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自己看看源代码
/*
* @(#)InputStream.java 1.37 00/07/18
*
* Copyright 1994-2000 Sun Microsystems, Inc. All Rights Reserved.
*
* This software is the proprietary information of Sun Microsystems, Inc.
* Use is subject to license terms.
*
*/package java.io;/**
* This abstract class is the superclass of all classes representing
* an input stream of bytes.
*
* 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
* @version 1.37, 07/18/00
* @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 { // SKIP_BUFFER_SIZE is used to determine the size of skipBuffer
 private static final int SKIP_BUFFER_SIZE = 2048;
 // skipBuffer is initialized in skip(long), if needed.
 private static byte[] skipBuffer; /**
 * 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.
 *
 * 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.
 *
 * If <code>b</code> is <code>null</code>, a
 * <code>NullPointerException</code> is thrown. 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 end of file, the value
 * <code>-1</code> is returned; otherwise, at least one byte is read and
 * stored into <code>b</code>.
 *
 * 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 k be the
 * number of bytes actually read; these bytes will be stored in elements
 * <code>b[0]</code> through <code>b[</code>k<code>-1]</code>,
 * leaving elements <code>b[</code>k<code>]</code> through
 * <code>b[b.length-1]</code> unaffected.
 *
 * If the first byte cannot be read for any reason other than end of
 * file, then an <code>IOException</code> is thrown. In particular, an
 * <code>IOException</code> is thrown if the input stream has been closed.
 *
 * 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> is there is no more data because the end of
 * the stream has been reached.
 * @exception IOException if an I/O error occurs.
 * @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, possibly
 * zero. 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.
 *
 * If <code>b</code> is <code>null</code>, a
 * <code>NullPointerException</code> is thrown.
 *
 * If <code>off</code> is negative, or <code>len</code> is negative, or
 * <code>off+len</code> is greater than the length of the array
 * <code>b</code>, then an <code>IndexOutOfBoundsException</code> is
 * thrown.
 *
 * 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>.
 *
 * 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 k be the number of
 * bytes actually read; these bytes will be stored in elements
 * <code>b[off]</code> through <code>b[off+</code>k<code>-1]</code>,
 * leaving elements <code>b[off+</code>k<code>]</code> through
 * <code>b[off+len-1]</code> unaffected.
 *
 * 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.
 *
 * If the first byte cannot be read for any reason other than end of
 * file, then an <code>IOException</code> is thrown. In particular, an
 * <code>IOException</code> is thrown if the input stream has been closed.
 *
 * 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. 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 an I/O error occurs.
 * @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) || (off > b.length) || (len < 0) ||
 ((off + len) > b.length) || ((off + len) < 0)) {
 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;
}
if (b != null) {
 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</code> is
 * negative, no bytes are skipped.
 *
 * The <code>skip</code> method of <code>InputStream</code> 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.
 *
 * @param n the number of bytes to be skipped.
 * @return the actual number of bytes skipped.
 * @exception IOException if an I/O error occurs.
 */
 public long skip(long n) throws IOException { long remaining = n;
int nr;
if (skipBuffer == null)
 skipBuffer = new byte[SKIP_BUFFER_SIZE]; byte[] localSkipBuffer = skipBuffer;

if (n <= 0) {
 return 0;
} while (remaining > 0) {
 nr = read(localSkipBuffer, 0,
 (int) Math.min(SKIP_BUFFER_SIZE, remaining));
 if (nr < 0) {
break;
 }
 remaining -= nr;
}

return n - remaining;
 } /**
 * Returns the number of bytes that can be read (or skipped over) from
 * this input stream without blocking by the next caller of a method for
 * this input stream. The next caller might be the same thread or or
 * another thread.
 *
 * The <code>available</code> method for class <code>InputStream</code>
 * always returns <code>0</code>.
 *
 * This method should be overridden by subclasses.
 *
 * @return the number of bytes that can be read from this input stream
 * without blocking.
 * @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.
 *
 * 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 ed
 * position so that subsequent reads re-read the same bytes.
 *
 * The <code>readlimit</code> arguments tells this input stream to
 * allow that many bytes to be read before the position gets
 * invalidated.
 *
 * The general contract of <code></code> is that, if the method
 * <code>Supported</code> returns <code>true</code>, the stream somehow
 * remembers all the bytes read after the call to <code></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.
 *
 * The <code></code> method of <code>InputStream</code> does
 * nothing.
 *
 * @param readlimit the maximum limit of bytes that can be read before
 * the position becomes invalid.
 * @see java.io.InputStream#reset()
 */
 public synchronized void (int readlimit) {} /**
 * Repositions this stream to the position at the time the
 * <code></code> method was last called on this input stream.
 *
 * The general contract of <code>reset</code> is:
 *
 * <ul>
 *
 * <li> If the method <code>Supported</code> returns
 * <code>true</code>, then:
 *
 * <ul><li> If the method <code></code> has not been called since
 * the stream was created, or the number of bytes read from the stream
 * since <code></code> was last called is larger than the argument
 * to <code></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></code> (or since the start of the
 * file, if <code></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>Supported</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>
 *
 * The method <code>reset</code> for class <code>InputStream</code>
 * does nothing and always throws an <code>IOException</code>.
 *
 * @exception IOException if this stream has not been ed or if the
 * has been invalidated.
 * @see java.io.InputStream#(int)
 * @see java.io.IOException
 */
 public synchronized void reset() throws IOException {
throw new IOException("/reset not supported");
 } /**
 * Tests if this input stream supports the <code></code> and
 * <code>reset</code> methods. Whether or not <code></code> and
 * <code>reset</code> are supported is an invariant property of a
 * particular input stream instance. The <code>Supported</code> method
 * of <code>InputStream</code> returns <code>false</code>.
 *
 * @return <code>true</code> if this stream instance supports the
 * and reset methods; <code>false</code> otherwise.
 * @see java.io.InputStream#(int)
 * @see java.io.InputStream#reset()
 */
 public boolean Supported() {
return false;
 }}

InputStream是从输入流读取字节类的基抽象类。
他的长度你可以通过read(byte[])取得，read(byte[])返回长度，必须注意的是你定义的byte[]要足够大，大于或等于InputStream的长度；
或者用skip(long)也可以，long一样要>=InputStream的长度。

流(stream)形式
InputStreamReadermy_Read=new InputStreamReader(eBookStream);
int how_much=my_Read.read(char[] cbuf);
how_much就是长度!

不好意思,没看清楚!错了.错了!应该是:
流(stream)形式
int how_much=eBookStream.read(char[] cbuf);
how_much就是长度!

调试易

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