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() {}@Overridepublic 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.xsdhttp://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsdhttp://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsdhttp://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.1.xsdhttp://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.0.xsdhttp://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？

下面以厨师制作蛋糕为例子。

（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，我们把需要制作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;@Overridepublic 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.xsdhttp://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsdhttp://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsdhttp://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.1.xsdhttp://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.0.xsdhttp://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 {@Autowiredprivate ApplicationContext applicationContext;@Testpublic 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();}@Overridepublic 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.xsdhttp://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsdhttp://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsdhttp://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.1.xsdhttp://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.0.xsdhttp://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：http://blog.csdn.net/raylee2007/article/details/50611627 

 

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