Spring中的依赖检查及常见异常

Spring中的依赖检查及常见异常

 

 

Spring除了能对容器中bean的依赖设置进行检查外，还可以检查bean定义中实际属性值的设置，当然也包括采用自动装配方式设置属性值的检查。

当需要确保bean的所有属性值（或者属性类型）被正确设置的时候，那么这个功能会非常有用。当然，在很多情况下，bean类的某些属性会具有默认值，或者有些属性并不会在所有场景下使用，因此这项功能会存在一定的局限性。就像自动装配一样，依赖检查也可以针对每一个bean进行设置。依赖检查默认为not，它有几种不同的使用模式，在xml配置文件中，可以在bean定义中为dependency-check属性使用以下几种值：

模式	说明
none	没有依赖检查，如果bean的属性没有值的话可以不用设置。
simple	对于原始类型及集合（除协作者外的一切东西）执行依赖检查
object	仅对协作者执行依赖检查
all	对协作者，原始类型及集合执行依赖检查

 

下面我们用实例来证明，准备三个类如下： 

 

 

public class AddressServiceImpl {	
	/**住址*/
	private String address;		
	public void setAddress(String address){
		this.address=address;
	}
}

	
public class HomeAddressServiceImpl extends AddressServiceImpl {
	
	private String address;
	
	public void setAddress(String address){
		this.address=address;
	}
	
	public HomeAddressServiceImpl() {
		super();
	}
	public HomeAddressServiceImpl(String address){
		this.address=address;
	}

}

public class EmpServiceImpl {	
	/**公司地址*/
	private AddressServiceImpl companyAddress;	
	public void setCompanyAddress(AddressServiceImpl companyAddress){
		this.companyAddress=companyAddress;
	}
	}

 

 

 

  Spring中的配置文件

 <?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd">
	<bean id="homeAddressServiceImpl" class="cn.csdn.service.HomeAddressServiceImpl"
		scope="singleton">
		<property name="address">
			<value>北京海淀上地软件园</value>
		</property>	
	</bean>   
   <bean id="addressServiceImpl" class="cn.csdn.service.AddressServiceImpl" scope="singleton"/>
	-->
	<bean id="empServiceImpl" class="cn.csdn.service.EmpServiceImpl"
		scope="singleton" autowire="byType" dependency-check="objects" />
</beans>

 

 

 

  

 

 

声明：

 

 dependency-check="objects":依赖对象检查 ，如果对象不存在就会出现bug

 dependency-check:

    none:没有依赖检查

    simple(除了协作者)原始数据、集合执行依赖检查

     objects仅对协作者的依赖检查

 all 所有

 

 

 

注意异常：

  

<!-- 当有多个相同类型的bean时,会出现bug如下： org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'empServiceImpl' defined in file [D:\Workspaces\MyEclipse 8.6\20110419_01\bin\applicationContext.xml]: Unsatisfied dependency expressed through bean property 'companyAddress': : No unique bean of type [cn.csdn.service.AddressServiceImpl] is defined: expected single matching bean but found 2: [homeAddressServiceImpl, addressServiceImpl]; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [cn.csdn.service.AddressServiceImpl] is defined: expected single matching bean but found 2: [homeAddressServiceImpl, addressServiceImpl] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1091) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:982) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:472) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409) at java.security.AccessController.doPrivileged(Native Method) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380) at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264) at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164) at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:429) at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:728) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:380) at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139) at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83) at cn.csdn.service.App.test(App.java:12) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20) at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28) at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:73) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:46) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:180) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:41) at org.junit.runners.ParentRunner$1.evaluate(ParentRunner.java:173) at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28) at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31) at org.junit.runners.ParentRunner.run(ParentRunner.java:220) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:46) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197) Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [cn.csdn.service.AddressServiceImpl] is defined: expected single matching bean but found 2: [homeAddressServiceImpl, addressServiceImpl] at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:621) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1076) ... 40 more

 

 

结束语：

 

 这通过xml的配置文件来进行配置；假若你在使用Java 5，也可以采用源代码级的注解（annotations）来进行配置。

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评论

1 楼 javawangli 2011-04-21  

常用的是simple值