从头认识Spring-1.4 怎样通过构造器注入Bean？

这一章节我们来介绍一下通过构造器注入Bean。
1.怎样声明一个Bean？
（1）创建类

package com.raylee.my_new_spring.my_new_spring.ch01.topic_1_2;

public class Song {

	private String name;

	public Song(String name) {
		this.name = name;
	}

	public Song() {
	}

	@Override
	public String toString() {
		return "the song:" + name;
	}
}

（2）配置XML

<?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" xmlns:tx="http://www.springframework.org/schema/tx"
	xmlns:aop="http://www.springframework.org/schema/aop"
	xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
	 http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd
	 http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsd
	 http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.1.xsd
	 http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.0.xsd
	 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">
	
	<bean id="song"
		class="com.raylee.my_new_spring.my_new_spring.ch01.topic_1_2.Song">
		<constructor-arg value="there will be" />
	</bean>
	

</beans>

2.怎样通过构造器注入Bean？
下面以厨师***蛋糕为例子。
（1）创建厨师类

package com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4;

public class Chief {
	private Cake cake = null;

	public Chief(Cake cake) {//构造器注入的地方
		this.cake = cake;
	}

	public void makeOneCake() {
		System.out.println(cake.toString());
	}
}

在构建厨师的对象时，我们把需要***的蛋糕的对象也传进去。

（2）创建蛋糕类

package com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4;

public class Cake {

	private final int id = index++;

	private static int index = 0;

	@Override
	public String toString() {
		return "create the cake,its id:" + id;
	}
}

通过final来标识每一个对象的id
然后创建之后只是打印一句已经创建即可

（3）配置文件

<?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" xmlns:tx="http://www.springframework.org/schema/tx"
	xmlns:aop="http://www.springframework.org/schema/aop"
	xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
	 http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd
	 http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsd
	 http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.1.xsd
	 http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.0.xsd
	 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">
	<bean id="cake"
		class="com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4.Cake" />
	<bean id="chief"
		class="com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4.Chief">
		<constructor-arg ref="cake" />
	</bean>

</beans>

配置文件这里主要通过Bean标签来配置
在Bean标签里面还可以写入constructor-arg，这里就是通过构造器注入，他里面有两个参数，一个是ref，引用上面某个bean，一个是value，直接写入值

（4）创建测试类

package com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

@RunWith(SpringJUnit4ClassRunner.class)
// @ContextConfiguration(locations = {
// "classpath:ApplicationContext-test.xml" })
@ContextConfiguration(locations = {
		"/com/raylee/my_new_spring/my_new_spring/ch01/topic_1_4/ApplicationContext-test.xml" })
public class ChiefTest {

	@Autowired
	private ApplicationContext applicationContext;

	@Test
	public void testChief() {
		Chief chief = applicationContext.getBean(Chief.class);
		chief.makeOneCake();
	}
}

如果是单独的建立ApplicationContext，可以使用我上面注释的方式，由于我们这里是多项目放在一起，因此我引用的是绝对路径。

输出：
create the cake,its id:0

3.如果类没有公开的构造器，如果使用单例的类？
根据上面的代码，我们补充一个烤炉，而我们这个烤炉选择单例模式。

package com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4;

public class Oven {

	private Oven() {
	}

	public static Oven getInstance() {
		return new Oven();
	}

	@Override
	public String toString() {
		return "use old oven";
	}

}

然后厨师那里加上烤炉这个工具：

package com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4;

public class Chief {
	private Cake cake = null;

	private Oven oven = null;

	public Chief(Cake cake) {
		this.cake = cake;
	}

	public Chief(Cake cake, Oven oven) {
		this.cake = cake;
		this.oven = oven;
	}

	public void makeOneCake() {
		System.out.println(oven.toString() + cake.toString());
	}
}

配置的时候特别为烤炉配置一个工厂方法，factory-method就是为了单例这种情况来设置的：

<?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" xmlns:tx="http://www.springframework.org/schema/tx"
	xmlns:aop="http://www.springframework.org/schema/aop"
	xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
	 http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd
	 http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsd
	 http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.1.xsd
	 http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.0.xsd
	 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">
	<bean id="cake"
		class="com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4.Cake" />
	<bean id="chief"
		class="com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4.Chief">
		<constructor-arg ref="cake" />
		<constructor-arg ref="oven" />
	</bean>
	<bean id="oven"
		class="com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4.Oven"
		factory-method="getInstance" />

</beans>

测试输出：
use old ovencreate the cake,its id:0

总结：这一章节介绍了如何通过构造器注入Bean。
目录：/article/3641905.html

我的github：https://github.com/raylee2015/my_new_spring