Java tutorial
/* * Copyright 2001-2004 The Apache Software Foundation. * * Licensed 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. */ import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.io.OutputStream; import java.io.OutputStreamWriter; import java.io.Reader; import java.io.StringReader; import java.io.Writer; /** * <p> * This class provides static utility methods for buffered * copying between sources (<code>InputStream</code>, <code>Reader</code>, <code>String</code> and * <code>byte[]</code>) and destinations (<code>OutputStream</code>, <code>Writer</code>, * <code>String</code> and <code>byte[]</code>). * </p> * * <p>Unless otherwise noted, these <code>copy</code> methods do <em>not</em> flush or close the * streams. Often doing so would require making non-portable assumptions about the streams' origin * and further use. This means that both streams' <code>close()</code> methods must be called after * copying. if one omits this step, then the stream resources (sockets, file descriptors) are * released when the associated Stream is garbage-collected. It is not a good idea to rely on this * mechanism. For a good overview of the distinction between "memory management" and "resource * management", see <a href="http://www.unixreview.com/articles/1998/9804/9804ja/ja.htm">this * UnixReview article</a>.</p> * * <p>For byte-to-char methods, a <code>copy</code> variant allows the encoding * to be selected (otherwise the platform default is used). We would like to * encourage you to always specify the encoding because relying on the platform * default can lead to unexpected results.</p> * * <p>We don't provide special variants for the <code>copy</code> methods that * let you specify the buffer size because in modern VMs the impact on speed * seems to be minimal. We're using a default buffer size of 4 KB.</p> * * <p>The <code>copy</code> methods use an internal buffer when copying. It is therefore advisable * <em>not</em> to deliberately wrap the stream arguments to the <code>copy</code> methods in * <code>Buffered*</code> streams. For example, don't do the * following:</p> * * <code>copy( new BufferedInputStream( in ), new BufferedOutputStream( out ) );</code> * * <p>The rationale is as follows:</p> * * <p>Imagine that an InputStream's read() is a very expensive operation, which would usually suggest * wrapping in a BufferedInputStream. The BufferedInputStream works by issuing infrequent * {@link java.io.InputStream#read(byte[] b, int off, int len)} requests on the underlying InputStream, to * fill an internal buffer, from which further <code>read</code> requests can inexpensively get * their data (until the buffer runs out).</p> * <p>However, the <code>copy</code> methods do the same thing, keeping an internal buffer, * populated by {@link InputStream#read(byte[] b, int off, int len)} requests. Having two buffers * (or three if the destination stream is also buffered) is pointless, and the unnecessary buffer * management hurts performance slightly (about 3%, according to some simple experiments).</p> * * <p>Behold, intrepid explorers; a map of this class:</p> * <pre> * Method Input Output Dependency * ------ ----- ------ ------- * 1 copy InputStream OutputStream (primitive) * 2 copy Reader Writer (primitive) * * 3 copy InputStream Writer 2 * * 4 copy Reader OutputStream 2 * * 5 copy String OutputStream 2 * 6 copy String Writer (trivial) * * 7 copy byte[] Writer 3 * 8 copy byte[] OutputStream (trivial) * </pre> * * <p>Note that only the first two methods shuffle bytes; the rest use these * two, or (if possible) copy using native Java copy methods. As there are * method variants to specify the encoding, each row may * correspond to up to 2 methods.</p> * * <p>Origin of code: Apache Avalon (Excalibur)</p> * * @author Peter Donald * @author Jeff Turner * @author Matthew Hawthorne */ public class CopyUtils { /** * Instances should NOT be constructed in standard programming. */ private CopyUtils() { } /** * Copy bytes from a <code>byte[]</code> to an <code>OutputStream</code>. * @param input the byte array to read from * @param output the <code>OutputStream</code> to write to * @throws IOException In case of an I/O problem */ public static void copy(byte[] input, OutputStream output) throws IOException { output.write(input); } /** * Copy and convert bytes from a <code>byte[]</code> to chars on a * <code>Writer</code>. * The platform's default encoding is used for the byte-to-char conversion. * @param input the byte array to read from * @param output the <code>Writer</code> to write to * @throws IOException In case of an I/O problem */ public static void copy(byte[] input, Writer output) throws IOException { ByteArrayInputStream in = new ByteArrayInputStream(input); copy(in, output); } /** * Copy and convert bytes from a <code>byte[]</code> to chars on a * <code>Writer</code>, using the specified encoding. * @param input the byte array to read from * @param output the <code>Writer</code> to write to * @param encoding The name of a supported character encoding. See the * <a href="http://www.iana.org/assignments/character-sets">IANA * Charset Registry</a> for a list of valid encoding types. * @throws IOException In case of an I/O problem */ public static void copy(byte[] input, Writer output, String encoding) throws IOException { ByteArrayInputStream in = new ByteArrayInputStream(input); copy(in, output, encoding); } /** * Copy bytes from an <code>InputStream</code> to an <code>OutputStream</code>. * @param input the <code>InputStream</code> to read from * @param output the <code>OutputStream</code> to write to * @return the number of bytes copied * @throws IOException In case of an I/O problem */ public static int copy(InputStream input, OutputStream output) throws IOException { byte[] buffer = new byte[DEFAULT_BUFFER_SIZE]; int count = 0; int n = 0; while (-1 != (n = input.read(buffer))) { output.write(buffer, 0, n); count += n; } return count; } /** * Copy chars from a <code>Reader</code> to a <code>Writer</code>. * @param input the <code>Reader</code> to read from * @param output the <code>Writer</code> to write to * @return the number of characters copied * @throws IOException In case of an I/O problem */ public static int copy(Reader input, Writer output) throws IOException { char[] buffer = new char[DEFAULT_BUFFER_SIZE]; int count = 0; int n = 0; while (-1 != (n = input.read(buffer))) { output.write(buffer, 0, n); count += n; } return count; } /** * Copy and convert bytes from an <code>InputStream</code> to chars on a * <code>Writer</code>. * The platform's default encoding is used for the byte-to-char conversion. * @param input the <code>InputStream</code> to read from * @param output the <code>Writer</code> to write to * @throws IOException In case of an I/O problem */ public static void copy(InputStream input, Writer output) throws IOException { InputStreamReader in = new InputStreamReader(input); copy(in, output); } /** * Copy and convert bytes from an <code>InputStream</code> to chars on a * <code>Writer</code>, using the specified encoding. * @param input the <code>InputStream</code> to read from * @param output the <code>Writer</code> to write to * @param encoding The name of a supported character encoding. See the * <a href="http://www.iana.org/assignments/character-sets">IANA * Charset Registry</a> for a list of valid encoding types. * @throws IOException In case of an I/O problem */ public static void copy(InputStream input, Writer output, String encoding) throws IOException { InputStreamReader in = new InputStreamReader(input, encoding); copy(in, output); } /** * Serialize chars from a <code>Reader</code> to bytes on an * <code>OutputStream</code>, and flush the <code>OutputStream</code>. * @param input the <code>Reader</code> to read from * @param output the <code>OutputStream</code> to write to * @throws IOException In case of an I/O problem */ public static void copy(Reader input, OutputStream output) throws IOException { OutputStreamWriter out = new OutputStreamWriter(output); copy(input, out); // XXX Unless anyone is planning on rewriting OutputStreamWriter, we have to flush here. out.flush(); } /** * Serialize chars from a <code>String</code> to bytes on an <code>OutputStream</code>, and * flush the <code>OutputStream</code>. * @param input the <code>String</code> to read from * @param output the <code>OutputStream</code> to write to * @throws IOException In case of an I/O problem */ public static void copy(String input, OutputStream output) throws IOException { StringReader in = new StringReader(input); OutputStreamWriter out = new OutputStreamWriter(output); copy(in, out); // XXX Unless anyone is planning on rewriting OutputStreamWriter, we have to flush here. out.flush(); } /** * Copy chars from a <code>String</code> to a <code>Writer</code>. * @param input the <code>String</code> to read from * @param output the <code>Writer</code> to write to * @throws IOException In case of an I/O problem */ public static void copy(String input, Writer output) throws IOException { output.write(input); } /** * The name says it all. */ private static final int DEFAULT_BUFFER_SIZE = 1024 * 4; }