第二步，引入Spring并实现IoC特征

项目结构.png

在web.xml 中添加跟spring相关的配置信息

web.xml
</welcome-file-list>

    <!--加载Spring的配置文件到上下文中去 -->
    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>
            classpath*:/applicationContext.xml
        </param-value>
    </context-param>

    <!-- Spring监听器 -->
    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>

    <!-- 字符集过滤 -->

在resource中创建applicationContext.xml

applicationContext.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"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    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
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd">
    <!-- 自动扫描 -->
    <context:component-scan base-package="online.shixun.project">
        <!-- 扫描时跳过 @Controller 注解的JAVA类（控制器） -->
        <context:exclude-filter type="annotation"
            expression="org.springframework.stereotype.Controller" />
        <context:exclude-filter type="annotation"
            expression="org.springframework.web.bind.annotation.ControllerAdvice" />
    </context:component-scan>
</beans>

创建包service,在其中创建UserService.java

UserService.java
@Service
public class UserService {

    public String test(){
        return "hello";
    }
}

调整UserController.java,体现Spring IoC

@Controller
public class UserController {

    @Autowired
    private UserService userService;

    @RequestMapping(value="hello")
    public String hello(){
        return userService.test();
    }

}

现在我们启动一下项目，就能体现出IoC的特征了。