Spring：构造函数属性注入

通过构造函数注入属性基本和set方法注入类似，唯一不同的就是容器里面的标签不同

比如Demo类

package com.lihuia.ioc;

/**
 * Copyright (C), lihuia.com
 * FileName: Demo
 * Author:   lihui
 * Date:     2018/7/28
 */

public class Demo {
    
    private Girl girl;
    
    public Demo() {}
    public Demo(Girl girl) {
        this.girl = girl;
    }

    public void sayHello() {
        System.out.println("Hello, " + girl.myGirl());
    }
}

这里通过构造函数传入girl，同时Girl类不变

package com.lihuia.ioc;

/**
 * Copyright (C), lihuia.com
 * FileName: Girl
 * Author:   lihui
 * Date:     2018/7/28
 */

public class Girl {
    
    public String myGirl() {
        return "Lucy";
    }
}

此时XML换了一个标签

<?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 id="demo" class="com.lihuia.ioc.Demo">
      <constructor-arg name="girl" ref="girl"></constructor-arg>
   </bean>
   <bean id="girl" class="com.lihuia.ioc.Girl"></bean>

</beans>

通过constructor-arg，从字面意思也可以看出来是构造函数的参数，单要注意的是：

（1）name表示的是构造函数里传入的参数，如果构造函数里传入girl1，name这里constructor-arg的name也必须是girl1，保持一致

（2）ref引用的是本XML里已经存在的Girl类型的bean

测试类没什么变化

package com.lihuia.ioc;

import javax.annotation.Resource;

import org.testng.annotations.Test;

import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.testng.AbstractTestNGSpringContextTests;

/**
 * Copyright (C), lihuia.com
 * FileName: DemoTest
 * Author:   lihui
 * Date:     2018/7/28
 */

@ContextConfiguration(locations = {"classpath:ioc.xml"})
public class DemoTest extends AbstractTestNGSpringContextTests {

    @Resource(name = "demo")
    private Demo demo;
    
    @Test
    public void testSayHello() { 
        demo.sayHello();
    }
}

如果构造函数要传入多个参数，比如新增一个message，来传达要对girl说的话

package com.lihuia.ioc;

/**
 * Copyright (C), lihuia.com
 * FileName: Demo
 * Author:   lihui
 * Date:     2018/7/28
 */

public class Demo {
    
    private Girl girl;
    private String message;
    
    public Demo() {}
    public Demo(Girl girl, String message) {
        this.girl = girl;
        this.message = message;
    }

    public void sayHello() {
        System.out.println("Hello, " + girl.myGirl() + message);
    }
}

此时girl的传入方式不变，只需要在XML里新增一个message的参数声明

<?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 id="demo" class="com.lihuia.ioc.Demo">
      <constructor-arg name="girl" ref="girl"></constructor-arg>
      <constructor-arg name="message" value=", Congratulations"></constructor-arg>
   </bean>
   <bean id="girl" class="com.lihuia.ioc.Girl"></bean>

</beans>

任意新增的参数都可以在demo bean里进行添加