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Lucene example source code file (StringBuilderReader.java)

This example Lucene source code file (StringBuilderReader.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

illegalargumentexception, indexoutofboundsexception, io, ioexception, ioexception, override, override, read-ahead, reader, reader, stream, stringbuilder, stringbuilderreader, stringbuilderreader

The Lucene StringBuilderReader.java source code

package org.apache.lucene.benchmark.byTask.utils;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.io.Reader;

/**
 * Implements a {@link Reader} over a {@link StringBuilder} instance. Although
 * one can use {@link java.io.StringReader} by passing it
 * {@link StringBuilder#toString()}, it is better to use this class, as it
 * doesn't mark the passed-in {@link StringBuilder} as shared (which will cause
 * inner char[] allocations at the next append() attempt).<br>
 * Notes:
 * <ul>
 * <li>This implementation assumes the underlying {@link StringBuilder} is not
 * changed during the use of this {@link Reader} implementation.
 * <li>This implementation is thread-safe.
 * <li>The implementation looks very much like {@link java.io.StringReader} (for
 * the right reasons).
 * <li>If one wants to reuse that instance, then the following needs to be done:
 * <pre>
 * StringBuilder sb = new StringBuilder("some text");
 * Reader reader = new StringBuilderReader(sb);
 * ... read from reader - don't close it ! ...
 * sb.setLength(0);
 * sb.append("some new text");
 * reader.reset();
 * ... read the new string from the reader ...
 * </pre>
 * </ul>
 */
public class StringBuilderReader extends Reader {
  
  // The StringBuilder to read from.
  private StringBuilder sb;

  // The length of 'sb'.
  private int length;

  // The next position to read from the StringBuilder.
  private int next = 0;

  // The mark position. The default value 0 means the start of the text.
  private int mark = 0;

  public StringBuilderReader(StringBuilder sb) {
    set(sb);
  }

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

  @Override
  public void close() {
    synchronized (lock) {
      sb = null;
    }
  }

  /**
   * 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 StringBuilder, 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
   */
  @Override
  public void mark(int readAheadLimit) throws IOException {
    if (readAheadLimit < 0){
      throw new IllegalArgumentException("Read-ahead limit cannpt be negative: " + readAheadLimit);
    }
    synchronized (lock) {
      ensureOpen();
      mark = next;
    }
  }

  @Override
  public boolean markSupported() {
    return true;
  }

  @Override
  public int read() throws IOException {
    synchronized (lock) {
      ensureOpen();
      return next >= length ? -1 : sb.charAt(next++);
    }
  }

  @Override
  public int read(char cbuf[], int off, int len) throws IOException {
    synchronized (lock) {
      ensureOpen();

      // Validate parameters
      if (off < 0 || off > cbuf.length || len < 0 || off + len > cbuf.length) {
        throw new IndexOutOfBoundsException("off=" + off + " len=" + len + " cbuf.length=" + cbuf.length);
      }

      if (len == 0) {
        return 0;
      }

      if (next >= length) {
        return -1;
      }

      int n = Math.min(length - next, len);
      sb.getChars(next, next + n, cbuf, off);
      next += n;
      return n;
    }
  }

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

  @Override
  public void reset() throws IOException {
    synchronized (lock) {
      ensureOpen();
      next = mark;
      length = sb.length();
    }
  }

  public void set(StringBuilder sb) {
    synchronized (lock) {
      this.sb = sb;
      length = sb.length();
      next = mark = 0;
    }
  }
  
  @Override
  public long skip(long ns) throws IOException {
    synchronized (lock) {
      ensureOpen();
      if (next >= length) {
        return 0;
      }

      // Bound skip by beginning and end of the source
      long n = Math.min(length - next, ns);
      n = Math.max(-next, n);
      next += n;
      return n;
    }
  }

}

Other Lucene examples (source code examples)

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