29Spring_Autowriter的一些疑惑（很重要）

我用一个Autowriter去注解一个属性，而且我没有在Spring的配置文件中的bean.xml中注册bean(<bean id=""...);那么这个注解有用吗？答案是不行。也就是说要用Autowriter注解时，其实必须要保证在bean容器中注册过这个bean.

bean在bean容器中的注册分为两种：

1.手动：就是在spring.xml配置文件中，写上

<bean id="configa" class="com.guiugu.shen.bean2.HelloService">
    </bean>

2.自动注册，那就是要用自动扫描了。在spring.xml配置文件中写上：

<context:component-scan base-package="com.guiugu.shen.bean2"/>

自动扫描时：会去com.guiugu.shen.bean2这个包下面去寻找有没有被

@Service用于标注业务层组件

@Controller用于标注控制层组件

@Repository用于标注数据访问组件，即DAO组件

@Component泛指组件，当组件不好归类的时候，我们可以使用这个注解进行标注。

这些注解修饰过，有的话就会被自动注册到bean容器中。

只有用以上其中一个方法注册过才会用@Autowriter是有用。

案例如下：

案例结构：

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" 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先给出错误案例：

我最先的想法是：只要在applicationContext.xml中配一个自动扫描包，就可以了。如下

applicationContext.xml：

<?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"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
           http://www.springframework.org/schema/context
           http://www.springframework.org/schema/context/spring-context-3.0.xsd
           http://www.springframework.org/schema/aop
           http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
           http://www.springframework.org/schema/tx
           http://www.springframework.org/schema/tx/spring-tx-3.0.xsd"
    default-lazy-init="true">
<context:component-scan base-package="com.guiugu.shen.bean2"/>

</beans>

HelloService.java:

package com.guiugu.shen.bean2;

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

public class HelloService {

    public void sayHello()
    {
        System.out.print("hello");

    }

}

TestJavaSpring.java代码：

package com.guiugu.shen.bean2;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = "classpath:applicationContextt.xml")

public class TestJavaSpring {
    @Autowired
    private HelloService helloService;
    @Test
    public void testSayhell()
    {
        helloService.sayHello();

    }

}

运行结果：

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [com.guiugu.shen.bean2.HelloService] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}

很明显：上面的结果是找不到对应的bean.因为没有在bean容器中注册bean.

两个解决办法：1.手动在applicationContext.xml注册对应的bean.

<?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"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
           http://www.springframework.org/schema/context
           http://www.springframework.org/schema/context/spring-context-3.0.xsd
           http://www.springframework.org/schema/aop
           http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
           http://www.springframework.org/schema/tx
           http://www.springframework.org/schema/tx/spring-tx-3.0.xsd"
    default-lazy-init="true">
<!--  手动注册这个bean  >
<bean id="configa" class="com.guiugu.shen.bean2.HelloService">

    </bean>
</beans>

运行结果:正确。输出为hello。因为手动注册过了这个bean。

第二种解决办法：在applicationContext.xml用自动扫描器去扫描包。并且在HelloService上用@Component，因为这样自动扫描包才能识别。自动扫描包能识别的注解是：

@Service@Controller@Repository@Component。

ApplicationContext.xml代码:

<?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"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
           http://www.springframework.org/schema/context
           http://www.springframework.org/schema/context/spring-context-3.0.xsd
           http://www.springframework.org/schema/aop
           http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
           http://www.springframework.org/schema/tx
           http://www.springframework.org/schema/tx/spring-tx-3.0.xsd"
    default-lazy-init="true">
<--扫描到之后会自动会去注册bean-->
<context:component-scan base-package="com.guiugu.shen.bean2"/>

</beans>

HelloService代码：

package com.guiugu.shen.bean2;

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

@Component
public class HelloService {

    public void sayHello()
    {
        System.out.print("hello");

    }

}

TestJavaSpring.java:

package com.guiugu.shen.bean2;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = "classpath:applicationContextt.xml")

public class TestJavaSpring {
    @Autowired
    private HelloService helloService;
    @Test
    public void testSayhell()
    {
        helloService.sayHello();

    }

}

运行结果正确。

上面的执行流程是：

Spring启动，然后根据<context:component-scan base-package="com.guiugu.shen.bean2"/>去这个包下面去寻找被@Service@Controller@Repository@Component注册类，找到的话就把他自动注册到bean容器中。

这样当我们执行

@Autowired

private HelloService helloService;

就会从bean容器中把对应的类取出来实例化（因为之前已经注册进去了）