HttpClient之自定义HttpRequestRetryHa

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

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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;  
    }