為了支持全文檢索，有必要將HTML格式的文章轉化為純文本格式，因此我設計了一個基本的WebFormatter類，提供一個簡單的public static String html2text(String html)，將HTML格式轉化為Text：

/*
?* File: WebFormatter.java
?* Created on 2005-6-24
?* Author: Liao Xuefeng, asklxf@163.com
?* Copyright (C) 2005, Liao Xuefeng.
?*/
package com.mboker.blog.web.util;

import java.util.*;
import java.text.SimpleDateFormat;

/**
?* Do some format on web display.
?*
?* @author Xuefeng
?*/
public class WebFormatter {

??? public static String html2text(String html) {
??????? StringBuffer sb = new StringBuffer(html.length());
??????? char[] data = html.toCharArray();
??????? int start = 0;
??????? boolean previousIsPre = false;
??????? Token token = null;
??????? for(;;) {
??????????? token = parse(data, start, previousIsPre);
??????????? if(token==null)
??????????????? break;
??????????? previousIsPre = token.isPreTag();
??????????? sb = sb.append(token.getText());
??????????? start += token.getLength();
??????? }
??????? return sb.toString();
??? }

??? private static Token parse(char[] data, int start, boolean previousIsPre) {
??????? if(start>=data.length)
??????????? return null;
??????? // try to read next char:
??????? char c = data[start];
??????? if(c=='<') {
??????????? // this is a tag or comment or script:
??????????? int end_index = indexOf(data, start+1, '>');
??????????? if(end_index==(-1)) {
??????????????? // the left is all text!
??????????????? return new Token(Token.TOKEN_TEXT, data, start, data.length, previousIsPre);
??????????? }
??????????? String s = new String(data, start, end_index-start+1);
??????????? // now we got s="<...>":
??????????? if(s.startsWith("<!--")) { // this is a comment!
??????????????? int end_comment_index = indexOf(data, start+1, "-->");
??????????????? if(end_comment_index==(-1)) {
??????????????????? // illegal end, but treat as comment:
??????????????????? return new Token(Token.TOKEN_COMMENT, data, start, data.length, previousIsPre);
??????????????? }
??????????????? else
??????????????????? return new Token(Token.TOKEN_COMMENT, data, start, end_comment_index+3, previousIsPre);
??????????? }
??????????? String s_lowerCase = s.toLowerCase();
??????????? if(s_lowerCase.startsWith("<script")) { // this is a script:
??????????????? int end_script_index = indexOf(data, start+1, "</script>");
??????????????? if(end_script_index==(-1))
??????????????????? // illegal end, but treat as script:
??????????????????? return new Token(Token.TOKEN_SCRIPT, data, start, data.length, previousIsPre);
??????????????? else
??????????????????? return new Token(Token.TOKEN_SCRIPT, data, start, end_script_index+9, previousIsPre);
??????????? }
??????????? else { // this is a tag:
??????????????? return new Token(Token.TOKEN_TAG, data, start, start+s.length(), previousIsPre);
??????????? }
??????? }
??????? // this is a text:
??????? int next_tag_index = indexOf(data, start+1, '<');
??????? if(next_tag_index==(-1))
??????????? return new Token(Token.TOKEN_TEXT, data, start, data.length, previousIsPre);
??????? return new Token(Token.TOKEN_TEXT, data, start, next_tag_index, previousIsPre);
??? }

??? private static int indexOf(char[] data, int start, String s) {
??????? char[] ss = s.toCharArray();
??????? // TODO: performance can improve!
??????? for(int i=start; i<(data.length-ss.length); i++) {
??????????? // compare from data[i] with ss[0]:
??????????? boolean match = true;
??????????? for(int j=0; j<ss.length; j++) {
??????????????? if(data[i+j]!=ss[j]) {
??????????????????? match = false;
??????????????????? break;
??????????????? }
??????????? }
??????????? if(match)
??????????????? return i;
??????? }
??????? return (-1);
??? }

??? private static int indexOf(char[] data, int start, char c) {
??????? for(int i=start; i<data.length; i++) {
??????????? if(data[i]==c)
??????????????? return i;
??????? }
??????? return (-1);
??? }

}

class Token {

??? public static final int TOKEN_TEXT??? = 0; // html text.
??? public static final int TOKEN_COMMENT = 1; // comment like <!-- comments... -->
??? public static final int TOKEN_TAG???? = 2; // tag like <pre>, <font>, etc.
??? public static final int TOKEN_SCRIPT? = 3;

??? private static final char[] TAG_BR? = "<br".toCharArray();
??? private static final char[] TAG_P?? = "<p".toCharArray();
??? private static final char[] TAG_LI? = "<li".toCharArray();
??? private static final char[] TAG_PRE = "<pre".toCharArray();
??? private static final char[] TAG_HR? = "<hr".toCharArray();

??? private static final char[] END_TAG_TD = "</td>".toCharArray();
??? private static final char[] END_TAG_TR = "</tr>".toCharArray();
??? private static final char[] END_TAG_LI = "</li>".toCharArray();

??? private static final Map SPECIAL_CHARS = new HashMap();

??? private int type;
??? private String html;?????????? // original html
??? private String text = null;??? // text!
??? private int length = 0;??????? // html length
??? private boolean isPre = false; // isPre tag?

??? static {
??????? SPECIAL_CHARS.put("&quot;", "\"");
??????? SPECIAL_CHARS.put("&lt;",?? "<");
??????? SPECIAL_CHARS.put("&gt;",?? ">");
??????? SPECIAL_CHARS.put("&amp;",? "&");
??????? SPECIAL_CHARS.put("&reg;",? "(r)");
??????? SPECIAL_CHARS.put("&copy;", "(c)");
??????? SPECIAL_CHARS.put("&nbsp;", " ");
??????? SPECIAL_CHARS.put("&pound;", "?");
??? }

??? public Token(int type, char[] data, int start, int end, boolean previousIsPre) {
??????? this.type = type;
??????? this.length = end - start;
??????? this.html = new String(data, start, length);
??????? System.out.println("[Token] html=" + html + ".");
??????? parseText(previousIsPre);
??????? System.out.println("[Token] text=" + text + ".");
??? }

??? public int getLength() {
??????? return length;
??? }

??? public boolean isPreTag() {
??????? return isPre;
??? }

??? private void parseText(boolean previousIsPre) {
??????? if(type==TOKEN_TAG) {
??????????? char[] cs = html.toCharArray();
??????????? if(compareTag(TAG_BR, cs) || compareTag(TAG_P, cs))
??????????????? text = "\n";
??????????? else if(compareTag(TAG_LI, cs))
??????????????? text = "\n* ";
??????????? else if(compareTag(TAG_PRE, cs))
??????????????? isPre = true;
??????????? else if(compareTag(TAG_HR, cs))
??????????????? text = "\n--------\n";
??????????? else if(compareString(END_TAG_TD, cs))
??????????????? text = "\t";
??????????? else if(compareString(END_TAG_TR, cs) || compareString(END_TAG_LI, cs))
??????????????? text = "\n";
??????? }
??????? // text token:
??????? else if(type==TOKEN_TEXT) {
??????????? text = toText(html, previousIsPre);
??????? }
??? }

??? public String getText() {
??????? return text==null ? "" : text;
??? }

??? private String toText(String html, final boolean isPre) {
??????? char[] cs = html.toCharArray();
??????? StringBuffer buffer = new StringBuffer(cs.length);
??????? int start = 0;
??????? boolean continueSpace = false;
??????? char current, next;
??????? for(;;) {
??????????? if(start>=cs.length)
??????????????? break;
??????????? current = cs[start]; // read current char
??????????? if(start+1<cs.length) // and next char
??????????????? next = cs[start+1];
??????????? else
??????????????? next = '\0';
??????????? if(current==' ') {
??????????????? if(isPre || !continueSpace)
??????????????????? buffer = buffer.append(' ');
??????????????? continueSpace = true;
??????????????? // continue loop:
??????????????? start++;
??????????????? continue;
??????????? }
??????????? // not ' ', so:
??????????? if(current=='\r' && next=='\n') {
??????????????? if(isPre)
??????????????????? buffer = buffer.append('\n');
??????????????? // continue loop:
??????????????? start+=2;
??????????????? continue;
??????????? }
??????????? if(current=='\n' || current=='\r') {
??????????????? if(isPre)
??????????????????? buffer = buffer.append('\n');
??????????????? // continue loop:
??????????????? start++;
??????????????? continue;
??????????? }
??????????? // cannot continue space:
??????????? continueSpace = false;
??????????? if(current=='&') {
??????????????? // maybe special char:
??????????????? int length = readUtil(cs, start, ';', 10);
??????????????? if(length==(-1)) { // just '&':
??????????????????? buffer = buffer.append('&');
??????????????????? // continue loop:
??????????????????? start++;
??????????????????? continue;
??????????????? }
??????????????? else { // check if special character:
??????????????????? String spec = new String(cs, start, length);
??????????????????? String specChar = (String)SPECIAL_CHARS.get(spec);
??????????????????? if(specChar!=null) { // special chars!
??????????????????????? buffer = buffer.append(specChar);
??????????????????????? // continue loop:
??????????????????????? start+=length;
??????????????????????? continue;
??????????????????? }
??????????????????? else { // check if like '&#1234':
??????????????????????? if(next=='#') { // maybe a char
??????????????????????????? String num = new String(cs, start+2, length-3);
??????????????????????????? try {
??????????????????????????????? int code = Integer.parseInt(num);
??????????????????????????????? if(code>0 && code<65536) { // this is a special char:
??????????????????????????????????? buffer = buffer.append((char)code);
??????????????????????????????????? // continue loop:
??????????????????????????????????? start++;
??????????????????????????????????? continue;
??????????????????????????????? }
??????????????????????????? }
??????????????????????????? catch(Exception e) {}
??????????????????????????? // just normal char:
??????????????????????????? buffer = buffer.append("&#");
??????????????????????????? // continue loop:
??????????????????????????? start+=2;
??????????????????????????? continue;
??????????????????????? }
??????????????????????? else { // just '&':
??????????????????????????? buffer = buffer.append('&');
??????????????????????????? // continue loop:
??????????????????????????? start++;
??????????????????????????? continue;
??????????????????????? }
??????????????????? }
??????????????? }
??????????? }
??????????? else { // just a normal char!
??????????????? buffer = buffer.append(current);
??????????????? // continue loop:
??????????????? start++;
??????????????? continue;
??????????? }
??????? }
??????? return buffer.toString();
??? }

??? // read from cs[start] util meet the specified char 'util',
??? // or null if not found:
??? private int readUtil(final char[] cs, final int start, final char util, final int maxLength) {
??????? int end = start+maxLength;
??????? if(end>cs.length)
??????????? end = cs.length;
??????? for(int i=start; i<start+maxLength; i++) {
??????????? if(cs[i]==util) {
??????????????? return i-start+1;
??????????? }
??????? }
??????? return (-1);
??? }

??? // compare standard tag "<input" with tag "<INPUT value=aa>"
??? private boolean compareTag(final char[] ori_tag, char[] tag) {
??????? if(ori_tag.length>=tag.length)
??????????? return false;
??????? for(int i=0; i<ori_tag.length; i++) {
??????????? if(Character.toLowerCase(tag[i])!=ori_tag[i])
??????????????? return false;
??????? }
??????? // the following char should not be a-z:
??????? if(tag.length>ori_tag.length) {
??????????? char c = Character.toLowerCase(tag[ori_tag.length]);
??????????? if(c<'a' || c>'z')
??????????????? return true;
??????????? return false;
??????? }
??????? return true;
??? }

??? private boolean compareString(final char[] ori, char[] comp) {
??????? if(ori.length>comp.length)
??????????? return false;
??????? for(int i=0; i<ori.length; i++) {
??????????? if(Character.toLowerCase(comp[i])!=ori[i])
??????????????? return false;
??????? }
??????? return true;
??? }

??? public String toString() {
??????? return html;
??? }
}

注意，請先將html中的<body>...</body>部分提取出來，再交給WebFormatter處理，因為html->text轉換實質是刪除所有標簽（某些標簽如<br>被轉化為'\n'）、Script和注釋，對于JavaScript生成的動態內容（例如document.write）無能為力。