InputStream
InputStream
/*
* Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
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 <code>InputStream</code>
* must always provide a method that returns the next byte of input.
*
* @author Arthur van Hoff
* @see java.io.BufferedInputStream
* @see java.io.ByteArrayInputStream
* @see java.io.DataInputStream
* @see java.io.FilterInputStream
* @see java.io.InputStream#read()
* @see java.io.OutputStream
* @see java.io.PushbackInputStream
* @since JDK1.0
*/
public abstract class InputStream implements Closeable {
// MAX_SKIP_BUFFER_SIZE is used to determine the maximum buffer size to
// use when skipping.
private static final int MAX_SKIP_BUFFER_SIZE = 2048;
/**
* Reads the next byte of data from the input stream. The value byte is
* returned as an <code>int</code> in the range <code>0</code> to
* <code>255</code>. If no byte is available because the end of the stream
* has been reached, the value <code>-1</code> is returned. This method
* blocks until input data is available, the end of the stream is detected,
* or an exception is thrown.
*
* <p> A subclass must provide an implementation of this method.
*
* @return the next byte of data, or <code>-1</code> if the end of the
* stream is reached.
* @exception IOException if an I/O error occurs.
*/
public abstract int read() throws IOException;
/**
* Reads some number of bytes from the input stream and stores them into
* the buffer array <code>b</code>. The number of bytes actually read is
* returned as an integer. This method blocks until input data is
* available, end of file is detected, or an exception is thrown.
*
* <p> If the length of <code>b</code> is zero, then no bytes are read and
* <code>0</code> is returned; otherwise, there is an attempt to read at
* least one byte. If no byte is available because the stream is at the
* end of the file, the value <code>-1</code> is returned; otherwise, at
* least one byte is read and stored into <code>b</code>.
*
* <p> The first byte read is stored into element <code>b[0]</code>, the
* next one into <code>b[1]</code>, and so on. The number of bytes read is,
* at most, equal to the length of <code>b</code>. Let <i>k</i> be the
* number of bytes actually read; these bytes will be stored in elements
* <code>b[0]</code> through <code>b[</code><i>k</i><code>-1]</code>,
* leaving elements <code>b[</code><i>k</i><code>]</code> through
* <code>b[b.length-1]</code> unaffected.
*
* <p> The <code>read(b)</code> method for class <code>InputStream</code>
* has the same effect as: <pre><code> read(b, 0, b.length) </code></pre>
*
* @param b the buffer into which the data is read.
* @return the total number of bytes read into the buffer, or
* <code>-1</code> 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</code> is <code>null</code>.
* @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</code> bytes of data from the input stream into
* an array of bytes. An attempt is made to read as many as
* <code>len</code> 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 <code>len</code> is zero, then no bytes are read and
* <code>0</code> 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</code> is returned; otherwise, at least one
* byte is read and stored into <code>b</code>.
*
* <p> The first byte read is stored into element <code>b[off]</code>, the
* next one into <code>b[off+1]</code>, and so on. The number of bytes read
* is, at most, equal to <code>len</code>. Let <i>k</i> be the number of
* bytes actually read; these bytes will be stored in elements
* <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>,
* leaving elements <code>b[off+</code><i>k</i><code>]</code> through
* <code>b[off+len-1]</code> unaffected.
*
* <p> In every case, elements <code>b[0]</code> through
* <code>b[off]</code> and elements <code>b[off+len]</code> through
* <code>b[b.length-1]</code> are unaffected.
*
* <p> The <code>read(b,</code> <code>off,</code> <code>len)</code> method
* for class <code>InputStream</code> simply calls the method
* <code>read()</code> repeatedly. If the first such call results in an
* <code>IOException</code>, that exception is returned from the call to
* the <code>read(b,</code> <code>off,</code> <code>len)</code> method. If
* any subsequent call to <code>read()</code> results in a
* <code>IOException</code>, 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</code> 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</code> 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</code>
* 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</code> 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</code> is <code>null</code>.
* @exception IndexOutOfBoundsException If <code>off</code> is negative,
* <code>len</code> is negative, or <code>len</code> is greater than
* <code>b.length - off</code>
* @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</code> bytes of data from this input
* stream. The <code>skip</code> method may, for a variety of reasons, end
* up skipping over some smaller number of bytes, possibly <code>0</code>.
* This may result from any of a number of conditions; reaching end of file
* before <code>n</code> 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 <code>skip</code> method of this class creates a
* byte array and then repeatedly reads into it until <code>n</code> 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 <code>close</code> method of <code>InputStream</code> 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</code> method repositions this stream at the last marked
* position so that subsequent reads re-read the same bytes.
*
* <p> The <code>readlimit</code> arguments tells this input stream to
* allow that many bytes to be read before the mark position gets
* invalidated.
*
* <p> The general contract of <code>mark</code> is that, if the method
* <code>markSupported</code> returns <code>true</code>, the stream somehow
* remembers all the bytes read after the call to <code>mark</code> and
* stands ready to supply those same bytes again if and whenever the method
* <code>reset</code> is called. However, the stream is not required to
* remember any data at all if more than <code>readlimit</code> bytes are
* read from the stream before <code>reset</code> is called.
*
* <p> Marking a closed stream should not have any effect on the stream.
*
* <p> The <code>mark</code> method of <code>InputStream</code> 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</code> method was last called on this input stream.
*
* <p> The general contract of <code>reset</code> is:
*
* <ul>
* <li> If the method <code>markSupported</code> returns
* <code>true</code>, then:
*
* <ul><li> If the method <code>mark</code> has not been called since
* the stream was created, or the number of bytes read from the stream
* since <code>mark</code> was last called is larger than the argument
* to <code>mark</code> at that last call, then an
* <code>IOException</code> might be thrown.
*
* <li> If such an <code>IOException</code> 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</code> (or since the start of the
* file, if <code>mark</code> has not been called) will be resupplied
* to subsequent callers of the <code>read</code> method, followed by
* any bytes that otherwise would have been the next input data as of
* the time of the call to <code>reset</code>. </ul>
*
* <li> If the method <code>markSupported</code> returns
* <code>false</code>, then:
*
* <ul><li> The call to <code>reset</code> may throw an
* <code>IOException</code>.
*
* <li> If an <code>IOException</code> 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</code> method depend on the
* particular type of the input stream. </ul></ul>
*
* <p>The method <code>reset</code> for class <code>InputStream</code>
* does nothing except throw an <code>IOException</code>.
*
* @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</code> and
* <code>reset</code> methods. Whether or not <code>mark</code> and
* <code>reset</code> are supported is an invariant property of a
* particular input stream instance. The <code>markSupported</code> method
* of <code>InputStream</code> returns <code>false</code>.
*
* @return <code>true</code> if this stream instance supports the mark
* and reset methods; <code>false</code> otherwise.
* @see java.io.InputStream#mark(int)
* @see java.io.InputStream#reset()
*/
public boolean markSupported() {
return false;
}
}
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