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