Spring装配Bean -- 自动化装配Bean

小鱼儿 2022-05-27 08:59 502阅读 0赞

## **Spring从两个角度来实现自动化装配:** ##

组件扫描(component scanning):Spring会自动发现应用上下文中所创建的Bean

自动装配(autowiring):Spring自动满足Bean之间的依赖

组件扫描和自动装配组合在一起能将显式配置降低到最少

## **创建可被发现的Bean:** ##

创建CD接口:

package main.java.Demo1;
    
    /**
     * @author myvina@qq.com
     * @date 18-4-15 下午6:53
     */
    
    public interface CompactDisc {
        void play();
    }

创建BeatlesCD类实现CD接口:

package main.java.Demo1;
    
    import org.springframework.stereotype.Component;
    
    /**
     * @author myvina@qq.com
     * @date 18-4-15 下午8:50
     */
    
    @Component
    public class BeatlesCD implements CompactDisc {
        @Override
        public void play() {
            System.out.println("Playing Beatles");
        }
    }

使用@Component注解表明该类会作为组件类.

不过组件类默认是不启用的.需要显式配置一下Spring,从而命令它去寻找带有@Component注解的类,并为其创建Bean,如下:

package main.java.Demo1;
    
    import org.springframework.context.annotation.ComponentScan;
    import org.springframework.context.annotation.Configuration;
    
    /**
     * @author myvina@qq.com
     * @date 18-4-15 下午8:54
     */
    
    @Configuration
    @ComponentScan
    public class CompactDiskConfig {
    }

类CompactDiskConfig通过Java代码定义了Spring的装配规则.

使用@Configuration注解的类表示该文件是一个配置类.

使用@ComponentScan注解表示在Spring中启用组件扫描,如果没有其他配置,会默认扫描与配置类相同的包及其子包.(也可通过XML配置来启动组件扫描,如下)

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xmlns:context="http://www.springframework.org/schema/context"
           xsi:schemaLocation="http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
    
        <context:component-scan base-package="main.java.Demo1"/>
        
    </beans>

下面来创建一个测试类:

package main.java.Demo1;
    
    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;
    
    import static org.junit.Assert.assertNotNull;
    
    /**
     * @author myvina@qq.com
     * @date 18-4-15 下午6:56
     */
    
    @RunWith(SpringJUnit4ClassRunner.class)
    @ContextConfiguration(classes = CompactDiskConfig.class)
    public class CDPlayerTest {
        @Autowired
        private BeatlesCD cd;
    
        @Test
        public void cdShouldNotNull(){
            assertNotNull(cd);
        }
    }

测试结果如下:

四月 15, 2018 9:06:30 下午 org.springframework.test.context.support.DefaultTestContextBootstrapper getDefaultTestExecutionListenerClassNames
    信息: Loaded default TestExecutionListener class names from location [META-INF/spring.factories]: [org.springframework.test.context.web.ServletTestExecutionListener, org.springframework.test.context.support.DirtiesContextBeforeModesTestExecutionListener, org.springframework.test.context.support.DependencyInjectionTestExecutionListener, org.springframework.test.context.support.DirtiesContextTestExecutionListener, org.springframework.test.context.transaction.TransactionalTestExecutionListener, org.springframework.test.context.jdbc.SqlScriptsTestExecutionListener]
    四月 15, 2018 9:06:30 下午 org.springframework.test.context.support.DefaultTestContextBootstrapper getTestExecutionListeners
    信息: Using TestExecutionListeners: [org.springframework.test.context.support.DirtiesContextBeforeModesTestExecutionListener@2ed94a8b, org.springframework.test.context.support.DependencyInjectionTestExecutionListener@38082d64, org.springframework.test.context.support.DirtiesContextTestExecutionListener@dfd3711, org.springframework.test.context.transaction.TransactionalTestExecutionListener@42d3bd8b, org.springframework.test.context.jdbc.SqlScriptsTestExecutionListener@26ba2a48]
    四月 15, 2018 9:06:31 下午 org.springframework.context.support.GenericApplicationContext prepareRefresh
    信息: Refreshing org.springframework.context.support.GenericApplicationContext@6cc4c815: startup date [Sun Apr 15 21:06:31 CST 2018]; root of context hierarchy
    
    Process finished with exit code 0

无错误,表示运行成功.

## **为组件扫描的Bean命名:** ##

@Component("name")将该组件命名为name

设置组件扫描的基础包:

@ComponentScan("packageName")设置需要扫描的基础包

还可设置扫描多个包:@ComponentScan(basePackages=\{"package1", "package2"\},这样该配置类会扫描多个包:

除了可以设置为String类型之外,还可制定包中所包含的类或接口:@ComponentScan(basePackageClasses=\{class1, class2\}

## **通过为Bean添加注解实现自动装配:** ##

package main.java.Demo1;
    
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Component;
    
    /**
     * @author myvina@qq.com
     * @date 18-4-15 下午9:16
     */
    
    @Component
    public class CDPlayer {
        private CompactDisc cd;
    
        @Autowired
        public CDPlayer(CompactDisc cd){
            this.cd = cd;
        }
    
        public void play(){
            cd.play();
        }
    }

@Autowired注解表明创建CDPlayer Bean的时候,会通过这个构造器来进行实例化并且会传入一个可设置给CompactDisc类型的Bean,该注解不仅能用在构造器上,还能用在属性的Setter方法上.

验证自动装配(紧接上一个Test):

运行结果如下:

四月 15, 2018 9:21:47 下午 org.springframework.test.context.support.DefaultTestContextBootstrapper getDefaultTestExecutionListenerClassNames
    信息: Loaded default TestExecutionListener class names from location [META-INF/spring.factories]: [org.springframework.test.context.web.ServletTestExecutionListener, org.springframework.test.context.support.DirtiesContextBeforeModesTestExecutionListener, org.springframework.test.context.support.DependencyInjectionTestExecutionListener, org.springframework.test.context.support.DirtiesContextTestExecutionListener, org.springframework.test.context.transaction.TransactionalTestExecutionListener, org.springframework.test.context.jdbc.SqlScriptsTestExecutionListener]
    四月 15, 2018 9:21:47 下午 org.springframework.test.context.support.DefaultTestContextBootstrapper getTestExecutionListeners
    信息: Using TestExecutionListeners: [org.springframework.test.context.support.DirtiesContextBeforeModesTestExecutionListener@38082d64, org.springframework.test.context.support.DependencyInjectionTestExecutionListener@dfd3711, org.springframework.test.context.support.DirtiesContextTestExecutionListener@42d3bd8b, org.springframework.test.context.transaction.TransactionalTestExecutionListener@26ba2a48, org.springframework.test.context.jdbc.SqlScriptsTestExecutionListener@5f2050f6]
    四月 15, 2018 9:21:47 下午 org.springframework.context.support.GenericApplicationContext prepareRefresh
    信息: Refreshing org.springframework.context.support.GenericApplicationContext@3a82f6ef: startup date [Sun Apr 15 21:21:47 CST 2018]; root of context hierarchy
    Playing Beatles
    
    Process finished with exit code 0

以上就为Spring中自动化装配Bean的详解.