HiddenHttpMethodFilter

HiddenHttpMethodFilter：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 添加了一个过滤器，可以将这些请求转换 为标准的 http 方法，使得支持 GET、POST、PUT 与 DELETE 请求。

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;

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 {

        String paramValue = request.getParameter(this.methodParam);
        if ("POST".equals(request.getMethod()) && StringUtils.hasLength(paramValue)) {
            String method = paramValue.toUpperCase(Locale.ENGLISH);
            HttpServletRequest wrapper = new HttpMethodRequestWrapper(request, method);
            filterChain.doFilter(wrapper, response);
        }
        else {
            filterChain.doFilter(request, 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;
        }
    }

}