Java框架spring 学习笔记（九）：Spring的bean管理（@Required、@Component、@Autowired、@Resource注解）

注解：代码里面特殊的标记，使用注解可以完成相关功能

注解写法：@注解名称（属性名、属性值）

@Required

用在set方法上，一旦用了这个注解，那么容器在初始化bean的时候必须要进行set，也就是说必须对这个值进行依赖注入。

编写Student.java

 package com.example.spring;
 import org.springframework.beans.factory.annotation.Required;

 public class Student {
     private String name;

     @Required
     public void setName(String name){
         this.name = name;
     }

     public void print(){
         System.out.println("name:"+name);
     }
 }

编写Beans.xml

 <?xml version="1.0" encoding="UTF-8"?>
 2 <beans xmlns="http://www.springframework.org/schema/beans"
 3        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 4        xmlns:context="http://www.springframework.org/schema/context"
 5        xsi:schemaLocation="http://www.springframework.org/schema/beans
 6     http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
 7     http://www.springframework.org/schema/context
 8     http://www.springframework.org/schema/context/spring-context-3.0.xsd">

     <context:annotation-config/>

     <bean id="student" class="com.example.spring.Student" >
         <property name="name" value="XiaoMing"></property>
     </bean>

 </beans>

编写Application.java

 package com.example.spring;

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

 public class Application {
     public static void main(String[] args) {
         //bean配置文件所在位置 D:\\IdeaProjects\\spring\\src\\Beans.xml
         //使用AbstractApplicationContext容器
         AbstractApplicationContext context = new ClassPathXmlApplicationContext("file:D:\\IdeaProjects\\spring\\src\\Beans.xml");
         //得到配置创建的对象
         Student student = (Student) context.getBean("student");
         student.print();
     }
 }

创建对象的注解有四个注解

1. @Component ：对那些比较中立的类进行注释
2. @Controller　：WEB层
3. @Service　　：业务层
4. @Repository  ：持久层

@Component

在类定义上面使用，表示用注解方式创建对象，相当于在配置文件中，<bean id="" class="">

编写User.java

 package com.example.spring;

 import org.springframework.stereotype.Component;

 @Component(value = "user") //相当于beans.xml中的<bean id="user" class="com.example.spring.User">
 public class User {
     public void print(){
         System.out.println("user pirnt.");
     }
 }

编写Beans.xml

 <?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">

     <!--开启注解扫描，到包里面扫描类、方法、属性上面是否有注解-->
     <context:component-scan base-package="com.example.spring"></context:component-scan>

13 </beans>

编写Application.java

 package com.example.spring;

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

 public class Application {
     public static void main(String[] args) {
         //bean配置文件所在位置 D:\\IdeaProjects\\spring\\src\\Beans.xml
         //使用AbstractApplicationContext容器
         AbstractApplicationContext context = new ClassPathXmlApplicationContext("file:D:\\IdeaProjects\\spring\\src\\Beans.xml");
         //得到配置创建的对象
         User user = (User) context.getBean("user");
         user.print();
     }
 }

运行输出

user pirnt.

其他的注解创建对象方式类似

注入对象属性的注解：

1. @Autowired
2. @Resource

@Autowired

对象类型属性注入注解

编写UserDao.java

 package com.example.spring;

 import org.springframework.stereotype.Component;

 //@Component 创建对象注释，相当于在配置文件中中的<bean id="userDao" class="com.example.spring.UserDao">
 @Component(value = "userDao")
 public class UserDao {
     public void print(){
         System.out.println("Dao print.");
     }
 }

编写UserService.java

 package com.example.spring;

 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;

 //@Component 创建对象注释，相当于在配置文件中中的<bean id="userService" class="com.example.spring.UserService">
 @Component(value = "userService")
 public class UserService {
     //1、定义dao类型属性，在dao属性上面使用注解，完成对象注入
     //@Autowired 相当于配置文件中的对象类型注入（如下）
     //  <bean id="userDao" class="com.example.spring.UserDao"></bean>
     //  <bean id="userService" class="com.example.spring.UserService" >
     //      <property name="userDao" ref="userDao"></property>
     //  </bean>
     @Autowired
     private UserDao userDao;
     //2、使用注解方式时候不需要set方法
     //public void setUserDao(UserDao userDao){
     //    this.userDao = userDao;
     //}

     public void print(){
         System.out.println("Service print.");
         userDao.print();
     }
 }

编写Beans.xml

 <?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">

     <!--开启注解扫描，到包里面扫描类、方法、属性上面是否有注解-->
     <context:component-scan base-package="com.example.spring"></context:component-scan>

 </beans>

编写Application.java

 package com.example.spring;

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

 public class Application {
     public static void main(String[] args) {
         //bean配置文件所在位置 D:\\IdeaProjects\\spring\\src\\Beans.xml
         //使用AbstractApplicationContext容器
         AbstractApplicationContext context = new ClassPathXmlApplicationContext("file:D:\\IdeaProjects\\spring\\src\\Beans.xml");
         //得到配置创建的对象
         UserService user = (UserService) context.getBean("userService");
         user.print();
     }
 }

运行输出

Service print.
Dao print.

@Resource

@Autowired是通过类名来自动注入，和@Component(value = "userDao")中的value值无关，这时就引出了@Resource注解，@Resource(name="userDao")，就会查找@Component(value = "userDao")注解的类并注入。