Java tutorial
/** * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.hadoop.util; import java.io.*; import java.net.Socket; import java.nio.ByteBuffer; import java.nio.channels.FileChannel; import java.nio.channels.WritableByteChannel; import org.apache.commons.logging.Log; /** * An utility class for I/O related functionality. */ public class IOUtils { /** * Copies from one stream to another. * * @param in InputStrem to read from * @param out OutputStream to write to * @param buffSize the size of the buffer * @param close whether or not close the InputStream and * OutputStream at the end. The streams are closed in the finally clause. */ public static void copyBytes(InputStream in, OutputStream out, int buffSize, boolean close) throws IOException { try { copyBytes(in, out, buffSize); if (close) { out.close(); out = null; in.close(); in = null; } } finally { if (close) { closeStream(out); closeStream(in); } } } /** * Copies from one stream to another. * * @param in InputStrem to read from * @param out OutputStream to write to * @param buffSize the size of the buffer */ public static void copyBytes(InputStream in, OutputStream out, int buffSize) throws IOException { PrintStream ps = out instanceof PrintStream ? (PrintStream) out : null; byte buf[] = new byte[buffSize]; int bytesRead = in.read(buf); while (bytesRead >= 0) { out.write(buf, 0, bytesRead); if ((ps != null) && ps.checkError()) { throw new IOException("Unable to write to output stream."); } bytesRead = in.read(buf); } } /** * Copies from one stream to another. <strong>closes the input and output streams * at the end</strong>. * * @param in InputStrem to read from * @param out OutputStream to write to * @param conf the Configuration object */ public static void copyBytes(InputStream in, OutputStream out) throws IOException { copyBytes(in, out, 4096, true); } /** * Copies from one stream to another. * * @param in InputStream to read from * @param out OutputStream to write to * @param conf the Configuration object * @param close whether or not close the InputStream and * OutputStream at the end. The streams are closed in the finally clause. */ public static void copyBytes(InputStream in, OutputStream out, boolean close) throws IOException { copyBytes(in, out, 4096, close); } /** * Copies count bytes from one stream to another. * * @param in InputStream to read from * @param out OutputStream to write to * @param count number of bytes to copy * @param close whether to close the streams * @throws IOException if bytes can not be read or written */ public static void copyBytes(InputStream in, OutputStream out, long count, boolean close) throws IOException { byte buf[] = new byte[4096]; long bytesRemaining = count; int bytesRead; try { while (bytesRemaining > 0) { int bytesToRead = (int) (bytesRemaining < buf.length ? bytesRemaining : buf.length); bytesRead = in.read(buf, 0, bytesToRead); if (bytesRead == -1) break; out.write(buf, 0, bytesRead); bytesRemaining -= bytesRead; } if (close) { out.close(); out = null; in.close(); in = null; } } finally { if (close) { closeStream(out); closeStream(in); } } } /** * Utility wrapper for reading from {@link InputStream}. It catches any errors * thrown by the underlying stream (either IO or decompression-related), and * re-throws as an IOException. * * @param is - InputStream to be read from * @param buf - buffer the data is read into * @param off - offset within buf * @param len - amount of data to be read * @return number of bytes read */ public static int wrappedReadForCompressedData(InputStream is, byte[] buf, int off, int len) throws IOException { try { return is.read(buf, off, len); } catch (IOException ie) { throw ie; } catch (Throwable t) { throw new IOException("Error while reading compressed data", t); } } /** * Reads len bytes in a loop. * * @param in InputStream to read from * @param buf The buffer to fill * @param off offset from the buffer * @param len the length of bytes to read * @throws IOException if it could not read requested number of bytes * for any reason (including EOF) */ public static void readFully(InputStream in, byte buf[], int off, int len) throws IOException { int toRead = len; while (toRead > 0) { int ret = in.read(buf, off, toRead); if (ret < 0) { throw new IOException("Premature EOF from inputStream"); } toRead -= ret; off += ret; } } /** * Similar to readFully(). Skips bytes in a loop. * @param in The InputStream to skip bytes from * @param len number of bytes to skip. * @throws IOException if it could not skip requested number of bytes * for any reason (including EOF) */ public static void skipFully(InputStream in, long len) throws IOException { long amt = len; while (amt > 0) { long ret = in.skip(amt); if (ret == 0) { // skip may return 0 even if we're not at EOF. Luckily, we can // use the read() method to figure out if we're at the end. int b = in.read(); if (b == -1) { throw new EOFException( "Premature EOF from inputStream after " + "skipping " + (len - amt) + " byte(s)."); } ret = 1; } amt -= ret; } } /** * Close the Closeable objects and <b>ignore</b> any {@link IOException} or * null pointers. Must only be used for cleanup in exception handlers. * * @param log the log to record problems to at debug level. Can be null. * @param closeables the objects to close */ public static void cleanup(Log log, java.io.Closeable... closeables) { for (java.io.Closeable c : closeables) { if (c != null) { try { c.close(); } catch (IOException e) { if (log != null && log.isDebugEnabled()) { log.debug("Exception in closing " + c, e); } } } } } /** * Closes the stream ignoring {@link IOException}. * Must only be called in cleaning up from exception handlers. * * @param stream the Stream to close */ public static void closeStream(java.io.Closeable stream) { cleanup(null, stream); } /** * Closes the socket ignoring {@link IOException} * * @param sock the Socket to close */ public static void closeSocket(Socket sock) { if (sock != null) { try { sock.close(); } catch (IOException ignored) { } } } /** * The /dev/null of OutputStreams. */ public static class NullOutputStream extends OutputStream { @Override public void write(byte[] b, int off, int len) throws IOException { } @Override public void write(int b) throws IOException { } } /** * Write a ByteBuffer to a WritableByteChannel, handling short writes. * * @param bc The WritableByteChannel to write to * @param buf The input buffer * @throws IOException On I/O error */ public static void writeFully(WritableByteChannel bc, ByteBuffer buf) throws IOException { do { bc.write(buf); } while (buf.remaining() > 0); } /** * Write a ByteBuffer to a FileChannel at a given offset, * handling short writes. * * @param fc The FileChannel to write to * @param buf The input buffer * @param offset The offset in the file to start writing at * @throws IOException On I/O error */ public static void writeFully(FileChannel fc, ByteBuffer buf, long offset) throws IOException { do { offset += fc.write(buf, offset); } while (buf.remaining() > 0); } }