Spring MVC

April 20, 2023

java spring

https://docs.spring.io/spring-framework/docs/current/reference/html/web.html
https://springdoc.cn/spring/web.html

关于 servlet 接口参见此处

MVC

Model: 模型是数据源到对象的映射（e.g. javaBean）

View: 视图层是用户看见的 GUI 界面，在代码中则体现为 HTML 模板（e.g. jsp）

Controller: 控制器提供了视图层的数据源（e.g. servlet）

Spring MVC

启用 Spring MVC

java

@Configuration
@ComponentScan
@EnableWebMvc // 启用Spring MVC
@EnableTransactionManagement
@PropertySource("classpath:/jdbc.properties")
public class AppConfig {
    // ...
}

配置 SpringWebMvc （非必须）

java

// 将 /static/** 路由映射为本地的 /static/ 路径，作静态资源处理
@Bean
WebMvcConfigurer createWebMvcConfigurer() {
    return new WebMvcConfigurer() {
        @Override
        public void addResourceHandlers(ResourceHandlerRegistry registry) {
            registry.addResourceHandler("/static/**").addResourceLocations("/static/");
        }
    };
}


// 配置 Pebble 模板引擎
@Bean
ViewResolver createViewResolver(@Autowired ServletContext servletContext) {
    var engine = new PebbleEngine.Builder().autoEscaping(true)
            // cache:
            .cacheActive(false)
            // loader:
            .loader(new Servlet5Loader(servletContext))
            .build();
    var viewResolver = new PebbleViewResolver(engine);
    viewResolver.setPrefix("/WEB-INF/templates/");
    viewResolver.setSuffix("");
    return viewResolver;
}

编写 SpringMVC 的 Controller

参见：https://springdoc.cn/spring/web.html#mvc-ann-requestmapping

java

@Controller  // 使用 @Controller 标记而不是 @Component
@RequestMapping("/user") // 可以通过 RequestMapping 对路由进行分组
public class UserController {
    @Autowired
    UserService userService;

    // 返回ModelAndView用于模板渲染（具体能返回什么，参见上面的文档）
    @GetMapping("/")
    public ModelAndView index() {
        return new ModelAndView("redirect:/signin")
    }
    // 或者，可以直接返回String来重定向
    public String index() {
        if (...) {
            return "redirect:/signin";
        } else {
            return "redirect:/profile";
        }
    }

    // Controller方法具体能使用什么注解，能带什么参数，参见上面的文档
    @PostMapping("/signin")
    public ModelAndView doSignin(
        @RequestParam("email") String email,
        @RequestParam("password") String password,
        HttpSession session) {
        // ...
    }

    @GetMapping("/download")
    public void download(HttpServletResponse response) throws IOException {
        byte[] data = /* ... */
        response.setContentType("application/octet-stream");
        OutputStream output = response.getOutputStream();
        output.write(data);
        output.flush();
    }

    @PostMapping(value = "/json",
            consumes = "application/json;charset=UTF-8",
            produces = "application/json;charset=UTF-8")
    @ResponseBody
    public String rest(@RequestBody User user) {
        return "{\"success\":true}";
    }
}

实现 Restful 接口

使用 @RestController 替代 @Controller 就可以实现 Restful 接口
注：需要安装 com.fasterxml.jackson.core:jackson-databind

java

@RequestMapping("/api")
public class ApiController {
    @Autowired
    UserService userService;

    @GetMapping("/users")
    public List<User> users() {
        return userService.getUsers();
    }

    @GetMapping("/users/{id}")
    public User user(@PathVariable("id") long id) {
        return userService.getUserById(id);
    }

    public static class SignInRequest {
        public String email;
        public String password;
    }
    @PostMapping("/signin")
    public Map<String, Object> signin(@RequestBody SignInRequest signinRequest) {
        try {
            User user = userService.signin(signinRequest.email, signinRequest.password);
            return Map.of("user", user);
        } catch (Exception e) {
            return Map.of("error", "SIGNIN_FAILED", "message", e.getMessage());
        }
    }
}

由于 Spring 使用 Jackson 进行序列化，故应参见 Jackson 文档来应用其序列化规则

java

public class User {
    /* ... */

    @JsonIgnore
    public String getInnerProperty() {
        return innerProperty;
    }

    @JsonProperty(access = Access.WRITE_ONLY)
    public String getPassword() {
        return password;
    }
}

Filter

配置 web.xml

xml

<web-app>
    <filter>
        <filter-name>authFilter</filter-name>
        <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
        <!-- 这里是 Spring 提供的 DelegatingFilterProxy 类，而不是我们的 AuthFilter 类 -->
        <!-- 该类通过代理模式，使得我们的类可以像其它 Spring 类一样利用 IoC 特性 -->
    </filter>

    <filter-mapping>
        <filter-name>authFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
    ...
</web-app>

若 Filter 名称与 Spring 容器的 Bean 名称不一致

xml

<filter>
    <filter-name>basicAuthFilter</filter-name>
    <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
    <init-param>
        <!-- 此处指定 Bean 的名称 -->
        <param-name>targetBeanName</param-name>
        <param-value>authFilter</param-value>
    </init-param>
</filter>

下面的 Filter 拦截 Authorization 请求头

java

@Component
public class AuthFilter implements Filter {
    @Autowired
    UserService userService;

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) request;
        // 获取Authorization头:
        String authHeader = req.getHeader("Authorization");
        if (authHeader != null && authHeader.startsWith("Basic ")) {
            // 从Header中提取email和password:
            String email = prefixFrom(authHeader);
            String password = suffixFrom(authHeader);
            // 登录:
            User user = userService.signin(email, password);
            // 放入Session:
            req.getSession().setAttribute(UserController.KEY_USER, user);
        }
        // 继续处理请求:
        chain.doFilter(request, response);
    }
}