簡介

Parser類負責將從伺服器得到的byte[]資料（儲存在Page物件裡）進行解析，按照binary,text,html的型別，分別呼叫相應的parseData類>。這裡有個容易混淆的點：類BinaryParseData，TextParseData，HtmlParseDat命名有點不好，它們表示的意思是pase之後得到的關於網頁的規範化的Data，而不是動名詞結構(parse data)。

原始碼

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是一個內容分析工具，自帶全面的parser工具類，
// 能解析基本所有常見格式的檔案，得到檔案的metadata，content等內容，返回格式化資訊
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;

//二進位制檔案解析類
public class BinaryParseData implements ParseData {

  private static final Logger logger = LoggerFactory.getLogger(BinaryParseData.class);
  private static final String DEFAULT_ENCODING = "UTF-8";   // 預設編碼utf-8
  private static final String DEFAULT_OUTPUT_FORMAT = "html";   //預設輸出格式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();
  // 頁面的所有外鏈
  private Set<WebURL> outgoingUrls = new HashSet<>();

  // 從二進位制資料中得到的html內容
  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 <code>null</code> 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<WebURL> getOutgoingUrls() {
    return outgoingUrls;
  }

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

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