Java网络爬虫crawler4j学习笔记 Parser 类

简介

Parser类负责将从服务器得到的byte[]数据（存储在Page对象里）进行解析，按照binary,text,html的类型，分别调用相应的parseData类>。这里有个容易混淆的点：类BinaryParseData，TextParseData，HtmlParseDat命名有点不好，它们表示的意思是pase之后得到的关于网页的规范化的Data，而不是动名词结构(parse data)。

源代码

package edu.uci.ics.crawler4j.parser;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintStream;
import java.io.UnsupportedEncodingException;
import java.util.HashSet;
import java.util.Set;

import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.sax.SAXTransformerFactory;
import javax.xml.transform.sax.TransformerHandler;
import javax.xml.transform.stream.StreamResult;

import edu.uci.ics.crawler4j.url.WebURL;

// Tika是一个内容分析工具，自带全面的parser工具类，
// 能解析基本所有常见格式的文件，得到文件的metadata，content等内容，返回格式化信息
import org.apache.tika.metadata.Metadata;
import org.apache.tika.parser.AutoDetectParser;
import org.apache.tika.parser.ParseContext;
import org.apache.tika.parser.Parser;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

//二进制文件解析类
public class BinaryParseData implements ParseData {

  private static final Logger logger = LoggerFactory.getLogger(BinaryParseData.class);
  private static final String DEFAULT_ENCODING = "UTF-8";   // 默认编码utf-8
  private static final String DEFAULT_OUTPUT_FORMAT = "html";   //默认输出格式html

  // Creates an auto-detecting parser instance using the default Tika configuration.
  private static final Parser AUTO_DETECT_PARSER = new AutoDetectParser();
  private static final SAXTransformerFactory SAX_TRANSFORMER_FACTORY = (SAXTransformerFactory) SAXTransformerFactory.newInstance();

  // Parse context. Used to pass context information to Tika parsers.
  private final ParseContext context = new ParseContext();
  // 页面的所有外链
  private Set outgoingUrls = new HashSet<>();

  // 从二进制数据中得到的html内容
  private String html = null;

  public BinaryParseData() {
    context.set(Parser.class, AUTO_DETECT_PARSER);
  }

  public void setBinaryContent(byte[] data) {
    InputStream inputStream = new ByteArrayInputStream(data);
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();

    try {
      TransformerHandler handler = getTransformerHandler(outputStream, DEFAULT_OUTPUT_FORMAT, DEFAULT_ENCODING);
      AUTO_DETECT_PARSER.parse(inputStream, handler, new Metadata(), context);

      // Hacking the following line to remove Tika's inserted DocType
      String htmlContent = new String(outputStream.toByteArray(), DEFAULT_ENCODING).replace("http://www.w3.org/1999/xhtml", "");
      setHtml(htmlContent);
    } catch (Exception e) {
      logger.error("Error parsing file", e);
    }
  }

  /**
   * Returns a transformer handler that serializes incoming SAX events to
   * XHTML or HTML (depending the given method) using the given output encoding.
   *
   * @param encoding output encoding, or null for the platform default
   */
  private static TransformerHandler getTransformerHandler(OutputStream out, String method, String encoding)
        throws TransformerConfigurationException {

    TransformerHandler transformerHandler = SAX_TRANSFORMER_FACTORY.newTransformerHandler();
    Transformer transformer = transformerHandler.getTransformer();
    transformer.setOutputProperty(OutputKeys.METHOD, method); // html
    //  the Transformer may add additional whitespace when outputting the result tree;
    transformer.setOutputProperty(OutputKeys.INDENT, "yes");  

    if (encoding != null) {
      transformer.setOutputProperty(OutputKeys.ENCODING, encoding);
    }

    transformerHandler.setResult(new StreamResult(new PrintStream(out)));
    return transformerHandler;
  }

  /** @return Parsed binary content or null */
  public String getHtml() {
    return html;
  }

  public void setHtml(String html) {
    this.html = html;
  }

  @Override
  public Set getOutgoingUrls() {
    return outgoingUrls;
  }

  @Override
  public void setOutgoingUrls(Set outgoingUrls) {
    this.outgoingUrls = outgoingUrls;
  }

  @Override
  public String toString() {
    return (html == null || html.isEmpty()) ? "No data parsed yet" : getHtml();
  }
}