Spring框架-Spring MVC详解

Spring MVC详解

Spring MVC简介

Spring MVC是Spring框架的一个模块，专门用于开发Web应用。它实现了模型-视图-控制器(MVC)设计模式，将业务逻辑、数据模型和视图渲染分离，使代码更加简洁、可维护。作为Java领域最流行的Web开发框架之一，Spring MVC提供了强大且灵活的功能支持。

Spring MVC工作流程

1. 客户端（浏览器）发送请求到前端控制器DispatcherServlet
2. DispatcherServlet根据请求信息调用HandlerMapping，解析请求对应的Handler
3. 解析到对应的Handler（Controller控制器）后，由HandlerAdapter适配器处理
4. HandlerAdapter执行Handler，返回ModelAndView对象（包含模型数据和视图名）
5. ViewResolver解析视图名，查找实际的View对象
6. View使用模型数据渲染结果，通过DispatcherServlet返回给客户端

配置Spring MVC

XML配置方式

<web-app>
    <!-- 配置DispatcherServlet -->
    <servlet>
        <servlet-name>dispatcher</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>/WEB-INF/spring-mvc-config.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>dispatcher</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
</web-app>

<!-- spring-mvc-config.xml -->
<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">

    <!-- 启用注解驱动 -->
    <mvc:annotation-driven/>
    
    <!-- 组件扫描 -->
    <context:component-scan base-package="com.example.controller"/>
    
    <!-- 视图解析器 -->
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/views/"/>
        <property name="suffix" value=".jsp"/>
    </bean>
    
    <!-- 静态资源处理 -->
    <mvc:resources mapping="/resources/**" location="/resources/"/>
</beans>

Java配置方式

@Configuration
@EnableWebMvc
@ComponentScan("com.example.controller")
public class WebConfig implements WebMvcConfigurer {
    
    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        registry.addResourceHandler("/resources/**")
                .addResourceLocations("/resources/");
    }
    
    @Bean
    public ViewResolver viewResolver() {
        InternalResourceViewResolver resolver = new InternalResourceViewResolver();
        resolver.setPrefix("/WEB-INF/views/");
        resolver.setSuffix(".jsp");
        return resolver;
    }
}

public class WebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {

    @Override
    protected Class<?>[] getRootConfigClasses() {
        return new Class<?>[] { RootConfig.class };
    }

    @Override
    protected Class<?>[] getServletConfigClasses() {
        return new Class<?>[] { WebConfig.class };
    }

    @Override
    protected String[] getServletMappings() {
        return new String[] { "/" };
    }
}

控制器(Controller)开发

基本Controller

@Controller
public class UserController {
    
    private final UserService userService;
    
    @Autowired
    public UserController(UserService userService) {
        this.userService = userService;
    }
    
    @RequestMapping(value = "/users", method = RequestMethod.GET)
    public String listUsers(Model model) {
        model.addAttribute("users", userService.getAllUsers());
        return "users/list"; // 返回视图名
    }
    
    @RequestMapping(value = "/users/{id}", method = RequestMethod.GET)
    public String getUserById(@PathVariable("id") Long id, Model model) {
        model.addAttribute("user", userService.getUserById(id));
        return "users/detail";
    }
}

REST风格Controller

@RestController
@RequestMapping("/api/users")
public class UserRestController {
    
    private final UserService userService;
    
    @Autowired
    public UserRestController(UserService userService) {
        this.userService = userService;
    }
    
    @GetMapping
    public List<User> getAllUsers() {
        return userService.getAllUsers();
    }
    
    @GetMapping("/{id}")
    public User getUser(@PathVariable Long id) {
        return userService.getUserById(id);
    }
    
    @PostMapping
    @ResponseStatus(HttpStatus.CREATED)
    public User createUser(@RequestBody User user) {
        return userService.createUser(user);
    }
    
    @PutMapping("/{id}")
    public User updateUser(@PathVariable Long id, @RequestBody User user) {
        return userService.updateUser(id, user);
    }
    
    @DeleteMapping("/{id}")
    @ResponseStatus(HttpStatus.NO_CONTENT)
    public void deleteUser(@PathVariable Long id) {
        userService.deleteUser(id);
    }
}

请求处理注解

注解	描述
@RequestMapping	为控制器类或方法指定URL映射
@GetMapping	处理HTTP GET请求
@PostMapping	处理HTTP POST请求
@PutMapping	处理HTTP PUT请求
@DeleteMapping	处理HTTP DELETE请求
@PatchMapping	处理HTTP PATCH请求
@PathVariable	获取URL路径中的变量
@RequestParam	获取请求参数
@RequestBody	获取请求体并转换为Java对象
@RequestHeader	获取请求头
@ModelAttribute	添加属性到模型中或绑定表单参数
@SessionAttribute	获取Session属性
@CookieValue	获取Cookie值
@ResponseBody	标记方法返回值直接写入响应体
@ResponseStatus	定义HTTP响应状态码

表单处理

@Controller
@RequestMapping("/register")
public class RegisterController {
    
    private final UserService userService;
    
    @Autowired
    public RegisterController(UserService userService) {
        this.userService = userService;
    }
    
    // 显示注册表单
    @GetMapping
    public String showRegistrationForm(Model model) {
        model.addAttribute("user", new UserForm());
        return "register";
    }
    
    // 处理表单提交
    @PostMapping
    public String processRegistration(@Valid @ModelAttribute("user") UserForm userForm,
                                     BindingResult result) {
        // 表单验证失败
        if (result.hasErrors()) {
            return "register";
        }
        
        // 处理注册逻辑
        userService.register(userForm);
        
        return "redirect:/login";
    }
}

文件上传

@Controller
public class FileUploadController {
    
    @PostMapping("/upload")
    public String handleFileUpload(@RequestParam("file") MultipartFile file,
                                  RedirectAttributes redirectAttributes) {
        
        if (file.isEmpty()) {
            redirectAttributes.addFlashAttribute("message", "请选择要上传的文件");
            return "redirect:/uploadForm";
        }

        try {
            String filename = file.getOriginalFilename();
            byte[] bytes = file.getBytes();
            Path path = Paths.get("uploads/" + filename);
            Files.write(path, bytes);
            
            redirectAttributes.addFlashAttribute("message", 
                "成功上传文件 '" + filename + "'");

        } catch (IOException e) {
            e.printStackTrace();
        }

        return "redirect:/uploadStatus";
    }
}

异常处理

@ExceptionHandler方法

@Controller
public class UserController {
    
    @ExceptionHandler(UserNotFoundException.class)
    public ModelAndView handleUserNotFoundException(UserNotFoundException ex) {
        ModelAndView mav = new ModelAndView("error/not-found");
        mav.addObject("message", ex.getMessage());
        return mav;
    }
    
    // 控制器方法...
}

全局异常处理器

@ControllerAdvice
public class GlobalExceptionHandler {
    
    @ExceptionHandler(Exception.class)
    public ModelAndView handleGlobalException(Exception ex) {
        ModelAndView mav = new ModelAndView("error/generic");
        mav.addObject("message", ex.getMessage());
        return mav;
    }
    
    @ExceptionHandler(UserNotFoundException.class)
    @ResponseStatus(HttpStatus.NOT_FOUND)
    public ModelAndView handleUserNotFoundException(UserNotFoundException ex) {
        ModelAndView mav = new ModelAndView("error/not-found");
        mav.addObject("message", ex.getMessage());
        return mav;
    }
    
    @ExceptionHandler(DataAccessException.class)
    @ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
    public ModelAndView handleDataAccessException(DataAccessException ex) {
        ModelAndView mav = new ModelAndView("error/database");
        mav.addObject("message", "数据库访问错误");
        return mav;
    }
}

拦截器(Interceptor)

public class LoggingInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, 
                           Object handler) throws Exception {
        System.out.println("请求前调用: " + request.getRequestURI());
        return true; // 返回true才会继续执行
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, 
                         Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("控制器执行后调用: " + request.getRequestURI());
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, 
                              Object handler, Exception ex) throws Exception {
        System.out.println("视图渲染后调用: " + request.getRequestURI());
    }
}

注册拦截器：

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
    
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LoggingInterceptor())
                .addPathPatterns("/**")
                .excludePathPatterns("/admin/**");
    }
}

总结

Spring MVC是一个强大的Web开发框架，提供了完整的MVC实现，使开发人员可以轻松构建可扩展的Web应用程序。它的特点包括：

1. 清晰的角色分离，遵循MVC设计模式
2. 灵活的配置选项（XML或Java配置）
3. 强大的注解支持，减少样板代码
4. 与Spring生态系统的无缝集成
5. 丰富的功能支持：表单处理、文件上传、异常处理等
6. REST API支持

随着微服务架构和前后端分离的兴起，Spring MVC被广泛用于构建RESTful服务，而Spring Boot更是简化了Spring MVC的配置，使开发者可以专注于业务逻辑的实现。