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Spring - Java 8 Stream support in ObjectProvider to retrieve beans stream

[Updated: Nov 1, 2018, Created: Nov 1, 2018]

Spring 5.1 added following new methods in ObjectProvider interface which provides Java 8 Stream support.


default java.util.stream.Stream<T> stream()

This method returns a sequential Stream over all matching bean instances, without specific ordering guarantees (but typically in registration order).


default java.util.stream.Stream<T> orderedStream()

This method returns a sequential Stream over all matching object instances. By default elements of the stream are pre-ordered according to the bean factory's common order comparator. We can specify our own order by using @Order annotation or by implementing Ordered`interface.


Starting Spring 5.1, ObjectProvider also extends java.lang.Iterable<T> interface, that means default methods Iterable#forEach(..) and Iterable#spliterator() can also be used, along with Iterable#iterator() which is implemented by ObjectProvider.

Examples

Example bean

public class MsgBean {
  private String msg;

  public MsgBean(String msg) {
      this.msg = msg;
  }

  public void showMessage() {
      System.out.println("msg: " + msg);
  }
    .............
}

stream() example

@Configuration
public class StreamExample {

  @Bean
  MsgBean msgBean() {
      return new MsgBean("test msg 1");
  }

  @Bean
  MsgBean msgBean2() {
      return new MsgBean("test msg 2");
  }

  public static void main(String[] args) {
      AnnotationConfigApplicationContext context =
              new AnnotationConfigApplicationContext(StreamExample.class);
      ObjectProvider<MsgBean> beanProvider = context.getBeanProvider(MsgBean.class);
      beanProvider.iterator().forEachRemaining(System.out::println);
  }
}
MsgBean{msg='test msg 1'}
MsgBean{msg='test msg 2'}

orderedStream() examples

Using @Ordered annotation

@Configuration
public class OrderedStreamExample {

  @Bean
  @Order(2)
  MsgBean msgBean() {
      return new MsgBean("test msg 1");
  }

  @Bean
  @Order(1)
  MsgBean msgBean2() {
      return new MsgBean("test msg 2");
  }

  public static void main(String[] args) {
      AnnotationConfigApplicationContext context =
              new AnnotationConfigApplicationContext(OrderedStreamExample.class);
      ObjectProvider<MsgBean> beanProvider = context.getBeanProvider(MsgBean.class);
      System.out.println("-- default order --");
      beanProvider.stream().forEach(System.out::println);
      System.out.println("-- ordered by @Order --");
      beanProvider.orderedStream().forEach(System.out::println);
  }
}
-- default order --
MsgBean{msg='test msg 1'}
MsgBean{msg='test msg 2'}
-- ordered by @Order --
MsgBean{msg='test msg 2'}
MsgBean{msg='test msg 1'}

Using Ordered interface

public class MsgBean2 implements Ordered {
  private String msg;
  private int order;

  public MsgBean2(String msg, int order) {
      this.msg = msg;
      this.order = order;
  }

  public void showMessage() {
      System.out.println("msg: " + msg);
  }

  @Override
  public int getOrder() {
      return order;
  }
    .............
}
@Configuration
public class OrderedStreamExample2 {

  @Bean
  MsgBean2 msgBean() {
      return new MsgBean2("test msg 1", 2);
  }

  @Bean
  MsgBean2 msgBean2() {
      return new MsgBean2("test msg 2", 1);
  }

  public static void main(String[] args) {
      AnnotationConfigApplicationContext context =
              new AnnotationConfigApplicationContext(OrderedStreamExample2.class);
      ObjectProvider<MsgBean2> beanProvider = context.getBeanProvider(MsgBean2.class);
      System.out.println("-- default order --");
      beanProvider.stream().forEach(System.out::println);
      System.out.println("-- ordered by Ordered interface --");
      beanProvider.orderedStream().forEach(System.out::println);
  }
}
-- default order --
MsgBean2{msg='test msg 1'}
MsgBean2{msg='test msg 2'}
-- ordered by Ordered interface --
MsgBean2{msg='test msg 2'}
MsgBean2{msg='test msg 1'}

Using Iterable methods

Using Iterable#forEach() method:

@Configuration
public class IteratorExample {

  @Bean
  MsgBean msgBean() {
      return new MsgBean("test msg 1");
  }

  @Bean
  MsgBean msgBean2() {
      return new MsgBean("test msg 2");
  }

  public static void main(String[] args) {
      AnnotationConfigApplicationContext context =
              new AnnotationConfigApplicationContext(IteratorExample.class);
      ObjectProvider<MsgBean> beanProvider = context.getBeanProvider(MsgBean.class);
      beanProvider.forEach(System.out::println);
  }
}
MsgBean{msg='test msg 1'}
MsgBean{msg='test msg 2'}

Using Iterable#iterator() method:

@Configuration
public class IteratorExample2 {

  @Bean
  MsgBean msgBean() {
      return new MsgBean("test msg 1");
  }

  @Bean
  MsgBean msgBean2() {
      return new MsgBean("test msg 2");
  }

  public static void main(String[] args) {
      AnnotationConfigApplicationContext context =
              new AnnotationConfigApplicationContext(IteratorExample2.class);
      ObjectProvider<MsgBean> beanProvider = context.getBeanProvider(MsgBean.class);
      beanProvider.iterator().forEachRemaining(System.out::println);
  }
}
MsgBean{msg='test msg 1'}
MsgBean{msg='test msg 2'}

Example Project

Dependencies and Technologies Used:

  • spring-context 5.1.2.RELEASE: Spring Context.
  • JDK 1.8
  • Maven 3.5.4

Bean Stream Retrieval via ObjectProvider Select All Download
  • spring-object-provider-bean-stream-retrieval
    • src
      • main
        • java
          • com
            • logicbig
              • example
                • StreamExample.java

    See Also