爬虫程序采集网站必须使用动态代理，才能避免出现网站访问频繁的限制，这是众所周知的。但是在具体采集网站的过程中，即使使用了动态代理依然会出现403、503或429的反爬错误，这是为什么呢？根据以往的经验，一般来说是因为以下几个原因造成的：
1、动态User-Agent的修改
爬虫程序采集网站，正常的HTTP请求都需要进行ua（User-Agent）优化，因为ua是浏览器标识，如果http请求没有ua，甚至有些爬虫程序主动标示为采集，那么目标网站拒绝采集的可能性很高
2、控制单个代理IP的请求频率
虽然爬虫程序使用了动态代理，但是如果程序的多线程控制实现不好，会导致单个代理IP在短时间内发出大量的请求，导致该IP被访问频繁
3、IP有效时间的管理
动态代理IP使用过程中，必须进行存活检查，一旦发现延迟较高、带宽很低的代理IP，应该主动丢弃，避免使用过程中出现超时的情况
如果觉得上面的工作太麻烦，推荐使用自动转发的爬虫代理加强版，这种产品能实现每个http请求自动分配不同的代理IP转发，同时进行IP池的自动多线程管理，确保了请求联通率99%以上同时延迟低于300ms，可以快速上手采集网站，下面是产品demo可以直接复制使用，配置代理参数（proxyHost、proxyPort、proxyUser、proxyPass）和目标网站（targetUrl）就可以Run：
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.net.URI;
import java.util.Arrays;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import org.apache.http.Header;
import org.apache.http.HeaderElement;
import org.apache.http.HttpHost;
import org.apache.http.auth.AuthScope;
import org.apache.http.auth.UsernamePasswordCredentials;
import org.apache.http.client.AuthCache;
import org.apache.http.client.CredentialsProvider;
import org.apache.http.client.HttpRequestRetryHandler;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.config.AuthSchemes;
import org.apache.http.client.entity.GzipDecompressingEntity;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.methods.HttpRequestBase;
import org.apache.http.client.protocol.HttpClientContext;
import org.apache.http.config.Registry;
import org.apache.http.config.RegistryBuilder;
import org.apache.http.conn.socket.ConnectionSocketFactory;
import org.apache.http.conn.socket.LayeredConnectionSocketFactory;
import org.apache.http.conn.socket.PlainConnectionSocketFactory;
import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.impl.auth.BasicScheme;
import org.apache.http.impl.client.BasicAuthCache;
import org.apache.http.impl.client.BasicCredentialsProvider;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.client.ProxyAuthenticationStrategy;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.apache.http.message.BasicHeader;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.NameValuePair;
import org.apache.http.util.EntityUtils;
public class Demo
{
// 代理服务器(产品官网 www.16yun.cn)
final static String proxyHost = "t.16yun.cn";
final static Integer proxyPort = 31000;
// 代理验证信息
final static String proxyUser = "username";
final static String proxyPass = "password";
private static PoolingHttpClientConnectionManager cm = null;
private static HttpRequestRetryHandler httpRequestRetryHandler = null;
private static HttpHost proxy = null;
private static CredentialsProvider credsProvider = null;
private static RequestConfig reqConfig = null;
static {
ConnectionSocketFactory plainsf = PlainConnectionSocketFactory.getSocketFactory();
LayeredConnectionSocketFactory sslsf = SSLConnectionSocketFactory.getSocketFactory();
Registry registry = RegistryBuilder.create()
.register("http", plainsf)
.register("https", sslsf)
.build();
cm = new PoolingHttpClientConnectionManager(registry);
cm.setMaxTotal(20);
cm.setDefaultMaxPerRoute(5);
proxy = new HttpHost(proxyHost, proxyPort, "http");
credsProvider = new BasicCredentialsProvider();
credsProvider.setCredentials(AuthScope.ANY, new UsernamePasswordCredentials(proxyUser, proxyPass));
reqConfig = RequestConfig.custom()
.setConnectionRequestTimeout(5000)
.setConnectTimeout(5000)
.setSocketTimeout(5000)
.setExpectContinueEnabled(false)
.setProxy(new HttpHost(proxyHost, proxyPort))
.build();
}
public static void doRequest(HttpRequestBase httpReq) {
CloseableHttpResponse httpResp = null;
try {
setHeaders(httpReq);
httpReq.setConfig(reqConfig);
CloseableHttpClient httpClient = HttpClients.custom()
.setConnectionManager(cm)
.setDefaultCredentialsProvider(credsProvider)
.build();
AuthCache authCache = new BasicAuthCache();
authCache.put(proxy, new BasicScheme());
HttpClientContext localContext = HttpClientContext.create();
localContext.setAuthCache(authCache);
httpResp = httpClient.execute(httpReq, localContext);
int statusCode = httpResp.getStatusLine().getStatusCode();
System.out.println(statusCode);
BufferedReader rd = new BufferedReader(new InputStreamReader(httpResp.getEntity().getContent()));
String line = "";
while((line = rd.readLine()) != null) {
System.out.println(line);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if (httpResp != null) {
httpResp.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* 设置请求头
*
* @param httpReq
*/
private static void setHeaders(HttpRequestBase httpReq) {
// 设置Proxy-Tunnel
// Random random = new Random();
// int tunnel = random.nextInt(10000);
// httpReq.setHeader("Proxy-Tunnel", String.valueOf(tunnel));
httpReq.setHeader("Accept-Encoding", null);
}
public static void doGetRequest() {
// 要访问的目标页面
String targetUrl = "https://httpbin.org/ip";
try {
HttpGet httpGet = new HttpGet(targetUrl);
doRequest(httpGet);
} catch (Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
doGetRequest();
}
}
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