Source Home >> Java Source 1.5.0 >> java.io.InputStream V 0.09

001/*
002 * @(#)InputStream.java	1.45 04/02/19
003 *
004 * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
005 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
006 */
007
008package java.io;
009
010/**
011 * This abstract class is the superclass of all classes representing
012 * an input stream of bytes.
013 *
014 * <p> Applications that need to define a subclass of <code>InputStream</code>
015 * must always provide a method that returns the next byte of input.
016 *
017 * @author  Arthur van Hoff
018 * @version 1.45, 02/19/04
019 * @see     java.io.BufferedInputStream
020 * @see     java.io.ByteArrayInputStream
021 * @see     java.io.DataInputStream
022 * @see     java.io.FilterInputStream
023 * @see     java.io.InputStream#read()
024 * @see     java.io.OutputStream
025 * @see     java.io.PushbackInputStream
026 * @since   JDK1.0
027 */
028public abstract class InputStream implements Closeable {
029
030    // SKIP_BUFFER_SIZE is used to determine the size of skipBuffer
031    private static final int SKIP_BUFFER_SIZE = 2048;
032    // skipBuffer is initialized in skip(long), if needed.
033    private static byte[] skipBuffer;
034
035    /**
036     * Reads the next byte of data from the input stream. The value byte is
037     * returned as an <code>int</code> in the range <code>0</code> to
038     * <code>255</code>. If no byte is available because the end of the stream
039     * has been reached, the value <code>-1</code> is returned. This method
040     * blocks until input data is available, the end of the stream is detected,
041     * or an exception is thrown.
042     *
043     * <p> A subclass must provide an implementation of this method.
044     *
045     * @return     the next byte of data, or <code>-1</code> if the end of the
046     *             stream is reached.
047     * @exception  IOException  if an I/O error occurs.
048     */
049    public abstract int read() throws IOException;
050
051    /**
052     * Reads some number of bytes from the input stream and stores them into
053     * the buffer array <code>b</code>. The number of bytes actually read is
054     * returned as an integer.  This method blocks until input data is
055     * available, end of file is detected, or an exception is thrown.
056     *
057     * <p> If <code>b</code> is <code>null</code>, a
058     * <code>NullPointerException</code> is thrown.  If the length of
059     * <code>b</code> is zero, then no bytes are read and <code>0</code> is
060     * returned; otherwise, there is an attempt to read at least one byte. If
061     * no byte is available because the stream is at end of file, the value
062     * <code>-1</code> is returned; otherwise, at least one byte is read and
063     * stored into <code>b</code>.
064     *
065     * <p> The first byte read is stored into element <code>b[0]</code>, the
066     * next one into <code>b[1]</code>, and so on. The number of bytes read is,
067     * at most, equal to the length of <code>b</code>. Let <i>k</i> be the
068     * number of bytes actually read; these bytes will be stored in elements
069     * <code>b[0]</code> through <code>b[</code><i>k</i><code>-1]</code>,
070     * leaving elements <code>b[</code><i>k</i><code>]</code> through
071     * <code>b[b.length-1]</code> unaffected.
072     *
073     * <p> If the first byte cannot be read for any reason other than end of
074     * file, then an <code>IOException</code> is thrown. In particular, an
075     * <code>IOException</code> is thrown if the input stream has been closed.
076     *
077     * <p> The <code>read(b)</code> method for class <code>InputStream</code>
078     * has the same effect as: <pre><code> read(b, 0, b.length) </code></pre>
079     *
080     * @param      b   the buffer into which the data is read.
081     * @return     the total number of bytes read into the buffer, or
082     *             <code>-1</code> is there is no more data because the end of
083     *             the stream has been reached.
084     * @exception  IOException  if an I/O error occurs.
085     * @exception  NullPointerException  if <code>b</code> is <code>null</code>.
086     * @see        java.io.InputStream#read(byte[], int, int)
087     */
088    public int read(byte b[]) throws IOException {
089	return read(b, 0, b.length);
090    }
091
092    /**
093     * Reads up to <code>len</code> bytes of data from the input stream into
094     * an array of bytes.  An attempt is made to read as many as
095     * <code>len</code> bytes, but a smaller number may be read.
096     * The number of bytes actually read is returned as an integer.
097     *
098     * <p> This method blocks until input data is available, end of file is
099     * detected, or an exception is thrown.
100     *
101     * <p> If <code>b</code> is <code>null</code>, a
102     * <code>NullPointerException</code> is thrown.
103     *
104     * <p> If <code>off</code> is negative, or <code>len</code> is negative, or
105     * <code>off+len</code> is greater than the length of the array
106     * <code>b</code>, then an <code>IndexOutOfBoundsException</code> is
107     * thrown.
108     *
109     * <p> If <code>len</code> is zero, then no bytes are read and
110     * <code>0</code> is returned; otherwise, there is an attempt to read at
111     * least one byte. If no byte is available because the stream is at end of
112     * file, the value <code>-1</code> is returned; otherwise, at least one
113     * byte is read and stored into <code>b</code>.
114     *
115     * <p> The first byte read is stored into element <code>b[off]</code>, the
116     * next one into <code>b[off+1]</code>, and so on. The number of bytes read
117     * is, at most, equal to <code>len</code>. Let <i>k</i> be the number of
118     * bytes actually read; these bytes will be stored in elements
119     * <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>,
120     * leaving elements <code>b[off+</code><i>k</i><code>]</code> through
121     * <code>b[off+len-1]</code> unaffected.
122     *
123     * <p> In every case, elements <code>b[0]</code> through
124     * <code>b[off]</code> and elements <code>b[off+len]</code> through
125     * <code>b[b.length-1]</code> are unaffected.
126     *
127     * <p> If the first byte cannot be read for any reason other than end of
128     * file, then an <code>IOException</code> is thrown. In particular, an
129     * <code>IOException</code> is thrown if the input stream has been closed.
130     *
131     * <p> The <code>read(b,</code> <code>off,</code> <code>len)</code> method
132     * for class <code>InputStream</code> simply calls the method
133     * <code>read()</code> repeatedly. If the first such call results in an
134     * <code>IOException</code>, that exception is returned from the call to
135     * the <code>read(b,</code> <code>off,</code> <code>len)</code> method.  If
136     * any subsequent call to <code>read()</code> results in a
137     * <code>IOException</code>, the exception is caught and treated as if it
138     * were end of file; the bytes read up to that point are stored into
139     * <code>b</code> and the number of bytes read before the exception
140     * occurred is returned.  Subclasses are encouraged to provide a more
141     * efficient implementation of this method.
142     *
143     * @param      b     the buffer into which the data is read.
144     * @param      off   the start offset in array <code>b</code>
145     *                   at which the data is written.
146     * @param      len   the maximum number of bytes to read.
147     * @return     the total number of bytes read into the buffer, or
148     *             <code>-1</code> if there is no more data because the end of
149     *             the stream has been reached.
150     * @exception  IOException  if an I/O error occurs.
151     * @exception  NullPointerException  if <code>b</code> is <code>null</code>.
152     * @see        java.io.InputStream#read()
153     */
154    public int read(byte b[], int off, int len) throws IOException {
155	if (b == null) {
156	    throw new NullPointerException();
157	} else if ((off < 0) || (off > b.length) || (len < 0) ||
158		   ((off + len) > b.length) || ((off + len) < 0)) {
159	    throw new IndexOutOfBoundsException();
160	} else if (len == 0) {
161	    return 0;
162	}
163
164	int c = read();
165	if (c == -1) {
166	    return -1;
167	}
168	b[off] = (byte)c;
169
170	int i = 1;
171	try {
172	    for (; i < len ; i++) {
173		c = read();
174		if (c == -1) {
175		    break;
176		}
177		if (b != null) {
178		    b[off + i] = (byte)c;
179		}
180	    }
181	} catch (IOException ee) {
182	}
183	return i;
184    }
185
186    /**
187     * Skips over and discards <code>n</code> bytes of data from this input
188     * stream. The <code>skip</code> method may, for a variety of reasons, end
189     * up skipping over some smaller number of bytes, possibly <code>0</code>.
190     * This may result from any of a number of conditions; reaching end of file
191     * before <code>n</code> bytes have been skipped is only one possibility.
192     * The actual number of bytes skipped is returned.  If <code>n</code> is
193     * negative, no bytes are skipped.
194     *
195     * <p> The <code>skip</code> method of <code>InputStream</code> creates a
196     * byte array and then repeatedly reads into it until <code>n</code> bytes
197     * have been read or the end of the stream has been reached. Subclasses are
198     * encouraged to provide a more efficient implementation of this method.
199     *
200     * @param      n   the number of bytes to be skipped.
201     * @return     the actual number of bytes skipped.
202     * @exception  IOException  if an I/O error occurs.
203     */
204    public long skip(long n) throws IOException {
205
206	long remaining = n;
207	int nr;
208	if (skipBuffer == null)
209	    skipBuffer = new byte[SKIP_BUFFER_SIZE];
210
211	byte[] localSkipBuffer = skipBuffer;
212		
213	if (n <= 0) {
214	    return 0;
215	}
216
217	while (remaining > 0) {
218	    nr = read(localSkipBuffer, 0,
219		      (int) Math.min(SKIP_BUFFER_SIZE, remaining));
220	    if (nr < 0) {
221		break;
222	    }
223	    remaining -= nr;
224	}
225	
226	return n - remaining;
227    }
228
229    /**
230     * Returns the number of bytes that can be read (or skipped over) from
231     * this input stream without blocking by the next caller of a method for
232     * this input stream.  The next caller might be the same thread or
233     * another thread.
234     *
235     * <p> The <code>available</code> method for class <code>InputStream</code>
236     * always returns <code>0</code>.
237     *
238     * <p> This method should be overridden by subclasses.
239     *
240     * @return     the number of bytes that can be read from this input stream
241     *             without blocking.
242     * @exception  IOException  if an I/O error occurs.
243     */
244    public int available() throws IOException {
245	return 0;
246    }
247
248    /**
249     * Closes this input stream and releases any system resources associated
250     * with the stream.
251     *
252     * <p> The <code>close</code> method of <code>InputStream</code> does
253     * nothing.
254     *
255     * @exception  IOException  if an I/O error occurs.
256     */
257    public void close() throws IOException {}
258
259    /**
260     * Marks the current position in this input stream. A subsequent call to
261     * the <code>reset</code> method repositions this stream at the last marked
262     * position so that subsequent reads re-read the same bytes.
263     *
264     * <p> The <code>readlimit</code> arguments tells this input stream to
265     * allow that many bytes to be read before the mark position gets
266     * invalidated.
267     *
268     * <p> The general contract of <code>mark</code> is that, if the method
269     * <code>markSupported</code> returns <code>true</code>, the stream somehow
270     * remembers all the bytes read after the call to <code>mark</code> and
271     * stands ready to supply those same bytes again if and whenever the method
272     * <code>reset</code> is called.  However, the stream is not required to
273     * remember any data at all if more than <code>readlimit</code> bytes are
274     * read from the stream before <code>reset</code> is called.
275     *
276     * <p> The <code>mark</code> method of <code>InputStream</code> does
277     * nothing.
278     *
279     * @param   readlimit   the maximum limit of bytes that can be read before
280     *                      the mark position becomes invalid.
281     * @see     java.io.InputStream#reset()
282     */
283    public synchronized void mark(int readlimit) {}
284
285    /**
286     * Repositions this stream to the position at the time the
287     * <code>mark</code> method was last called on this input stream.
288     *
289     * <p> The general contract of <code>reset</code> is:
290     *
291     * <p><ul>
292     *
293     * <li> If the method <code>markSupported</code> returns
294     * <code>true</code>, then:
295     *
296     *     <ul><li> If the method <code>mark</code> has not been called since
297     *     the stream was created, or the number of bytes read from the stream
298     *     since <code>mark</code> was last called is larger than the argument
299     *     to <code>mark</code> at that last call, then an
300     *     <code>IOException</code> might be thrown.
301     *
302     *     <li> If such an <code>IOException</code> is not thrown, then the
303     *     stream is reset to a state such that all the bytes read since the
304     *     most recent call to <code>mark</code> (or since the start of the
305     *     file, if <code>mark</code> has not been called) will be resupplied
306     *     to subsequent callers of the <code>read</code> method, followed by
307     *     any bytes that otherwise would have been the next input data as of
308     *     the time of the call to <code>reset</code>. </ul>
309     *
310     * <li> If the method <code>markSupported</code> returns
311     * <code>false</code>, then:
312     *
313     *     <ul><li> The call to <code>reset</code> may throw an
314     *     <code>IOException</code>.
315     *
316     *     <li> If an <code>IOException</code> is not thrown, then the stream
317     *     is reset to a fixed state that depends on the particular type of the
318     *     input stream and how it was created. The bytes that will be supplied
319     *     to subsequent callers of the <code>read</code> method depend on the
320     *     particular type of the input stream. </ul></ul>
321     *
322     * <p>The method <code>reset</code> for class <code>InputStream</code>
323     * does nothing except throw an <code>IOException</code>.
324     *
325     * @exception  IOException  if this stream has not been marked or if the
326     *               mark has been invalidated.
327     * @see     java.io.InputStream#mark(int)
328     * @see     java.io.IOException
329     */
330    public synchronized void reset() throws IOException {
331	throw new IOException("mark/reset not supported");
332    }
333
334    /**
335     * Tests if this input stream supports the <code>mark</code> and
336     * <code>reset</code> methods. Whether or not <code>mark</code> and
337     * <code>reset</code> are supported is an invariant property of a
338     * particular input stream instance. The <code>markSupported</code> method
339     * of <code>InputStream</code> returns <code>false</code>.
340     *
341     * @return  <code>true</code> if this stream instance supports the mark
342     *          and reset methods; <code>false</code> otherwise.
343     * @see     java.io.InputStream#mark(int)
344     * @see     java.io.InputStream#reset()
345     */
346    public boolean markSupported() {
347	return false;
348    }
349
350}