使用代理IP发送请求，出现502错误 java.io.IOException: Unable to tunnel through proxy. Proxy returns “HTTP/1.1 502

今天有客户咨询使用代理IP请求一个国外网址（https://read.qxmd.com/），这个网址在国内打开速度比较慢，然后报错了 java.io.IOException: Unable to tunnel through proxy. Proxy returns “HTTP/1.1 502 Bad Gateway”

HTTP 502 – 网关错误

此处一般指Nginx做反向代理服务器时，所连接的Web应用服务器无响应导致的。一般是因为后端的Tomcat，Jetty，Tornado等服务器没有启动。我们知道，Nginx属于HTTP服务器，不属于Web应用服务器。

出现“HTTP 502 – 网关错误”，需要重启Web应用服务器。

排查问题解决方案：

确保目标网站的URL能够正常打开，如果打不开或者长时间不响应（打开很慢），那么这种情况下考虑是网址URL有问题，没有更好的解决方案，只能忽略个别错误。
目标URL打开正常，所以试一下不使用代理IP的情况下，能否正常返回，如果返回正常，可以继续第三步排查。如果返回仍然为502或者50X的错误，那么这种情况下考虑是网址URL有问题，没有更好的解决方案，只能忽略个别错误。
考虑是代理IP在可用时间范围内，无法正确打开URL导致最终无响应，解决办法就是换下一个新IP。

下面是我的测试代码：


import java.io.BufferedInputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.util.ArrayList;
import java.util.List;import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;import com.gargoylesoftware.htmlunit.BrowserVersion;
import com.gargoylesoftware.htmlunit.ProxyConfig;
import com.gargoylesoftware.htmlunit.WebClient;
import com.gargoylesoftware.htmlunit.html.HtmlPage;public class TestDynamicIp {public static List<String> ipList = new ArrayList<>();public static boolean gameOver = false;public static void main(String[] args) {long fetchIpSeconds = 3;int threadNum = 2;int testTime = 5;// 请填写无忧代理IP订单号，填写之后才可以提取到IP哦, https://www.data5u.com 获取String order = "请填写无忧代理IP订单号";// 这里换成百度贴吧的URL，可以把这里封装成一个方法，接收URL参数，实现不同的URL采集String targetUrl = "https://www.iqiyi.com/v_19rrlcvy50.html?pltfm=11&pos=title&flashvars=videoIsFromQidan%3Ditemviewclk_a#vfrm=5-6-0-1";// 是否加载JS，加载JS会导致速度变慢boolean useJS = false;// 请求超时时间，单位毫秒，默认5秒int timeOut = 5000;if (order == null || "".equals(order)) {System.err.println("请输入无忧代理IP动态代理订单号");return;}System.out.println(">>>>>>>>>>>>>>无忧代理动态IP测试开始<<<<<<<<<<<<<<");System.out.println("***************");System.out.println("接口返回IP为国内各地区，每次最多返回10个");System.out.println("提取IP间隔 " + fetchIpSeconds + " 秒 ");System.out.println("开启爬虫线程 " + threadNum);System.out.println("爬虫目标网址  " + targetUrl);System.out.println("测试次数 3 ");System.out.println("***************\n");TestDynamicIp tester = new TestDynamicIp();new Thread(tester.new GetIP(fetchIpSeconds * 1000, testTime, order)).start();for (int i = 0; i < threadNum; i++) {tester.new Crawler(200, targetUrl, useJS, timeOut).start();}while(!gameOver){try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}}System.out.println(">>>>>>>>>>>>>>无忧代理动态IP测试结束<<<<<<<<<<<<<<");System.exit(0);}// 采集部分public class Crawler extends Thread{@Overridepublic void run() {while(!gameOver){webParseHtml(targetUrl);try {Thread.sleep(sleepMs);} catch (InterruptedException e) {e.printStackTrace();}}}long sleepMs = 200;boolean useJs = false;String targetUrl = "";int timeOut = 5000;public Crawler(long sleepMs, String targetUrl, boolean useJs, int timeOut) {this.sleepMs = sleepMs;this.targetUrl = targetUrl;this.useJs = useJs;this.timeOut = timeOut;}public String webParseHtml(String url) {String html = "";BrowserVersion[] versions = {BrowserVersion.CHROME, BrowserVersion.BEST_SUPPORTED};WebClient client = new WebClient(versions[(int)(versions.length * Math.random())]);try {client.addRequestHeader("Referer", "https://tieba.baidu.com/");client.getOptions().setThrowExceptionOnFailingStatusCode(false);client.getOptions().setJavaScriptEnabled(useJs);client.getOptions().setCssEnabled(false);client.getOptions().setThrowExceptionOnScriptError(false);client.getOptions().setTimeout(timeOut);client.getOptions().setAppletEnabled(true);client.getOptions().setGeolocationEnabled(true);client.getOptions().setRedirectEnabled(true);client.getOptions().setUseInsecureSSL(true);String ipport = getAProxy();if (ipport != null) {ProxyConfig proxyConfig = new ProxyConfig(ipport.split(":")[0], Integer.parseInt(ipport.split(":")[1]));client.getOptions().setProxyConfig(proxyConfig);}else {System.out.print(".");return "";}HtmlPage page = client.getPage(url);html = page.asXml();Document doc = Jsoup.parse(html);System.out.println(getName() + " 使用代理 " + ipport + "请求目标网址返回：" + doc.select("title").text() + doc.select("body").text());} catch (Exception e) {System.err.println(e.getMessage());} finally {client.close();}return html;}private String getAProxy() {if (ipList.size() > 0) {String ip = ipList.get((int)(Math.random() * ipList.size()));return ip ;}return null;}}// 定时获取动态IPpublic class GetIP implements Runnable{long sleepMs = 1000;int maxTime = 3;String order = "";public GetIP(long sleepMs, int maxTime, String order) {this.sleepMs = sleepMs;this.maxTime = maxTime;this.order = order;}@Overridepublic void run() {long getIpTime = 0;int time = 1;while(!gameOver){if(time >= 4){gameOver = true;break;}try {// http://soft.data5u.com/vpn/get/a/2d1bb3388b9182cfabc9f88cac1ffd68.html?ttl&areaCN=海南海口联通java.net.URL url = new java.net.URL("http://api.ip.data5u.com/dynamic/get.html?order=" + order + "&ttl&random=1");HttpURLConnection connection = (HttpURLConnection)url.openConnection();connection.setConnectTimeout(3000);connection = (HttpURLConnection)url.openConnection();InputStream raw = connection.getInputStream();  InputStream in = new BufferedInputStream(raw);  byte[] data = new byte[in.available()];int bytesRead = 0;  int offset = 0;  while(offset < data.length) {  bytesRead = in.read(data, offset, data.length - offset);  if(bytesRead == -1) {  break;  }  offset += bytesRead;  }  in.close();  raw.close();String[] res = new String(data, "UTF-8").split("\n");List<String> ipList = new ArrayList<>();for (String ip : res) {try {System.out.println(ip);String[] parts = ip.split(",");if (Integer.parseInt(parts[1]) > 0) {ipList.add(parts[0]);}} catch (Exception e) {}}if (ipList.size() > 0) {TestDynamicIp.ipList = ipList;System.out.println("第" + ++getIpTime + "次获取动态IP " + ipList.size() + " 个");time += 1;}} catch (Exception e) {e.printStackTrace();System.err.println(">>>>>>>>>>>>>>获取IP出错");}try {Thread.sleep(sleepMs);} catch (InterruptedException e) {e.printStackTrace();}}}}}

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