注解介绍

1. 代码里的特殊标记，使用注解可以完成功能
2. 写法：@注解名称（属性名称=value）
3. 注解使用在 类上面，方法上面，属性上
4. 作用：替代配置文件完成对象生成，属性注入，但是注解并不能完全脱离配置文件

Spring注解开发准备

1. applicationContext.xml中引入新的约束

<?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-4.0.xsd">
</beans>

2. 约束中开启注解扫描

<?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-4.0.xsd">
<!--开启注解扫描，base-package中写要扫描的包，如果有多个包，用逗号隔开或者写包的共同前缀-->
<!--扫描包里面的类、方法、属性上是否有注解-->
    <context:component-scan base-package="\"></context:component-scan>
</beans>

注解创建对象

import org.springframework.stereotype.Component;

@Component(value="person")   //等于<bean id="user" class = "Person"/>
public class Person{
    public void say(){
        System.out.println("hi");
    }
}

public class test {
    public static void main(String args []){
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        Person person = (Person) context.getBean("person");
        person.say();
    }
}

创建对象一共有4个注解

• @Component
• @Controller：WEB层
• @Service ： 业务层
• @Repository：持久层
  目前这四个注解功能一样

创建单实例对象：

@Component(value="person")   //等于<bean id="user" class = "Person"/>
@Scope(value = "singleton")  //prototype创建多实例
public class Person{
    public void say(){
        System.out.println("hi");
    }
}

public class test {
    public static void main(String args []){
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        Person person1 = (Person) context.getBean("person");
        Person person2 = (Person) context.getBean("person");
        System.out.println(person1==person2);
    }
}

image.png

注解注入属性

1. 注解注入对象
   场景：Service中注入Dao对象

@Component("studentDao")
public class studentDao {
    public void say(){
        System.out.println("this is dao");
    }
}

@Service("studentService")
public class StudentService {
    //在SerVice中注入Dao对象

    //创建Dao类型的属性,在属性上使用@Autowired实现对象注入（自动装配）
    @Autowired
    private studentDao studentDao;
    public void say2(){
        System.out.println("this is Service");
        studentDao.say();
    }
}

其实更常用对象注入的注解是：@Resource（name=" "）

@Service("studentService")
public class StudentService {
    //在SerVice中注入Dao对象
    //创建Dao类型的属性,在属性上使用@Resource实现对象注入
    @Resource(name = "studentDao")
    private studentDao studentDao;
    public void say2(){
        System.out.println("this is Service");
        studentDao.say();
    }
}

测试：

public class test {
    public static void main(String args []){
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        StudentService studentService = (StudentService) context.getBean("studentService");
        studentService.say2();
    }
}

image.png