Two ways, via:

• Constructor
• A setter

Dependency Injection in Spring

Create classes and interface to package spitter.web.services (/src/main/java/spitter/web/services folder)

• IWriter
• Writer
• NiceWriter
• WriterRunner

Ref: http://www.vogella.com/tutorials/SpringDependencyInjection/article.html

Use junit, spring-test and mockito. Download libraries from Maven, update pom.xml

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
            <version>4.3.8.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-all</artifactId>
            <version>1.9.5</version>
        </dependency>

• Create test package spitter.web.services (/src/test/java/spitter/web/services folder)
• Create test class for WriterRunner

• Create dependent and independent classes with @Component annotation

They are considered as candidates for auto detection when using configuration annotations and class-path scanning.

@Component
public class WriterRunner { ... }

@Component
public class Writer implements IWriter { ... }

• Add @Autowired to constructor or field or setter of dependent class

They will be autowired by Spring's DI facilities

    @Autowired
    public WriterRunner(IWriter writer) {
        this.writer = writer;
    }

    @Autowired
    public void setWriter(IWriter writer) { this.writer = writer; }

• Bootstrapping @Configuration, the classes may be processed by Spring container to generate beans.
  • Use @Import

  Defining the classes will be used, they no need marked as @Component

     @Configuration
     @Import({Writer.class, WriterRunner.class})
     public class WriterConfig {
     }

  • Use @ComponentScan

  Scanning all class marked as component in a package

     @Configuration
     @ComponentScan("spitter.web.services")
     public class WriterConfig {
     }

• Unit test class must be:
  • Run with Spring's runner
  • Set context configuration

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes=WriterConfig.class)
public class WriterRunnerAutoWiredTest {