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Java > Open Source Codes > org > apache > oro > text > awk > AwkStreamInput


1 package org.apache.oro.text.awk;
2
3 /* ====================================================================
4  * The Apache Software License, Version 1.1
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6  * Copyright (c) 2000 The Apache Software Foundation. All rights
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41  * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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55  *
56  * Portions of this software are based upon software originally written
57  * by Daniel F. Savarese. We appreciate his contributions.
58  */
59
60 import java.io.*;
61 import org.apache.oro.text.regex.*;
62
63 /**
64  * The AwkStreamInput class is used to look for pattern matches in an
65  * input stream (actually a java.io.Reader instance) in conjunction with
66  * the AwkMatcher class. It is called
67  * AwkStreamInput instead of AwkInputStream to stress that it is a form
68  * of streamed input for the AwkMatcher class to use rather than a subclass of
69  * InputStream.
70  * AwkStreamInput performs special internal buffering to accelerate
71  * pattern searches through a stream. You can determine the size of this
72  * buffer and how it grows by using the appropriate constructor.
73  * <p>
74  * If you want to perform line by line
75  * matches on an input stream, you should use a DataInput or BufferedReader
76  * instance in conjunction
77  * with one of the PatternMatcher methods taking a String, char[], or
78  * PatternMatcherInput as an argument. The DataInput and BufferedReader
79  * readLine() methods will likely be implemented as native methods and
80  * therefore more efficient than supporting line by line searching within
81  * AwkStreamInput.
82  * <p>
83  * In the future the programmer will be able to set this class to save
84  * all the input it sees so that it can be accessed later. This will avoid
85  * having to read a stream more than once for whatever reason.
86
87  @author <a HREF="dfs@savarese.org">Daniel F. Savarese</a>
88  @version $Id: AwkStreamInput.java,v 1.1.1.1 2000/07/23 23:08:50 jon Exp $
89
90  * @see AwkMatcher
91  */
92 public final class AwkStreamInput {
93   static final int _DEFAULT_BUFFER_INCREMENT = 2048;
94   private Reader __searchStream;
95   private int __bufferIncrementUnit;
96   boolean _endOfStreamReached;
97   // The offset into the stream corresponding to buffer[0]
98 int _bufferSize, _bufferOffset, _currentOffset;
99   char[] _buffer;
100
101   /**
102    * We use this default contructor only within the package to create a dummy
103    * AwkStreamInput instance.
104    */
105   AwkStreamInput() {
106     _currentOffset = 0;
107   }
108
109
110   /**
111    * Creates an AwkStreamInput instance bound to a Reader with a
112    * specified initial buffer size and default buffer increment.
113    * <p>
114    * @param input The InputStream to associate with the AwkStreamInput
115    * instance.
116    * @param bufferIncrement The initial buffer size and the default buffer
117    * increment to use when the input buffer has to be increased in
118    * size.
119    */
120   public AwkStreamInput(Reader input, int bufferIncrement) {
121     __searchStream = input;
122     __bufferIncrementUnit = bufferIncrement;
123     _buffer = new char[bufferIncrement];
124     _bufferOffset = _bufferSize = _currentOffset = 0;
125     _endOfStreamReached = false;
126   }
127
128
129   /**
130    * Creates an AwkStreamInput instance bound to a Reader with an
131    * initial buffer size and default buffer increment of 2048 bytes.
132    * <p>
133    * @param input The InputStream to associate with the AwkStreamInput
134    * instance.
135    */
136   public AwkStreamInput(Reader input) {
137     this(input, _DEFAULT_BUFFER_INCREMENT);
138   }
139
140   // Only called when buffer overflows
141 int _reallocate(int initialOffset) throws IOException {
142     int offset, bytesRead;
143     char[] tmpBuffer;
144
145     if(_endOfStreamReached)
146       return _bufferSize;
147
148     offset = _bufferSize - initialOffset;
149     tmpBuffer = new char[offset + __bufferIncrementUnit];
150
151     bytesRead =
152       __searchStream.read(tmpBuffer, offset, __bufferIncrementUnit);
153
154     if(bytesRead <= 0){
155       _endOfStreamReached = true;
156       /* bytesRead should never equal zero, but if it does, we don't
157      want to continue to try and read, running the risk of entering
158      an infinite loop. Throw an IOException instead, because this
159      really IS an exception. */
160       if(bytesRead == 0)
161     throw new IOException("read from input stream returned 0 bytes.");
162       return _bufferSize;
163     } else {
164       _bufferOffset += initialOffset;
165       _bufferSize = offset + bytesRead;
166
167       System.arraycopy(_buffer, initialOffset, tmpBuffer, 0, offset);
168       _buffer = tmpBuffer;
169     }
170
171     return offset;
172   }
173
174   boolean read() throws IOException {
175     _bufferOffset+=_bufferSize;
176     _bufferSize = __searchStream.read(_buffer);
177     _endOfStreamReached = (_bufferSize == -1);
178     return (!_endOfStreamReached);
179   }
180
181   public boolean endOfStream() { return _endOfStreamReached; }
182
183 }
184
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