Springboot笔记<6>Rest的使用和请求参数注解@PathVariable、@RequestHeader、@ModelAttribute、@RequestParam、@MatrixVariable、@CookieValue、@RequestBody

Rest的使用和原理

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。

看下面的一个例子，这是一个表单：

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <title>hah</title>

</head>

<body>

<form action="/user" method="get">

    <input value="get" type="submit">

</form>

<form action="/user" method="post">

    <input value="post" type="submit">

</form>

<form action="/user" method="post">

    <input value="put" type="submit">

</form>

<form action="/user" method="post">

    <input value="delete" type="submit">

</form>

</body>

</html>

处理上述表单提交的controller。但是我们以put方式和delete方式提交表单时，发现返回的都是GET-张三，不支持put和delete请求。

@RestController

public class UserController {

    @RequestMapping(value = "/user",method = RequestMethod.GET)

    public String getUser(){

        return "GET-张三";

    }

    @RequestMapping(value = "/user",method = RequestMethod.POST)

    public String saveUser(){

        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";

    }

}

在WebMvcAutoConfiguration中hiddenHttpMethodFilter方法，返回一个filter->OrderedHiddenHttpMethodFilter。OrderedHiddenHttpMethodFilter继承自HiddenHttpMethodFilter。@ConditionalOnMissingBean({HiddenHttpMethodFilter.class})需要之前HiddenHttpMethodFilter没有被注入，并且 @ConditionalOnProperty(prefix = "spring.mvc.hiddenmethod.filter", name = {"enabled"})要求spring.mvc.hiddenmethod.filter.enabled=true.

@Bean

    @ConditionalOnMissingBean({HiddenHttpMethodFilter.class})

    @ConditionalOnProperty(

        prefix = "spring.mvc.hiddenmethod.filter",

        name = {"enabled"}

    )

    public OrderedHiddenHttpMethodFilter hiddenHttpMethodFilter() {

        return new OrderedHiddenHttpMethodFilter();

    }

public class OrderedHiddenHttpMethodFilter extends HiddenHttpMethodFilter implements OrderedFilter {

   /**

    * The default order is high to ensure the filter is applied before Spring Security.

    */

   public static final int DEFAULT_ORDER = REQUEST_WRAPPER_FILTER_MAX_ORDER - 10000;

   private int order = DEFAULT_ORDER;

   @Override

   public int getOrder() {

      return this.order;

   }

   public void setOrder(int order) {

      this.order = order;

   }

}

HiddenHttpMethodFilter中有个DEFAULT_METHOD_PARAM字段"_method"。所以我们在提交表单时也要提交一个"_method"参数。并且spring.mvc.hiddenmethod.filter.enabled=true.

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()));

   public static final String DEFAULT_METHOD_PARAM = "_method";

   private String methodParam = 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);

   }

   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;

      }

   }

}

因此修改表单如下：

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <title>hah</title>

</head>

<body>

<form action="/user" method="get">

    <input value="get" type="submit">

</form>

<form action="/user" method="post">

    <input value="post" type="submit">

</form>

<form action="/user" method="post">

    <input name="_method" type="hidden" value="put">

    <input value="put" type="submit">

</form>

<form action="/user" method="post">

    <input name="_method" type="hidden" value="delete">

    <input value="delete" type="submit">

</form>

</body>

</html>

配置yaml:

spring:

  mvc:

    hiddenmethod:

      filter:

        enabled: true #开启页面表单的Rest功能

修改表单，配置yaml之后，再点击delete 和put就可以发送delete 和put请求了。

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
1.如果请求正常，并且是POST（if ("POST".equals(request.getMethod()) && request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) == null) ）则获取_method的值
- 2.获取到_method的值，如果是ALLOWED_METHODS里的方法（PUT.DELETE.PATCH）则将方法传给包装模式类requesWrapper，requesWrapper只改变了请求方式。

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。

@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) {

      // paramValue拿到的是_method

       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);

}

private static final List<String> ALLOWED_METHODS =

      Collections.unmodifiableList(Arrays.asList(HttpMethod.PUT.name(),

            HttpMethod.DELETE.name(), HttpMethod.PATCH.name()));

requesWrapper:

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;

		}

	}

将_method改成其他名字

将_method改成了_m,此时因为程序中无法获取_m，所以我们表单中点击delete依然是post,因此我们需要再更改表单即可。

//自定义filter

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

import org.springframework.web.filter.HiddenHttpMethodFilter;

@Configuration(proxyBeanMethods = false)

public class RestConfig {

    @Bean

    public HiddenHttpMethodFilter hiddenHttpMethodFilter(){

        HiddenHttpMethodFilter methodFilter = new HiddenHttpMethodFilter();

        methodFilter.setMethodParam("_m");

        return methodFilter;

    }

}

修改form表单，添加_m：

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <title>hah</title>

</head>

<body>

<form action="/user" method="get">

    <input value="get" type="submit">

</form>

<form action="/user" method="post">

    <input value="post" type="submit">

</form>

<form action="/user" method="post">

    <input name="_method" type="hidden" value="put">

    <input name="_m" type="hidden" value="put">

    <input value="put" type="submit">

</form>

<form action="/user" method="post">

    <input name="_method" type="hidden" value="delete">

    <input name="_m" type="hidden" value="delete">

    <input value="delete" type="submit">

</form>

</body>

</html>

Rest使用客户端工具

如PostMan直接发送Put、delete等方式请求，无需Filter。表单只能用get,post请求。

请求处理----参数注解

@PathVariable、@RequestHeader、@ModelAttribute、@RequestParam、@MatrixVariable、@CookieValue、@RequestBody

参数注解作用

@PathVariable

作用：@PathVariable是spring3.0的一个新功能：接收请求路径中占位符的值，将URL中占位符参数{xxx}绑定到处理器类的方法形参中@PathVariable(“xxx“)，上如果有多个占位符，形参列表需要定义多个参数，不是很方便，可以直接定义一个map集合 @PathVariable Map<String,String> kv，会自动映射多个参数；

@RequestParam

@RequestParam主要用于将请求参数区域的数据映射到控制层方法的参数上

@RequestParam(value=”参数名”,required=”true/false”,defaultValue=””)

value：请求中传入参数的名称，即前端传过来时定义的参数名。如果不设置value值，则前端定义的参数名必须和后端接口参数名相同
required：该参数是否为必传项。默认是true，表示请求中一定要传入对应的参数，否则会报404错误；如果设置为false，当请求中没有此参数，将会默认为null。而对于基本数据类型的变量，则必须有值，这时会抛出空指针异常。如果允许空值，则接口中变量需要使用包装类来声明。
defaultValue：参数的默认值，如果请求中没有同名的参数时，该变量默认为此值。

@RequestBody

作用：@RequestBody主要用来接收前端传递给后端的json字符串中的数据的(请求体中的数据的)

GET方式无请求体，所以使用@RequestBody接收数据时，前端不能使用GET方式提交数据，而是用POST方式进行提交
在后端的同一个接收方法里，@RequestBody与@RequestParam()可以同时使用，@RequestBody最多只能有一个，而@RequestParam()可以有多个
如果参数时放在请求体application/json传入后台的话，那么后台要用@RequestBody才能接收到
如果不是放在请求体中的话，那么后台接收前台传过来的参数时，要用@RequestParam来接收，或者形参前什么也不写也能接收

@CookieValue

同请求头类似，可以获取cookie属性，也可以将获取到的属性封装为cookie对象

@RequestAttribute

获取请求域中的信息

@Controller

public class GoController {

    @GetMapping("/goto")

    public String goPage(HttpServletRequest request){

        request.setAttribute("msg","成功");

        request.setAttribute("code","200");

        return "forward:/success";

    }

    @ResponseBody

    @GetMapping("/success")

    public Map<String,Object> getmap(@RequestAttribute("msg") String msg,

                                     @RequestAttribute("code") String code){

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

        map.put("msg",msg);

        map.put("code",code);

        return map;

    }

}

@MatrixVariable

读取矩阵变量，矩阵变量语法如下，每一个变量之间用分号隔开

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

//cars/sell;low=34;brand=byd,audi,yd

@GetMapping("/car/{path}")

public Map test2(@MatrixVariable("low") String low,

                 @MatrixVariable("brand") List<String> brand,

                 @PathVariable("path") String path){

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

    map.put("low",low);

    map.put("brand",brand);

    map.put("path",path);

    return map;

}

//{"path":"sell","low":34,"brand":["byd","audi","yd"]}

示例：

请求地址如果为：http://localhost:9999/car/2/owner/zhangsan?age=18&inters=basketball&inters=football

@PathVariable("id") Integer id: 获取路径中{id}

@PathVariable("username") String name：获取路径中{username}

@PathVariable Map<String, String> pv：获取路径中所有的路径变量

@RequestHeader("User-Agent") String userAgent：获取请求头中userAgent

@RequestHeader Map<String, String> header：获取请求头中所有参数

@RequestParam("age") Integer age：获取请求参数中"age"

@RequestParam("inters") List<String> inters：获取请求参数中"inters"

@RequestParam Map<String, String> params：获取所有的请求参数

@CookieValue("_ga") String _ga：获取cookie中_ga的值

@CookieValue("_ga") Cookie cookie) ：获取cookie

import javax.servlet.http.Cookie;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

@RestController

public class ParameterTestController {

    //  http://localhost:9999/car/2/owner/zhangsan?age=18&inters=basketball&inters=football

    @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;

    }

    //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进行解析。

    //              removeSemicolonContent（移除分号内容）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

    @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;

    }

}