stringreader.java

J2me实现的MSN Messeger客户端程序。聊天、添加好友、删除好友、阻止好友

/*
 * @(#)StringReader.java	1.17 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */



package vitular.msnp.util;

import java.io.*;

/**
 * A character stream whose source is a string.
 *
 * @version 	1.17, 03/01/23
 * @author	Mark Reinhold
 * @since	JDK1.1
 */



public class StringReader
    extends Reader {
  private String str;
  private int length;
  private int next = 0;
  private int mark = 0;

  /**
   * Create a new string reader.
   *
   * @param s  String providing the character stream.
   */

  public StringReader(String s) {
    this.str = s;
    this.length = s.length();
  }



  /** Check to make sure that the stream has not been closed */
  private void ensureOpen() throws IOException {
    if (str == null) {
      throw new IOException("Stream closed");
    }
  }



  /**
   * Read a single character.
   *
   * @return     The character read, or -1 if the end of the stream has been
   *             reached
   *
   * @exception  IOException  If an I/O error occurs
   */

  public int read() throws IOException {
    synchronized (lock) {
      ensureOpen();
      if (next >= length) {
        return -1;
      }
      return str.charAt(next++);
    }
  }



  /**
   * Read characters into a portion of an array.
   *
   * @param      cbuf  Destination buffer
   * @param      off   Offset at which to start writing characters
   * @param      len   Maximum number of characters to read
   *
   * @return     The number of characters read, or -1 if the end of the
   *             stream has been reached
   *
   * @exception  IOException  If an I/O error occurs
   */

  public int read(char cbuf[], int off, int len) throws IOException {
    synchronized (lock) {
      ensureOpen();
      if ( (off < 0) || (off > cbuf.length) || (len < 0) ||
          ( (off + len) > cbuf.length) || ( (off + len) < 0)) {
        throw new IndexOutOfBoundsException();
      }
      else if (len == 0) {
        return 0;
      }
      if (next >= length) {
        return -1;
      }
      int n = Math.min(length - next, len);
      str.getChars(next, next + n, cbuf, off);
      next += n;
      return n;
    }

  }

  /**
   * Skip characters.
   *
   * @exception  IOException  If an I/O error occurs
   */

  public long skip(long ns) throws IOException {
    synchronized (lock) {
      ensureOpen();
      if (next >= length) {
        return 0;
      }
      long n = Math.min(length - next, ns);
      next += n;
      return n;
    }
  }


  /**

   * Tell whether this stream is ready to be read.

   *

   * @return True if the next read() is guaranteed not to block for input

   *

   * @exception  IOException  If the stream is closed

   */

  public boolean ready() throws IOException {
    synchronized (lock) {
      ensureOpen();
      return true;
    }
  }



  /**

   * Tell whether this stream supports the mark() operation, which it does.

   */

  public boolean markSupported() {
    return true;
  }



  /**

   * Mark the present position in the stream.  Subsequent calls to reset()

   * will reposition the stream to this point.

   *

   * @param  readAheadLimit  Limit on the number of characters that may be

   *                         read while still preserving the mark.  Because

   *                         the stream's input comes from a string, there

   *                         is no actual limit, so this argument must not

   *                         be negative, but is otherwise ignored.

   *

   * @exception  IllegalArgumentException  If readAheadLimit is < 0

   * @exception  IOException  If an I/O error occurs

   */

  public void mark(int readAheadLimit) throws IOException {
    if (readAheadLimit < 0) {
      throw new IllegalArgumentException("Read-ahead limit < 0");
    }
    synchronized (lock) {
      ensureOpen();
      mark = next;
    }
  }



  /**

   * Reset the stream to the most recent mark, or to the beginning of the

   * string if it has never been marked.

   *

   * @exception  IOException  If an I/O error occurs

   */

  public void reset() throws IOException {
    synchronized (lock) {
      ensureOpen();
      next = mark;
    }
  }



  /**

   * Close the stream.

   */

  public void close() {
    str = null;
  }

}