spring实战之autowire="byType"

通常我们用spring的时候注入的属性都是指定的类实例或者List或Array，对于这一类的应用通常我们都是使用spring默认的根据bean的id或者name来在容器里查找，但是有些时候在一些特殊应用中对于一个bean的某个属性并不是固定的，此时就可以用到spring的另外一种注入方式就是autowire="byType"。如下例子：

一个接口类和几个实现类MyIdProvider.java

public interface MyIdProvider { String getId(); } class MyIdProviderImpl1 implements MyIdProvider { public String getId() { return "provider1_" + System.currentTimeMillis(); } } class MyIdProviderImpl2 implements MyIdProvider { public String getId() { return "provider2_" + System.currentTimeMillis(); } } class MyIdProviderImpl3 implements MyIdProvider { public String getId() { return "provider3_" + System.currentTimeMillis(); } }

MyIdProviderManager.java一个管理类，其中定义了一些对MyIdProvider的引用

import java.util.List; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class MyIdProviderManager { private String name; private List<MyIdProvider> myIdProviders; public String getName() { return name; } public void setName(String name) { this.name = name; } public List<MyIdProvider> getMyIdProviders() { return myIdProviders; } public void setMyIdProviders(List<MyIdProvider> myIdProviders) { this.myIdProviders = myIdProviders; } }

Test.java一个测试类

import java.util.List; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class Test { public static void main(String[] args) throws Exception { ApplicationContext ctx = new ClassPathXmlApplicationContext("/org/garbagecan/springstudy/beansfactory/spring-provider.xml"); MyIdProviderManager manager = (MyIdProviderManager) ctx.getBean("myIdProviderManager"); System.out.println(manager.getName()); List<MyIdProvider> myIdProviders = manager.getMyIdProviders(); for (MyIdProvider myIdProvider : myIdProviders) { System.out.println(myIdProvider.getId()); } } }

spring.xml

<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:lang="http://www.springframework.org/schema/lang" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.0.xsd http://www.springframework.org/schema/lang http://www.springframework.org/schema/lang/spring-lang-2.0.xsd" default-lazy-init="true"> <bean id="myIdProviderManager" class="MyIdProviderManager" autowire="byType"> <property name="name"><value>hello</value></property> </bean> <bean id="myIdProvider1" class="MyIdProviderImpl1"/> <bean id="myIdProvider2" class="MyIdProviderImpl2"/> <bean id="myIdProvider3" class="MyIdProviderImpl3"/> </beans>

运行Test类，得到如下输出

hello

provider1_1290559324155

provider2_1290559324155

provider3_1290559324155

对于byType注入个人认为还是应该少用，因为他确实提供了足够的灵活性，但是确牺牲了类依赖的清晰性，最后有可能导致出现问题了很难找到，因此还是应该谨慎使用，只有在byName不能解决问题的情况在再慎重使用。