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The source code

/*
 * 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.
 */
package org.apache.commons.io;

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;

/**
 * 

* This class provides static utility methods for buffered * copying between sources (InputStream, Reader, String and * byte[]) and destinations (OutputStream, Writer, * String and byte[]). *

* *

Unless otherwise noted, these copy methods do not 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' close() 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 this * UnixReview article.

* *

For byte-to-char methods, a copy 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.

* *

We don't provide special variants for the copy 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.

* *

The copy methods use an internal buffer when copying. It is therefore advisable * not to deliberately wrap the stream arguments to the copy methods in * Buffered* streams. For example, don't do the * following:

* * copy( new BufferedInputStream( in ), new BufferedOutputStream( out ) ); * *

The rationale is as follows:

* *

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 read requests can inexpensively get * their data (until the buffer runs out).

*

However, the copy 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).

* *

Behold, intrepid explorers; a map of this class:

*
 *       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)
 * 
* *

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.

* *

Origin of code: Apache Avalon (Excalibur)

* * @author Peter Donald * @author Jeff Turner * @author Matthew Hawthorne * @version $Id: CopyUtils.java,v 1.6 2004/04/24 23:49:25 bayard Exp $ */ public class CopyUtils { /** * The name says it all. */ private static final int DEFAULT_BUFFER_SIZE = 1024 * 4; /** * Instances should NOT be constructed in standard programming. */ public CopyUtils() {} // ---------------------------------------------------------------- // byte[] -> OutputStream // ---------------------------------------------------------------- /** * Copy bytes from a byte[] to an OutputStream. * @param input the byte array to read from * @param output the OutputStream 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); } // ---------------------------------------------------------------- // byte[] -> Writer // ---------------------------------------------------------------- /** * Copy and convert bytes from a byte[] to chars on a * Writer. * The platform's default encoding is used for the byte-to-char conversion. * @param input the byte array to read from * @param output the Writer 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 byte[] to chars on a * Writer, using the specified encoding. * @param input the byte array to read from * @param output the Writer to write to * @param encoding The name of a supported character encoding. See the * IANA * Charset Registry 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); } // ---------------------------------------------------------------- // Core copy methods // ---------------------------------------------------------------- /** * Copy bytes from an InputStream to an OutputStream. * @param input the InputStream to read from * @param output the OutputStream 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; } // ---------------------------------------------------------------- // Reader -> Writer // ---------------------------------------------------------------- /** * Copy chars from a Reader to a Writer. * @param input the Reader to read from * @param output the Writer 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; } // ---------------------------------------------------------------- // InputStream -> Writer // ---------------------------------------------------------------- /** * Copy and convert bytes from an InputStream to chars on a * Writer. * The platform's default encoding is used for the byte-to-char conversion. * @param input the InputStream to read from * @param output the Writer 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 InputStream to chars on a * Writer, using the specified encoding. * @param input the InputStream to read from * @param output the Writer to write to * @param encoding The name of a supported character encoding. See the * IANA * Charset Registry 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); } // ---------------------------------------------------------------- // Reader -> OutputStream // ---------------------------------------------------------------- /** * Serialize chars from a Reader to bytes on an * OutputStream, and flush the OutputStream. * @param input the Reader to read from * @param output the OutputStream 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(); } // ---------------------------------------------------------------- // String -> OutputStream // ---------------------------------------------------------------- /** * Serialize chars from a String to bytes on an OutputStream, and * flush the OutputStream. * @param input the String to read from * @param output the OutputStream 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(); } // ---------------------------------------------------------------- // String -> Writer // ---------------------------------------------------------------- /** * Copy chars from a String to a Writer. * @param input the String to read from * @param output the Writer 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); } } // CopyUtils
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