Spring：Bean的自动装配AutoWiring

首先一张图，说明都有什么装配方式：

下面分别给出byName，byType和Constructor三种自动装配方式的例子。

1.byName

//1.xml文件
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd" 
        default-autowire="byName">
        
        <bean id="autoWiringService" class="com.imooc.autowiring.AutoWiringService" ></bean>
        <bean id="autoWiringDAO" class="com.imooc.autowiring.AutoWiringDAO" ></bean>
 </beans>

//2.Service类
package com.imooc.autowiring;

public class AutoWiringService {
	
	private AutoWiringDAO autoWiringDAO;
	//set方法必须加上，写上标识输出语句
	public void setAutoWiringDAO(AutoWiringDAO autoWiringDAO) {
		System.out.println("setAutoWiringDAO");
		this.autoWiringDAO = autoWiringDAO;
	}
	
	public void say(String word) {
		this.autoWiringDAO.say(word);
	}

}

//3.DAO类
package com.imooc.autowiring;

public class AutoWiringDAO {
	//只有一个say（）方法
	public void say(String word) {
		System.out.println("AutoWiringDAO : " + word);
	}

}

//测试类
package com.imooc.test.autowiring;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.BlockJUnit4ClassRunner;

import com.imooc.autowiring.AutoWiringService;
import com.imooc.test.base.UnitTestBase;

@RunWith(BlockJUnit4ClassRunner.class)
public class TestAutoWiring extends UnitTestBase {
	
	public TestAutoWiring() {
		super("classpath:spring-autowiring.xml");
	}
	
	@Test
	public void testSay() {
		AutoWiringService service = super.getBean("autoWiringService");
		service.say(" this is a test");
	}

}

输出结果为：

8月 02, 2018 2:08:53 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
信息: Refreshing [e-mail]146044d7: startup date [Thu Aug 02 14:08:53 CST 2018]; root of context hierarchy
8月 02, 2018 2:08:53 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [spring-autowiring.xml]
setAutoWiringDAO
AutoWiringDAO :  this is a test
8月 02, 2018 2:08:54 下午 org.springframework.context.support.AbstractApplicationContext doClose
信息: Closing [e-mail]146044d7: startup date [Thu Aug 02 14:08:53 CST 2018]; root of context hierarchy

从输出结果可以看出，通过name的方式在bean容器中自动查找到了autoWiringDAO对象，并且注入到了service的set方法中，第一句输出可以看出是通过set方法注入的。

2.byType方式

这个其他部分和byName方式一样，只是xml文件改为：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd" 
        default-autowire="byType">
        
        <bean id="autoWiringService" class="com.imooc.autowiring.AutoWiringService" ></bean> 
        <bean  class="com.imooc.autowiring.AutoWiringDAO" ></bean>
 </beans>

xml文件中还去掉了类AutoWiringDAO的id，实验结果

8月 02, 2018 2:22:22 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
信息: Refreshing [e-mail]146044d7: startup date [Thu Aug 02 14:22:22 CST 2018]; root of context hierarchy
8月 02, 2018 2:22:22 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [spring-autowiring.xml]
setAutoWiringDAO
AutoWiringDAO :  this is a test
8月 02, 2018 2:22:22 下午 org.springframework.context.support.AbstractApplicationContext doClose
信息: Closing [e-mail]: startup date [Thu Aug 02 14:22:22 CST 2018]; root of context hierarchy

一样，在bean容器中找到了对应的bean并注入到set方法。

3.constructor方式，这种方式采用的是type形式的寻找，所以xml文件可以写做：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd" 
        default-autowire="byType">
        
        <bean id="autoWiringService" class="com.imooc.autowiring.AutoWiringService" ></bean>
        <bean  class="com.imooc.autowiring.AutoWiringDAO" ></bean>
 </beans>

同时，service类里面加入构造函数

package com.imooc.autowiring;

public class AutoWiringService {
	
	private AutoWiringDAO autoWiringDAO;
	
	public AutoWiringService(AutoWiringDAO autoWiringDAO) {
		System.out.println("AutoWiringService");
		this.autoWiringDAO = autoWiringDAO;
	}

	public void setAutoWiringDAO(AutoWiringDAO autoWiringDAO) {
		System.out.println("setAutoWiringDAO");
		this.autoWiringDAO = autoWiringDAO;
	}
	
	public void say(String word) {
		this.autoWiringDAO.say(word);
	}

}

输出结果为：

8月 02, 2018 2:24:53 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
信息: Refreshing [e-mail]146044d7: startup date [Thu Aug 02 14:24:53 CST 2018]; root of context hierarchy
8月 02, 2018 2:24:53 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [spring-autowiring.xml]
AutoWiringService
AutoWiringDAO :  this is a test
8月 02, 2018 2:24:53 下午 org.springframework.context.support.AbstractApplicationContext doClose
信息: Closing [e-mail]146044d7: startup date [Thu Aug 02 14:24:53 CST 2018]; root of context hierarchy

从结果信息看出，这种方式在没有id的情况下，仍然找到了相应的bean，验证了type寻找方式。

同时可以看出，这次是注入到service的构造函数，而不是set函数。