SpringBoot(五)

请求处理

1.Rest 映射及源码解析

请求映射

  • @xxxMapping;

    • @GetMapping
    • @PostMapping
    • @PutMapping
    • @DeleteMapping

  • Rest 风格支持（使用HTTP请求方式动词来表示对资源的操作）

    • 以前：
      • /getUser 获取用户
      • /deleteUser 删除用户
      • /editUser 修改用户
      • /saveUser 保存用户
    • 现在： /user
      • GET-获取用户
      • DELETE-删除用户
      • PUT-修改用户
      • POST-保存用户
    • 核心 Filter；HiddenHttpMethodFilter

用法

  • 开启页面表单的 Rest 功能
  • 页面 form 的属性 method=post，隐藏域 _method=put、delete 等（如果直接 get 或 post，无需隐藏域）
  • 编写请求映射
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spring:
  mvc:
    hidden method:
      filter:
        enabled: true #开启页面表单的Rest功能

index

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<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>REST Form Submissions</title>
  </head>
  <body>
    <form action="/user" method="get">
      <input value="REST-GET提交" type="submit" />
    </form>

    <form action="/user" method="post">
      <input value="REST-POST提交" type="submit" />
    </form>

    <form action="/user" method="post">
      <input name="_method" type="hidden" value="DELETE" />
      <input value="REST-DELETE 提交" type="submit" />
    </form>

    <form action="/user" method="post">
      <input name="_method" type="hidden" value="PUT" />
      <input value="REST-PUT提交" type="submit" />
    </form>
  </body>
</html>

HelloController

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@RequestMapping(value = "/user", method = RequestMethod.GET)
    public String getUser() {
        return "GET-张三";
    }

    @RequestMapping(value = "/user", method = RequestMethod.POST)
    public String postUser() {
        return "POST-张三";
    }

    @RequestMapping(value = "/user", method = RequestMethod.PUT)
    public String putUser() {
        return "PUT-张三";
    }

    @RequestMapping(value = "/user", method = RequestMethod.DELETE)
    public String deleteUser() {
        return "DELETE-张三";
    }

Rest 原理（表单提交要使用 REST 的时候）

  • 表单提交会带上\_method=PUT
  • 请求过来被HiddenHttpMethodFilter拦截
    • 请求是否正常，并且是 POST
      • 获取到\_method的值。
      • 兼容以下请求；PUT.DELETE.PATCH
      • 原生 request（post），包装模式 requesWrapper 重写了 getMethod 方法，返回的是传入的值。
      • 过滤器链放行的时候用 wrapper。以后的方法调用 getMethod 是调用 requesWrapper 的。

HiddenHttpMethodFilter

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public class HiddenHttpMethodFilter extends OncePerRequestFilter {

	private static final List<String> ALLOWED_METHODS =
			Collections.unmodifiableList(Arrays.asList(HttpMethod.PUT.name(),
					HttpMethod.DELETE.name(), HttpMethod.PATCH.name()));

	/** Default method parameter: {@code _method}. */
	public static final String DEFAULT_METHOD_PARAM = "_method";

	private String methodParam = DEFAULT_METHOD_PARAM;


	/**
	 * Set the parameter name to look for HTTP methods.
	 * @see #DEFAULT_METHOD_PARAM
	 */
	public void setMethodParam(String methodParam) {
		Assert.hasText(methodParam, "'methodParam' must not be empty");
		this.methodParam = methodParam;
	}

	@Override
	protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
			throws ServletException, IOException {

		HttpServletRequest requestToUse = request;

		if ("POST".equals(request.getMethod()) && request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) == null) {
			String paramValue = request.getParameter(this.methodParam);
			if (StringUtils.hasLength(paramValue)) {
				String method = paramValue.toUpperCase(Locale.ENGLISH);
				if (ALLOWED_METHODS.contains(method)) {
					requestToUse = new HttpMethodRequestWrapper(request, method);
				}
			}
		}

		filterChain.doFilter(requestToUse, response);
	}


	/**
	 * Simple {@link HttpServletRequest} wrapper that returns the supplied method for
	 * {@link HttpServletRequest#getMethod()}.
	 */
	private static class HttpMethodRequestWrapper extends HttpServletRequestWrapper {

		private final String method;

		public HttpMethodRequestWrapper(HttpServletRequest request, String method) {
			super(request);
			this.method = method;
		}

		@Override
		public String getMethod() {
			return this.method;
		}
	}

}

Rest使用客户端工具。

  • 如PostMan可直接发送put、delete等方式请求。

2.怎么改变默认的_method

WebMvcAutoConfiguration

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@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class,
		ValidationAutoConfiguration.class })
public class WebMvcAutoConfiguration {

    ...
    
    @Bean
    @ConditionalOnMissingBean(HiddenHttpMethodFilter.class)
    @ConditionalOnProperty(prefix = "spring.mvc.hiddenmethod.filter", name = "enabled", matchIfMissing = false)
    public OrderedHiddenHttpMethodFilter hiddenHttpMethodFilter() {
        return new OrderedHiddenHttpMethodFilter();
    }
    
    ...
}

@ConditionalOnMissingBean(HiddenHttpMethodFilter.class)意味着在没有HiddenHttpMethodFilter时，才执行hiddenHttpMethodFilter()。因此，我们可以自定义filter，改变默认的\_method。例如：

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@Configuration(proxyBeanMethods = false)
public class WebConfig{
    //自定义filter
    @Bean
    public HiddenHttpMethodFilter hiddenHttpMethodFilter(){
        HiddenHttpMethodFilter methodFilter = new HiddenHttpMethodFilter();
        methodFilter.setMethodParam("_m");
        return methodFilter;
    }    
}

将\_method改成_m。

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<form action="/user" method="post">
    <input name="_method" type="hidden" value="DELETE"/>
    <input value="REST-DELETE 提交" type="submit"/>
</form>

<form action="/user" method="post">
    <input name="_method" type="hidden" value="PUT" />
    <input value="REST-PUT提交" type="submit" />
</form>

3.请求映射原理

20241112114603

SpringMVC功能分析都从 org.springframework.web.servlet.DispatcherServlet -> doDispatch()

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protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    HttpServletRequest processedRequest = request;
    HandlerExecutionChain mappedHandler = null;
    boolean multipartRequestParsed = false;

    WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

    try {
        ModelAndView mv = null;
        Exception dispatchException = null;

        try {
            processedRequest = checkMultipart(request);
            multipartRequestParsed = (processedRequest != request);

            // 找到当前请求使用哪个Handler（Controller的方法）处理
            mappedHandler = getHandler(processedRequest);

            //HandlerMapping：处理器映射。/xxx->>xxxx
    ...
}

getHandler()方法如下：

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@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
    if (this.handlerMappings != null) {
        for (HandlerMapping mapping : this.handlerMappings) {
            HandlerExecutionChain handler = mapping.getHandler(request);
            if (handler != null) {
                return handler;
            }
        }
    }
    return null;
}

this.handlerMappings在Debug模式下展现的内容：
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其中，保存了所有@RequestMapping 和handler的映射规则。
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所有的请求映射都在HandlerMapping中：

  • SpringBoot自动配置欢迎页的 WelcomePageHandlerMapping 。访问 /能访问到index.html；

  • SpringBoot自动配置了默认 的 RequestMappingHandlerMapping

  • 请求进来，挨个尝试所有的HandlerMapping看是否有请求信息。

    • 如果有就找到这个请求对应的handler
    • 如果没有就是下一个 HandlerMapping

  • 我们需要一些自定义的映射处理，我们也可以自己给容器中放HandlerMapping。自定义 HandlerMapping

IDEA快捷键：

  • Ctrl + Alt + U : 以UML的类图展现类有哪些继承类，派生类以及实现哪些接口。
  • Crtl + Alt + Shift + U : 同上，区别在于上条快捷键结果在新页展现，而本条快捷键结果在弹窗展现。
  • Ctrl + H : 以树形方式展现类层次结构图。

4.常用参数注解使用

注解：

  • @PathVariable 路径变量
  • @RequestHeader 获取请求头
  • @RequestParam 获取请求参数（指问号后的参数，url?a=1&b=2）
  • @CookieValue 获取Cookie值
  • @RequestAttribute 获取request域属性
  • @RequestBody 获取请求体[POST]
  • @MatrixVariable 矩阵变量
  • @ModelAttribute
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@RestController
public class ParameterTestController {


    //  car/2/owner/zhangsan
    @GetMapping("/car/{id}/owner/{username}")
    public Map<String,Object> getCar(@PathVariable("id") Integer id,
                                     @PathVariable("username") String name,
                                     @PathVariable Map<String,String> pv,
                                     @RequestHeader("User-Agent") String userAgent,
                                     @RequestHeader Map<String,String> header,
                                     @RequestParam("age") Integer age,
                                     @RequestParam("inters") List<String> inters,
                                     @RequestParam Map<String,String> params,
                                     @CookieValue("_ga") String _ga,
                                     @CookieValue("_ga") Cookie cookie){

        Map<String,Object> map = new HashMap<>();

//        map.put("id",id);
//        map.put("name",name);
//        map.put("pv",pv);
//        map.put("userAgent",userAgent);
//        map.put("headers",header);
        map.put("age",age);
        map.put("inters",inters);
        map.put("params",params);
        map.put("_ga",_ga);
        System.out.println(cookie.getName()+"===>"+cookie.getValue());
        return map;
    }


    @PostMapping("/save")
    public Map postMethod(@RequestBody String content){
        Map<String,Object> map = new HashMap<>();
        map.put("content",content);
        return map;
    }
}

5.@RequestAttribute

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@Controller
public class RequestController {

    @GetMapping("/goto")
    public String goToPage(HttpServletRequest request){

        request.setAttribute("msg","成功了...");
        request.setAttribute("code",200);
        return "forward:/success";  //转发到  /success请求
    }

    @GetMapping("/params")
    public String testParam(Map<String,Object> map,
                            Model model,
                            HttpServletRequest request,
                            HttpServletResponse response){
        map.put("hello","world666");
        model.addAttribute("world","hello666");
        request.setAttribute("message","HelloWorld");

        Cookie cookie = new Cookie("c1","v1");
        response.addCookie(cookie);
        return "forward:/success";
    }

    ///<-----------------主角@RequestAttribute在这个方法
    @ResponseBody
    @GetMapping("/success")
    public Map success(@RequestAttribute(value = "msg",required = false) String msg,
                       @RequestAttribute(value = "code",required = false)Integer code,
                       HttpServletRequest request){
        Object msg1 = request.getAttribute("msg");

        Map<String,Object> map = new HashMap<>();
        Object hello = request.getAttribute("hello");
        Object world = request.getAttribute("world");
        Object message = request.getAttribute("message");

        map.put("reqMethod_msg",msg1);
        map.put("annotation_msg",msg);
        map.put("hello",hello);
        map.put("world",world);
        map.put("message",message);

        return map;
    }
}

6.@MatrixVariable与UrlPathHelper

  1. 语法： 请求路径：/cars/sell;low=34;brand=byd,audi,yd

  2. SpringBoot默认是禁用了矩阵变量的功能

    • 手动开启：原理。对于路径的处理。UrlPathHelper的removeSemicolonContent设置为false，让其支持矩阵变量的。

  3. 矩阵变量必须有url路径变量才能被解析

手动开启矩阵变量：

  • 实现WebMvcConfigurer接口：
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@Configuration(proxyBeanMethods = false)
public class WebConfig implements WebMvcConfigurer {
    @Override
    public void configurePathMatch(PathMatchConfigurer configurer) {

        UrlPathHelper urlPathHelper = new UrlPathHelper();
        // 不移除；后面的内容。矩阵变量功能就可以生效
        urlPathHelper.setRemoveSemicolonContent(false);
        configurer.setUrlPathHelper(urlPathHelper);
    }
}
  • 创建返回WebMvcConfigurerBean：
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@Configuration(proxyBeanMethods = false)
public class WebConfig{
    @Bean
    public WebMvcConfigurer webMvcConfigurer(){
        return new WebMvcConfigurer() {
                        @Override
            public void configurePathMatch(PathMatchConfigurer configurer) {
                UrlPathHelper urlPathHelper = new UrlPathHelper();
                // 不移除；后面的内容。矩阵变量功能就可以生效
                urlPathHelper.setRemoveSemicolonContent(false);
                configurer.setUrlPathHelper(urlPathHelper);
            }
        }
    }
}

@MatrixVariable的用例

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@RestController
public class ParameterTestController {

    ///cars/sell;low=34;brand=byd,audi,yd
    @GetMapping("/cars/{path}")
    public Map carsSell(@MatrixVariable("low") Integer low,
                        @MatrixVariable("brand") List<String> brand,
                        @PathVariable("path") String path){
        Map<String,Object> map = new HashMap<>();

        map.put("low",low);
        map.put("brand",brand);
        map.put("path",path);
        return map;
    }

    // /boss/1;age=20/2;age=10

    @GetMapping("/boss/{bossId}/{empId}")
    public Map boss(@MatrixVariable(value = "age",pathVar = "bossId") Integer bossAge,
                    @MatrixVariable(value = "age",pathVar = "empId") Integer empAge){
        Map<String,Object> map = new HashMap<>();

        map.put("bossAge",bossAge);
        map.put("empAge",empAge);
        return map;

    }

}