构造httpclient的时候可以setRetryHandler(HttpRequestRetryHandler) ** HttpRequestRetryHandler是Http请求出错后的重试的处理接口类,对于了某些要求比较严格的业务情况下这个参数还是比较重要的。
HttpRequestRetryHandler** 的已知实现类有 DefaultHttpRequestRetryHandler和继承了DefaultHttpRequestRetryHandler的StandardHttpRequestRetryHandler
DefaultHttpRequestRetryHandler
/*
* ====================================================================
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* <http://www.apache.org/>.
*
*/
package org.apache.http.impl.client;
import java.io.IOException;
import java.io.InterruptedIOException;
import java.net.ConnectException;
import java.net.UnknownHostException;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashSet;
import java.util.Set;
import javax.net.ssl.SSLException;
import org.apache.http.HttpEntityEnclosingRequest;
import org.apache.http.HttpRequest;
import org.apache.http.annotation.Immutable;
import org.apache.http.client.HttpRequestRetryHandler;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.client.protocol.HttpClientContext;
import org.apache.http.protocol.HttpContext;
import org.apache.http.util.Args;
/**
* The default {@link HttpRequestRetryHandler} used by request executors.
*
* @since 4.0
*/
@Immutable
public class DefaultHttpRequestRetryHandler implements HttpRequestRetryHandler {
public static final DefaultHttpRequestRetryHandler INSTANCE = new DefaultHttpRequestRetryHandler();
/** the number of times a method will be retried */
private final int retryCount;
/** Whether or not methods that have successfully sent their request will be retried */
private final boolean requestSentRetryEnabled;
private final Set<Class<? extends IOException>> nonRetriableClasses;
/**
* Create the request retry handler using the specified IOException classes
*
* @param retryCount how many times to retry; 0 means no retries
* @param requestSentRetryEnabled true if it's OK to retry requests that have been sent
* @param clazzes the IOException types that should not be retried
* @since 4.3
*/
protected DefaultHttpRequestRetryHandler(
final int retryCount,
final boolean requestSentRetryEnabled,
final Collection<Class<? extends IOException>> clazzes) {
super();
this.retryCount = retryCount;
this.requestSentRetryEnabled = requestSentRetryEnabled;
this.nonRetriableClasses = new HashSet<Class<? extends IOException>>();
for (final Class<? extends IOException> clazz: clazzes) {
this.nonRetriableClasses.add(clazz);
}
}
/**
* Create the request retry handler using the following list of
* non-retriable IOException classes: <br>
* <ul>
* <li>InterruptedIOException</li>
* <li>UnknownHostException</li>
* <li>ConnectException</li>
* <li>SSLException</li>
* </ul>
* @param retryCount how many times to retry; 0 means no retries
* @param requestSentRetryEnabled true if it's OK to retry non-idempotent requests that have been sent
*/
@SuppressWarnings("unchecked")
public DefaultHttpRequestRetryHandler(final int retryCount, final boolean requestSentRetryEnabled) {
this(retryCount, requestSentRetryEnabled, Arrays.asList(
InterruptedIOException.class,
UnknownHostException.class,
ConnectException.class,
SSLException.class));
}
/**
* Create the request retry handler with a retry count of 3, requestSentRetryEnabled false
* and using the following list of non-retriable IOException classes: <br>
* <ul>
* <li>InterruptedIOException</li>
* <li>UnknownHostException</li>
* <li>ConnectException</li>
* <li>SSLException</li>
* </ul>
*/
public DefaultHttpRequestRetryHandler() {
this(3, false);
}
/**
* Used {@code retryCount} and {@code requestSentRetryEnabled} to determine
* if the given method should be retried.
*/
@Override
public boolean retryRequest(
final IOException exception,
final int executionCount,
final HttpContext context) {
Args.notNull(exception, "Exception parameter");
Args.notNull(context, "HTTP context");
if (executionCount > this.retryCount) {
// Do not retry if over max retry count
return false;
}
if (this.nonRetriableClasses.contains(exception.getClass())) {
return false;
} else {
for (final Class<? extends IOException> rejectException : this.nonRetriableClasses) {
if (rejectException.isInstance(exception)) {
return false;
}
}
}
final HttpClientContext clientContext = HttpClientContext.adapt(context);
final HttpRequest request = clientContext.getRequest();
if(requestIsAborted(request)){
return false;
}
if (handleAsIdempotent(request)) {
// Retry if the request is considered idempotent
return true;
}
if (!clientContext.isRequestSent() || this.requestSentRetryEnabled) {
// Retry if the request has not been sent fully or
// if it's OK to retry methods that have been sent
return true;
}
// otherwise do not retry
return false;
}
/**
* @return {@code true} if this handler will retry methods that have
* successfully sent their request, {@code false} otherwise
*/
public boolean isRequestSentRetryEnabled() {
return requestSentRetryEnabled;
}
/**
* @return the maximum number of times a method will be retried
*/
public int getRetryCount() {
return retryCount;
}
/**
* @since 4.2
*/
protected boolean handleAsIdempotent(final HttpRequest request) {
return !(request instanceof HttpEntityEnclosingRequest);
}
/**
* @since 4.2
*
* @deprecated (4.3)
*/
@Deprecated
protected boolean requestIsAborted(final HttpRequest request) {
HttpRequest req = request;
if (request instanceof RequestWrapper) { // does not forward request to original
req = ((RequestWrapper) request).getOriginal();
}
return (req instanceof HttpUriRequest && ((HttpUriRequest)req).isAborted());
}
}
默认构造函数是
public DefaultHttpRequestRetryHandler() {
this(3, false);
}
参数requestSentRetryEnabled是请求是否发送成功都重试 这里设置了false，一般情况下都不要为true我觉得。
主要实现的方法是
boolean retryRequest(IOException exception, int executionCount, HttpContext context);
类StandardHttpRequestRetryHandler并没有重写该方法
@Immutable
public class StandardHttpRequestRetryHandler extends DefaultHttpRequestRetryHandler {
private final Map<String, Boolean> idempotentMethods;
public StandardHttpRequestRetryHandler(final int retryCount, final boolean requestSentRetryEnabled) {
super(retryCount, requestSentRetryEnabled);
this.idempotentMethods = new ConcurrentHashMap<String, Boolean>();
this.idempotentMethods.put("GET", Boolean.TRUE);
this.idempotentMethods.put("HEAD", Boolean.TRUE);
this.idempotentMethods.put("PUT", Boolean.TRUE);
this.idempotentMethods.put("DELETE", Boolean.TRUE);
this.idempotentMethods.put("OPTIONS", Boolean.TRUE);
this.idempotentMethods.put("TRACE", Boolean.TRUE);
}
public StandardHttpRequestRetryHandler() {
this(3, false);
}
@Override
protected boolean handleAsIdempotent(final HttpRequest request) {
final String method = request.getRequestLine().getMethod().toUpperCase(Locale.ROOT);
final Boolean b = this.idempotentMethods.get(method);
return b != null && b.booleanValue();
}
}
只是重写了
protected boolean handleAsIdempotent(final HttpRequest request)
我们参考后完全可以实现自己的HttpRequestRetryHandler
初始化httpClient
在httpClient4.5中，初始化的方式已经和以前版有差异
static CloseableHttpClient client = HttpClients.createDefault();
和
static CloseableHttpClient httpClient=HttpClients.custom().build();
在该方式中可以添加一些网络请求的设置
可以直接使用匿名类
HttpRequestRetryHandler handler = new HttpRequestRetryHandler() {
@Override
public boolean retryRequest(IOException arg0, int retryTimes, HttpContext arg2) {
if (retryTimes > 5) {
return false;
}
if (arg0 instanceof UnknownHostException || arg0 instanceof ConnectTimeoutException
|| !(arg0 instanceof SSLException) || arg0 instanceof NoHttpResponseException) {
return true;
}
HttpClientContext clientContext = HttpClientContext.adapt(arg2);
HttpRequest request = clientContext.getRequest();
boolean idempotent = !(request instanceof HttpEntityEnclosingRequest);
if (idempotent) {
// 如果请求被认为是幂等的，那么就重试。即重复执行不影响程序其他效果的
return true;
}
return false;
}
};
还可以设置路由策略 即设置代理方式访问
HttpHost proxy = new HttpHost("127.0.0.1", 80);// 设置代理ip
DefaultProxyRoutePlanner routePlanner = new DefaultProxyRoutePlanner(proxy);
CloseableHttpClient httpClient = HttpClients.custom().setRoutePlanner(routePlanner).setRetryHandler(handler)
.setConnectionTimeToLive(1, TimeUnit.DAYS).setDefaultCookieStore(cookieStore).build();
附录：
Httpclient4.5后对于get请求方式的改变
static RequestConfig config = RequestConfig.custom().setConnectTimeout(6000).setSocketTimeout(6000)
.setCookieSpec(CookieSpecs.STANDARD).build(); // 设置超时及cookie策略
public static String getDemo(String url) {
HttpGet get = new HttpGet(url);
get.setConfig(config);
HttpResponse response = null;
String html = null;
try {
response = client.execute(get);
int statusCode = response.getStatusLine().getStatusCode();// 连接代码
Header[] headers = response.getAllHeaders();
// 用于得到返回的文件头
for (Header header : headers) {
System.out.println(header);
}
html = new String(EntityUtils.toString(response.getEntity()).getBytes("gb2312"), "utf8");
// 在后面参数输入网站的编码，一般为utf-8
// 返回的html代码,避免发生编码错误
System.out.println(html);
} catch (IOException e) {
e.printStackTrace();
}
return html;
}
大致流程：新建httpget对象->用httpClient执行->解析返回的response得到自己需要的内容
cookieSpec:即cookie策略。参数为cookiespecs的一些字段。作用：1、如果网站header中有set-cookie字段时，采用默认方式可能会被cookie reject，无法写入cookie。将此属性设置成CookieSpecs.STANDARD_STRICT可避免此情况。2、如果要想忽略cookie访问，则将此属性设置成CookieSpecs.IGNORE_COOKIES。
tips：注意网站编码，否则容易出现乱码
执行post请求：
public static void postDemo(String url) {
HttpPost post = new HttpPost(url);
post.setConfig(config);
post.setHeader("User-Agent",
"Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.93 Safari/537.36");
post.setHeader("Connection", "keep-alive");
List<NameValuePair> list = new ArrayList<NameValuePair>();
list.add(new BasicNameValuePair("key", "value"));
list.add(new BasicNameValuePair("key", "value"));
list.add(new BasicNameValuePair("key", "value"));
list.add(new BasicNameValuePair("key", "value"));
list.add(new BasicNameValuePair("key", "value"));
try {
HttpEntity entity = new UrlEncodedFormEntity(list, "utf-8");
post.setEntity(entity);
HttpResponse response = client.execute(post);
String responseHtml = EntityUtils.toString(response.getEntity());
System.out.println(responseHtml);
} catch (IOException e) {
e.printStackTrace();
}
}
大致流程：新建post对象->新建需要的表单页->将表单内容设置入请求中->执行并获得response
解析response
//得到返回内容
String responseHtml = EntityUtils.toString(response.getEntity());
int statusCode = response.getStatusLine().getStatusCode();// 连接代码
//得到response header
response.getFirstHeader("key");// 得到第一个名字为key的header
response.getHeaders("key");// 得到名字为key的所有header，返回一个数组
response.getLastHeader("key");
//得到inputstream：（下载网络部分资源的时候有可能会对cookie有要求，此时需要用到httpClient来下载。）例如验证码等等。
InputStream inputStream = response.getEntity().getContent();
管理cookie
CookieStore cookieStore = new BasicCookieStore();
CloseableHttpClient httpClient= HttpClients.custom()
.setDefaultCookieStore(cookieStore).build();
httpClient里默认自动管理cookie，如果想要提取cookie或者发送自定义的cookie，则需要在httpClient对象初始化时设置一个默认的cookiestore来保存。（方法见初始化httpClient对象里的setDefaultCookieStore）。
得到当前所有cookie：
List<Cookie> list = cookieStore.getCookies();// get all cookies
System.out.println("cookie is:");
System.out.println("-----------------------");
for (Cookie cookie : list) {
System.out.println(cookie);
}
System.out.println("-----------------------");
清除所有cookie：
cookieStore.clear();
发送自定义cookie：（new了一个对象之后可以设置多种属性。）
BasicClientCookie cookie = new BasicClientCookie("name", "value");
// new a cookie
cookie.setDomain("domain");
cookie.setExpiryDate(new Date());
// set the properties of the cookie
cookieStore.addCookie(cookie);
管理header：
在平常抓取过程中，经常需要在请求中加入许多header伪装成一个正常的浏览器。以免被服务器认出是爬虫而被封。
设置一些常见header：
post.setHeader("User-Agent",
"Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.93 Safari/537.36");
post.setHeader("Connection", "keep-alive");
注意：下载某些网站的资源时，服务器会获取你的来源站，并发出对应的相应。如果来源站不对，可能会被服务器拒绝。此时只需要在请求中加个header就行。
get1.setHeader("Referer", "http://www.a.com");
ps：
1、爬虫也要遵守基本法，在多次请求的之中为了不给对方服务器造成负担（避免被封），尽量在请求间sleep一个随机数值。
2、爬取非英文网站时注意编码格式，国内一般为utf-8，也有一些是gb2312.获取时注意转码。
3、多获得一些可靠IP（备胎），一旦自身ip被封，赶快去找备胎。附带一个简单的判断网站是否需要代理方法：
// 判断访问目标网站是否需要代理
private boolean isNeedProxy() {
boolean result = true;
URL url;
try {
url = new URL("http://apkpure.com/");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setConnectTimeout(6000);
// int i = connection.getResponseCode();
int i = connection.getContentLength();
if (i > 0) {
result = false;
}
} catch (IOException e) {
e.printStackTrace();
}
return result;
}
