servlet解决浏览器的跨域

概述：

在做一些web请求时，会涉及到很麻烦的浏览器跨域问题，因此，一般都会通过后台处理再给前台。本文讲述通过servlet解决浏览器的跨域问题。

实现：

在工程下新建一个servlet，实现代码如下：

package lzugis.web.agent;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* Servlet implementation class WebAgent
*/
@WebServlet(name="WebAgent",urlPatterns="/web/agent")
public class WebAgent extends HttpServlet {
private static final long serialVersionUID = 1L;
private String debug = "false";

/**
* Default constructor.
*/
public WebAgent() {
// TODO Auto-generated constructor stub
}

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
String encoding = getInitParameter("encoding");
if ((encoding != null) && (!"".equals(encoding))) {
request.setCharacterEncoding(encoding);
}
String url = request.getParameter("url");
if (!"".equals(url)) {
responseFile(request, response, url);
return;
}
}

/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
String encoding = getInitParameter("encoding");
if ((encoding != null) && (!"".equals(encoding))) {
request.setCharacterEncoding(encoding);
}
String url = request.getParameter("url");
if (!"".equals(url)) {
responseFile(request, response, url);
return;
}

if ("true".equals(this.debug)) {
String data = readXMLFromRequestBody(request);
System.out.println(data);
}
}

public void responseFile(HttpServletRequest req, HttpServletResponse resp, String url) {
try {
URL u = new URL(url);

URLConnection urlc = u.openConnection();
urlc.setConnectTimeout(3000);
urlc.setReadTimeout(100000);

resp.setContentType(urlc.getContentType());

ServletOutputStream out = null;
BufferedInputStream input = null;
byte[] data = new byte[1024];
int length = -1;
input = new BufferedInputStream(urlc.getInputStream());
out = resp.getOutputStream();
while ((length = input.read(data)) != -1) {
out.write(data, 0, length);
}
input.close();
out.flush();
out.close();
}
catch (IOException localIOException)
{
}
}

private String readXMLFromRequestBody(HttpServletRequest request) {
StringBuffer strBuf = new StringBuffer();
try {
BufferedReader reader = request.getReader();
String line = null;
while ((line = reader.readLine()) != null)
strBuf.append(line).append("\n");
} catch (IOException e) {
e.printStackTrace();
}
return strBuf.toString();
}
}

说明：

servlet是通过注解的方式配的，访问路径为：localhost:8080/lzugis/web/agent?url=http://localhost:6080/arcgis/rest/services/?f=pjson。