Spring学习（8）--- @Autowired注解(一)-优快云博客

本文链接：https://blog.youkuaiyun.com/Json_wangqiang/article/details/85276086

本文详细介绍了Spring框架中@Autowired注解的使用方式，包括将其应用于传统setter方法、构造器和成员变量，以及如何通过配置避免autowiring失败。通过创建接口和其实现类，并使用XML配置进行实例化，演示了@Autowired注解在实际项目中的应用。此外，展示了如何在单元测试中验证注解功能，确保其正确性。

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Spring学习（8）--- @Autowired注解(一)

可以将@Autowired注解为“传统”的setter方法

package com.mypackage;

import org.springframework.beans.factory.annotation.Autowired;

public class SimpleMovieLister {
	private MovieFinder movieFinder;

	@Autowired
	public void setMovieFinder(MovieFinder movieFinder) {
		this.movieFinder = movieFinder;
	}
	
	//.....
}

可用于构造器或成员变量

package com.mypackage;

import org.springframework.beans.factory.annotation.Autowired;

public class SimpleMovieLister {
	
	@Autowired
	private BeanAnnotation beanAnnotation;
	
	private MovieFinder movieFinder;

	@Autowired
	public void setMovieFinder(MovieFinder movieFinder) {
		this.movieFinder = movieFinder;
	}
	
	//.....
}

默认情况下，如果因找不到合适的bean将会导致autowiring失败抛出异常，可以通过下面的方式避免

package com.mypackage;

import org.springframework.beans.factory.annotation.Autowired;

public class SimpleMovieLister {
	private MovieFinder movieFinder;

	@Autowired(required=false)
	public void setMovieFinder(MovieFinder movieFinder) {
		this.movieFinder = movieFinder;
	}
	
	//.....
}

每个类只能有一个构造器被标记为required=true
@Autowired的必要属性，建议会用@Required注解

例子：

先新建两个接口（InjectionService、InjectionDAO），及实现类

package com.mypackage;

public interface InjectionDAO {
	
	public void save(String args);
}

package com.mypackage;

import org.springframework.stereotype.Repository;

@Repository
public class InjectionDAOImpl implements InjectionDAO {

	public void save(String args) {
		//模拟数据库操作
		System.out.println("DAO保存数据：" + args);
	}

}

package com.mypackage;

public interface InjectionService {

	public void save(String args);
}

package com.mypackage;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class InjectionServiceImpl implements InjectionService{

	@Autowired
	private InjectionDAO injectionDAO;

	public void save(String s){
		//模拟业务操作
		System.out.println("Service接收参数:"+s);
		s=s+":"+this.hashCode();
		injectionDAO.save(s);
	}
}

XML配置：

<?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-4.1.xsd
            http://www.springframework.org/schema/context
            http://www.springframework.org/schema/context/spring-context-4.1.xsd">
        
        <context:component-scan base-package="com.mypackage">
        </context:component-scan>    
</beans>

单元测试：

package com.mypackage;

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;


public class UnitTest {
	
	@Test
	public void testAutoWired(){
		ApplicationContext context = new ClassPathXmlApplicationContext("classpath:spring-beanannotation.xml");  
		InjectionService service=(InjectionService)context.getBean("injectionServiceImpl");
		service.save("this is autowired");;
		
	}
}

结果：

2015-7-6 15:52:26 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@1342a80d: startup date [Mon Jul 06 15:52:26 CST 2015]; root of context hierarchy
2015-7-6 15:52:26 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [spring-beanannotation.xml]
Service接收参数:this is autowired
DAO保存数据：this is autowired:1811560891

@Autowired也可应用于构造器

修改InjectionServiceImpl实现类（添加setter）

package com.mypackage;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class InjectionServiceImpl implements InjectionService{
	
	private InjectionDAO injectionDAO;
	
	@Autowired
	public void setInjectionDAO(InjectionDAO injectionDAO) {
		this.injectionDAO = injectionDAO;
	}

	public void save(String s){
		//模拟业务操作
		System.out.println("Service接收参数:"+s);
		s=s+":"+this.hashCode();
		injectionDAO.save(s);
	}
}

测试结果：

2015-7-6 15:55:23 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@939b78e: startup date [Mon Jul 06 15:55:23 CST 2015]; root of context hierarchy
2015-7-6 15:55:23 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [spring-beanannotation.xml]
Service接收参数:this is autowired
DAO保存数据：this is autowired:1860295362