[Java知识库]细说spring IOC三种开发模式

1. 基于Xml 元数据模式（XML-based metadata）

1.1开发环境搭建（基于maven）
a.在pom文件中引入IOC核心依赖

<!--  IOC 核心jar，引入该jar可以使用springIOC 90%的功能      -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>5.3.23</version>
        </dependency>

b.在类路径下创建spring.xml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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

</beans>

c.添加需要托管的JavaBean：

package cn.shanxincd.ih.service;

/**
 * @ClassName UserService
 * @Description TODO
 * @Author @yangfeng
 * @Date 2022/11/1 17:48
 * @Version 1.0
 */
public class UserService {

    public void sayHello(String name){
        System.out.println("向"+name+"问好");
    }
}

d.注册javaBean到spring容器中

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
      <beans>
          <bean id="userService" class="cn.shanxincd.ih.service.UserService">

          </bean>

      </beans>
</beans>

e.创建测试类测试

package cn.shanxincd.ih.test;

import cn.shanxincd.ih.service.UserService;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @ClassName XmlContainerTest
 * @Description TODO
 * @Author @yangfeng
 * @Date 2022/11/1 17:54
 * @Version 1.0
 */
public class XmlContainerTest {
    public static void main(String[] args) {
      ClassPathXmlApplicationContext ct = new ClassPathXmlApplicationContext("spring.xml");
        UserService userService = (UserService) ct.getBean("userService");
        userService.sayHello("张三");

    }

}

上面一个简单的入门已经实现了spring IOC基本的功能（将对象的管理交给spring容器，在使用时从spring容器中获取Bean实例）

2. 基于注解的配置（ Annotation-based configuration）

2.1在开发模式1的基础上，在spring.xml中添加context的命名空间和约束，并添加开启注解扫描和包扫描（context:annotation-config</context:annotation-config>可以省略，spring5.0中已经和context:component-scan合并，添加包扫描即可）

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       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.xsd">

    <context:annotation-config></context:annotation-config>
    <context:component-scan base-package="cn.shanxincd.ih"/>

          <bean id="userService" class="cn.shanxincd.ih.service.UserService">
          </bean>


</beans>

2.2添加JavaBean，通过@Component将该bean注册到spring容器中

package cn.shanxincd.ih.service;

import org.springframework.stereotype.Component;

/**
 * @ClassName UserService
 * @Description TODO
 * @Author @yangfeng
 * @Date 2022/11/1 17:48
 * @Version 1.0
 */
@Component
public class UserService2 {

    public void sayHello(String name){
        System.out.println("UserService2 sayHello() 向"+name+"问好");
    }
}

2.3测试调用

package cn.shanxincd.ih.test;

import cn.shanxincd.ih.service.UserService;
import cn.shanxincd.ih.service.UserService2;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @ClassName XmlContainerTest
 * @Description TODO
 * @Author @yangfeng
 * @Date 2022/11/1 17:54
 * @Version 1.0
 */
public class XmlContainerTest {
    public static void main(String[] args) {
      ClassPathXmlApplicationContext ct = new ClassPathXmlApplicationContext("spring.xml");
        UserService userService = (UserService) ct.getBean("userService");
        userService.sayHello("张三");

        System.out.println("通过注解管理的Bean测试======================");

        UserService2 userService2 = (UserService2) ct.getBean("userService2");
        userService2.sayHello("李四");



    }

}

3. 基于Java config（Java-based configuration）

基于Java config的IOC开发，可以完全摆脱xml配置，改为完全由Java代码替代，这也是最简洁的一种IOC开发模式，强烈推荐
3.1将spring.xml配置文件删除或者修改后缀名称，不删除也可，应为这种模式下spring的启动容器和xml模式下spring的启动容器不是同一个，不会影响
3.2新建spring配置类：AppConfig.java，该类添加@Configuration和包扫描注解@ComponentScan

package cn.shanxincd.ih.config;

import org.mybatis.spring.SqlSessionFactoryBean;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.*;
import org.springframework.jdbc.datasource.DriverManagerDataSource;

import javax.sql.DataSource;

/**
 * @ClassName AppConfig
 * @Description TODO
 * @Author @yangfeng
 * @Date 2022/10/21 15:27
 * @Version 1.0
 */
@Configuration
@ComponentScan(value = "cn.shanxincd.ih")
public class AppConfig {
  

}

3.3将要托管给spring容器的JavaBean添加注解（@Repository、@Service、@Controller、@Component）

package cn.shanxincd.ih.service;

import org.springframework.stereotype.Service;

/**
 * @ClassName UserService
 * @Description TODO
 * @Author @yangfeng
 * @Date 2022/11/1 17:48
 * @Version 1.0
 */
@Service
public class UserService {

    public void sayHello(String name){
        System.out.println("向"+name+"问好");
    }
}

3.4添加测试类测试调用

package cn.shanxincd.ih.test;

import cn.shanxincd.ih.config.AppConfig;
import cn.shanxincd.ih.service.UserService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

/**
 * @ClassName ContainerTest
 * @Description TODO
 * @Author @yangfeng
 * @Date 2022/10/20 15:31
 * @Version 1.0
 */
public class ContainerTest {
    public static void main(String[] args) {
        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(AppConfig.class);
        UserService userService = applicationContext.getBean(UserService.class);
        userService.sayHello("张三");

    }
}

使用AnnotationConfigApplicationContext类，将配置类传入AnnotationConfigApplicationContext构造器中执行spring注解容器启动操作

4.三种模式混合使用

4.1保留xml模式下spring.xml配置文件，在模式3的AppConfig配置类中引入spring.xml配置文件：@ImportResource(“classpath:spring.xml”)
4.2如果是在配置类中进行包扫描则在配置类中使用@ComponentScan(value = “cn.shanxincd.ih”)即可，如果是在配置文件中进行包扫描则在spring.xml中添加<context:component-scan base-package=“cn.shanxincd.ih”/> 标签即可，这两种方式任选其一即可；base-package中的字符串是要扫描的包名，使用中尽量缩小包扫描的范围，这样能提高程序执行的效率

package cn.shanxincd.ih.config;

import org.mybatis.spring.SqlSessionFactoryBean;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.*;
import org.springframework.jdbc.datasource.DriverManagerDataSource;

import javax.sql.DataSource;

/**
 * @ClassName AppConfig
 * @Description TODO
 * @Author @yangfeng
 * @Date 2022/10/21 15:27
 * @Version 1.0
 */
@Configuration
@ComponentScan(value = "cn.shanxincd.ih")

/**
 * @ImportResource 可以引入xml到配置文件中
 **/
@ImportResource("classpath:spring.xml")
@MapperScan("cn.shanxincd.ih.mapper")
public class AppConfig {
}