【Spring实战】—— 2 构造注入

本文讲解了构造注入以及spring的基本使用方式，通过一个杂技演员的例子，讲述了依赖注入属性或者对象的使用方法。

　　如果想要使用spring来实现依赖注入，需要几个重要的步骤：

　　1 定义主要的类和需要分离的属性。这里主要的类，是指程序的主要对象，在例子中是Juggler杂技员。而想要分离构造的属性，是它手中的袋子的数目beanBags。

　　2 配置bean.xml。通过配置文件，确定主要的类和属性之间的关系，以及实现类。

　　3 通过应用上下文，获取bean，并进行使用。

注入属性

　　实例代码：

　　1 表演者接口：Performer.java

package com.spring.test.action1;public interface Performer {    void perform() throws PerformanceException;}

　　2 杂技员：Juggler，继承了表演者接口

package com.spring.test.action1;public class Juggler implements Performer{    private int beanBags = 3;        public Juggler(){            }        public Juggler(int beanBags){        this.beanBags = beanBags;    }        public void perform() throws PerformanceException {        System.out.println("Juggler "+beanBags+" beanBags");    }}

　　3 Spring配置文件：bean.xml

<?xml version="1.0" encoding="UTF-8"?><beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xmlns="http://www.springframework.org/schema/beans"    xsi:schemaLocation="http://www.springframework.org/schema/beans    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">     <bean id="duke" class="com.spring.test.action1.Juggler">         <constructor-arg value="15"/>     </bean></beans>

　　4 应用上下文获取指定的bean

package com.spring.test.action1;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;public class test {    public static void main(String[] args) {        ApplicationContext ctx = new ClassPathXmlApplicationContext("bean.xml");        Performer performer = (Performer)ctx.getBean("duke");        try {            performer.perform();        } catch (PerformanceException e) {            e.printStackTrace();        }    }}

　　执行结果如下：

Juggler 15 beanBags

 

注入对象

　　1 例如，上面的杂技演员不仅仅会仍袋子，还会表演诗歌，那么诗歌这个对象就需要注入到表演者的构造函数中，可以如下表示会朗诵诗歌的杂技演员：PoeticJuggler

package com.spring.test.action1;public class PoeticJuggler extends Juggler{    private Poem poem;        public PoeticJuggler(Poem poem){        super();        this.poem = poem;    }        public PoeticJuggler(int beanBags,Poem poem){        super(beanBags);        this.poem = poem;    }        public void perform() throws PerformanceException {        super.perform();        System.out.println("While reciting...");        poem.recite();    }}

　　2 诗歌对象：Sonnet29

package com.spring.test.action1;public class Sonnet29 implements Poem{    private static String lines = "嘛咪嘛咪哄";        public Sonnet29() {            }        public void recite() {        System.out.println(lines);    }}

　　3 Bean.xml配置文件如下

<?xml version="1.0" encoding="UTF-8"?><beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xmlns="http://www.springframework.org/schema/beans"    xsi:schemaLocation="http://www.springframework.org/schema/beans    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">     <bean id="duke" class="com.spring.test.action1.Juggler">         <constructor-arg value="15"/>     </bean>     <bean id="sonnet29" class="com.spring.test.action1.Sonnet29"/>     <bean id="poeticDuke" class="com.spring.test.action1.PoeticJuggler">         <constructor-arg value="15"/>         <constructor-arg ref="sonnet29"/>     </bean></beans>

　　4 主要的执行代码，通过应用上下文获取制定的bean

package com.spring.test.action1;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;public class test {    public static void main(String[] args) {        ApplicationContext ctx = new ClassPathXmlApplicationContext("bean.xml");//        Performer performer = (Performer)ctx.getBean("duke");        Performer performer1 = (Performer)ctx.getBean("poeticDuke");        try {//            performer.perform();            performer1.perform();        } catch (PerformanceException e) {            e.printStackTrace();        }    }}

　　5 执行结果如下

一月 24, 2015 4:40:46 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@35bf8de1: startup date [Sat Jan 24 16:40:46 CST 2015]; root of context hierarchy一月 24, 2015 4:40:46 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions信息: Loading XML bean definitions from class path resource [bean.xml]一月 24, 2015 4:40:46 下午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons信息: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@3401a0ad: defining beans [duke,sonnet29,poeticDuke]; root of factory hierarchyJuggler 15 beanBagsWhile reciting...嘛咪嘛咪哄