Spring自定义@Qualifier注解

其他 2018-08-09 14:16:23 阅读次数: 0

正常情况下，注入bean时，如果存在多个资源，就会出错，可以用@Qualifier指定名字，如下

比如有一个Speak接口

package shuai.spring.study.zhujie;

public interface Speak {
    public void speak();

}

有两个实现Hello，Nihao 

package shuai.spring.study.zhujie;

public class SpeakHello implements Speak {

    @Override
    public void speak() {
        System.out.println("hello");
    }

}

package shuai.spring.study.zhujie;

public class SpeakNihao implements Speak {

    @Override
    public void speak() {
        System.out.println("nihao");
    }

}

配置文件可以这么写 

<?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" 
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans 
        http://www.springframework.org/schema/beans/spring-beans.xsd 
        http://www.springframework.org/schema/aop 
        http://www.springframework.org/schema/aop/spring-aop.xsd 
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">
        
        <context:annotation-config/>
        
        <bean id="speakHello" class="shuai.spring.study.zhujie.SpeakHello"/>
        
     <bean id="speakNihao" class="shuai.spring.study.zhujie.SpeakNihao"/>
        
     <bean id="hello" class="shuai.spring.study.HelloImpl6"/>


</beans>

然后需要注入Speak的HelloImpl6,java可以这样写 

package shuai.spring.study;

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

import shuai.spring.study.zhujie.Speak;

public class HelloImpl6 implements HelloApi {

    private Speak speak;

    public Speak getSpeak() {
        return speak;
    }

    @Autowired
    public void setSpeak(@Qualifier("speakNihao") Speak speak) {
        this.speak = speak;
    }

    @Override
    public void sayHello() {
        speak.speak();
    }

}

使用@Autowired自动注入，使用@Qualifier("speakNihao")确定注入的是具体的是什么，因为speakNihao和speakHello都是Speak类型的。

其实可以自定义一个注解，就可以不用@Qualifier("speakNihao")这种形式了。

先定义两个自定义注解

package shuai.spring.study.zhujie;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

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

@Target({ ElementType.TYPE, ElementType.FIELD, ElementType.PARAMETER })
@Retention(RetentionPolicy.RUNTIME)
@Qualifier
public @interface Nihao {
}

package shuai.spring.study.zhujie;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

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

@Target({ ElementType.TYPE, ElementType.FIELD, ElementType.PARAMETER })
@Retention(RetentionPolicy.RUNTIME)
@Qualifier
public @interface Nihao {
}

上面的两个注解@Target、@Retention的意思可以看下面的连接，感觉每个自定义注解都得有

http://blog.csdn.net/sw5131899/article/details/54947192

配置文件修改下

<?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"
    xmlns:aop="http://www.springframework.org/schema/aop" 
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans 
        http://www.springframework.org/schema/beans/spring-beans.xsd 
        http://www.springframework.org/schema/aop 
        http://www.springframework.org/schema/aop/spring-aop.xsd 
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">
        
        <context:annotation-config/>
        
        <bean class="shuai.spring.study.zhujie.SpeakHello">
        	<qualifier type="shuai.spring.study.zhujie.Hello"/>
        </bean>
        
        <bean class="shuai.spring.study.zhujie.SpeakNihao">
        	<qualifier type="shuai.spring.study.zhujie.Nihao"/>
        </bean>
        
        <bean id="hello" class="shuai.spring.study.HelloImpl6"/>


</beans>

HelloImpl6修改下 

package shuai.spring.study;

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

import shuai.spring.study.zhujie.Nihao;
import shuai.spring.study.zhujie.Speak;

public class HelloImpl6 implements HelloApi {

    private Speak speak;

    public Speak getSpeak() {
        return speak;
    }

    @Autowired
    public void setSpeak(@Nihao Speak speak) {
        this.speak = speak;
    }

    @Override
    public void sayHello() {
        speak.speak();
    }

}

注意那个注解@Nihao

测试一下

package shuai.spring.test;

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

import shuai.spring.study.HelloApi;

public class HelloTest {
    @Test
    public void testHelloWorld() {

        @SuppressWarnings("resource")
        ApplicationContext context = new ClassPathXmlApplicationContext("HelloWorld.xml");

        HelloApi helloApi = context.getBean("hello", HelloApi.class);
        helloApi.sayHello();
    }
}

测试结果：

nihao


带参数的自定义注解

上面的例子需要写两个自定义注解，也可以写到一起，用参数做区分就行了

定义一个自定义注解

package shuai.spring.study.zhujie;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

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

@Target({ ElementType.TYPE, ElementType.FIELD, ElementType.PARAMETER })
@Retention(RetentionPolicy.RUNTIME)
@Qualifier
public @interface MySpeak {
    String name();

    String note();

}
也可以给参数默认值 

String note() default "good";

修改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"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:aop="http://www.springframework.org/schema/aop" 
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans 
        http://www.springframework.org/schema/beans/spring-beans.xsd 
        http://www.springframework.org/schema/aop 
        http://www.springframework.org/schema/aop/spring-aop.xsd 
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">
        
        <context:annotation-config/>
        
        <bean class="shuai.spring.study.zhujie.SpeakHello">
        	<qualifier type="shuai.spring.study.zhujie.MySpeak">
        		<attribute key="name" value="hello"/>
        		<attribute key="note" value="well"/>
        	</qualifier>
        </bean>
        
        <bean class="shuai.spring.study.zhujie.SpeakNihao">
        	<qualifier type="shuai.spring.study.zhujie.MySpeak">
        		<attribute key="name" value="nihao"/>
        		<attribute key="note" value="good"/>
        	</qualifier>
        </bean>
        
        <bean id="hello" class="shuai.spring.study.HelloImpl6"/>


</beans>
修改HelloImpl6 
package shuai.spring.study;

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

import shuai.spring.study.zhujie.MySpeak;
import shuai.spring.study.zhujie.Speak;

public class HelloImpl6 implements HelloApi {

    private Speak speak;

    public Speak getSpeak() {
        return speak;
    }

    @Autowired
    public void setSpeak(@MySpeak(name = "hello", note = "well") Speak speak) {
        this.speak = speak;
    }

    @Override
    public void sayHello() {
        speak.speak();
    }

}

注解的参数值要跟配置文件对应上。

如果使用有默认值，那个参数就可以不写了

@Autowired
public void setSpeak(@MySpeak(name = "nihao") Speak speak) {
   this.speak = speak;
}

用上面的测试测试结果是一样的。

配置文件还可以这么写

<?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" 
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans 
        http://www.springframework.org/schema/beans/spring-beans.xsd 
        http://www.springframework.org/schema/aop 
        http://www.springframework.org/schema/aop/spring-aop.xsd 
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">
        
        <context:annotation-config/>
        
        <bean class="shuai.spring.study.zhujie.SpeakHello">
        	<meta key="name" value="hello"/>
        	<meta key="note" value="well"/>
        </bean>
        
        <bean class="shuai.spring.study.zhujie.SpeakNihao">
        	<meta key="name" value="nihao"/>
        	<meta key="note" value="good"/>
        </bean>
        
        <bean id="hello" class="shuai.spring.study.HelloImpl6"/>
 
</beans>

【摘抄】开发者也可以启用<meta/>元素，配置示例如下。当在同一受管Bean中同时指定<qualifier/>和<meta/>元素时，DI容器会优先使用<qualifier/>

貌似不用指定自定义注解类的位置

http://book.51cto.com/art/201004/193381.htm


上面的自定义注解类我们都加了@Qualifier，如果不加，可以在配置文件里注册

比如把MySpeak上面的@Qualifier去掉，然后修改配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:aop="http://www.springframework.org/schema/aop" 
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans 
        http://www.springframework.org/schema/beans/spring-beans.xsd 
        http://www.springframework.org/schema/aop 
        http://www.springframework.org/schema/aop/spring-aop.xsd 
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">
        
        <context:annotation-config/>
        
        <bean class="shuai.spring.study.zhujie.SpeakHello">
        	<meta key="name" value="hello"/>
        	<meta key="note" value="well"/>
        </bean>
        
        <bean class="shuai.spring.study.zhujie.SpeakNihao">
        	<meta key="name" value="nihao"/>
        	<meta key="note" value="good"/>
        </bean>
        
        <bean id="hello" class="shuai.spring.study.HelloImpl6"/>

	<bean id="customAutowireConfigurer" class="org.springframework.beans.factory.annotation.CustomAutowireConfigurer">  
	    <property name="customQualifierTypes">  
	        <set>  
	            <value>shuai.spring.study.zhujie.MySpeak</value>  
	        </set>  
	    </property>  
	</bean> 

</beans>

就是在后面加一个bean，【引用】注解没有应用类一级的@Qualifier注解时，开发者必须借助如下对象注册它。（就是最下面那个bean）


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