當存在兩個型別一致的bean時，將會有什麼情況出現。我們一起來看看下面的例子：

例子

說明：如果已經看了上一篇教程，可以直接跳到第二步

第一步：建立bean

Customer類

package com.main.autowrite.autowired.annotation;
 
import org.springframework.beans.factory.annotation.Autowired;
 
public class Customer {
    //即將自動裝配的屬性
    private Person person;
    private String type;
    @Autowired
    public Customer(Person person) {
        this.person = person;
    }
    //getter and setter methods
    //toString methods
}
 

Person類

package com.main.autowrite.autowired.annotation;
 
public class Person {
    private String name;
    private int age;
    //getter and setter methods
    //toString methods
}

第二步：修改beans.xml配置檔案

說明：這裡存在了兩個person bean，一個是person1，一個是person2

<!--?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">
  <bean class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor">
  <bean class="com.main.autowrite.autowired.annotation.Customer" id="customer">
        <property name="type" value="user"></property>
  </bean>
  <bean class="com.main.autowrite.autowired.annotation.Person" id="person1">
        <property name="name" value="jack">
        <property name="age" value="18">
  </property></property></bean>
  <bean class="com.main.autowrite.autowired.annotation.Person" id="person2">
        <property name="name" value="tom">
        <property name="age" value="28">
  </property></property></bean>
</bean></beans>
 

第三步：編寫測試程式碼

@Test
public void test(){
 
    ApplicationContext context = 
            new ClassPathXmlApplicationContext("com/main/autowrite/autowired/annotation/beans.xml");
 
    Customer customer = (Customer)context.getBean("customer");
 
    System.out.print(customer.toString());
}

測試結果如下：（丟擲異常）

這是因為Customer在進行自動裝配時，不清楚要裝載person1，還是要裝載person2，這時我們就應該使用@Qualifier

這是因為Customer在進行自動裝配時，不清楚要裝載person1，還是要裝載person2，這時我們就應該使用@Qualifier註解來告訴它，我們想要的是哪一個！

為解決上述問題，這裡引入@Qualifier註解

@Qualifier示例

修改你的Customer類如下：

package com.main.autowrite.autowired.annotation;
 
import java.lang.annotation.Retention;
 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
 
public class Customer {
    //即將自動裝配的屬性
    @Autowired
    @Qualifier("person2")
    private Person person;
    private String type;
 
    //getter and setter methods 
    //toString methods
}

此時應該將引入spring上下文以及context:annotation-config標籤

<!--?xml version="1.0" encoding="UTF-8"?-->
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:context="http://www.springframework.org/schema/context" 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-2.5.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-2.5.xsd">
  <context:annotation-config>
  <bean class="com.main.autowrite.autowired.annotation.Customer" id="customer">
        <property name="type" value="user"></property>
  </bean>
  <bean class="com.main.autowrite.autowired.annotation.Person" id="person1">
 
        <property name="name" value="jack">
        <property name="age" value="18">
  </property></property></bean>
  <bean class="com.main.autowrite.autowired.annotation.Person" id="person2">
        <property name="name" value="tom">
        <property name="age" value="28">
  </property></property></bean>
</context:annotation-config></beans>

此時Customer bean將會自動裝配person2 bean

執行結果如下：