過濾器（Filter）解決跨域問題

最近在作一個項目，前端資源與服務端單獨部署。遇到一個跨域問題，常見的跨域問題能夠經過jsonp方式解決。下面介紹另外一種解決方式：
服務端環境：spring + dubbo + tomcat
第一步：在WEB-INF目錄下添加一個crossdomain.xml文件，內容以下：

<cross-domain-policy>
<allow-access-from domain="*"/>
</cross-domain-policy>

表示web服務器容許任何domain的請求。
第二步：
在web.xml中添加一個新的過濾器Filter--crossDomainFilter。

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">
  <display-name>Archetype CreatedWeb Application</display-name>
  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath*:spring-main.xml</param-value>
  </context-param>
  <context-param>
    <param-name>timeoutMinutes</param-name>
    <param-value>120</param-value>
  </context-param>
  <filter>
    <filter-name>encodingFilter</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <init-param>
      <param-name>encoding</param-name>
      <param-value>UTF-8</param-value>
    </init-param>
    <init-param>
      <param-name>forceEncoding</param-name>
      <param-value>true</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>encodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <filter>
  <filter-name>crossDomainFilter</filter-name>
    <filter-class>com.*.resource.web.utils.CrossDomainFilter</filter-class>
    <init-param>
        <param-name>file</param-name>
        <param-value>/WEB-INF/web-config.properties</param-value>
    </init-param>
  </filter>
  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>
  <servlet>
    <servlet-name>dispatcher</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath*:springmvc-servlet.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>dispatcher</servlet-name>
    <url-pattern>*.do</url-pattern>
  </servlet-mapping>
  <filter-mapping>
    <filter-name>crossDomainFilter</filter-name>
    <url-pattern>*.do</url-pattern>
  </filter-mapping>
  <session-config>
    <session-timeout>120</session-timeout>
  </session-config>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
  </welcome-file-list>
</web-app>

crossDomainFilter中增長crossDomain方法：

package com.*.resource.web.utils;

import java.io.FileInputStream;
import java.io.IOException;
import java.util.Properties;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.lang.exception.ExceptionUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

/**
 *
 * @author 
 * @date
 */
public class CrossDomainFilter implements Filter {

    private static final Logger log = LoggerFactory.getLogger(CrossDomainFilter.class);

    private Properties pp = new Properties();

    private FilterConfig config;

    private String allowDomain = "http://allow.com";

    @Override
    public void destroy() {
        pp = null;
        this.config = null;
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {

        HttpServletRequest req = (HttpServletRequest) request;
        HttpServletResponse resp = (HttpServletResponse) response;

        // 獲得請求的uri和url
        String reqUri = req.getRequestURI();
        String reqUrl = req.getRequestURL().toString();
        log.info(" reqUri:{} ,reqUrl:{} ", reqUri, reqUrl);

        // 跨域處理
        this.crossDomain(req, resp, reqUrl);
        chain.doFilter(req, resp);

    }

    @Override
    public void init(FilterConfig config) throws ServletException {

    }

    /**
     * 處理跨域問題
     */
    private void crossDomain(HttpServletRequest request, HttpServletResponse response, String url) {
        response.setHeader("Content-type", "text/html;charset=UTF-8");
        response.setCharacterEncoding("UTF-8");
        response.setHeader("Access-Control-Allow-Credentials", "true");

        log.info("REFERER:{}", request.getHeader("REFERER"));
        String referer = request.getHeader("REFERER");
        String reqRefererDomain = "";
        if (referer != null && referer.length() > referer.indexOf(".com") + 4) {
            reqRefererDomain = referer.substring(0, referer.indexOf(".com") + 4);
            log.info("reqRefererDomain:{}", reqRefererDomain);
            if (reqRefererDomain.equals(allowDomain)) {
                response.setHeader("Access-Control-Allow-Origin", allowDomain );
            }
        }

        response.setHeader("Access-Control-Allow-Credentials", "true");
        response.setHeader("Access-Control-Allow-Methods", "GET, POST, OPTIONS");
        response.setHeader("Access-Control-Allow-Headers",
                "Origin, No-Cache, X-Requested-With, If-Modified-Since, Pragma, Last-Modified, Cache-Control, Expires, Content-Type, X-E4M-With");

    }

}

解決跨域的關鍵：

response.setHeader("Access-Control-Allow-Origin", allowDomain );