淘先锋技术网

首页 1 2 3 4 5 6 7

一个Spring注入问题,首先看一个普通Spring Bean,

public class Foo {
	@Autowired
	Bar bar;
	
	public void doSomething(){
		bar.doSomething();
	}
}

Spring配置一:

<bean id="bar" class="com.test.Bar"></bean>
<bean id="foo" class="com.test.Foo"></bean>

单元测试:

        @Test
	public void test_doSomthing(){
		ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext-test.xml");
		Foo foo = ctx.getBean(Foo.class);
		foo.doSomething();
	}

执行上述测试方法,报错

java.lang.NullPointerException
	at com.test.Foo.doSomething(Foo.java:15)
	at com.test.FooTest.test_doSomthing(FooTest.java:13)

即foo bean中的bar并未注入。

Spring配置二:

<context:component-scan base-package="com.test"></context:component-scan>

当改成配置二后执行上述单元测试方法便能成功通过。经分析日志及查看源代码,发现使用配置二时供装载了6个bean,如下所示:

DEBUG org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:216)  Loaded 6 bean definitions from location pattern [applicationContext-test.xml]
DEBUG org.springframework.context.support.AbstractApplicationContext.obtainFreshBeanFactory(AbstractApplicationContext.java:530)  Bean factory for org.springframework.context.support.ClassPathXmlApplicationContext@3c4e80d3: org.springframework.beans.factory.support.DefaultListableBeanFactory@14cc51c8: defining beans [bar,foo,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor]; root of factory hierarchy

而使用配置一时只有两个bean,如下所示:

DEBUG org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:216)  Loaded 2 bean definitions from location pattern [applicationContext-test.xml]
DEBUG org.springframework.context.support.AbstractApplicationContext.obtainFreshBeanFactory(AbstractApplicationContext.java:530)  Bean factory for org.springframework.context.support.ClassPathXmlApplicationContext@45ebbb93: org.springframework.beans.factory.support.DefaultListableBeanFactory@18481697: defining beans [bar,foo]; root of factory hierarchy

配置二执行单元测试通过的原因似乎就在于多出的这几个bean。是不是只要有context:component-scan元素在自动就会有这几个bean的产生?验证此假设

在配置一中添加一个无实际意义的context:component-scan元素,如下所示:

<context:component-scan base-package="com.nonexist"></context:component-scan>

这时执行单元测试能通过,同配置二一样也会装载6个bean。那么这6个bean中到底哪个对注入bar到Foo中起了作用呢?

经过断点调试发现是AutowiredAnnotationBeanPostProcessor bean起了作用,见输出日志:

2015-04-25 20:23:09 DEBUG org.springframework.beans.factory.annotation.InjectionMetadata.<init>(InjectionMetadata.java:60)  Found injected element on class [com.test.Foo]: AutowiredFieldElement for com.test.Bar com.test.Foo.bar
2015-04-25 20:23:09 DEBUG org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:85)  Processing injected method of bean 'foo': AutowiredFieldElement for com.test.Bar com.test.Foo.bar
2015-04-25 20:23:09 DEBUG org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:245)  Returning cached instance of singleton bean 'bar'
2015-04-25 20:23:09 DEBUG org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.registerDependentBeans(AutowiredAnnotationBeanPostProcessor.java:424)  Autowiring by type from bean name 'foo' to bean named 'bar'
2015-04-25 20:23:09 DEBUG org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:458)  Finished creating instance of bean 'foo'

那么直接在配置一种显式添加AutowiredAnnotationBeanPostProcessor bean呢?如下所示:

<bean id="bar" class="com.tcl.account.service.test.Bar"></bean>
<bean id="foo" class="com.tcl.account.service.test.Foo"></bean>
<bean id="autowiredAnnotationBeanPostProcessor" class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor"></bean>

测试会不会通过?会通过。见日志:

DEBUG org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:216)  Loaded 3 bean definitions from location pattern [applicationContext-test.xml]
DEBUG org.springframework.context.support.AbstractApplicationContext.obtainFreshBeanFactory(AbstractApplicationContext.java:530)  Bean factory for org.springframework.context.support.ClassPathXmlApplicationContext@7767d3c1: org.springframework.beans.factory.support.DefaultListableBeanFactory@1924ed52: defining beans [bar,foo,autowiredAnnotationBeanPostProcessor]; root of factory hierarchy
DEBUG org.springframework.beans.factory.annotation.InjectionMetadata.<init>(InjectionMetadata.java:60)  Found injected element on class [com.test.Foo]: AutowiredFieldElement for com.test.Bar com.test.Foo.bar
DEBUG org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:85)  Processing injected method of bean 'foo': AutowiredFieldElement for com.test.Bar com.test.Foo.bar
DEBUG org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:245)  Returning cached instance of singleton bean 'bar'
DEBUG org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.registerDependentBeans(AutowiredAnnotationBeanPostProcessor.java:424)  Autowiring by type from bean name 'foo' to bean named 'bar'
DEBUG org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:458)  Finished creating instance of bean 'foo'

那么为什么在配置文件中添加了context:    componet-scan元素后就会自动添加那另外4个bean呢?经过断点调试发现Spring隐式装载的4个bean是在如下方法中加载的:

其调用链如下所示:

213617_9TNk_1175066.png

补充一:

若仍用配置一,但单元测试改成如下形式也可以测试通过。

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = { "classpath:/applicationContext-test.xml" })
public class FooTest2 {
	@Autowired
	private Foo foo;
	@Test
	public void test_doSomthing(){
		foo.doSomething();
	}
}

当然一点都不意外,这种方式也会隐式加载那4个bean,见日志:

DEBUG org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:216)  Loaded 2 bean definitions from location pattern [classpath:/applicationContext-test.xml]
INFO  org.springframework.context.support.AbstractApplicationContext.prepareRefresh(AbstractApplicationContext.java:500)  Refreshing org.springframework.context.support.GenericApplicationContext@51f3336e: startup date [Sun Apr 26 17:27:35 CST 2015]; root of context hierarchy
DEBUG org.springframework.context.support.AbstractApplicationContext.obtainFreshBeanFactory(AbstractApplicationContext.java:530)  Bean factory for org.springframework.context.support.GenericApplicationContext@51f3336e: org.springframework.beans.factory.support.DefaultListableBeanFactory@4f9d1352: defining beans [bar,foo,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor]; root of factory hierarchy

补充二,若使用的是@Value,效果同@Autowired,即也需要隐式加载AutowiredAnnotationBeanPostProcessor bean。

public class Foo {
	@Value("${bar}")
	String bar;
	
	public void doSomething(){
		System.out.println(bar);
	}
}

补充三:

若使用配置一,@PostConstruct标注的方法也不会被执行,但此时需要隐式加载的Spring bean是:org.springframework.context.annotation.CommonAnnotationBeanPostProcessor

补充四:

在配置一中添加如下配置

<context:annotation-config/>

也会隐式加载那4个bean

spring注入bean失败

Causedby:org.springframework.beans.factory.BeanCurrentlyInCreationException:Errorcreatingbeanwithname‘appSignCheck’:Beanwithname‘appSignCheck’hasbeeninjectedintootherbeans[appSignCheck]initsrawversion...

spring配置文件设置自动注入

前提在spring配置文件中,对象名和ref=“id”id名相同,使用自动注入,可以不配置两种配置方式①在<bean>中配置autowire=“”;②在<beans>中配置全局属性default-autowire=“byName”,设置时,所有的标签都设置了自动注入,...