Spring MVC 入門實戰：從零構建返回字符串的簡單控制器

項目結構預覽

核心配置文件：spring-servlet.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="https://www.springframework.org/schema/beans"
       xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
       xmlns:p="https://www.springframework.org/schema/p"
       xmlns:context="https://www.springframework.org/schema/context"
       xmlns:aop="https://www.springframework.org/schema/aop"
       xsi:schemaLocation="
           https://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans-3.0.xsd
           https://www.springframework.org/schema/aop https://www.springframework.org/schema/aop/spring-aop-3.0.xsd
           https://www.springframework.org/schema/tx https://www.springframework.org/schema/tx/spring-tx-3.0.xsd
           https://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context-3.0.xsd">

    <!-- 啟用 @AspectJ AOP 支持 -->
    <aop:aspectj-autoproxy/>

    <!-- 掃描 com.yxl 包及子包下所有帶註解的類 -->
    <context:component-scan base-package="com.yxl.*" />

    <!-- 配置返回值處理器：支持 String 直接返回、對象自動轉 JSON -->
    <bean id="handleAdapter" class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter">
        <property name="messageConverters">
            <list>
                <ref bean="mappingJacksonHttpMessageConverter" /> <!-- JSON 轉換器 -->
                <ref bean="mappingStringHttpMessageConverter" /> <!-- String 轉換器 -->
            </list>
        </property>
    </bean>

    <bean id="mappingJacksonHttpMessageConverter" class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter" />
    <bean id="mappingStringHttpMessageConverter" class="org.springframework.http.converter.StringHttpMessageConverter" />

    <!-- 視圖解析器：JSP 前綴/後綴 -->
    <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/jsp/" />
        <property name="suffix" value=".jsp" />
        <property name="order" value="1" />
    </bean>

    <!-- 文件上傳編碼 -->
    <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver" p:defaultEncoding="utf-8" />

</beans>

Web 部署描述符：web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
         xmlns="https://java.sun.com/xml/ns/javaee"
         xmlns:web="https://java.sun.com/xml/ns/javaee/web-app_2.5.xsd"
         xsi:schemaLocation="https://java.sun.com/xml/ns/javaee https://java.sun.com/xml/ns/javaee/web-app_2.5.xsd"
         id="WebApp_ID" version="2.5">

    <display-name>springmvc1</display-name>
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>

    <!-- 編碼過濾器 -->
    <filter>
        <filter-name>characterEncodingFilter</filter-name>
        <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
        <init-param><param-name>encoding</param-name><param-value>UTF-8</param-value></init-param>
        <init-param><param-name>forceEncoding</param-name><param-value>true</param-value></init-param>
    </filter>
    <filter-mapping><filter-name>characterEncodingFilter</filter-name><url-pattern>/*</url-pattern></filter-mapping>

    <!-- DispatcherServlet 核心控制器 -->
    <servlet>
        <servlet-name>Spring MVC Dispatcher Servlet</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>/WEB-INF/spring-servlet.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>Spring MVC Dispatcher Servlet</servlet-name>
        <url-pattern>/</url-pattern> <!-- 攔截所有請求 -->
    </servlet-mapping>

</web-app>

控制器實現

@Controller
@RequestMapping("/demo")
public class StringController {

    @RequestMapping("/hello")
    @ResponseBody  // 直接返回字符串，不經視圖解析
    public String hello() {
        return "Hello Spring MVC!";
    }

    @RequestMapping("/json")
    @ResponseBody
    public User jsonDemo() {
        return new User("張三", 25); // 自動轉 JSON
    }
}

關鍵點總結

1. DispatcherServlet 是前端控制器，攔截 / 所有請求
2. context:component-scan 開啟註解掃描，自動註冊 @Controller
3. AnnotationMethodHandlerAdapter + MessageConverter 實現 @ResponseBody 直接返回數據
4. InternalResourceViewResolver 解析 JSP 視圖路徑
5. 編碼過濾器確保中文不亂碼

現代化升級建議

• Spring Boot 2.3+：spring-boot-starter-web 零配置啟動
• 使用 @RestController 合併 @Controller + @ResponseBody
• 視圖層遷移 Thymeleaf/FreeMarker 或前後端分離 (Vue/React)
• 配置類替代 XML：@Configuration + @EnableWebMvc