Spring 之自动化装配 bean 尝试

【Spring之自动化装配bean尝试】

1、添加dependencies如下所示（不是每一个都用得到

  <dependencies>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>4.3.9.RELEASE</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-test</artifactId>
      <version>4.3.5.RELEASE</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-core</artifactId>
      <version>4.3.7.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-beans</artifactId>
        <version>4.3.9.RELEASE</version>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12</version>
    </dependency>
  </dependencies>

2、创建可以被发现的“ bean ”

首先定义CD的概念

package soundsystem;

public interface CompactDisc {
    void play();
}

创建带有 @Component 注解的实现类

package soundsystem;
import org.springframework.stereotype.*;

@Component
public class SgtPeppers implements CompactDisc {

    private String title = "Sgt. Pepper‘s Lonely Hearts Club Band";
    private String artist = "The Beatles";

    public void play() {
        System.out.println("Playing" + title + " by " + artist);
    }
}

@Component 注解的作用

1. 表明该类会作为组件类
2. 告知 Spring 要为这个类创建 bean

3、声明组件扫描，下面这个类与 CD 实现类在同一个包下。

package soundsystem;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

@Configuration
@ComponentScan
public class CDplayerConfig {

}

注解 1 @Configuration 告知 Spring的应用上下文 要在该类中加载配置

注解 2 @ComponentScan 告知 Spring的应用上下文  要启用组件扫描，默认扫描与配置类相同的包

4、测试自动化装配 bean

package soundsystem;

import static org.junit.Assert.*;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = CDplayerConfig.class)
public class CDPlayerTest {

    @Autowired
    private CompactDisc cd;

    @Test
    public void cdShouldNotBeNull() {
        assertNotNull(cd);
    }
}

- @RunWith 创建 Spring的应用上下文

- @ContextConfiguration 加载配置 --> 启用组件扫描 --> 扫描组件，发现带 @Component 注解的 CD实现类 --> 自动创建 bean

- @Autowired 将 CD实现类 对象 注入到测试代码中

5、自动装配 bean 的数量是不限的

public class CDPlayerTest {

    @Autowired
    private CompactDisc cd;

    @Autowired
    private CompactDisc cd2;

    @Autowired
    private CompactDisc cd3;

    @Autowired
    .........

    @Autowired
    private CompactDisc cdn;

    @Test
    public void cdShouldNotBeNull() {
        assertNotNull(cd);
        assertNotNull(cd2);
    }
}