从头认识Spring-2.1 自动装配（3）-constructor

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这一章节我们来讨论一下自动装配的第三种方式-constructor

1.domain

蛋糕类：（不变）

package com.raylee.my_new_spring.my_new_spring.ch02.topic_1_4;

public class Cake {
	
	private String name = "";

	public String getName() {
		return name;
	}

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

}

厨师类：（由于是使用构造器方式，因此下面的代码需要改变一下）

package com.raylee.my_new_spring.my_new_spring.ch02.topic_1_4;

public class Chief {
	private Cake cake = null;

	private String name = "";

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

	public String getName() {
		return name;
	}

	public Cake makeOneCake() {
		System.out.println(getName() + " make " + cake.getName());
		return cake;
	}

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

}

2.测试类：（不变）

package com.raylee.my_new_spring.my_new_spring.ch02.topic_1_1;

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 = {
		"/com/raylee/my_new_spring/my_new_spring/ch02/topic_1_4/ApplicationContext-test.xml" })
public class ChiefTest {

	@Autowired
	private ApplicationContext applicationContext;

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

3.配置文件（重点）

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:context="http://www.springframework.org/schema/context" xmlns:p="http://www.springframework.org/schema/p"
	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" xmlns:util="http://www.springframework.org/schema/util"
	xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
        http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-2.0.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="blueberryCheeseCake"
		class="com.raylee.my_new_spring.my_new_spring.ch02.topic_1_4.Cake"
		p:name="blueberryCheeseCake" scope="prototype" />

	<bean id="jack"
		class="com.raylee.my_new_spring.my_new_spring.ch02.topic_1_4.Chief"
		p:name="jack" autowire="constructor" />
</beans>

根据上面的配置文件测试输出：

jack make blueberryCheeseCake

在上面的配置文件里面我们需要注意的地方：

在jack里面，没有了cake属性的注入，但是增加了autowire="constructor"这一句。

autowire="constructor"：表示当Bean的类型跟构造器注入的类型相一致、或者Bean的id跟构造器注入的名称相一致的时候，即可注入，也就是，当jack的构造器需要注入Cake类型，而在配置文件里面有一个bean的类型是Cake，那么，系统就会自动的把bean注入到属性里面去，或者当jack的构造器需要注入的是cake名称的对象，而在配置文件里面有那么一个bean，系统就可以自动注入。

但是这里有一个问题，当配置文件里面有多个Cake，这时候系统会抛异常

下面，我们将给出不同的配置文件以及输出结果，以供参考：

（1）当有两个Cake，但是其中一个bean的id跟注入的名字相同

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:context="http://www.springframework.org/schema/context" xmlns:p="http://www.springframework.org/schema/p"
	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" xmlns:util="http://www.springframework.org/schema/util"
	xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
        http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-2.0.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.ch02.topic_1_4.Cake"
		p:name="cake" scope="prototype" />

	<bean id="blueberryCheeseCake"
		class="com.raylee.my_new_spring.my_new_spring.ch02.topic_1_4.Cake"
		p:name="blueberryCheeseCake" scope="prototype" />

	<bean id="jack"
		class="com.raylee.my_new_spring.my_new_spring.ch02.topic_1_4.Chief"
		p:name="jack" autowire="constructor" />
</beans>

根据上面的配置文件测试输出：

jack make cake

（2）当没有相同名称的时候，但是又存在两个Cake的Bean，就会抛异常

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:context="http://www.springframework.org/schema/context" xmlns:p="http://www.springframework.org/schema/p"
	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" xmlns:util="http://www.springframework.org/schema/util"
	xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
        http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-2.0.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="cake2"
		class="com.raylee.my_new_spring.my_new_spring.ch02.topic_1_4.Cake"
		p:name="cake2" scope="prototype" />

	<bean id="blueberryCheeseCake"
		class="com.raylee.my_new_spring.my_new_spring.ch02.topic_1_4.Cake"
		p:name="blueberryCheeseCake" scope="prototype" />

	<bean id="jack"
		class="com.raylee.my_new_spring.my_new_spring.ch02.topic_1_4.Chief"
		p:name="jack" autowire="constructor" />
</beans>

我们把上面的cake的名称改成cake2以示区别

根据上面的配置文件测试输出：

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [com.raylee.my_new_spring.my_new_spring.ch02.topic_1_4.Cake] is defined: expected single matching bean but found 2: [cake2, blueberryCheeseCake]
 at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:796)
 at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:703)
 at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:795)
 at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:723)
 ... 40 more

（3）为了解决上面的问题，我们引入之前一章节提到的autowire-candidate

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:context="http://www.springframework.org/schema/context" xmlns:p="http://www.springframework.org/schema/p"
	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" xmlns:util="http://www.springframework.org/schema/util"
	xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
        http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-2.0.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="cake2"
		class="com.raylee.my_new_spring.my_new_spring.ch02.topic_1_4.Cake"
		p:name="cake2" scope="prototype" autowire-candidate="false"/>

	<bean id="blueberryCheeseCake"
		class="com.raylee.my_new_spring.my_new_spring.ch02.topic_1_4.Cake"
		p:name="blueberryCheeseCake" scope="prototype" />

	<bean id="jack"
		class="com.raylee.my_new_spring.my_new_spring.ch02.topic_1_4.Chief"
		p:name="jack" autowire="constructor" />
</beans>

我们在上面的cake2里面加上了autowire-candidate属性，自我排除候选

根据上面的配置文件测试输出：

jack make blueberryCheeseCake

总结：这一章节主要介绍了autowire属性里面的constructor选项的使用以及相应的注意点。

目录：http://blog.csdn.net/raylee2007/article/details/50611627 

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

从头认识Spring-2.1 自动装配（3）-constructor

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原文地址：http://blog.csdn.net/raylee2007/article/details/50654235