]

The problems

Debugability


java.lang.IllegalArgumentException: Cannot find cache named 'vets' for Builder[public abstract java.util.Collection com.example.petclinic.vet.VetRepository.findAll() throws org.springframework.dao.DataAccessException] caches=[vets] | key='' | keyGenerator='' | cacheManager='' | cacheResolver='' | condition='' | unless='' | sync='false'
    at org.springframework.cache.interceptor.AbstractCacheResolver.resolveCaches(AbstractCacheResolver.java:92) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.cache.interceptor.CacheAspectSupport.getCaches(CacheAspectSupport.java:252) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.cache.interceptor.CacheAspectSupport$CacheOperationContext.(CacheAspectSupport.java:707) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.cache.interceptor.CacheAspectSupport.getOperationContext(CacheAspectSupport.java:265) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.cache.interceptor.CacheAspectSupport$CacheOperationContexts.(CacheAspectSupport.java:598) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.cache.interceptor.CacheAspectSupport.execute(CacheAspectSupport.java:345) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.cache.interceptor.CacheInterceptor.invoke(CacheInterceptor.java:61) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212) ~[spring-aop-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at com.sun.proxy.$Proxy133.findAll(Unknown Source) ~[na:na]
    at com.example.petclinic.vet.VetController.showVetList(VetController.java:44) ~[classes/:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:189) ~[spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:800) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1038) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:897) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) ~[tomcat-embed-core-9.0.16.jar:9.0.16]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.16.jar:9.0.16]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.16.jar:9.0.16]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.16.jar:9.0.16]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.16.jar:9.0.16]

The problems

Difficult path to modules due to reflection

The problems

Difficult path to modules due to reflection


WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.springframework.cglib.core.ReflectUtils$1 (jar:file:/home/huzhifeng/tmp/demo/build/libs/demo-0.0.1-SNAPSHOT.jar!/BOOT-INF/lib/spring-core-5.0.1.RELEASE.jar!/) to method java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain)
WARNING: Please consider reporting this to the maintainers of org.springframework.cglib.core.ReflectUtils$1
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

The solution

λ

Also, plain Java

Frameworks and libraries

Many existed before lambdas were introduced


  • 2004 → Annotations
  • 2014 → Lambdas

What if …

  • they dropped annotations?

  • and embraced lambdas?

Parallel Java


No annotations!


No magic!


Just plain Java

Testing

In your universe



@Test
public void indexOfReturnsTheCorrectIndex() {
    int actual = "hello world".indexOf('w');
    assertEquals(6, actual);
}

In your universe



@Test
public void indexOfReturnsTheCorrectIndex() {
    int actual = "hello world".indexOf('w');
    assertEquals(6, actual);
}

JUnit 3 👹



public void testIndexOfReturnsTheCorrectIndex() {
    int actual = "hello world".indexOf('w');
    assertEquals(6, actual);
}

JUnit 3 👹



public void testIndexOfReturnsTheCorrectIndex() {
    int actual = "hello world".indexOf('w');
    assertEquals(6, actual);
}

In the parallel universe



test("indexOf returns the correct index", () -> {
    int actual = "hello world".indexOf('w');
    assertThat(actual).isEqualTo(6);
});

In the parallel universe



test("indexOf returns the correct index", () -> {
    int actual = "hello world".indexOf('w');
    assertThat(actual).isEqualTo(6);
});

Before 2014



test("indexOf returns the correct index", new Runnable() {
    @Override
    public void run() {
        int actual = "hello world".indexOf('w');
        assertThat(actual).isEqualTo(6);
    }
});

Before 2014



test("indexOf returns the correct index", new Runnable() {
    @Override
    public void run() {
        int actual = "hello world".indexOf('w');
        assertThat(actual).isEqualTo(6);
    }
});

In the parallel universe



test("indexOf returns the correct index", () -> {
    int actual = "hello world".indexOf('w');
    assertThat(actual).isEqualTo(6);
});

λ

Pros & cons

  • Con ugly without lambdas


  • Pro clear description of test

Web

In your universe



@GetMapping("/todo/{id}")
public String getTodo(@PathVariable("id") String id) {
    return fetch(id);
}

In your universe



@GetMapping("/todo/{id}")
public String getTodo(@PathVariable("id") String id) {
    return fetch(id);
}

In your universe



@GetMapping("/todo/{id}")
public String getTodo(@PathVariable("id") String id) {
    return fetch(id);
}

In the parallel universe



get("/todo/:id", (request, response) -> {
    return fetch(request.params("id"));
});

In the parallel universe



get("/todo/:id", (request, response) -> {
    return fetch(request.params("id"));
});

Before 2014



get("/todo/:id", new Route() {
    @Override
    public Object handle(Request request, Response response) throws Exception {
        return fetch(request.params("id"));
    }
});

Before 2014



get("/todo/:id", new Route() {
    @Override
    public Object handle(Request request, Response response) throws Exception {
        return fetch(request.params("id"));
    }
});

In the parallel universe



get("/todo/:id", (request, response) -> {
    return fetch(request.params("id"));
});

λ

Separating concerns



public void defineRoutes() {
    get("/todo/:id", this::handleGet);
}

// ...

public String handleGet(Request request, Response response) {
    return fetch(request.params("id"));
}

Separating concerns



public void defineRoutes() {
    get("/todo/:id", this::handleGet);
}

// ...

public String handleGet(Request request, Response response) {
    return fetch(request.params("id"));
}

Cross-cutting concerns



before((request, response) -> {
    if (!authenticated(request)) {
        halt(401, "nope");
    }
});

Pros & Cons

  • Con ugly without lambdas


  • Pro clean separation of concerns
  • Pro generate endpoints

Database

In your universe



@Entity
@Table(name = "todo")
public class Todo {
    @Id
    @GeneratedValue
    @Column(name = "id")
    private String id;

    @Column(name = "title")
    private String title;

    public Todo() {
        // empty
    }
}

In your universe



@Entity
@Table(name = "todo")
public class Todo {
    @Id
    @GeneratedValue
    @Column(name = "id")
    private String id;

    @Column(name = "title")
    private String title;

    public Todo() {
        // empty
    }
}

In your universe



@Entity
@Table(name = "todo")
public class Todo {
    @Id
    @GeneratedValue
    @Column(name = "id")
    private String id;

    @Column(name = "title")
    private String title;

    public Todo() {
        // empty
    }
}

In your universe



@Entity
@Table(name = "todo")
public class Todo {
    @Id
    @GeneratedValue
    @Column(name = "id")
    private String id;

    @Column(name = "title")
    private String title;

    public Todo() {
        // empty
    }
}

In the parallel universe



public class Todo {
    private final String id;
    private final String title;

    // No default constructor
}

In the parallel universe



List<Todo> todos = engine.query(handle -> {
    return handle
        .createQuery("SELECT * FROM todo WHERE id = :id")
        .bind("id", id)
        .mapToBean(Todo.class)
        .list();
});

In the parallel universe



List<Todo> todos = engine.query(handle -> {
    return handle
        .createQuery("SELECT * FROM todo WHERE id = :id")
        .bind("id", id)
        .mapToBean(Todo.class)
        .list();
});

In the parallel universe



List<Todo> todos = engine.query(handle -> {
    return handle
        .createQuery("SELECT * FROM todo WHERE id = :id")
        .bind("id", id)
        .mapToBean(Todo.class)
        .list();
});

How about transactions?



String query = "SELECT * FROM todo WHERE title = :title";
String update = "UPDATE todo SET completed = TRUE WHERE id = :id";

engine.execute(handle -> {
    return handle.inTransaction(h -> {
        Todo todo = h.createQuery(query)
                .bind("title", "rewrite annotations")
                .mapToBean(Todo.class)
                .findFirst();

        h.createUpdate(update)
                .bind("id", todo.id)
                .execute();
    });
});

How about transactions?



String query = "SELECT * FROM todo WHERE title = :title";
String update = "UPDATE todo SET completed = TRUE WHERE id = :id";

engine.execute(handle -> {
    return handle.inTransaction(h -> {
        Todo todo = h.createQuery(query)
                .bind("title", "rewrite annotations")
                .mapToBean(Todo.class)
                .findFirst();

        h.createUpdate(update)
                .bind("id", todo.id)
                .execute();
    });
});

Pros & Cons

  • Con write SQL directly
  • Con still some reflection magic
  • Con duplication between code and SQL


  • Pro write SQL directly
  • Pro clean separation of concerns
  • Pro immutable domain classes

Dependency Injection

In your universe


  • Spring
  • Guice

DI with Spring

DI with Spring



public class INeedSomething {
    @Autowired
    private Something needed;
}

public class IHaveSomething {
    @Bean
    public Something something = ...;
}

DI with Spring



public class INeedSomething {
    @Autowired
    private Something needed;
}

public class IHaveSomething {
    @Bean
    public Something something = ...;
}

DI with Spring



public class INeedSomething {
    @Autowired
    private Something needed;
}

public class IHaveSomething {
    @Bean
    public Something something = ...;
}

DI with Spring



public class INeedSomething {
    @Autowired
    private Something needed;
}

public class IHaveSomething {
    @Bean
    public Something something = ...;
}

DI with Spring



public class INeedSomething {
    @Autowired
    public INeedSomething(Something needed) { ... }
}

public class IHaveSomething {
    @Bean
    public Something something = ...;
}

DI with Spring



public class INeedSomething {

    public INeedSomething(Something needed) { ... }
}

public class IHaveSomething {
    @Bean
    public Something something = ...;
}

DI with Spring

Architectural boundaries

DI with Spring



public class INeedSomething {

    public INeedSomething(Something needed) { ... }
}

public class IHaveSomething {
    @Bean
    public Something something = ...;
}

DI with Spring



public class INeedSomething {

    public INeedSomething(Something needed) { ... }
}

public class IHaveSomething {
    @Bean
    public Something something = ...;
}

DI with Spring



public class INeedSomething {

    public INeedSomething(Something needed) { ... }
}

public class Main {
    @Bean
    public Something something = ...;
}

DI with Spring



public class INeedSomething {

    public INeedSomething(Something needed) { ... }
}

public class EmployeeDAO {
    @Bean
    public Something something = ...;
}

DI with Spring



public class INeedSomething {

    public INeedSomething(Something needed) { ... }
}

public class Util {
    @Bean
    public Something something = ...;
}

DI with Spring

A mistake: no match

DI with Spring



public class INeedSomething {

    public INeedSomething(Something needed) { ... }
}

public class IHaveSomething {
    // Forgot to put @Bean here!
    public Something something = ...;
}

DI with Spring



public class INeedSomething {

    public INeedSomething(Something needed) { .. }
}

public class IHaveSomething {
    // Forgot to put @Bean here!
    public Something something = ...;
}

DI with Spring


org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'petController': Unsatisfied dependency expressed through field 'something'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.example.petclinic.model.Something' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:596) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:90) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:374) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1395) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:592) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:849) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:877) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:142) ~[spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:775) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:316) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at com.example.petclinic.PetClinicApplication.main(PetClinicApplication.java:32) [classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_181]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_181]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_181]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_181]
    at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) [spring-boot-devtools-2.1.3.RELEASE.jar:2.1.3.RELEASE]
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.example.petclinic.model.Something' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1654) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1213) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1167) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:593) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    ... 24 common frames omitted

DI with Spring


org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'petController': Unsatisfied dependency expressed through field 'something'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.example.petclinic.model.Something' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:596) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:90) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:374) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1395) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:592) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:849) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:877) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:142) ~[spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:775) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:316) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at com.example.petclinic.PetClinicApplication.main(PetClinicApplication.java:32) [classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_181]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_181]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_181]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_181]
    at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) [spring-boot-devtools-2.1.3.RELEASE.jar:2.1.3.RELEASE]
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.example.petclinic.model.Something' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1654) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1213) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1167) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:593) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    ... 24 common frames omitted

DI with Spring


org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'petController': Unsatisfied dependency expressed through field 'something'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.example.petclinic.model.Something' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:596) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:90) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:374) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1395) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:592) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:849) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:877) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:142) ~[spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:775) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:316) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at com.example.petclinic.PetClinicApplication.main(PetClinicApplication.java:32) [classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_181]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_181]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_181]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_181]
    at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) [spring-boot-devtools-2.1.3.RELEASE.jar:2.1.3.RELEASE]
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.example.petclinic.model.Something' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1654) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1213) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1167) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:593) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    ... 24 common frames omitted

DI with Spring


org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'petController': Unsatisfied dependency expressed through field 'something'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.example.petclinic.model.Something' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:596) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:90) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:374) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1395) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:592) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:849) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:877) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:142) ~[spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:775) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:316) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248) [spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
    at com.example.petclinic.PetClinicApplication.main(PetClinicApplication.java:32) [classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_181]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_181]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_181]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_181]
    at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) [spring-boot-devtools-2.1.3.RELEASE.jar:2.1.3.RELEASE]
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.example.petclinic.model.Something' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1654) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1213) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1167) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:593) ~[spring-beans-5.1.5.RELEASE.jar:5.1.5.RELEASE]
    ... 24 common frames omitted

DI with Spring

A mistake: two matches

DI with Spring



public class INeedSomething {

    public INeedSomething(Something needed) { ... }
}

public class IHaveSomething {
    @Bean
    public Something something = ...;

    @Bean
    public Something somethingElse = ...;
}

DI with Spring



public class INeedSomething {

    public INeedSomething(Something needed) { ... }
}

public class IHaveSomething {
    @Bean
    public Something something = ...;

    @Bean
    public Something somethingElse = ...;
}

DI with Spring



***************************
APPLICATION FAILED TO START
***************************

Description:

Field needed in com.example.petclinic.owner.PetController required a single bean, but 2 were found:
    - something: defined by method 'something' in class path resource [com/example/petclinic/system/CacheConfiguration.class]
    - somethingElse: defined by method 'somethingElse' in class path resource [com/example/petclinic/system/CrashController.class]


Action:

Consider marking one of the beans as @Primary, updating the consumer to accept multiple beans, or using @Qualifier to identify the bean that should be consumed



logging.level.org.springframework=OFF

DI with Spring

A mistake: cyclic dependencies

DI with Spring



public class INeedSomething {

    public INeedSomething(Something needed) { ... }
}

public class IHaveSomething {
    @Bean
    public Something something(SomethingElse somethingElse) {}

    @Bean
    public SomethingElse somethingElse(Something something) {}
}

DI with Spring



public class INeedSomething {

    public INeedSomething(Something needed) { ... }
}

public class IHaveSomething {
    @Bean
    public Something something(SomethingElse somethingElse) {}

    @Bean
    public SomethingElse somethingElse(Something something) {}
}

DI with Spring



***************************
APPLICATION FAILED TO START
***************************

Description:

The dependencies of some of the beans in the application context form a cycle:

   petController defined in file [/spring-petclinic/target/classes/org/springframework/samples/petclinic/owner/PetController.class]
┌─────┐
|  something defined in class path resource [org/springframework/samples/petclinic/owner/OwnerController.class]
↑     ↓
|  somethingElse defined in class path resource [org/springframework/samples/petclinic/owner/OwnerController.class]
└─────┘

DI with Guice

DI with Guice



public class INeedSomething {
    @Inject
    public INeedSomething(Something needed) { ... }
}

public class Module extends AbstractModule {
    public void configure() {
        bind(Something.class).toInstance(...);
    }
}

DI with Guice



public class INeedSomething {
    @Inject
    public INeedSomething(Something needed) { ... }
}

public class Module extends AbstractModule {
    public void configure() {
        bind(Something.class).toInstance(...);
    }
}

DI with Guice



public class INeedSomething {
    @Inject
    public INeedSomething(Something needed) { ... }
}

public class Module extends AbstractModule {
    public void configure() {
        bind(Something.class).toInstance(...);
    }
}

DI with Guice

A mistake: no match

DI with Guice



public class INeedSomething {
    @Inject
    public INeedSomething(Something needed) { ... }
}

public class Module extends AbstractModule {
    public void configure() {
        // bind(Something.class).toInstance(...);
    }
}

DI with Guice



public class INeedSomething {
    @Inject
    public INeedSomething(Something needed) { ... }
}

public class Module extends AbstractModule {
    public void configure() {
        // bind(Something.class).toInstance(...);
    }
}

DI with Guice



com.google.inject.CreationException: Unable to create injector, see the following errors:

1) No implementation for Something was bound.
  while locating Something
    for the 1st parameter of controllers.CountController.<init>(CountController.java:22)
  while locating controllers.CountController
    for the 3rd parameter of router.Routes.<init>(Routes.scala:38)
  at play.api.inject.RoutesProvider$.bindingsFromConfiguration(BuiltinModule.scala:123):
Binding(class router.Routes to self) (via modules: com.google.inject.util.Modules$OverrideModule -> play.api.inject.guice.GuiceableModuleConversions$$anon$4)

1 error
    at com.google.inject.internal.Errors.throwCreationExceptionIfErrorsExist(Errors.java:543)
    at com.google.inject.internal.InternalInjectorCreator.initializeStatically(InternalInjectorCreator.java:159)
    at com.google.inject.internal.InternalInjectorCreator.build(InternalInjectorCreator.java:106)
    at com.google.inject.Guice.createInjector(Guice.java:87)
    at com.google.inject.Guice.createInjector(Guice.java:78)
    at play.api.inject.guice.GuiceBuilder.injector(GuiceInjectorBuilder.scala:186)
    at play.api.inject.guice.GuiceApplicationBuilder.build(GuiceApplicationBuilder.scala:139)
    at play.api.inject.guice.GuiceApplicationLoader.load(GuiceApplicationLoader.scala:21)
    at play.core.server.DevServerStart$$anon$1.$anonfun$reload$3(DevServerStart.scala:176)
    at play.utils.Threads$.withContextClassLoader(Threads.scala:22)

DI with Guice



com.google.inject.CreationException: Unable to create injector, see the following errors:

1) No implementation for Something was bound.
  while locating Something
    for the 1st parameter of controllers.CountController.<init>(CountController.java:22)
  while locating controllers.CountController
    for the 3rd parameter of router.Routes.<init>(Routes.scala:38)
  at play.api.inject.RoutesProvider$.bindingsFromConfiguration(BuiltinModule.scala:123):
Binding(class router.Routes to self) (via modules: com.google.inject.util.Modules$OverrideModule -> play.api.inject.guice.GuiceableModuleConversions$$anon$4)

1 error
    at com.google.inject.internal.Errors.throwCreationExceptionIfErrorsExist(Errors.java:543)
    at com.google.inject.internal.InternalInjectorCreator.initializeStatically(InternalInjectorCreator.java:159)
    at com.google.inject.internal.InternalInjectorCreator.build(InternalInjectorCreator.java:106)
    at com.google.inject.Guice.createInjector(Guice.java:87)
    at com.google.inject.Guice.createInjector(Guice.java:78)
    at play.api.inject.guice.GuiceBuilder.injector(GuiceInjectorBuilder.scala:186)
    at play.api.inject.guice.GuiceApplicationBuilder.build(GuiceApplicationBuilder.scala:139)
    at play.api.inject.guice.GuiceApplicationLoader.load(GuiceApplicationLoader.scala:21)
    at play.core.server.DevServerStart$$anon$1.$anonfun$reload$3(DevServerStart.scala:176)
    at play.utils.Threads$.withContextClassLoader(Threads.scala:22)

DI with Guice

A mistake: two matches

DI with Guice



public class INeedSomething {
    @Inject
    public INeedSomething(Something needed) { ... }
}

public class Module extends AbstractModule {
    public void configure() {
        bind(Something.class).toInstance(...);
        bind(Something.class).toInstance(...);
    }
}

DI with Guice



public class INeedSomething {
    @Inject
    public INeedSomething(Something needed) { ... }
}

public class Module extends AbstractModule {
    public void configure() {
        bind(Something.class).toInstance(...);
        bind(Something.class).toInstance(...);
    }
}

DI with Guice



com.google.inject.CreationException: Unable to create injector, see the following errors:

1) A binding to Something was already configured at Module.configure(Module.java:29) (via modules: com.google.inject.util.Modules$OverrideModule -> Module).
  at Module.configure(Module.java:30) (via modules: com.google.inject.util.Modules$OverrideModule -> Module)

1 error
    at com.google.inject.internal.Errors.throwCreationExceptionIfErrorsExist(Errors.java:543)
    at com.google.inject.internal.InternalInjectorCreator.initializeStatically(InternalInjectorCreator.java:159)
    at com.google.inject.internal.InternalInjectorCreator.build(InternalInjectorCreator.java:106)
    at com.google.inject.Guice.createInjector(Guice.java:87)
    at com.google.inject.Guice.createInjector(Guice.java:78)
    at play.api.inject.guice.GuiceBuilder.injector(GuiceInjectorBuilder.scala:186)
    at play.api.inject.guice.GuiceApplicationBuilder.build(GuiceApplicationBuilder.scala:139)
    at play.api.inject.guice.GuiceApplicationLoader.load(GuiceApplicationLoader.scala:21)
    at play.core.server.DevServerStart$$anon$1.$anonfun$reload$3(DevServerStart.scala:176)
    at play.utils.Threads$.withContextClassLoader(Threads.scala:22)

DI with Guice



com.google.inject.CreationException: Unable to create injector, see the following errors:

1) A binding to Something was already configured at Module.configure(Module.java:29) (via modules: com.google.inject.util.Modules$OverrideModule -> Module).
  at Module.configure(Module.java:30) (via modules: com.google.inject.util.Modules$OverrideModule -> Module)

1 error
    at com.google.inject.internal.Errors.throwCreationExceptionIfErrorsExist(Errors.java:543)
    at com.google.inject.internal.InternalInjectorCreator.initializeStatically(InternalInjectorCreator.java:159)
    at com.google.inject.internal.InternalInjectorCreator.build(InternalInjectorCreator.java:106)
    at com.google.inject.Guice.createInjector(Guice.java:87)
    at com.google.inject.Guice.createInjector(Guice.java:78)
    at play.api.inject.guice.GuiceBuilder.injector(GuiceInjectorBuilder.scala:186)
    at play.api.inject.guice.GuiceApplicationBuilder.build(GuiceApplicationBuilder.scala:139)
    at play.api.inject.guice.GuiceApplicationLoader.load(GuiceApplicationLoader.scala:21)
    at play.core.server.DevServerStart$$anon$1.$anonfun$reload$3(DevServerStart.scala:176)
    at play.utils.Threads$.withContextClassLoader(Threads.scala:22)

DI with Spring

A mistake: cyclic dependencies


Probably possible?

In the parallel universe


Manual DI

Manual DI



public class INeedSomething {
    public INeedSomething(Something needed) { ... }
}

public class Main {
    public static void main(String... args) {
        Something needed = ...;
        INeedSomething iNeedSomething =
            new INeedSomething(needed);
    }
}

Manual DI



public class INeedSomething {
    public INeedSomething(Something needed) { ... }
}

public class Main {
    public static void main(String... args) {
        Something needed = ...;
        INeedSomething iNeedSomething =
            new INeedSomething(needed);
    }
}

Manual DI



public class INeedSomething {
    public INeedSomething(Something needed) { ... }
}

public class Main {
    public static void main(String... args) {
        Something needed = ...;
        INeedSomething iNeedSomething =
            new INeedSomething(needed);
    }
}

Manual DI



public class INeedSomething {
    public INeedSomething(Something needed) { ... }
}

public class Main {
    public static void main(String... args) {
        Something needed = ...;
        INeedSomething iNeedSomething =
            new INeedSomething(needed);
    }
}

Manual DI

A mistake: no matches

Manual DI



public class INeedSomething {
    public INeedSomething(Something needed) { ... }
}

public class Main {
    public static void main(String... args) {
        // Something needed = ...;
        INeedSomething iNeedSomething =
            new INeedSomething(needed);
    }
}

Manual DI



public class INeedSomething {
    public INeedSomething(Something needed) { ... }
}

public class Main {
    public static void main(String... args) {
        // Something needed = ...;
        INeedSomething iNeedSomething =
            new INeedSomething(needed);
    }
}

Manual DI



[ERROR] COMPILATION ERROR :
[ERROR] [...]/Main.java:[34,82] cannot find symbol
  symbol:   variable needed
  location: class nl.jqno.paralleljava.Main

Manual DI

A mistake: two matches

Manual DI



public class INeedSomething {
    public INeedSomething(Something needed) { ... }
}

public class Main {
    public static void main(String... args) {
        Something needed = ...;
        Something somethingElse = ...;
        INeedSomething iNeedSomething =
            new INeedSomething(???);
    }
}

Manual DI



public class INeedSomething {
    public INeedSomething(Something needed) { ... }
}

public class Main {
    public static void main(String... args) {
        Something needed = ...;
        Something somethingElse = ...;
        INeedSomething iNeedSomething =
            new INeedSomething(???);
    }
}

Manual DI

A mistake: cyclic dependencies

Manual DI



public class Something {
    public Something(SomethingElse needed) { ... }
}

public class SomethingElse {
    public SomethingElse(Something needed) { ... }
}

public class Main {
    public static void main(String... args) {
        Something s = new Something(...);
        SomethingElse se = new SomethingElse(s);
    }
}

Manual DI



public class Something {
    public Something(SomethingElse needed) { ... }
}

public class SomethingElse {
    public SomethingElse(Something needed) { ... }
}

public class Main {
    public static void main(String... args) {
        Something s = new Something(...);
        SomethingElse se = new SomethingElse(s);
    }
}

Manual DI



public class Something {
    public Something(SomethingElse needed) { ... }
}

public class SomethingElse {
    public SomethingElse(Something needed) { ... }
}

public class Main {
    public static void main(String... args) {
        Something s = new Something(...);
        SomethingElse se = new SomethingElse(s);
    }
}

Manual DI



public class Something {
    public Something(SomethingElse needed) { ... }
}

public class SomethingElse {
    public SomethingElse(Something needed) { ... }
}

public class Main {
    public static void main(String... args) {
        SomethingElse se = new SomethingElse(...);
        Something s = new Something(se);
    }
}

Manual DI


Illegal states are

unrepresentable

Pros & Cons

  • Con some boilerplate
  • Con one dirty class

Pros & Cons

  • Con some boilerplate
  • Con one dirty class

over Spring and Guice

  • Pro illegal states unrepresentable
  • Pro problems found at compile time

Pros & Cons

  • Con some boilerplate
  • Con one dirty class

over Spring

  • Pro illegal states unrepresentable
  • Pro problems found at compile time
  • Pro clear architectural boundaries
  • Pro boots much faster

Pros & Cons

  • Con some boilerplate

Pros & Cons

  • Pro some boilerplate

Pros & Cons

  • Pro some boilerplate


  • Everything is explicit
  • Everything is in the same place

Pros & Cons

  • Pro some boilerplate


Helps discovering a new project

Pros & Cons

  • Pro some boilerplate


Helps when things get complicated

Other annotations

Bad annotations

  • Serialization
  • Validation
  • Code generation

So-so annotations

  • @NonNull
  • @Immutable
  • @SuppressWarnings

Good annotations

  • @Override
  • @Deprecated

Parallel Java

Yeah right



It’s all real

TodoBackend.com

TodoBackend.com

fully compliant

Some code

Some code


modelVersion: 4.0.0
groupId: nl.jqno.paralleljava
artifactId: parallel-java
version: 1.0
packaging: jar
name: parallel-java

properties: {
  encoding: utf-8,
  maven.compiler.source: 11,
  maven.compiler.target: 11
}

dependencies:
  - { groupId: com.sparkjava, artifactId: spark-core, version: 2.7.2 }
  - { groupId: com.google.code.gson, artifactId: gson, version: 2.8.5 }
  - { groupId: org.jdbi, artifactId: jdbi3-core }
  - { groupId: org.postgresql, artifactId: postgresql, version: 42.2.5 }

Some code


modelVersion: 4.0.0
groupId: nl.jqno.paralleljava
artifactId: parallel-java
version: 1.0
packaging: jar
name: parallel-java

properties: {
  encoding: utf-8,
  maven.compiler.source: 11,
  maven.compiler.target: 11
}

dependencies:
  - { groupId: com.sparkjava, artifactId: spark-core, version: 2.7.2 }
  - { groupId: com.google.code.gson, artifactId: gson, version: 2.8.5 }
  - { groupId: org.jdbi, artifactId: jdbi3-core }
  - { groupId: org.postgresql, artifactId: postgresql, version: 42.2.5 }

Some code


<module name = "Checker">
    <property name="charset" value="UTF-8"/>
    <property name="severity" value="error"/>

    <module name="TreeWalker">
        <module name="Regexp">
            <property name="format" value="@"/>
            <property name="illegalPattern" value="true"/>
            <property name="ignoreComments" value="true"/>
            <property name="message" value="Annotations are not allowed!"/>
        </module>
    </module>
</module>

Some code


<module name = "Checker">
    <property name="charset" value="UTF-8"/>
    <property name="severity" value="error"/>

    <module name="TreeWalker">
        <module name="Regexp">
            <property name="format" value="@"/>
            <property name="illegalPattern" value="true"/>
            <property name="ignoreComments" value="true"/>
            <property name="message" value="Annotations are not allowed!"/>
        </module>
    </module>
</module>

Some code


<module name = "Checker">
    <property name="charset" value="UTF-8"/>
    <property name="severity" value="error"/>

    <module name="TreeWalker">
        <module name="Regexp">
            <property name="format" value="@"/>
            <property name="illegalPattern" value="true"/>
            <property name="ignoreComments" value="true"/>
            <property name="message" value="Annotations are not allowed!"/>
        </module>
    </module>
</module>

Some code


<module name = "Checker">
    <property name="charset" value="UTF-8"/>
    <property name="severity" value="error"/>

    <module name="TreeWalker">
        <module name="Regexp">
            <property name="format" value="@"/>
            <property name="illegalPattern" value="true"/>
            <property name="ignoreComments" value="true"/>
            <property name="message" value="Annotations are not allowed!"/>
        </module>
    </module>
</module>

Some code


public void architecture() {
    test("only SparkServer and SparkServerTest access Spark classes", () -> {
        assertBoundary("spark..", SparkServer.class.getPackage());
    });

    test("only DatabaseRepository accesses Engine classes", () -> {
        assertBoundary("org.jdbi..", DatabaseRepository.class.getPackage());
    });
}

Some code


public void run() {
    port(port);
    enableCors();

    get(endpoint, (req, resp) -> controller.get());
    get(endpoint + "/:id", (req, resp) -> controller.get(req.params("id")));
    post(endpoint, (req, resp) -> controller.post(req.body()));
}

Some code


public Try<Void> create(Todo todo) {
    return engine.execute(handle -> {
        String sql = "INSERT INTO todo (id, title, completed, index)" +
            "VALUES (:id, :title, :completed, :order)";
        return handle.createUpdate(sql)
            .bind("id", todo.id().toString())
            .bind("title", todo.title())
            .bind("completed", todo.completed())
            .bind("order", todo.order())
            .execute());
    }
}

Some code


public class Main {
    public static void main(String... args) {
        LoggerFactory loggerFactory =
                c -> new Slf4jLogger(org.slf4j.LoggerFactory.getLogger(c));

        // ...

        var todoMapper = new TodoMapper(fullUrl);
        var dbEngine = new JdbiEngine(jdbcUrl, todoMapper, loggerFactory);
        var repository = new DatabaseRepository(dbEngine);

        var idGenerator = new RandomIdGenerator();
        var serializer = GsonSerializer.create(loggerFactory);
        var controller = new DefaultController(fullUrl, repository, idGenerator, serializer, loggerFactory);
        var server = new SparkServer(Environment.ENDPOINT, port, controller, loggerFactory);

        var runner = new Runner(repository, server, loggerFactory);
        runner.startup();
    }
}

Libraries used

PicoTest

Code


Conclusion

Conclusion

Think about your libraries


Do you really need them?

Are they good citizens?

Conclusion

Think about your frameworks


Will they infect your architecture?

Are there alternatives?

(Spring Functional Web Framework)

Conclusion

Think about your languages

Language of the Year

Conclusion

Think about your languages

Language of the Year

Scala

Conclusion

Think about your languages

Language of the Year

Kotlin

Conclusion

Think about your languages

Language of the Year

Parallel Java

Conclusion

Think about your universe

Rate this session

in the J-Spring app

Questions?


jqno.nl/talks/paralleljava

    #jspring    #paralleljava

Photo credits: Hafidh Satyanto, freestocks.org and Mitch Lensink on Unsplash - Joke credit: Ryan North