Java example source code file (InputStream.java)
The InputStream.java Java example source code/* * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.io; /** * This abstract class is the superclass of all classes representing * an input stream of bytes. * * <p> Applications that need to define a subclass of* * @param b the buffer into which the data is read. * @return the total number of bytes read into the buffer, or * <code>-1 if there is no more data because the end of * the stream has been reached. * @exception IOException If the first byte cannot be read for any reason * other than the end of the file, if the input stream has been closed, or * if some other I/O error occurs. * @exception NullPointerException if <code>b is null.
* @see java.io.InputStream#read(byte[], int, int)
*/
public int read(byte b[]) throws IOException {
return read(b, 0, b.length);
}
/**
* Reads up to <code>len bytes of data from the input stream into
* an array of bytes. An attempt is made to read as many as
* <code>len bytes, but a smaller number may be read.
* The number of bytes actually read is returned as an integer.
*
* <p> This method blocks until input data is available, end of file is
* detected, or an exception is thrown.
*
* <p> If len is zero, then no bytes are read and
* <code>0 is returned; otherwise, there is an attempt to read at
* least one byte. If no byte is available because the stream is at end of
* file, the value <code>-1 is returned; otherwise, at least one
* byte is read and stored into <code>b.
*
* <p> The first byte read is stored into element b[off], the
* next one into <code>b[off+1], and so on. The number of bytes read
* is, at most, equal to <code>len. Let k be the number of
* bytes actually read; these bytes will be stored in elements
* <code>b[off] through b[off+k-1],
* leaving elements <code>b[off+k] through
* <code>b[off+len-1] unaffected.
*
* <p> In every case, elements b[0] through
* <code>b[off] and elements b[off+len] through
* <code>b[b.length-1] are unaffected.
*
* <p> The read(b, off, len) method
* for class <code>InputStream simply calls the method
* <code>read() repeatedly. If the first such call results in an
* <code>IOException, that exception is returned from the call to
* the <code>read(b, off, len) method. If
* any subsequent call to <code>read() results in a
* <code>IOException, the exception is caught and treated as if it
* were end of file; the bytes read up to that point are stored into
* <code>b and the number of bytes read before the exception
* occurred is returned. The default implementation of this method blocks
* until the requested amount of input data <code>len has been read,
* end of file is detected, or an exception is thrown. Subclasses are encouraged
* to provide a more efficient implementation of this method.
*
* @param b the buffer into which the data is read.
* @param off the start offset in array <code>b
* at which the data is written.
* @param len the maximum number of bytes to read.
* @return the total number of bytes read into the buffer, or
* <code>-1 if there is no more data because the end of
* the stream has been reached.
* @exception IOException If the first byte cannot be read for any reason
* other than end of file, or if the input stream has been closed, or if
* some other I/O error occurs.
* @exception NullPointerException If <code>b is null.
* @exception IndexOutOfBoundsException If <code>off is negative,
* <code>len is negative, or len is greater than
* <code>b.length - off
* @see java.io.InputStream#read()
*/
public int read(byte b[], int off, int len) throws IOException {
if (b == null) {
throw new NullPointerException();
} else if (off < 0 || len < 0 || len > b.length - off) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return 0;
}
int c = read();
if (c == -1) {
return -1;
}
b[off] = (byte)c;
int i = 1;
try {
for (; i < len ; i++) {
c = read();
if (c == -1) {
break;
}
b[off + i] = (byte)c;
}
} catch (IOException ee) {
}
return i;
}
/**
* Skips over and discards <code>n bytes of data from this input
* stream. The <code>skip method may, for a variety of reasons, end
* up skipping over some smaller number of bytes, possibly <code>0.
* This may result from any of a number of conditions; reaching end of file
* before <code>n bytes have been skipped is only one possibility.
* The actual number of bytes skipped is returned. If {@code n} is
* negative, the {@code skip} method for class {@code InputStream} always
* returns 0, and no bytes are skipped. Subclasses may handle the negative
* value differently.
*
* <p> The skip method of this class creates a
* byte array and then repeatedly reads into it until <code>n bytes
* have been read or the end of the stream has been reached. Subclasses are
* encouraged to provide a more efficient implementation of this method.
* For instance, the implementation may depend on the ability to seek.
*
* @param n the number of bytes to be skipped.
* @return the actual number of bytes skipped.
* @exception IOException if the stream does not support seek,
* or if some other I/O error occurs.
*/
public long skip(long n) throws IOException {
long remaining = n;
int nr;
if (n <= 0) {
return 0;
}
int size = (int)Math.min(MAX_SKIP_BUFFER_SIZE, remaining);
byte[] skipBuffer = new byte[size];
while (remaining > 0) {
nr = read(skipBuffer, 0, (int)Math.min(size, remaining));
if (nr < 0) {
break;
}
remaining -= nr;
}
return n - remaining;
}
/**
* Returns an estimate of the number of bytes that can be read (or
* skipped over) from this input stream without blocking by the next
* invocation of a method for this input stream. The next invocation
* might be the same thread or another thread. A single read or skip of this
* many bytes will not block, but may read or skip fewer bytes.
*
* <p> Note that while some implementations of {@code InputStream} will return
* the total number of bytes in the stream, many will not. It is
* never correct to use the return value of this method to allocate
* a buffer intended to hold all data in this stream.
*
* <p> A subclass' implementation of this method may choose to throw an
* {@link IOException} if this input stream has been closed by
* invoking the {@link #close()} method.
*
* <p> The {@code available} method for class {@code InputStream} always
* returns {@code 0}.
*
* <p> This method should be overridden by subclasses.
*
* @return an estimate of the number of bytes that can be read (or skipped
* over) from this input stream without blocking or {@code 0} when
* it reaches the end of the input stream.
* @exception IOException if an I/O error occurs.
*/
public int available() throws IOException {
return 0;
}
/**
* Closes this input stream and releases any system resources associated
* with the stream.
*
* <p> The close method of InputStream does
* nothing.
*
* @exception IOException if an I/O error occurs.
*/
public void close() throws IOException {}
/**
* Marks the current position in this input stream. A subsequent call to
* the <code>reset method repositions this stream at the last marked
* position so that subsequent reads re-read the same bytes.
*
* <p> The readlimit arguments tells this input stream to
* allow that many bytes to be read before the mark position gets
* invalidated.
*
* <p> The general contract of mark is that, if the method
* <code>markSupported returns true, the stream somehow
* remembers all the bytes read after the call to <code>mark and
* stands ready to supply those same bytes again if and whenever the method
* <code>reset is called. However, the stream is not required to
* remember any data at all if more than <code>readlimit bytes are
* read from the stream before <code>reset is called.
*
* <p> Marking a closed stream should not have any effect on the stream.
*
* <p> The mark method of InputStream does
* nothing.
*
* @param readlimit the maximum limit of bytes that can be read before
* the mark position becomes invalid.
* @see java.io.InputStream#reset()
*/
public synchronized void mark(int readlimit) {}
/**
* Repositions this stream to the position at the time the
* <code>mark method was last called on this input stream.
*
* <p> The general contract of reset is:
*
* <ul>
* <li> If the method markSupported returns
* <code>true, then:
*
* <ul>mark has not been called since
* the stream was created, or the number of bytes read from the stream
* since <code>mark was last called is larger than the argument
* to <code>mark at that last call, then an
* <code>IOException might be thrown.
*
* <li> If such an IOException is not thrown, then the
* stream is reset to a state such that all the bytes read since the
* most recent call to <code>mark (or since the start of the
* file, if <code>mark has not been called) will be resupplied
* to subsequent callers of the <code>read method, followed by
* any bytes that otherwise would have been the next input data as of
* the time of the call to <code>reset.
*
* <li> If the method markSupported returns
* <code>false, then:
*
* <ul>reset may throw an
* <code>IOException.
*
* <li> If an IOException is not thrown, then the stream
* is reset to a fixed state that depends on the particular type of the
* input stream and how it was created. The bytes that will be supplied
* to subsequent callers of the <code>read method depend on the
* particular type of the input stream. </ul>
*
* <p>The method reset for class InputStream
* does nothing except throw an <code>IOException.
*
* @exception IOException if this stream has not been marked or if the
* mark has been invalidated.
* @see java.io.InputStream#mark(int)
* @see java.io.IOException
*/
public synchronized void reset() throws IOException {
throw new IOException("mark/reset not supported");
}
/**
* Tests if this input stream supports the <code>mark and
* <code>reset methods. Whether or not mark and
* <code>reset are supported is an invariant property of a
* particular input stream instance. The <code>markSupported method
* of <code>InputStream returns false.
*
* @return <code>true if this stream instance supports the mark
* and reset methods; <code>false otherwise.
* @see java.io.InputStream#mark(int)
* @see java.io.InputStream#reset()
*/
public boolean markSupported() {
return false;
}
}
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