从头学习爬虫（二十二）重构篇----WebMagic框架分析之downloader

这系列文章主要分析分析webmagic框架，没有实战内容，如有实战问题可以讨论，也可以提供技术支持。

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Downloader

我们先来看看接口

package us.codecraft.webmagic.downloader;

import us.codecraft.webmagic.Page;
import us.codecraft.webmagic.Request;
import us.codecraft.webmagic.Task;

/**
 * Downloader is the part that downloads web pages and store in Page object. 

 * Downloader has {@link #setThread(int)} method because downloader is always the bottleneck of a crawler,
 * there are always some mechanisms such as pooling in downloader, and pool size is related to thread numbers.
 *
 * @author [email protected] 

 * @since 0.1.0
 */
public interface Downloader {

    /**
     * Downloads web pages and store in Page object.
     *
     * @param request request
     * @param task task
     * @return page
     */
    public Page download(Request request, Task task);

    /**
     * Tell the downloader how many threads the spider used.
     * @param threadNum number of threads
     */
    public void setThread(int threadNum);
}

提供了两个方法,一个是线程数控制，还有个是下载方法

我们再来看看默认调用实现downloader的那个类HttpClientDownloader

package us.codecraft.webmagic.downloader;

import org.apache.commons.io.IOUtils;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.util.EntityUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import us.codecraft.webmagic.Page;
import us.codecraft.webmagic.Request;
import us.codecraft.webmagic.Site;
import us.codecraft.webmagic.Task;
import us.codecraft.webmagic.proxy.Proxy;
import us.codecraft.webmagic.proxy.ProxyProvider;
import us.codecraft.webmagic.selector.PlainText;
import us.codecraft.webmagic.utils.CharsetUtils;
import us.codecraft.webmagic.utils.HttpClientUtils;

import java.io.IOException;
import java.nio.charset.Charset;
import java.util.HashMap;
import java.util.Map;


/**
 * The http downloader based on HttpClient.
 *
 * @author [email protected] 

 * @since 0.1.0
 */
public class HttpClientDownloader extends AbstractDownloader {

    private Logger logger = LoggerFactory.getLogger(getClass());

    private final Map httpClients = new HashMap();
    //下载方法包装类
    private HttpClientGenerator httpClientGenerator = new HttpClientGenerator();

    private HttpUriRequestConverter httpUriRequestConverter = new HttpUriRequestConverter();
    //代理提供类
    private ProxyProvider proxyProvider;

    private boolean responseHeader = true;

    public void setHttpUriRequestConverter(HttpUriRequestConverter httpUriRequestConverter) {
        this.httpUriRequestConverter = httpUriRequestConverter;
    }

    public void setProxyProvider(ProxyProvider proxyProvider) {
        this.proxyProvider = proxyProvider;
    }
    
    //通过site 构造 CloseableHttpClient
    private CloseableHttpClient getHttpClient(Site site) {
        if (site == null) {
            return httpClientGenerator.getClient(null);
        }
        String domain = site.getDomain();
        CloseableHttpClient httpClient = httpClients.get(domain);
        if (httpClient == null) {
            synchronized (this) {
                httpClient = httpClients.get(domain);
                if (httpClient == null) {
                    httpClient = httpClientGenerator.getClient(site);
                    httpClients.put(domain, httpClient);
                }
            }
        }
        return httpClient;
    }

    @Override
    public Page download(Request request, Task task) {
        //如果要重写主要改造下面直到page = handleResponse（）；
    	if (task == null || task.getSite() == null) {
            throw new NullPointerException("task or site can not be null");
        }
        CloseableHttpResponse httpResponse = null;
        //解析site 里面的header 以及传递参数 主要调用的是HttpClientGenerator
        CloseableHttpClient httpClient = getHttpClient(task.getSite());
        //判断有没有代理
        Proxy proxy = proxyProvider != null ? proxyProvider.getProxy(task) : null;
        HttpClientRequestContext requestContext = httpUriRequestConverter.convert(request, task.getSite(), proxy);
        //初始化page
        Page page = Page.fail();
        try {
        	//发送请求HttpUriRequest 方法,HttpUriRequest 内容
            httpResponse = httpClient.execute(requestContext.getHttpUriRequest(), requestContext.getHttpClientContext());
            //包装page
            page = handleResponse(request, request.getCharset() != null ? request.getCharset() : task.getSite().getCharset(), httpResponse, task);
            onSuccess(request);
            logger.info("downloading page success {}", request.getUrl());
            return page;
        } catch (IOException e) {
            logger.warn("download page {} error", request.getUrl(), e);
            onError(request);
            return page;
        } finally {
            if (httpResponse != null) {
                //ensure the connection is released back to pool
                EntityUtils.consumeQuietly(httpResponse.getEntity());
            }
            if (proxyProvider != null && proxy != null) {
               //未实现
            	proxyProvider.returnProxy(proxy, page, task);
            }
        }
    }

    @Override
    public void setThread(int thread) {
        httpClientGenerator.setPoolSize(thread);
    }

    protected Page handleResponse(Request request, String charset, HttpResponse httpResponse, Task task) throws IOException {
        byte[] bytes = IOUtils.toByteArray(httpResponse.getEntity().getContent());
        String contentType = httpResponse.getEntity().getContentType() == null ? "" : httpResponse.getEntity().getContentType().getValue();
        Page page = new Page();
        page.setBytes(bytes);
        if (!request.isBinaryContent()){
            if (charset == null) {
                charset = getHtmlCharset(contentType, bytes);
            }
            page.setCharset(charset);
            page.setRawText(new String(bytes, charset));
        }
        page.setUrl(new PlainText(request.getUrl()));
        page.setRequest(request);
        page.setStatusCode(httpResponse.getStatusLine().getStatusCode());
        page.setDownloadSuccess(true);
        if (responseHeader) {
            page.setHeaders(HttpClientUtils.convertHeaders(httpResponse.getAllHeaders()));
        }
        return page;
    }

    private String getHtmlCharset(String contentType, byte[] contentBytes) throws IOException {
        String charset = CharsetUtils.detectCharset(contentType, contentBytes);
        if (charset == null) {
            charset = Charset.defaultCharset().name();
            logger.warn("Charset autodetect failed, use {} as charset. Please specify charset in Site.setCharset()", Charset.defaultCharset());
        }
        return charset;
    }
}

比较主要的还有个类HttpClientGenerator，主要是提供下载参数构造的

这边不解析了 有疑问老规矩

package us.codecraft.webmagic.downloader;

import org.apache.http.HttpException;
import org.apache.http.HttpRequest;
import org.apache.http.HttpRequestInterceptor;
import org.apache.http.client.CookieStore;
import org.apache.http.config.Registry;
import org.apache.http.config.RegistryBuilder;
import org.apache.http.config.SocketConfig;
import org.apache.http.conn.socket.ConnectionSocketFactory;
import org.apache.http.conn.socket.PlainConnectionSocketFactory;
import org.apache.http.conn.ssl.DefaultHostnameVerifier;
import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.impl.client.*;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.apache.http.impl.cookie.BasicClientCookie;
import org.apache.http.protocol.HttpContext;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import us.codecraft.webmagic.Site;

import javax.net.ssl.SSLContext;
import javax.net.ssl.TrustManager;
import javax.net.ssl.X509TrustManager;
import java.io.IOException;
import java.security.KeyManagementException;
import java.security.NoSuchAlgorithmException;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import java.util.Map;

/**
 * @author [email protected] 

 * @since 0.4.0
 */
public class HttpClientGenerator {
	
	private transient Logger logger = LoggerFactory.getLogger(getClass());
	
    private PoolingHttpClientConnectionManager connectionManager;

    public HttpClientGenerator() {
        Registry reg = RegistryBuilder.create()
                .register("http", PlainConnectionSocketFactory.INSTANCE)
                .register("https", buildSSLConnectionSocketFactory())
                .build();
        connectionManager = new PoolingHttpClientConnectionManager(reg);
        connectionManager.setDefaultMaxPerRoute(100);
    }

	private SSLConnectionSocketFactory buildSSLConnectionSocketFactory() {
		try {
            return new SSLConnectionSocketFactory(createIgnoreVerifySSL(), new String[]{"SSLv3", "TLSv1", "TLSv1.1", "TLSv1.2"},
                    null,
                    new DefaultHostnameVerifier()); // 优先绕过安全证书
		} catch (KeyManagementException e) {
            logger.error("ssl connection fail", e);
        } catch (NoSuchAlgorithmException e) {
            logger.error("ssl connection fail", e);
        }
		return SSLConnectionSocketFactory.getSocketFactory();
	}

	private SSLContext createIgnoreVerifySSL() throws NoSuchAlgorithmException, KeyManagementException {
		// 实现一个X509TrustManager接口，用于绕过验证，不用修改里面的方法
		X509TrustManager trustManager = new X509TrustManager() {

			@Override
			public void checkClientTrusted(X509Certificate[] chain, String authType) throws CertificateException {
			}

			@Override
			public void checkServerTrusted(X509Certificate[] chain, String authType) throws CertificateException {
			}

			@Override
			public X509Certificate[] getAcceptedIssuers() {
				return null;
			}
			
		};
		
		SSLContext sc = SSLContext.getInstance("SSLv3");
		sc.init(null, new TrustManager[] { trustManager }, null);
		return sc;
	}
    
    public HttpClientGenerator setPoolSize(int poolSize) {
        connectionManager.setMaxTotal(poolSize);
        return this;
    }

    public CloseableHttpClient getClient(Site site) {
        return generateClient(site);
    }

    private CloseableHttpClient generateClient(Site site) {
        HttpClientBuilder httpClientBuilder = HttpClients.custom();
        
        httpClientBuilder.setConnectionManager(connectionManager);
        if (site.getUserAgent() != null) {
            httpClientBuilder.setUserAgent(site.getUserAgent());
        } else {
            httpClientBuilder.setUserAgent("");
        }
        if (site.isUseGzip()) {
            httpClientBuilder.addInterceptorFirst(new HttpRequestInterceptor() {

                public void process(
                        final HttpRequest request,
                        final HttpContext context) throws HttpException, IOException {
                    if (!request.containsHeader("Accept-Encoding")) {
                        request.addHeader("Accept-Encoding", "gzip");
                    }
                }
            });
        }
        //解决post/redirect/post 302跳转问题
        httpClientBuilder.setRedirectStrategy(new CustomRedirectStrategy());

        SocketConfig.Builder socketConfigBuilder = SocketConfig.custom();
        socketConfigBuilder.setSoKeepAlive(true).setTcpNoDelay(true);
        socketConfigBuilder.setSoTimeout(site.getTimeOut());
        SocketConfig socketConfig = socketConfigBuilder.build();
        httpClientBuilder.setDefaultSocketConfig(socketConfig);
        connectionManager.setDefaultSocketConfig(socketConfig);
        httpClientBuilder.setRetryHandler(new DefaultHttpRequestRetryHandler(site.getRetryTimes(), true));
        generateCookie(httpClientBuilder, site);
        return httpClientBuilder.build();
    }

    private void generateCookie(HttpClientBuilder httpClientBuilder, Site site) {
        if (site.isDisableCookieManagement()) {
            httpClientBuilder.disableCookieManagement();
            return;
        }
        CookieStore cookieStore = new BasicCookieStore();
        for (Map.Entry cookieEntry : site.getCookies().entrySet()) {
            BasicClientCookie cookie = new BasicClientCookie(cookieEntry.getKey(), cookieEntry.getValue());
            cookie.setDomain(site.getDomain());
            cookieStore.addCookie(cookie);
        }
        for (Map.Entry> domainEntry : site.getAllCookies().entrySet()) {
            for (Map.Entry cookieEntry : domainEntry.getValue().entrySet()) {
                BasicClientCookie cookie = new BasicClientCookie(cookieEntry.getKey(), cookieEntry.getValue());
                cookie.setDomain(domainEntry.getKey());
                cookieStore.addCookie(cookie);
            }
        }
        httpClientBuilder.setDefaultCookieStore(cookieStore);
    }

}

扩展

目前还写了两个downloader,主要用于模拟浏览器，个人比较推荐selenium 用googledriver，目前比较重视自动化测试，更新很快。

直接贴代码

PhantomJSDownloader

package us.codecraft.webmagic.downloader;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import us.codecraft.webmagic.Page;
import us.codecraft.webmagic.Request;
import us.codecraft.webmagic.Task;
import us.codecraft.webmagic.selector.PlainText;

import java.io.*;

/**
 * this downloader is used to download pages which need to render the javascript
 *
 * @author [email protected]
 * @version 0.5.3
 */
public class PhantomJSDownloader extends AbstractDownloader {

    private static Logger logger = LoggerFactory.getLogger(PhantomJSDownloader.class);
    private static String crawlJsPath;
    private static String phantomJsCommand = "phantomjs"; // default

    private int retryNum;
    private int threadNum;

    public PhantomJSDownloader() {
        this.initPhantomjsCrawlPath();
    }
    
    /**
     * 添加新的构造函数，支持phantomjs自定义命令
     * 
     * example: 
     *    phantomjs.exe 支持windows环境
     *    phantomjs --ignore-ssl-errors=yes 忽略抓取地址是https时的一些错误
     *    /usr/local/bin/phantomjs 命令的绝对路径，避免因系统环境变量引起的IOException
     *   
     * @param phantomJsCommand phantomJsCommand
     */
    public PhantomJSDownloader(String phantomJsCommand) {
        this.initPhantomjsCrawlPath();
        PhantomJSDownloader.phantomJsCommand = phantomJsCommand;
    }
    
    /**
     * 新增构造函数，支持crawl.js路径自定义，因为当其他项目依赖此jar包时，runtime.exec()执行phantomjs命令时无使用法jar包中的crawl.js
     * 
     * crawl.js start --
     * 
     *   var system = require('system');
     *   var url = system.args[1];
     *   
     *   var page = require('webpage').create();
     *   page.settings.loadImages = false;
     *   page.settings.resourceTimeout = 5000;
     *   
     *   page.open(url, function (status) {
     *       if (status != 'success') {
     *           console.log("HTTP request failed!");
     *       } else {
     *           console.log(page.content);
     *       }
     *   
     *       page.close();
     *       phantom.exit();
     *   });
     *   
     * -- crawl.js end
     * 
     * 具体项目时可以将以上js代码复制下来使用
     *   
     * example:
     *    new PhantomJSDownloader("/your/path/phantomjs", "/your/path/crawl.js");
     * 
     * @param phantomJsCommand phantomJsCommand
     * @param crawlJsPath crawlJsPath
     */
    public PhantomJSDownloader(String phantomJsCommand, String crawlJsPath) {
      PhantomJSDownloader.phantomJsCommand = phantomJsCommand;
      PhantomJSDownloader.crawlJsPath = crawlJsPath;
    }
    
    private void initPhantomjsCrawlPath() {
        PhantomJSDownloader.crawlJsPath = new File(this.getClass().getResource("/").getPath()).getPath() + System.getProperty("file.separator") + "crawl.js ";
    }

    @Override
    public Page download(Request request, Task task) {
        if (logger.isInfoEnabled()) {
            logger.info("downloading page: " + request.getUrl());
        }
        String content = getPage(request);
        if (content.contains("HTTP request failed")) {
            for (int i = 1; i <= getRetryNum(); i++) {
                content = getPage(request);
                if (!content.contains("HTTP request failed")) {
                    break;
                }
            }
            if (content.contains("HTTP request failed")) {
                //when failed
                Page page = new Page();
                page.setRequest(request);
                return page;
            }
        }

        Page page = new Page();
        page.setRawText(content);
        page.setUrl(new PlainText(request.getUrl()));
        page.setRequest(request);
        page.setStatusCode(200);
        return page;
    }

    @Override
    public void setThread(int threadNum) {
        this.threadNum = threadNum;
    }

    protected String getPage(Request request) {
        try {
            String url = request.getUrl();
            Runtime runtime = Runtime.getRuntime();
            Process process = runtime.exec(phantomJsCommand + " " + crawlJsPath + " " + url);
            InputStream is = process.getInputStream();
            BufferedReader br = new BufferedReader(new InputStreamReader(is));
            StringBuffer stringBuffer = new StringBuffer();
            String line;
            while ((line = br.readLine()) != null) {
                stringBuffer.append(line).append("\n");
            }
            return stringBuffer.toString();
        } catch (IOException e) {
            e.printStackTrace();
        }

        return null;
    }

    public int getRetryNum() {
        return retryNum;
    }

    public PhantomJSDownloader setRetryNum(int retryNum) {
        this.retryNum = retryNum;
        return this;
    }
}

SeleniumDownloader

package us.codecraft.webmagic.downloader.selenium;

import org.apache.log4j.Logger;
import org.openqa.selenium.By;
import org.openqa.selenium.Cookie;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import us.codecraft.webmagic.Page;
import us.codecraft.webmagic.Request;
import us.codecraft.webmagic.Site;
import us.codecraft.webmagic.Task;
import us.codecraft.webmagic.downloader.Downloader;
import us.codecraft.webmagic.selector.Html;
import us.codecraft.webmagic.selector.PlainText;

import java.io.Closeable;
import java.io.IOException;
import java.util.Map;

/**
 * 使用Selenium调用浏览器进行渲染。目前仅支持chrome。

 * 需要下载Selenium driver支持。

 *
 * @author [email protected] 

 *         Date: 13-7-26 

 *         Time: 下午1:37 

 */
public class SeleniumDownloader implements Downloader, Closeable {

	private volatile WebDriverPool webDriverPool;

	private Logger logger = Logger.getLogger(getClass());

	private int sleepTime = 0;

	private int poolSize = 1;

	private static final String DRIVER_PHANTOMJS = "phantomjs";

	/**
	 * 新建
	 *
	 * @param chromeDriverPath chromeDriverPath
	 */
	public SeleniumDownloader(String chromeDriverPath) {
		System.getProperties().setProperty("webdriver.chrome.driver",
				chromeDriverPath);
	}

	/**
	 * Constructor without any filed. Construct PhantomJS browser
	 * 
	 * @author [email protected]
	 */
	public SeleniumDownloader() {
		// System.setProperty("phantomjs.binary.path",
		// "/Users/Bingo/Downloads/phantomjs-1.9.7-macosx/bin/phantomjs");
	}

	/**
	 * set sleep time to wait until load success
	 *
	 * @param sleepTime sleepTime
	 * @return this
	 */
	public SeleniumDownloader setSleepTime(int sleepTime) {
		this.sleepTime = sleepTime;
		return this;
	}

	@Override
	public Page download(Request request, Task task) {
		checkInit();
		WebDriver webDriver;
		try {
			webDriver = webDriverPool.get();
		} catch (InterruptedException e) {
			logger.warn("interrupted", e);
			return null;
		}
		logger.info("downloading page " + request.getUrl());
		webDriver.get(request.getUrl());
		try {
			Thread.sleep(sleepTime);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		WebDriver.Options manage = webDriver.manage();
		Site site = task.getSite();
		if (site.getCookies() != null) {
			for (Map.Entry cookieEntry : site.getCookies()
					.entrySet()) {
				Cookie cookie = new Cookie(cookieEntry.getKey(),
						cookieEntry.getValue());
				manage.addCookie(cookie);
			}
		}

		/*
		 * TODO You can add mouse event or other processes
		 * 
		 * @author: [email protected]
		 */

		WebElement webElement = webDriver.findElement(By.xpath("/html"));
		String content = webElement.getAttribute("outerHTML");
		Page page = new Page();
		page.setRawText(content);
		page.setHtml(new Html(content, request.getUrl()));
		page.setUrl(new PlainText(request.getUrl()));
		page.setRequest(request);
		webDriverPool.returnToPool(webDriver);
		return page;
	}

	private void checkInit() {
		if (webDriverPool == null) {
			synchronized (this) {
				webDriverPool = new WebDriverPool(poolSize);
			}
		}
	}

	@Override
	public void setThread(int thread) {
		this.poolSize = thread;
	}

	@Override
	public void close() throws IOException {
		webDriverPool.closeAll();
	}
}

总结

如果想要改下载器 可以写个类实现下这个接口downloader

然后形式不变采取其他组件下载或者配置动态代理

因为这部分不是很完整。