第一篇：Spring MVC 核心架构解析

1. 传统Servlet开发示例

包结构

src/main/java
└── crj
    └── example
        └── servlet
            ├── LegacyServlet.java

LegacyServlet.java

package crj.example.servlet;

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;

/**
 * 传统Servlet实现方式
 * 访问路径：http://localhost:8080/legacy
 */
public class LegacyServlet extends HttpServlet {
    
    @Override
    protected void doGet(HttpServletRequest request, 
                        HttpServletResponse response) 
                        throws ServletException, IOException {
        // 直接处理请求和响应
        response.setContentType("text/plain");
        response.getWriter().write("Legacy Servlet Response");
    }
}

---

2. Spring MVC 实现对比

包结构

src/main/java
└── crj
    └── example
        └── spring
            ├── config
            │   ├── WebInitializer.java  // 替代web.xml
            │   └── AppConfig.java       // Spring配置
            ├── controller
            │   └── DemoController.java
            └── custom
                └── CustomHandlerMapping.java

2.1 WebInitializer.java

package crj.example.spring.config;

import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;

/**
 * 替代传统web.xml配置
 * 相当于注册DispatcherServlet并指定配置类
 */
public class WebInitializer extends 
        AbstractAnnotationConfigDispatcherServletInitializer {

    // 根配置（非Web组件）
    @Override
    protected Class<?>[] getRootConfigClasses() {
        return new Class[0];
    }

    // DispatcherServlet配置类
    @Override
    protected Class<?>[] getServletConfigClasses() {
        return new Class[]{AppConfig.class};
    }

    // 映射路径（处理所有请求）
    @Override
    protected String[] getServletMappings() {
        return new String[]{"/"};
    }
}

2.2 AppConfig.java

package crj.example.spring.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.HandlerMapping;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping;

import crj.example.spring.custom.CustomHandlerMapping;

@Configuration
@EnableWebMvc
@ComponentScan(basePackages = "crj.example.spring.controller")
public class AppConfig {

    /**
     * 自定义HandlerMapping示例
     * 优先级高于默认的RequestMappingHandlerMapping
     */
    @Bean
    public HandlerMapping customHandlerMapping() {
        CustomHandlerMapping mapping = new CustomHandlerMapping();
        mapping.setOrder(0); // 设置最高优先级
        return mapping;
    }

    /**
     * 默认的注解驱动HandlerMapping
     */
    @Bean
    public RequestMappingHandlerMapping requestMappingHandlerMapping() {
        return new RequestMappingHandlerMapping();
    }
}

2.3 DemoController.java

package crj.example.spring.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
public class DemoController {

    /**
     * 注解驱动控制器示例
     * 访问路径：http://localhost:8080/spring
     */
    @GetMapping("/spring")
    @ResponseBody
    public String handleRequest() {
        return "Spring MVC Response";
    }
}

---

3. 自定义HandlerMapping实现

CustomHandlerMapping.java

package crj.example.spring.custom;

import javax.servlet.http.HttpServletRequest;

import org.springframework.core.Ordered;
import org.springframework.web.servlet.HandlerExecutionChain;
import org.springframework.web.servlet.handler.AbstractHandlerMapping;

/**
 * 自定义HandlerMapping示例
 * 处理以 /custom 开头的请求
 */
public class CustomHandlerMapping extends AbstractHandlerMapping {

    @Override
    protected Object getHandlerInternal(HttpServletRequest request) throws Exception {
        String uri = request.getRequestURI();
        
        // 匹配以/custom开头的请求
        if (uri.startsWith("/custom")) {
            return (Runnable) () -> {
                try {
                    request.getServletResponse()
                           .getWriter()
                           .write("Custom HandlerMapping Response");
                } catch (Exception e) {
                    throw new RuntimeException(e);
                }
            };
        }
        return null;
    }

    @Override
    public int getOrder() {
        return Ordered.HIGHEST_PRECEDENCE; // 最高优先级
    }
}

---

4. 测试对比

4.1 访问路径对比

请求类型	URL	响应内容
传统Servlet	/legacy	Legacy Servlet Response
注解驱动Controller	/spring	Spring MVC Response
自定义HandlerMapping	/custom/any	Custom HandlerMapping Response

4.2 处理流程对比图

---

5. 关键注解说明

注解/类	作用说明
@Controller	标记类为控制器，配合@RequestMapping使用
@EnableWebMvc	启用Spring MVC注解驱动配置
AbstractHandlerMapping	实现自定义请求映射逻辑的基类
DispatcherServlet	前端控制器，统一处理所有请求并协调各组件工作

---

6. 项目运行准备

1. 依赖配置（pom.xml）：

<dependencies>
    <!-- Spring MVC -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-webmvc</artifactId>
        <version>5.3.20</version>
    </dependency>

    <!-- Servlet API -->
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>4.0.1</version>
        <scope>provided</scope>
    </dependency>
</dependencies>

2. 部署说明：
   • 使用Tomcat 9+部署
   • 访问路径示例：
     • http://localhost:8080/legacy
     • http://localhost:8080/spring
     • http://localhost:8080/custom/test

---

下一篇预告：
《配置范式演进：XML、JavaConfig 与 Spring Boot》
将涵盖：

• 三种配置方式的详细对比
• 静态资源配置最佳实践
• 热部署技巧与性能调优