Bean用@Autowire注解自動裝配

舉例：一個人有兩隻寵物（貓和狗）

實體類

public class Cat {
    public void shout(){
        System.out.println("喵~");
    }
}
           

public class Dog {

    public void shout(){
        System.out.println("汪~");
    }

}
           

package com.pojo;
public class People {
    private Cat cat;
    private Dog dog;
    private String name;

    @Override
    public String toString() {
        return "People{" +
                "cat=" + cat +
                ", dog=" + dog +
                ", name='" + name + '\'' +
                '}';
    }

    public Cat getCat() {
        return cat;
    }

    public void setCat(Cat cat) {
        this.cat = cat;
    }

    public Dog getDog() {
        return dog;
    }

    public void setDog(Dog dog) {
        this.dog = dog;
    }

    public String getName() {
        return name;
    }

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

在配置檔案applicationContext.xml中設定支援注解

<?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
        https://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        https://www.springframework.org/schema/context/spring-context.xsd">
	<!--導入context限制，支援注解-->
    <context:annotation-config/>
    <!--配置Bean-->
    <bean id="cat" class="com.pojo.Cat"/>
    <bean id="dog" class="com.pojo.Dog"/>
    <bean id="people" class="com.pojo.People"></bean>

</beans>
           

使用@Autowire注解

修改People類：

@Autowire可以在屬性上個使用，這樣我們就可以不用編寫set方法了，Spring容器會根據byType()方法自動去比對相同類型的Bean，比如會去找Cat類型的Bean和Dog類型的Bean

public class People {
    @Autowired
    //@Qualifier(value="cat")
    private Cat cat;
    @Autowired
    //@Qualifier(value="dog")
    private Dog dog;
    private String name;
    public Cat getCat() {
        return cat;
    }

    public Dog getDog() {
        return dog;
    }

    public String getName() {
        return name;
    }

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

注意：如果@Autowired自動裝配環境比較複雜，比如一個接口有多個實作類的時候，這幾個實作類都實作了同個接口，當注入的類型為接口時，Spring容器通過内部的byType()方法發現很多實作類都屬于這個接口，但卻不知道具體要選擇哪一個實作類。這時我們可以使用@Qualifier(value = “具體實作類的Bean對應id”)去配合使用，指定一個唯一的實作類。

測試

import com.pojo.People;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Mytest {
    @Test
    public void test(){
        ApplicationContext context=new ClassPathXmlApplicationContext("applicationContext.xml");
        People people = context.getBean("people", People.class);
        people.getCat().shout();
    }
}