请求映射处理

RequestMappingHandlerMapping

在配置类


@Configuration
@ComponentScan
@PropertySource("classpath:application.properties")
@EnableConfigurationProperties({WebMvcProperties.class, ServerProperties.class})
public class WebConfig {
    // ⬅️内嵌 web 容器工厂
    @Bean
    public TomcatServletWebServerFactory tomcatServletWebServerFactory(ServerProperties serverProperties) {
        return new TomcatServletWebServerFactory(serverProperties.getPort());
    }

    // ⬅️创建 DispatcherServlet
    @Bean
    public DispatcherServlet dispatcherServlet() {
        return new DispatcherServlet();
    }

    // ⬅️注册 DispatcherServlet, Spring MVC 的入口
    @Bean
    public DispatcherServletRegistrationBean dispatcherServletRegistrationBean(
            DispatcherServlet dispatcherServlet, WebMvcProperties webMvcProperties) {
        DispatcherServletRegistrationBean registrationBean = new DispatcherServletRegistrationBean(dispatcherServlet, "/");
        registrationBean.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
        return registrationBean;
    }

    // 如果用 DispatcherServlet 初始化时默认添加的组件, 并不会作为 bean, 给测试带来困扰
    // ⬅️1. 加入RequestMappingHandlerMapping
    @Bean
    public RequestMappingHandlerMapping requestMappingHandlerMapping() {
        return new RequestMappingHandlerMapping();
    }


}

RequestMappingHandlerMapping 初始化时，会收集所有 @RequestMapping 映射信息，封装为 Map，其中

key 是 RequestMappingInfo 类型，包括请求路径、请求方法等信息

value 是 HandlerMethod 类型，包括控制器方法对象、控制器对象

有了这个 Map，就可以在请求到达时，快速完成映射，找到 HandlerMethod 并与匹配的拦截器一起返回给 DispatcherServlet


AnnotationConfigServletWebServerApplicationContext context =
                new AnnotationConfigServletWebServerApplicationContext(WebConfig.class);

        // 作用 解析 @RequestMapping 以及派生注解，生成路径与控制器方法的映射关系, 在初始化时就生成
        RequestMappingHandlerMapping handlerMapping = context.getBean(RequestMappingHandlerMapping.class);

        // 获取映射结果
        Map<RequestMappingInfo, HandlerMethod> handlerMethods = handlerMapping.getHandlerMethods();
        handlerMethods.forEach((k, v) -> {
            System.out.println(k + "=" + v);
        });


        // 请求来了，获取控制器方法  返回处理器执行链对象包括拦截器
        MockHttpServletRequest request = new MockHttpServletRequest("GET", "/test4");
        request.setParameter("name", "张三");
        request.addHeader("token", "某个令牌");
        MockHttpServletResponse response = new MockHttpServletResponse();
        HandlerExecutionChain chain = handlerMapping.getHandler(request);
        System.out.println(chain);

RequestMappingHandlerAdapter

WebConfig 中配置RequestMappingHandlerAdapter


@Configuration
@ComponentScan
@PropertySource("classpath:application.properties")
@EnableConfigurationProperties({WebMvcProperties.class, ServerProperties.class})
public class WebConfig {
    // ⬅️内嵌 web 容器工厂
    @Bean
    public TomcatServletWebServerFactory tomcatServletWebServerFactory(ServerProperties serverProperties) {
        return new TomcatServletWebServerFactory(serverProperties.getPort());
    }

    // ⬅️创建 DispatcherServlet
    @Bean
    public DispatcherServlet dispatcherServlet() {
        return new DispatcherServlet();
    }

    // ⬅️注册 DispatcherServlet, Spring MVC 的入口
    @Bean
    public DispatcherServletRegistrationBean dispatcherServletRegistrationBean(
            DispatcherServlet dispatcherServlet, WebMvcProperties webMvcProperties) {
        DispatcherServletRegistrationBean registrationBean = new DispatcherServletRegistrationBean(dispatcherServlet, "/");
        registrationBean.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
        return registrationBean;
    }

    // 如果用 DispatcherServlet 初始化时默认添加的组件, 并不会作为 bean, 给测试带来困扰
    // ⬅️1. 加入RequestMappingHandlerMapping
    @Bean
    public RequestMappingHandlerMapping requestMappingHandlerMapping() {
        return new RequestMappingHandlerMapping();
    }

    // ⬅️2. 继续加入RequestMappingHandlerAdapter, 会替换掉 DispatcherServlet 默认的 4 个 HandlerAdapter
    @Bean
    public MyRequestMappingHandlerAdapter requestMappingHandlerAdapter() {
        TokenArgumentResolver tokenArgumentResolver = new TokenArgumentResolver();
        YmlReturnValueHandler ymlReturnValueHandler = new YmlReturnValueHandler();
        MyRequestMappingHandlerAdapter handlerAdapter = new MyRequestMappingHandlerAdapter();
        return handlerAdapter;
    }


}

自定义RequestMappingHandlerAdapter


public class MyRequestMappingHandlerAdapter extends RequestMappingHandlerAdapter {
    @Override
    public ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
        return super.invokeHandlerMethod(request, response, handlerMethod);
    }
}


public class A20 {
    private static final Logger log = LoggerFactory.getLogger(A20.class);

    public static void main(String[] args) throws Exception {
        AnnotationConfigServletWebServerApplicationContext context =
                new AnnotationConfigServletWebServerApplicationContext(WebConfig.class);

        // 作用 解析 @RequestMapping 以及派生注解，生成路径与控制器方法的映射关系, 在初始化时就生成
        RequestMappingHandlerMapping handlerMapping = context.getBean(RequestMappingHandlerMapping.class);

        // 获取映射结果
        Map<RequestMappingInfo, HandlerMethod> handlerMethods = handlerMapping.getHandlerMethods();
        handlerMethods.forEach((k, v) -> {
            System.out.println(k + "=" + v);
        });

        // 请求来了，获取控制器方法  返回处理器执行链对象
        MockHttpServletRequest request = new MockHttpServletRequest("GET", "/test4");
        request.setParameter("name", "张三");
        request.addHeader("token", "某个令牌");
        MockHttpServletResponse response = new MockHttpServletResponse();
        HandlerExecutionChain chain = handlerMapping.getHandler(request);
        System.out.println(chain);

        System.out.println(">>>>>>>>>>>>>>>>>>>>>");
        // HandlerAdapter 作用: 调用控制器方法
        MyRequestMappingHandlerAdapter handlerAdapter = context.getBean(MyRequestMappingHandlerAdapter.class);
        handlerAdapter.invokeHandlerMethod(request, response, (HandlerMethod) chain.getHandler());
         // 检查响应
        byte[] content = response.getContentAsByteArray();
        System.out.println(new String(content, StandardCharsets.UTF_8));
    }
}

RequestMappingHandlerAdapter 的invokeHandlerMethod（）方法 最终会去调用控制器

参数解析器


System.out.println(">>>>>>>>>>>>>>>>>>>>> 所有参数解析器");
        for (HandlerMethodArgumentResolver resolver : handlerAdapter.getArgumentResolvers()) {
            System.out.println(resolver);
        }

自定义参数解析器


// 例如经常需要用到请求头中的 token 信息, 用下面注解来标注由哪个参数来获取它
// token=令牌
@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
public @interface Token {
}

实现HandlerMethodArgumentResolver


public class TokenArgumentResolver implements HandlerMethodArgumentResolver {
    @Override
    // 是否支持某个参数
    public boolean supportsParameter(MethodParameter parameter) {
        Token token = parameter.getParameterAnnotation(Token.class);
        return token != null;
    }

    @Override
    // 解析参数
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
                                  NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        return webRequest.getHeader("token");
    }
}

设置自定义参数处理器


@Bean
    public MyRequestMappingHandlerAdapter requestMappingHandlerAdapter() {
        TokenArgumentResolver tokenArgumentResolver = new TokenArgumentResolver();
        YmlReturnValueHandler ymlReturnValueHandler = new YmlReturnValueHandler();
        MyRequestMappingHandlerAdapter handlerAdapter = new MyRequestMappingHandlerAdapter();
        handlerAdapter.setCustomArgumentResolvers(List.of(tokenArgumentResolver));
        handlerAdapter.setCustomReturnValueHandlers(List.of(ymlReturnValueHandler));
        return handlerAdapter;
    }


@PutMapping("/test3")
    public ModelAndView test3(@Token String token) {
        log.debug("test3({})", token);
        return null;
    }


       // 请求来了，获取控制器方法  返回处理器执行链对象
        MockHttpServletRequest request = new MockHttpServletRequest("PUT", "/test3");
        request.setParameter("name", "张三");
        request.addHeader("token", "某个令牌");
        MockHttpServletResponse response = new MockHttpServletResponse();
        HandlerExecutionChain chain = handlerMapping.getHandler(request);
        System.out.println(chain);

        System.out.println(">>>>>>>>>>>>>>>>>>>>>");
        // HandlerAdapter 作用: 调用控制器方法
        MyRequestMappingHandlerAdapter handlerAdapter = context.getBean(MyRequestMappingHandlerAdapter.class);
        handlerAdapter.invokeHandlerMethod(request, response, (HandlerMethod) chain.getHandler());

        // 检查响应
        byte[] content = response.getContentAsByteArray();
        System.out.println(new String(content, StandardCharsets.UTF_8));

返回值解析器


System.out.println(">>>>>>>>>>>>>>>>>>>>> 所有返回值解析器");
        for (HandlerMethodReturnValueHandler handler : handlerAdapter.getReturnValueHandlers()) {
            System.out.println(handler);
        }

自定义返回值处理器


@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Yml {
}

实现HandlerMethodReturnValueHandler 接口


public class YmlReturnValueHandler implements HandlerMethodReturnValueHandler {
    @Override
    public boolean supportsReturnType(MethodParameter returnType) {
        Yml yml = returnType.getMethodAnnotation(Yml.class);
        return yml != null;
    }

    @Override                   //  返回值
    public void handleReturnValue(Object returnValue, MethodParameter returnType,
                                  ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
        // 1. 转换返回结果为 yaml 字符串
        String str = new Yaml().dump(returnValue);

        // 2. 将 yaml 字符串写入响应
        HttpServletResponse response = webRequest.getNativeResponse(HttpServletResponse.class);
        response.setContentType("text/plain;charset=utf-8");
        response.getWriter().print(str);

        // 3. 设置请求已经处理完毕
        mavContainer.setRequestHandled(true);
    }
}

配置类在handlerAdapter里添加自定义返回值处理器


@Bean
public MyRequestMappingHandlerAdapter requestMappingHandlerAdapter() {
        TokenArgumentResolver tokenArgumentResolver = new TokenArgumentResolver();
        YmlReturnValueHandler ymlReturnValueHandler = new YmlReturnValueHandler();
        MyRequestMappingHandlerAdapter handlerAdapter = new MyRequestMappingHandlerAdapter();
        handlerAdapter.setCustomArgumentResolvers(List.of(tokenArgumentResolver));
        handlerAdapter.setCustomReturnValueHandlers(List.of(ymlReturnValueHandler));
        return handlerAdapter;


    @RequestMapping("/test4")
    @Yml
    public User test4() {
        log.debug("test4");
        return new User("张三", 18);
    }