Java tutorial
/* * Copyright (c) 1994, 2019, 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; import java.util.ArrayList; import java.util.Arrays; import java.util.List; import java.util.Objects; /** * 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 1.0 */ 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; private static final int DEFAULT_BUFFER_SIZE = 8192; /** * Returns a new {@code InputStream} that reads no bytes. The returned * stream is initially open. The stream is closed by calling the * {@code close()} method. Subsequent calls to {@code close()} have no * effect. * * <p> While the stream is open, the {@code available()}, {@code read()}, * {@code read(byte[])}, {@code read(byte[], int, int)}, * {@code readAllBytes()}, {@code readNBytes(byte[], int, int)}, * {@code readNBytes(int)}, {@code skip(long)}, {@code skipNBytes(long)}, * and {@code transferTo()} methods all behave as if end of stream has been * reached. After the stream has been closed, these methods all throw * {@code IOException}. * * <p> The {@code markSupported()} method returns {@code false}. The * {@code mark()} method does nothing, and the {@code reset()} method * throws {@code IOException}. * * @return an {@code InputStream} which contains no bytes * * @since 11 */ public static InputStream nullInputStream() { return new InputStream() { private volatile boolean closed; private void ensureOpen() throws IOException { if (closed) { throw new IOException("Stream closed"); } } @Override public int available() throws IOException { ensureOpen(); return 0; } @Override public int read() throws IOException { ensureOpen(); return -1; } @Override public int read(byte[] b, int off, int len) throws IOException { Objects.checkFromIndexSize(off, len, b.length); if (len == 0) { return 0; } ensureOpen(); return -1; } @Override public byte[] readAllBytes() throws IOException { ensureOpen(); return new byte[0]; } @Override public int readNBytes(byte[] b, int off, int len) throws IOException { Objects.checkFromIndexSize(off, len, b.length); ensureOpen(); return 0; } @Override public byte[] readNBytes(int len) throws IOException { if (len < 0) { throw new IllegalArgumentException("len < 0"); } ensureOpen(); return new byte[0]; } @Override public long skip(long n) throws IOException { ensureOpen(); return 0L; } @Override public void skipNBytes(long n) throws IOException { ensureOpen(); if (n > 0) { throw new EOFException(); } } @Override public long transferTo(OutputStream out) throws IOException { Objects.requireNonNull(out); ensureOpen(); return 0L; } @Override public void close() throws IOException { closed = true; } }; } /** * 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-1]</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 { Objects.checkFromIndexSize(off, len, b.length); 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; } /** * The maximum size of array to allocate. * Some VMs reserve some header words in an array. * Attempts to allocate larger arrays may result in * OutOfMemoryError: Requested array size exceeds VM limit */ private static final int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8; /** * Reads all remaining bytes from the input stream. This method blocks until * all remaining bytes have been read and end of stream is detected, or an * exception is thrown. This method does not close the input stream. * * <p> When this stream reaches end of stream, further invocations of this * method will return an empty byte array. * * <p> Note that this method is intended for simple cases where it is * convenient to read all bytes into a byte array. It is not intended for * reading input streams with large amounts of data. * * <p> The behavior for the case where the input stream is <i>asynchronously * closed</i>, or the thread interrupted during the read, is highly input * stream specific, and therefore not specified. * * <p> If an I/O error occurs reading from the input stream, then it may do * so after some, but not all, bytes have been read. Consequently the input * stream may not be at end of stream and may be in an inconsistent state. * It is strongly recommended that the stream be promptly closed if an I/O * error occurs. * * @implSpec * This method invokes {@link #readNBytes(int)} with a length of * {@link Integer#MAX_VALUE}. * * @return a byte array containing the bytes read from this input stream * @throws IOException if an I/O error occurs * @throws OutOfMemoryError if an array of the required size cannot be * allocated. * * @since 9 */ public byte[] readAllBytes() throws IOException { return readNBytes(Integer.MAX_VALUE); } /** * Reads up to a specified number of bytes from the input stream. This * method blocks until the requested number of bytes have been read, end * of stream is detected, or an exception is thrown. This method does not * close the input stream. * * <p> The length of the returned array equals the number of bytes read * from the stream. If {@code len} is zero, then no bytes are read and * an empty byte array is returned. Otherwise, up to {@code len} bytes * are read from the stream. Fewer than {@code len} bytes may be read if * end of stream is encountered. * * <p> When this stream reaches end of stream, further invocations of this * method will return an empty byte array. * * <p> Note that this method is intended for simple cases where it is * convenient to read the specified number of bytes into a byte array. The * total amount of memory allocated by this method is proportional to the * number of bytes read from the stream which is bounded by {@code len}. * Therefore, the method may be safely called with very large values of * {@code len} provided sufficient memory is available. * * <p> The behavior for the case where the input stream is <i>asynchronously * closed</i>, or the thread interrupted during the read, is highly input * stream specific, and therefore not specified. * * <p> If an I/O error occurs reading from the input stream, then it may do * so after some, but not all, bytes have been read. Consequently the input * stream may not be at end of stream and may be in an inconsistent state. * It is strongly recommended that the stream be promptly closed if an I/O * error occurs. * * @implNote * The number of bytes allocated to read data from this stream and return * the result is bounded by {@code 2*(long)len}, inclusive. * * @param len the maximum number of bytes to read * @return a byte array containing the bytes read from this input stream * @throws IllegalArgumentException if {@code length} is negative * @throws IOException if an I/O error occurs * @throws OutOfMemoryError if an array of the required size cannot be * allocated. * * @since 11 */ public byte[] readNBytes(int len) throws IOException { if (len < 0) { throw new IllegalArgumentException("len < 0"); } List<byte[]> bufs = null; byte[] result = null; int total = 0; int remaining = len; int n; do { byte[] buf = new byte[Math.min(remaining, DEFAULT_BUFFER_SIZE)]; int nread = 0; // read to EOF which may read more or less than buffer size while ((n = read(buf, nread, Math.min(buf.length - nread, remaining))) > 0) { nread += n; remaining -= n; } if (nread > 0) { if (MAX_BUFFER_SIZE - total < nread) { throw new OutOfMemoryError("Required array size too large"); } total += nread; if (result == null) { result = buf; } else { if (bufs == null) { bufs = new ArrayList<>(); bufs.add(result); } bufs.add(buf); } } // if the last call to read returned -1 or the number of bytes // requested have been read then break } while (n >= 0 && remaining > 0); if (bufs == null) { if (result == null) { return new byte[0]; } return result.length == total ? result : Arrays.copyOf(result, total); } result = new byte[total]; int offset = 0; remaining = total; for (byte[] b : bufs) { int count = Math.min(b.length, remaining); System.arraycopy(b, 0, result, offset, count); offset += count; remaining -= count; } return result; } /** * Reads the requested number of bytes from the input stream into the given * byte array. This method blocks until {@code len} bytes of input data have * been read, end of stream is detected, or an exception is thrown. The * number of bytes actually read, possibly zero, is returned. This method * does not close the input stream. * * <p> In the case where end of stream is reached before {@code len} bytes * have been read, then the actual number of bytes read will be returned. * When this stream reaches end of stream, further invocations of this * method will return zero. * * <p> If {@code len} is zero, then no bytes are read and {@code 0} is * returned; otherwise, there is an attempt to read up to {@code len} bytes. * * <p> The first byte read is stored into element {@code b[off]}, the next * one in to {@code b[off+1]}, and so on. The number of bytes read is, at * most, equal to {@code len}. Let <i>k</i> be the number of bytes actually * read; these bytes will be stored in elements {@code b[off]} through * {@code b[off+}<i>k</i>{@code -1]}, leaving elements {@code b[off+}<i>k</i> * {@code ]} through {@code b[off+len-1]} unaffected. * * <p> The behavior for the case where the input stream is <i>asynchronously * closed</i>, or the thread interrupted during the read, is highly input * stream specific, and therefore not specified. * * <p> If an I/O error occurs reading from the input stream, then it may do * so after some, but not all, bytes of {@code b} have been updated with * data from the input stream. Consequently the input stream and {@code b} * may be in an inconsistent state. It is strongly recommended that the * stream be promptly closed if an I/O error occurs. * * @param b the byte array into which the data is read * @param off the start offset in {@code b} at which the data is written * @param len the maximum number of bytes to read * @return the actual number of bytes read into the buffer * @throws IOException if an I/O error occurs * @throws NullPointerException if {@code b} is {@code null} * @throws IndexOutOfBoundsException If {@code off} is negative, {@code len} * is negative, or {@code len} is greater than {@code b.length - off} * * @since 9 */ public int readNBytes(byte[] b, int off, int len) throws IOException { Objects.checkFromIndexSize(off, len, b.length); int n = 0; while (n < len) { int count = read(b, off + n, len - n); if (count < 0) break; n += count; } return n; } /** * 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 implementation 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 which might be zero. * @throws IOException if an I/O error occurs. * @see java.io.InputStream#skipNBytes(long) */ 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; } /** * Skips over and discards exactly {@code n} bytes of data from this input * stream. If {@code n} is zero, then no bytes are skipped. * If {@code n} is negative, then no bytes are skipped. * Subclasses may handle the negative value differently. * * <p> This method blocks until the requested number of bytes have been * skipped, end of file is reached, or an exception is thrown. * * <p> If end of stream is reached before the stream is at the desired * position, then an {@code EOFException} is thrown. * * <p> If an I/O error occurs, then the input stream may be * in an inconsistent state. It is strongly recommended that the * stream be promptly closed if an I/O error occurs. * * @implNote * Subclasses are encouraged to provide a more efficient implementation * of this method. * * @implSpec * If {@code n} is zero or negative, then no bytes are skipped. * If {@code n} is positive, the default implementation of this method * invokes {@link #skip(long) skip()} with parameter {@code n}. If the * return value of {@code skip(n)} is non-negative and less than {@code n}, * then {@link #read()} is invoked repeatedly until the stream is {@code n} * bytes beyond its position when this method was invoked or end of stream * is reached. If the return value of {@code skip(n)} is negative or * greater than {@code n}, then an {@code IOException} is thrown. Any * exception thrown by {@code skip()} or {@code read()} will be propagated. * * @param n the number of bytes to be skipped. * @throws EOFException if end of stream is encountered before the * stream can be positioned {@code n} bytes beyond its position * when this method was invoked. * @throws IOException if the stream cannot be positioned properly or * if an I/O error occurs. * @see java.io.InputStream#skip(long) */ public void skipNBytes(long n) throws IOException { if (n > 0) { long ns = skip(n); if (ns >= 0 && ns < n) { // skipped too few bytes // adjust number to skip n -= ns; // read until requested number skipped or EOS reached while (n > 0 && read() != -1) { n--; } // if not enough skipped, then EOFE if (n != 0) { throw new EOFException(); } } else if (ns != n) { // skipped negative or too many bytes throw new IOException("Unable to skip exactly"); } } } /** * Returns an estimate of the number of bytes that can be read (or skipped * over) from this input stream without blocking, which may be 0, or 0 when * end of stream is detected. The read might be on 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's 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 of {@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; } /** * Reads all bytes from this input stream and writes the bytes to the * given output stream in the order that they are read. On return, this * input stream will be at end of stream. This method does not close either * stream. * <p> * This method may block indefinitely reading from the input stream, or * writing to the output stream. The behavior for the case where the input * and/or output stream is <i>asynchronously closed</i>, or the thread * interrupted during the transfer, is highly input and output stream * specific, and therefore not specified. * <p> * If an I/O error occurs reading from the input stream or writing to the * output stream, then it may do so after some bytes have been read or * written. Consequently the input stream may not be at end of stream and * one, or both, streams may be in an inconsistent state. It is strongly * recommended that both streams be promptly closed if an I/O error occurs. * * @param out the output stream, non-null * @return the number of bytes transferred * @throws IOException if an I/O error occurs when reading or writing * @throws NullPointerException if {@code out} is {@code null} * * @since 9 */ public long transferTo(OutputStream out) throws IOException { Objects.requireNonNull(out, "out"); long transferred = 0; byte[] buffer = new byte[DEFAULT_BUFFER_SIZE]; int read; while ((read = this.read(buffer, 0, DEFAULT_BUFFER_SIZE)) >= 0) { out.write(buffer, 0, read); transferred += read; } return transferred; } }