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分享關于j2me xmlReader的輕量級實現

2019-11-18 12:46:26
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  一、kxml的前身--xmlpull
  
  xmlpull提供了為資源有限的環境(如j2me)和j2ee應用服務器使用的xml解析API,xml pull解析答應使用stream解析的方式。
  
  xmlpull的特點:
  
  * 簡單的接口-解析器包含一個接口、一個異常、一個建立解析器的factory;
  
  * 無實現依靠-模擬JAXP的factory類和很輕易的切換不同的XmlPull V1 API實現,而無需修改代碼;
  
  * 易用性-只有唯一的next()方法用來讀取下面5類事件中的一個:
  
  START DOCUMENT-文檔起始點,這時解析器還沒有預備好讀取文檔;
  
  START_TAG-解析器讀取到了element聲明的開始標簽,就是xml文件中聲明element用的"<";
  
  TEXT-解析器讀取到了element的內容,如element的各種屬性和value;
  
  END_TAG-解析器讀取到了element聲明的結束標簽,就是"/>"或者"</...>";
  
  END_DOCUMENT-解析器讀取到文檔的結尾,解析工作完畢。
  
  * 多功能性-由于提供了xml解析器的通用接口,所以答應多個實現和在特性和屬性上的擴展
  
  * 良好的性能-由于提供了通用的接口,可以說也就為使用快速的xml解析器提供了條件,但是目前最快的解析器,本人還沒碰到過。:-)
  
  * 最小化需要-設計上與j2me兼容,從而使其能工作于小型設備和建立使用微量內存的xmlPull兼容的解析器。
  
  二、建立在良好構架上的kxml
  
  xmlpull api提供的通用的xml內容解析功能使用方式:使用一個循環來遍歷到下一個事件,并切換到一個針對這個事件的分支語句處理。但是在使用xml解析器時,一些xml element不僅包括text還有其它的element(被稱為子元素或者內嵌元素)。對于這樣的xml數據,解析處理被簡單化到了使用xmlpull api的nextTag和nextText方法。另外,require方法也可以使用一個解析狀態的參數來表示希望取得數據的event類型。以上就是kxml使用方法。
  
  如解析下面內容的簡單xml文件:
  <elements>
  <text>text1</text>
  <text>text2</text></elements>
  
  解析代碼片斷如下:
  parser.nextTag();parser.require(XmlPullParser.START_TAG, null, "elements");
  while(parser.nextTag() == XmlPullParser.START_TAG) { parser.require(XmlPullParser.START_TAG, null, "text");
  // handle element content  System.out.  parser.require(XmlPullParser.END_TAG, null, "text");}parser.require(XmlPullParser.END_TAG, null, "elements");
  
  從上面的代碼看出,的確很簡單明了。
  
  三、背向kxml的原因
  
  但是假如真正的使用kxml開發j2me程序時會發現,kxml包和其依靠的xmlpull包不僅無形中增加了程序發布時的大小,而且由于沒有最好的解析器帶來的負面性能損耗會隨著xml文件的大小成非線性增長(還好不是指數級的)。這些成為了kxml的流行障礙。
  
  四、輕量級的xmlReader
  
  幸運的是kobject.org網站上提供了一個輕量級的xmlReader程序,大家可以到http://kobjects.sourceforge.net/utils/ 獲取。
  
  作為簡單的xml解析器,功能上與kxml類似,但是不支持命名空間和一些傳統的事件。整個jar文件大小小于5KB。
  
  以下便是其代碼:
  XmlReader.
java
  /* Copyright (c) 2002,2003, Stefan Haustein, Oberhausen, Rhld., Germany *
  * Permission is hereby granted, free of charge, to any person oBTaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or
  * sell copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  * IN THE SOFTWARE. */package org.kobjects.xml;import java.io.*;
  import java.util.*;
  /** A minimalistic XML pull parser, similar to kXML, but
  not supporting namespaces or legacy events. If you need
  support for namespaces, or access to XML comments or
  processing instrUCtions, please use kXML(2) instead. */public class XmlReader {
  /** Return value of getType before first call to next() */
  public final static int START_DOCUMENT = 0;
  /** Signal logical end of xml document */
  public final static int END_DOCUMENT = 1;
  /** Start tag was just read */  public final static int START_TAG = 2;
  /**   * End tag was just read
  */
  public final static int END_TAG = 3;
  /** Text was just read */
  public final static int TEXT = 4;
  final static int CDSECT = 5;
  final static int ENTITY_REF = 6;
  static final private String UNEXPECTED_EOF =
  "Unexpected EOF";
  static final private int LEGACY = 999;
  // general  public boolean relaxed;
  private Hashtable entityMap;
  private int depth;
  private String[] elementStack = new String[4];
  // source  private Reader reader;
  private char[] srcBuf =
  new char[Runtime.getRuntime().freeMemory() >= 1048576
  ? 8192
  : 128];
  private int srcPos;
  private int srcCount;
  private boolean eof;
  private int line;
  private int column;
  private int peek0;
  private int peek1;
  // txtbuffer
  private char[] txtBuf = new char[128];
  private int txtPos;
  // Event-related
  private int type;
  private String text;
  private boolean isWhitespace;
  private String name;
  private boolean degenerated;
  private int attributeCount;
  private String[] attributes = new String[16];
  private String[] TYPES =
  {
  "Start Document",
  "End Document",
  "Start Tag",
  "End Tag",
  "Text" };
  private final int read() throws IOException {
  int r = peek0;
  peek0 = peek1;
  if (peek0 == -1) {
  eof = true;
  return r;
  }    else if (r == '/n' r == '/r') {
  line++;
  column = 0;
  if (r == '/r' && peek0 == '/n')
  peek0 = 0;    }
  column++;
  if (srcPos >= srcCount) {
  srcCount = reader.read(srcBuf, 0, srcBuf.length);
  if (srcCount <= 0) {
  peek1 = -1;
  return r;
  }
  srcPos = 0;
  }
  peek1 = srcBuf[srcPos++];
  return r;
  }
  private final void exception(String desc)
  throws IOException {
  throw new IOException(
  desc + " pos: " + getPositionDescription());
  }
  private final void push(int c) {
  if (c == 0)
  return;
  if (txtPos == txtBuf.length) {
  char[] bigger = new char[txtPos * 4 / 3 + 4];
  System.arraycopy(txtBuf, 0, bigger, 0, txtPos);
  txtBuf = bigger;
  }
  txtBuf[txtPos++] = (char) c;
  }  private final void read(char c) throws IOException {
  if (read() != c) {
  if (relaxed) {
  if (c <= 32) {
  skip();
  read();
  }
  }
  else {
  exception("expected: '" + c + "'");
  }
  }
  }
  private final void skip() throws IOException {
  while (!eof && peek0 <= ' ')
  read();
  }
  private final String pop(int pos) {
  String result = new String(txtBuf, pos, txtPos - pos);
  txtPos = pos;
  return result;
  }
  private final String readName() throws IOException {
  int pos = txtPos;    int c = peek0;
  if ((c < 'a' c > 'z')
  && (c < 'A' c > 'Z')
  && c != '_'
  && c != ':'
  && !relaxed)

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