@Autowired 和 @Qualifier

一 无冲突

bean工厂

<?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-4.1.xsd">

    <!-- here1 -->
    <context:annotation-config />

    <beans>
        <bean id="person" class="cn.zno.hello.Person" >
            <property name="name" value="XiaoMing"></property>
            <property name="age" value="22"></property>
            <property name="savings" value="10000"></property>
        </bean>

        <bean id="car" class="cn.zno.hello.Car">
            <property name="brand" value="BYD"></property>
            <property name="price" value="54000"></property>
        </bean>
    </beans>

</beans>

测试主函数

    public static void main(String[] args) {

        ApplicationContext ctx = new ClassPathXmlApplicationContext("Beans.xml");

        Person person = (Person) ctx.getBean("person");//here2
        // Person person = new Person(); //here3
        System.out.println(person);
    }

javebean 片段

public class Person {

    private String name;

    private int age;

    private double savings;

    @Autowired
    private Car car;

    public void say(){
        System.out.println("Hello World!");
    }

    ...

说明：

here1 开启自动注入

here3 通过 new 的方式无法自动注入

here2 从bean工厂取的bean可以自动注入

二有冲突

package cn.zno.testmybatis;

public class QualifierBean {

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

    <bean id="a" class="cn.zno.testmybatis.QualifierBean">
        <property name="name" value="a1"></property>
    </bean>
    <bean id="b" class="cn.zno.testmybatis.QualifierBean">
        <property name="name" value="b1"></property>
    </bean>

单元测试：

    @Autowired @Qualifier("a")
    private QualifierBean qualifierBean1;

    @Autowired @Qualifier("b")
    private QualifierBean qualifierBean2;

注意：

@Qualifier 必须配合 @Autowired ，否则无法注入

@Qualifier 指定的值必须在<bean 中通过 id 或 name 指定，不存在时会抛异常（id 和 name 可同时存在且值不同，且都可以通过@Qualifier 指定）

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [cn.zno.testmybatis.QualifierBean] 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), @org.springframework.beans.factory.annotation.Qualifier(value=a)}
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:1301)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1047)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:942)
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:533)
	... 28 more

id 和 name 不能与其他bean 的 id 和 name 相同

Caused by: org.springframework.beans.factory.parsing.BeanDefinitionParsingException: Configuration problem: Bean name 'b' is already used in this <beans> element

三静态注入

@Component
public class Foo {

    public void say(String s) {
        System.out.println(s);
    }
}

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

@Component
public class SomeUtils {

    private static Foo foo;

    @Autowired
    public void setFoo(Foo foo) {
        SomeUtils.foo = foo;
    }

    public static void doSomeThing() {
        foo.say("1111");
    }

}

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class ZTestsetApplication {

    public static void main(String[] args) {
        SpringApplication.run(ZTestsetApplication.class, args);

        SomeUtils.doSomeThing();
    }

}