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【j2ee spring】一、使用注释@Resource进行注入

分类: IT文章 • 2022-05-01 13:33:44
【j2ee spring】1、使用注释@Resource进行注入

spring的依赖注入

spring的依赖注入有：

1、手工装配（注入值自己编写配置，注解@Autowired @Resource

2、自动装配


关于注解的方式注入

1、首先xml文档里面得加上一个命名空间

xmlns:context="http://www.springframework.org/schema/context"

http://www.springframework.org/schema/context
            http://www.springframework.org/schema/context/spring-context.xsd"

这个是为了使用

<context:annotation-config />


2、由于@Resource和@Autowired的功能差不多

@Resource 默认是按照名称来寻找相应的bean对象，如果按名称找不到对象就会转而用类型来寻找对象

@Autowired默认是使用类型来寻找对象的

并且@Resource是j2ee的一个包，不是spring里面的，所以解耦比Autowired比较好，所以建议使用@Resource


使用@Resource注入

比如一个类里面有这么两个数据成员：

        private PersonDao personDao;
	private String name = "cutter_point";

那么要对personDao如何进行注入呢？ 

@Resource private PersonDao personDao;	//通过注释来进行注入

这样，在xml文档里面会按名字来寻找 

<?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:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
			http://www.springframework.org/schema/beans/spring-beans.xsd
			http://www.springframework.org/schema/context
			http://www.springframework.org/schema/context/spring-context.xsd">
			
			<context:annotation-config />
			
           <bean id="personDao" class="cn.dao.impl.PersonDaoBean"></bean>
           
          <bean id="personService" class="cn.service.impl.PersonServiceBean"></bean>
          
</beans>

我们在JUnit里面调用一下函数 

package cn.service.impl;

import java.util.HashSet;
import java.util.Set;

import javax.annotation.Resource;

import cn.dao.PersonDao;
import cn.service.PersonService;

public class PersonServiceBean implements PersonService {
	@Resource private PersonDao personDao;	//通过注释来进行注入
	private String name = "cutter_point";
	
	public PersonServiceBean() 
	{
		// TODO Auto-generated constructor stub
	}
	
	
	/**
	 * @author xiaofeng
	 * @param 这个是可以生成的构造器
	 */
	public PersonServiceBean(PersonDao personDao, String name) 
	{
		this.personDao = personDao;
		this.name = name;
	}

	public void save(){
		System.out.println(name);
		personDao.add();
	}
}

调用里面的save方法 


package junit.test;

import org.junit.BeforeClass;
import org.junit.Test;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import cn.itcast.service.PersonService;

public class SpringTest {

	@BeforeClass
	public static void setUpBeforeClass() throws Exception {
	}

	@Test public void instanceSpring()
       {
		AbstractApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml");
		PersonService personService = (PersonService)ctx.getBean("personService");
		personService.save();	
		ctx.close();
		
	}
}

如果注入失败，那么调用
personService.save();
就会报错，空指针错误，比如我们把xml文档中的 

<bean id="personDao" class="cn.itcast.dao.impl.PersonDaoBean"></bean>

注释掉，程序报错：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'personService': Injection of resource methods failed; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [cn.itcast.dao.PersonDao] is defined: Unsatisfied dependency of type [interface cn.itcast.dao.PersonDao]: expected at least 1 matching bean
    at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessPropertyValues(CommonAnnotationBeanPostProcessor.java:305)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:998)
    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 junit.test.SpringTest.instanceSpring(SpringTest.java:18)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    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.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:76)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [cn.itcast.dao.PersonDao] is defined: Unsatisfied dependency of type [interface cn.itcast.dao.PersonDao]: expected at least 1 matching bean
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:613)
    at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.autowireResource(CommonAnnotationBeanPostProcessor.java:431)
    at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.getResource(CommonAnnotationBeanPostProcessor.java:409)
    at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor$ResourceElement.getResourceToInject(CommonAnnotationBeanPostProcessor.java:537)
    at org.springframework.beans.factory.annotation.InjectionMetadata$InjectedElement.inject(InjectionMetadata.java:192)
    at org.springframework.beans.factory.annotation.InjectionMetadata.injectMethods(InjectionMetadata.java:117)
    at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessPropertyValues(CommonAnnotationBeanPostProcessor.java:302)
    ... 39 more

【j2ee spring】一、使用注释@Resource进行注入


但是如果去掉注释

【j2ee spring】一、使用注释@Resource进行注入

注入成功！！


关于set方法注入

//使用set方法注释注入
	@Resource
	public void setPersonDao(PersonDao personDao)
	{
		this.personDao = personDao;
	}

效果和
@Resource private PersonDao personDao;	//通过注释来进行注入

一样！！！











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