注解

注解

概述

本文主要讲述一些Spring常用的注解

实践

先看代码 还是原来的背景：一人一猫一狗
猫类

package kuangstudy;

import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;

/**
 * 功能描述
 *
 * @since 2022-06-26
 */
@Component
@Scope("prototype")
public class Cat {
    public void shout() {
        System.out.println("miao~");
    }
}

狗类

package kuangstudy;

import org.springframework.stereotype.Component;

/**
 * 功能描述
 *
 * @since 2022-06-26
 */
@Component
public class Dog {
    public void shout() {
        System.out.println("wang~");
    }
}

人类

package kuangstudy;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;

/**
 * 功能描述
 *
 * @since 2022-06-26
 */
@Component
@Scope("prototype")
public class Person {
    @Value("xiaohong")
    private String name;

    @Autowired(required = false)
    private Cat cat;
    //
    @Autowired
    private Dog dog;

    public String getName() {
        return name;
    }

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

    public Cat getCat() {
        return cat;
    }

    public void setCat(Cat cat) {
        this.cat = cat;
    }

    public Dog getDog() {
        return dog;
    }

    public void setDog(Dog dog) {
        this.dog = dog;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", cat=" + cat +
                ", dog=" + dog +
                '}';
    }
}

测试类

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

import kuangstudy.Person;

/**
 * 功能描述
 *
 * @since 2022-06-28
 */
public class Test1 {
    @Test
    public void test01() {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
        Person person = applicationContext.getBean("person", Person.class);
        person.getCat().shout();
        person.getDog().shout();

        Person person1 = applicationContext.getBean("person", Person.class);
        System.out.println(person1.equals(person));
        System.out.println(person1.getCat().equals(person.getCat()));
        System.out.println(person1.getDog().equals(person.getDog()));
    }
}

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
  https://www.springframework.org/schema/beans/spring-beans.xsd
  http://www.springframework.org/schema/context
  https://www.springframework.org/schema/context/spring-context.xsd">

    <context:annotation-config />
    <context:component-scan base-package="kuangstudy"></context:component-scan>
</beans>

结果

miao~
wang~
false
false
true

重点分析

1. 从Spring4之后使用注解配置bean需要导入aop包
2. 配置文件中需要配置扫描包路径

<context:component-scan base-package="kuangstudy"></context:component-scan>

3. @Value注解注入属性，放在属性上面或者属性的set方法上面，相当于xml中的<property>配置
4. 衍生的注解, 按照mvc三层架构来分
   @Component
   @Repository dao层的注解
   @Service service层的注解
   @Controller controller层的注解
5. 自动装配的注解
   @Autowired
   @Qualifier
   @Resource
6. 作用域 @Scope 可以设置bean的作用域为单例或者原型 跟xml中scope作用相同

小结

xml与注解
xml更加万能，适用于任何场合！维护简单方便
注解更加简洁，需要理解
最佳实践：使用xml来管理bean,比较纯粹，使用注解注入属性