第五章 诠释注入

第五章 注释注入
?注释方法注入
采用注释方式的前提条件,
1.XML配置文件的改动
<?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-2.5.xsd
           http://www.springframework.org/schema/context
           http://www.springframework.org/schema/context/spring-context-2.5.xsd">              
     <context:annotation-config/>    
</beans>

蓝色部分为添加的内容,这一部分内容隐式注册注释处理器
AutowiredAnnotationBeanPostProcessor，CommonAnnotationBeanPostProcessor，PersistenceAnnotationBeanPostProcessor

2.依赖包的导入
见下图:



只需要选中 Spring2.5 J2EE 此选项后, 其他的项会自动选中,包括后面要学习的AOP的包也导入了.

在java代码中,可以使用@Autowired或 @Resource注释方式进行装配,这两个注解的区别是:
@Autowired默认按类型装配
@Resource 默认按名称装配,当找不到与名称匹配的bean时,再按类型装配.

@Autowired或 @Resource两者的区别:
@Autowired: Spring提供,使用后程序会具有侵入性.
@Resource: JDK提供,移植性强,推荐使用, 可以看到支撑类是: import javax.annotation.Resource; 只要是JDK1.5以上版本,JDK内置了此注释支撑类.

用法:
用在属性上
public class FruitServiceImpl implements FruitService {
@Resource
private FruitDao fruitDao;

@Override
public void create() {
fruitDao.create();
}

public void setFruitDao(FruitDao fruitDao) {
this.fruitDao = fruitDao;
}
}
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" xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
           http://www.springframework.org/schema/context
           http://www.springframework.org/schema/context/spring-context-2.5.xsd">
<context:annotation-config />
<bean id="fruitDao" />
<bean id="fruitService" />
</beans>
可以看到这里只是在容器中配置了两个bean对象, 他们之间并没有任何关系.但是在Java文件中,我们采用了注释语法,
这个时候@Resource注释语法会根据属性名称在Spring容器中去寻找和属性名称同名id的bean对象,然后将其注入到属性中.
Test:
public class Test {
public static void main(String[] args) {
ApplicationContext acx = new ClassPathXmlApplicationContext(
"chapter2.xml");
FruitService fruitService = (FruitService) acx.getBean("fruitService");
fruitService.create();
}
}

更改配置文件:
<bean id="myFruitDao" />
这个时候可以看到myFruitDao和属性名称并没有对应,但是执行Test文件后,可以看到还是成功执行了方法,为什么呢?
验证了我们刚才所说的,如果名称没有对应上,就会按类型自动对应,所以会执行成功.

我们还可以给@Resource加上name,请看下面的语法
public class FruitServiceImpl implements FruitService {
@Resource(name="myFruitDao")
private FruitDao fruitDao;

@Override
public void create() {
fruitDao.create();
}

public void setFruitDao(FruitDao fruitDao) {
this.fruitDao = fruitDao;
}
}
再次执行Test,同样可以执行成功.

用上属性的set方法上
public class FruitServiceImpl implements FruitService {

private FruitDao fruitDao;

@Override
public void create() {
fruitDao.create();
}

@Resource(name="myFruitDao")
public void setFruitDao(FruitDao fruitDao) {
this.fruitDao = fruitDao;
}
}
可以看到,用在属性上,或者用上属性的set方法上,效果是一模一样的,没有任何区别

注意:如果我这样配置:
@Resource(name="myFruitDaosss")
public void setFruitDao(FruitDao fruitDao) {
this.fruitDao = fruitDao;
}
而配置文件中又没有提供id为myFruitDaosss的bean,这个时候是会报错的:
Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'fruitService': Injection of resource methods failed; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'myFruitDaosss' is defined

@Autowired
请看下面的代码:
public class FruitServiceImpl implements FruitService {

private FruitDao fruitDao;

@Override
public void create() {
fruitDao.create();
}

@Autowired
public void setFruitDao(FruitDao fruitDao) {
this.fruitDao = fruitDao;
}
}
运行Test文件,可以看到效果一样.

同样,我们也可以把@Autowired改成按名称装配
public class FruitServiceImpl implements FruitService {
@Autowired()
@Qualifier("myaFruitDao")
private FruitDao fruitDao;

public void create() {
fruitDao.create();
}

public void setFruitDao(FruitDao fruitDao) {
this.fruitDao = fruitDao;
}
}
但是这里需要注意的是:
@Autowired()
@Qualifier("myaFruitDao")
private FruitDao fruitDao;
这两句只能用在属性上,不能用上方法上.

@Autowired的required属性
@Autowired(required=true)
@Qualifier("myFruitDao")
required=true : 必须为属性注入值,
required=false: 不是必须注入值,如果找不到对应的值注入,会注入null

示例:
@Autowired(required=false) @Qualifier("myXXXXXXFruitDao")
当配置文件中没有对应ID的Bean时,会出现java.lang.NullPointerException空指针异常

?通过在classpath自动扫描方式把组件纳入到spring容器中管理.
Spring2.5引入了组件自动扫描机制,他可以在类路径下寻找标注了@Component, @Service, @Controller, @Repository注解的类, 并把这些类纳入进Spring容器中管理,它的作用,和在XML文件中使用Bean节点配置组件是一样的,要使用自动扫描机制,我们需要打开以下配置信息
<?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-2.5.xsd
           http://www.springframework.org/schema/context
           http://www.springframework.org/schema/context/spring-context-2.5.xsd">
<context:component-scan base-package="com.wdpc.springdemo" />
</beans>
<context:component-scan base-package="com.wdpc.springdemo" />这一项配置了需要扫描的包,包含子包.

@Service: 用于标注业务层的类
@Controller: 用于标注控制层,如Action
@Repository: 用于标注Dao层
@Component: 用于标注组件层, 当组件不好归类的时候,可以用此标注
这四个注释功能一样,只不过是在逻辑层次上达到一个区分的目的.其实,用哪一个都可以.只要类上用到了这些注释,就是告诉Spring,我这个类要交给Spring管理.效果相当于在配置文件中配置的<bean id=”**” class=”**”/>

通过扫描机制, 基本上可以达到配置文件基本为空的效果, 这是Spring2.5新推出的功能, 老系统不能运用, 但是新系统中, 此功能运用的非常多.

示例:
Dao层:
package com.wdpc.springdemo.dao.impl;

import org.springframework.stereotype.Repository;

import com.wdpc.springdemo.dao.FruitDao;

@Repository
public class FruitDaoImpl implements FruitDao {
public void create() {
System.out.println("Dao层方法create被调用");
}
}
服务层:
package com.wdpc.springdemo.service.impl;

import org.springframework.stereotype.Service;

import com.wdpc.springdemo.dao.FruitDao;
import com.wdpc.springdemo.service.FruitService;

@Service
public class FruitServiceImpl implements FruitService {

private FruitDao fruitDao;

public void create() {
fruitDao.create();
}

public void setFruitDao(FruitDao fruitDao) {
this.fruitDao = fruitDao;
}
}
这个时候,我将Dao层,服务层的两个实现类交给Spring管理了,相当于以前配置了两个Bean,这个时候我们可以验证一下,我们是否可以从容器中获取对象
Test:
package com.wdpc.springdemo.service;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.wdpc.springdemo.dao.FruitDao;

public class Test {

public static void main(String[] args) {
ApplicationContext acx = new ClassPathXmlApplicationContext(
"chapter2.xml");
FruitDao fruitDao = (FruitDao)acx.getBean("fruitDaoImpl");
FruitService fruitService = (FruitService) acx.getBean("fruitServiceImpl");
System.out.println(fruitDao);
System.out.println(fruitService);
}
}
这里需要注意的是,当对象交给Spring管理后,Spring给对象起的ID名称是类的简单名称, 即类全名,但是首字母小写

自定义名称:
Dao层:
package com.wdpc.springdemo.dao.impl;

import org.springframework.stereotype.Repository;

import com.wdpc.springdemo.dao.FruitDao;

@Repository("fruitDao")
public class FruitDaoImpl implements FruitDao {
public void create() {
System.out.println("Dao层方法create被调用");
}
}

服务层:
package com.wdpc.springdemo.service.impl;

import org.springframework.stereotype.Service;

import com.wdpc.springdemo.dao.FruitDao;
import com.wdpc.springdemo.service.FruitService;

@Service("fruitService")
public class FruitServiceImpl implements FruitService {

private FruitDao fruitDao;

public void create() {
fruitDao.create();
}

public void setFruitDao(FruitDao fruitDao) {
this.fruitDao = fruitDao;
}
}
Test:
public class Test {
public static void main(String[] args) {
ApplicationContext acx = new ClassPathXmlApplicationContext(
"chapter2.xml");
FruitDao fruitDao = (FruitDao)acx.getBean("fruitDao");
FruitService fruitService = (FruitService) acx.getBean("fruitService");
System.out.println(fruitDao);
System.out.println(fruitService);
}
}

?改变对象的范围(单例或非单例)
@Repository("fruitDao")
@Scope("prototype")
加上@Scope("prototype")此注释即可,这个时候每次获取对象都会是一个新对象

?对象初始化方法和销毁方法的配置
@Repository("fruitDao")
@Scope("prototype")
public class FruitDaoImpl implements FruitDao {
public void create() {
System.out.println("Dao层方法create被调用");
}

@PostConstruct
public void init(){
System.out.println("调用init");
}

@PreDestroy
public void destory(){
System.out.println("调用destory");
}
}
如果对象是非单例模式,这个时候可以看到init方法会调用两次,而destroy方法不会调用.

将Dao层注入到服务层:
@Service("fruitService")
public class FruitServiceImpl implements FruitService {
@Resource(name="fruitDao")
private FruitDao fruitDao;

public void create() {
fruitDao.create();
}

public void setFruitDao(FruitDao fruitDao) {
this.fruitDao = fruitDao;
}
}