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。