从spring2.5起spring框架开始支持java注解的配置元数据.所以除了使用xml配置文件来描述bean的装配之外,你还
可以使用基于java注解的配置元数据来完成同样的功能。
spring框架最终装配bean的时候会首先根据注解配置元数据来装配,然后再按照xml配置文件来装配。这也就意味着
xml配置文件的配置信息会覆盖掉注解的配置信息。
spring容器默认情况下没有开启基于注解的装配。如果要使用基于java注解的元数据，我们需要首先在xml文件中引
入context命名空间.然后使用<context:annotation-config/>元素开启spring的注解配置元数据.模板如下：
<?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-3.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd"> <context:annotation-config/> <!-- bean definitions go here --> </beans>
下面我们分小节介绍常用的每个注解：
Required注解
该注解标注到bean的setter上,意味着bean的该属性必须由spring进行注入。如果没有注入的话,spring容器在启动
的时候就会报错.我们来看一个例子帮助理解:
1.新建包com.tutorialspoint.annotation.required,并在包中新建People.java和Address.java.内容如下:
//People.java package com.tutorialspoint.annotation.required; import org.springframework.beans.factory.annotation.Required; public class People { private Address home; private Address company; //标注Required注解的属性,必须由spring容器注入,否则会报错 @Required public void setHome(Address home) { this.home = home; } public void setCompany(Address company) { this.company = company; } public void print(){ System.out.println("home: "+home); System.out.println("company: "+company); } } //Address.java package com.tutorialspoint.annotation.required; public class Address { }
2.在src目录下新建annotation_required.xml配置文件,内容如下：
<?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-3.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd"> <context:annotation-config/> <bean id="home" class="com.tutorialspoint.annotation.required.Address"></bean> <bean id="company" class="com.tutorialspoint.annotation.required.Address"></bean> <bean id="people" class="com.tutorialspoint.annotation.required.People"> <!-- home属性必须注入,否则spring在启动的时候会报错 --> <property name="home" ref="home"></property> </bean> </beans>
3.在com.tutorialspoint.annotation.required包中新建MainApp.java.内容如下：
package com.tutorialspoint.annotation.required; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class MainApp { public static void main(String[] args) { ApplicationContext context = new ClassPathXmlApplicationContext("annotation_required.xml"); People people = (People) context.getBean("people"); people.print(); } }
4.运行程序，检查结果：
如果我们没有注入home属性,会得到如下错误：
Property 'home' is required for bean 'people'
Autowired和Qualifier注解
Autowired可以标注在字段、setter、构造函数上。默认是按类型进行装配。具体的工作流程如下：
1.如何一个字段、属性、构造方法被Autowired标注,spring在容器中相应的类型的bean
2.如果找不到对应类型的bean，直接报错
3.如果找到了多个该类型的bean,会按照名字进行装,如果无法按照名字装配则报错
通过配合使用Qualifier注解,可以使Autowired注解一开始就按照名字进行装配
下面来看个例子:
1.新建包com.tutorialspoint.annotation.autowired.并在包中新建People.java和Address.java,内容如下：
//People.java package com.tutorialspoint.annotation.autowired; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.annotation.Qualifier; public class People { //家庭地址 private Address home; //公司地址 private Address company; /** * @Autowired的注解还可以标注在字段上,如下 */ //现住地址 @Autowired @Qualifier(value="live") private Address live; public People(){} /** * Autowired的注解还可以标注在构造函数上。 */ @Autowired public People(Address home){ this.home=home; } /** * Autowired注解可以标注在setter方法上.被该注解标注的setter默认情况 * 下是必须由spring注入的，可以用@Autowired(required=false)写法覆盖 * 默认行为 * * Autowired注解默认按照类型进行装配.不过配合Qualifier使用可以达到按照名字进行匹配的目的 * 其中@Qualifier的value属性用来指明依赖bean的名字 * */ @Autowired @Qualifier(value="company") public void setCompany(Address company) { this.company = company; } public void setLive(Address live) { this.live = live; } public void print(){ System.out.println("home: "+home); System.out.println("company: "+company); System.out.println("live: "+live); } } //Address.java package com.tutorialspoint.annotation.autowired; public class Address { private String content; public void setContent(String content) { this.content = content; } @Override public String toString() { return content; } }
2.在src目录下新建配置文件annotation_autowired.xml,内容如下：
<?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-3.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd"> <context:annotation-config/> <bean id="home" class="com.tutorialspoint.annotation.autowired.Address"> <property name="content" value="home"></property> </bean> <bean id="company" class="com.tutorialspoint.annotation.autowired.Address"> <property name="content" value="company"></property> </bean> <bean id="live" class="com.tutorialspoint.annotation.autowired.Address"> <property name="content" value="live"></property> </bean> <bean id="people" class="com.tutorialspoint.annotation.autowired.People"> </bean> </beans>
3.在com.tutorialspoint.annotation.autowired包中新建MainApp.java,内容如下：
package com.tutorialspoint.annotation.autowired; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class MainApp { public static void main(String[] args) { ApplicationContext context = new ClassPathXmlApplicationContext("annotation_autowired.xml"); People people = (People)context.getBean("people"); people.print(); } }
4.运行程序，检查结果：
JSR-250注解
jsr-250提供了三个注解：PostConstruct、PreDestroy、Resource
PostConstruct相当于之前介绍的init-method属性,指定bean的初始化方法
PreDestroy相当于之前介绍的destroy-method属性,指定bean的销毁方法
Resource类似于Autowired注解,不过Resource是由jdk提供了,Autowired是spring提供的。
Resource直接默认情况下先按照名字进行注入,如果在容器中找不到相应的名字,就会按照类型装配,看个例子：
1.新建包com.tutorialspoint.annotation.jsr250,并在包中新建People.java和Address.java,内容如下：
//People.java package com.tutorialspoint.annotation.jsr250; import javax.annotation.PostConstruct; import javax.annotation.PreDestroy; import javax.annotation.Resource; public class People { private Address home; public People(){} public People(Address home){ this.home=home; } @PostConstruct public void init(){ System.out.println("init invoked ... "); } @PreDestroy public void destroy(){ System.out.println("destroy is invoked ... "); } @Resource public void setHome(Address home) { this.home = home; } public void print(){ System.out.println("address: "+home); } } //Address.java package com.tutorialspoint.annotation.jsr250; public class Address { private String content; public void setContent(String content) { this.content = content; } @Override public String toString() { return content; } }
2.在src目录下新建annotation_jsr250.xml配置文件,内容如下：
<?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-3.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd"> <context:annotation-config/> <bean id="home" class="com.tutorialspoint.annotation.jsr250.Address"> <property name="content" value="home"></property> </bean> <bean id="people" class="com.tutorialspoint.annotation.jsr250.People"></bean> </beans>
3.在包com.tutorialspoint.annotation.jsr250中新建MainApp.java.内容如下：
package com.tutorialspoint.annotation.jsr250; import org.springframework.context.support.AbstractApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class MainApp { public static void main(String[] args) { AbstractApplicationContext context = new ClassPathXmlApplicationContext("annotation_jsr250.xml"); People people = (People) context.getBean("people"); people.print(); context.registerShutdownHook(); } }
4.运行程序，检查结果：
