SpringMVC(四)：@RequestMapping结合org.springframework.web.filter.HiddenHttpMethodFilter实现REST请求

1）REST具体表现：

--- /account/1  HTTP GET       获取id=1的account

--- /account/1  HTTP DELETE 删除id=1的account

--- /aacount/1  HTTP PUT        更新id=1的account

--- /account      HTTP POST     新增account

2）SpringMVC中如何实现REST？

众所周知，浏览器form表单只支持GET与POST请求，而DELETE、PUT等method并不支持。Spring3.0增加了一个过滤器，可以将这些请求转化为标准的http方法，使得支持GET、POST、PUT及DELETE请求。

这个过滤器就是：org.springframework.web.filter.HiddenHttpMethodFilter

 package org.springframework.web.filter;

 import java.io.IOException;
 import java.util.Locale;
 import javax.servlet.FilterChain;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletRequestWrapper;
 import javax.servlet.http.HttpServletResponse;

 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 import org.springframework.web.util.WebUtils;

 /**
  * {@link javax.servlet.Filter} that converts posted method parameters into HTTP methods,
  * retrievable via {@link HttpServletRequest#getMethod()}. Since browsers currently only
  * support GET and POST, a common technique - used by the Prototype library, for instance -
  * is to use a normal POST with an additional hidden form field ({@code _method})
  * to pass the "real" HTTP method along. This filter reads that parameter and changes
  * the {@link HttpServletRequestWrapper#getMethod()} return value accordingly.
  *
  * <p>The name of the request parameter defaults to {@code _method}, but can be
  * adapted via the {@link #setMethodParam(String) methodParam} property.
  *
  * <p><b>NOTE: This filter needs to run after multipart processing in case of a multipart
  * POST request, due to its inherent need for checking a POST body parameter.</b>
  * So typically, put a Spring {@link org.springframework.web.multipart.support.MultipartFilter}
  * <i>before</i> this HiddenHttpMethodFilter in your {@code web.xml} filter chain.
  *
  * @author Arjen Poutsma
  * @author Juergen Hoeller
  * @since 3.0
  */
 public class HiddenHttpMethodFilter extends OncePerRequestFilter {

     /** 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)) {
                 requestToUse = new HttpMethodRequestWrapper(request, paramValue);
             }
         }

         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.toUpperCase(Locale.ENGLISH);
         }

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

 }

从这个filter代码中可以得知，该filter是通过POST方式提交表单，该表单中包含一个名称为_method的隐藏域，该隐藏域的值用来判定将要转化的请求方式。所谓的转化请求方式，就是在该filter中重新生成了一个新的、标准化的请求。

3）如何使用到springmvc项目中？

步骤一：在web.xml中添加filter配置：

    <filter>
        <filter-name>HiddenHttpMethodFilter</filter-name>
        <filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>HiddenHttpMethodFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

步骤二：在HelloWord.java中添加get/post/put/delete方法：

 package com.dx.springlearn.handlers;

 import org.springframework.stereotype.Controller;
 import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RequestMethod;

 @Controller
 @RequestMapping("class_requestmapping")
 public class HelloWord {
     private static String SUCCESS = "success";

     @RequestMapping(value = "/accountDelete/{id}", method = RequestMethod.DELETE)
     public String accountDelete(@PathVariable("id") Integer id) {
         System.out.println("test rest DELETE,account id:" + id);
         return SUCCESS;
     }

     @RequestMapping(value = "/accountPut/{id}", method = RequestMethod.PUT)
     public String accountPut(@PathVariable("id") Integer id) {
         System.out.println("test rest PUT,account id:" + id);
         return SUCCESS;
     }

     @RequestMapping(value = "/account", method = RequestMethod.POST)
     public String account() {
         System.out.println("test rest POST");
         return SUCCESS;
     }

     @RequestMapping(value = "/account/{id}", method = RequestMethod.GET)
     public String account(@PathVariable("id") Integer id) {
         System.out.println("test rest GET,account id:" + id);
         return SUCCESS;
     }
 }

步骤三：在index.jsp中添加get/post/put/delete方法请求的html脚本：

    <!-- delete提交 -->
    <form id="form_testRestMethod_DELETE" name="form_testRestMethod_DELETE" method="POST"
        action="class_requestmapping/accountDelete/2">
        <input type="hidden" name="_method" value="DELETE" />
        <button name="submit" id="submit">test rest DELETE</button>
    </form>
    <br>
    <!-- put提交 -->
    <form id="form_testRestMethod_PUT" name="form_testRestMethod_PUT" method="POST"
        action="class_requestmapping/accountPut/2">
        <input type="hidden" name="_method" value="PUT" />
        <button name="submit" id="submit">test rest PUT</button>
    </form>
    <br>
    <!-- post提交 -->
    <form id="form_testRestMethod_POST" name="form_testRestMethod_POST"
        method="POST" action="class_requestmapping/account">
        <button name="submit" id="submit">test rest POST</button>
    </form>
    <br>
    <!-- get提交 -->
    <a href="class_requestmapping/account/1">test rest GET</a>
    <br>

步骤四：测试打印结果为：

test rest GET,account id:1
test rest POST
test rest PUT,account id:2
test rest DELETE,account id:2