ioutil.java

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 * to you under the Apache License, Version 2.0 (the            *
 * "License"); you may not use this file except in compliance   *
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 * "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.                                           *
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package org.apache.james.util.io;

import java.io.BufferedInputStream;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
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.StringWriter;
import java.io.Writer;

/**
 * General IO Stream manipulation.
 * <p>
 * This class provides static utility methods for input/output operations, particularly 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 each <code>copy</code> method, a variant is provided that allows the caller to specify the
 * buffer size (the default is 4k). As the buffer size can have a fairly large impact on speed, this
 * may be worth tweaking. Often "large buffer -&gt; faster" does not hold, even for large data
 * transfers.</p>
 *
 * <p>For byte-to-char methods, a <code>copy</code> variant allows the encoding to be selected
 * (otherwise the platform default is used).</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>
 *
 * @author Peter Donald
 * @author <a href="mailto:[e-mail]">Jeff Turner</a>
 * @version CVS $Revision: 494012 $ $Date: 2007-01-08 11:23:58 +0100 (Mo, 08 Jan 2007) $
 * @since 4.0
 */

/*
 * 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     toString    InputStream         String          3
 * 5     toByteArray InputStream         byte[]          1
 *
 * 6     copy        Reader              OutputStream    2
 * 7     toString    Reader              String          2
 * 8     toByteArray Reader              byte[]          6
 *
 * 9     copy        String              OutputStream    2
 * 10    copy        String              Writer          (trivial)
 * 11    toByteArray String              byte[]          9
 *
 * 12    copy        byte[]              Writer          3
 * 13    toString    byte[]              String          12
 * 14    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 buffer size and encoding,
 * each row may correspond to up to 4 methods.
 *
 */

public final class IOUtil
{
    private static final int DEFAULT_BUFFER_SIZE = 1024 * 4;

    /**
     * Private constructor to prevent instantiation.
     */
    private IOUtil()
    {
    }

    /**
     * Unconditionally close an <code>Reader</code>.
     * Equivalent to {@link Reader#close()}, except any exceptions will be ignored.
     *
     * @param input A (possibly null) Reader
     */
    public static void shutdownReader( final Reader input )
    {
        if( null == input )
        {
            return;
        }

        try
        {
            input.close();
        }
        catch( final IOException ioe )
        {
        }
    }

    /**
     * Unconditionally close an <code>Writer</code>.
     * Equivalent to {@link Writer#close()}, except any exceptions will be ignored.
     *
     * @param output A (possibly null) Writer
     */
    public static void shutdownWriter( final Writer output )
    {
        if( null == output )
        {
            return;
        }

        try
        {
            output.close();
        }
        catch( final IOException ioe )
        {
        }
    }

    /**
     * Unconditionally close an <code>OutputStream</code>.
     * Equivalent to {@link OutputStream#close()}, except any exceptions will be ignored.
     * @param output A (possibly null) OutputStream
     */
    public static void shutdownStream( final OutputStream output )
    {
        if( null == output )
        {
            return;
        }

        try
        {
            output.close();
        }
        catch( final IOException ioe )
        {
        }
    }

    /**
     * Unconditionally close an <code>InputStream</code>.
     * Equivalent to {@link InputStream#close()}, except any exceptions will be ignored.
     * @param input A (possibly null) InputStream
     */
    public static void shutdownStream( final InputStream input )
    {
        if( null == input )
        {
            return;
        }

        try
        {
            input.close();
        }
        catch( final IOException ioe )
        {
        }
    }

    ///////////////////////////////////////////////////////////////
    // Core copy methods
    ///////////////////////////////////////////////////////////////

    /**
     * Copy bytes from an <code>InputStream</code> to an <code>OutputStream</code>.
     */
    public static void copy( final InputStream input, final OutputStream output )
        throws IOException
    {
        copy( input, output, DEFAULT_BUFFER_SIZE );
    }

    /**
     * Copy bytes from an <code>InputStream</code> to an <code>OutputStream</code>.
     * @param bufferSize Size of internal buffer to use.
     */
    public static void copy( final InputStream input,
                             final OutputStream output,
                             final int bufferSize )
        throws IOException
    {
        final byte[] buffer = new byte[ bufferSize ];
        int n = 0;
        while( -1 != ( n = input.read( buffer ) ) )
        {
            output.write( buffer, 0, n );
        }
    }

    /**
     * Copy chars from a <code>Reader</code> to a <code>Writer</code>.
     */
    public static void copy( final Reader input, final Writer output )
        throws IOException
    {
        copy( input, output, DEFAULT_BUFFER_SIZE );
    }

    /**
     * Copy chars from a <code>Reader</code> to a <code>Writer</code>.
     * @param bufferSize Size of internal buffer to use.
     */
    public static void copy( final Reader input, final Writer output, final int bufferSize )
        throws IOException
    {
        final char[] buffer = new char[ bufferSize ];
        int n = 0;
        while( -1 != ( n = input.read( buffer ) ) )
        {
            output.write( buffer, 0, n );
        }
    }

    ///////////////////////////////////////////////////////////////
    // Derived copy methods
    // InputStream -> *
    ///////////////////////////////////////////////////////////////


    ///////////////////////////////////////////////////////////////
    // InputStream -> Writer

    /**
     * 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.
     */
    public static void copy( final InputStream input, final Writer output )
        throws IOException
    {
        copy( input, output, DEFAULT_BUFFER_SIZE );
    }

    /**
     * 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 bufferSize Size of internal buffer to use.
     */
    public static void copy( final InputStream input, final Writer output, final int bufferSize )
        throws IOException
    {
        final InputStreamReader in = new InputStreamReader( input );
        copy( in, output, bufferSize );
    }

    /**
     * Copy and convert bytes from an <code>InputStream</code> to chars on a
     * <code>Writer</code>, using the specified encoding.
     * @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.
     */
    public static void copy( final InputStream input, final Writer output, final String encoding )
        throws IOException
    {
        final InputStreamReader in = new InputStreamReader( input, encoding );
        copy( in, output );
    }

    /**
     * Copy and convert bytes from an <code>InputStream</code> to chars on a
     * <code>Writer</code>, using the specified encoding.
     * @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.
     * @param bufferSize Size of internal buffer to use.
     */
    public static void copy( final InputStream input,
                             final Writer output,
                             final String encoding,
                             final int bufferSize )
        throws IOException
    {
        final InputStreamReader in = new InputStreamReader( input, encoding );
        copy( in, output, bufferSize );
    }


    ///////////////////////////////////////////////////////////////
    // InputStream -> String

    /**
     * Get the contents of an <code>InputStream</code> as a String.
     * The platform's default encoding is used for the byte-to-char conversion.
     */
    public static String toString( final InputStream input )
        throws IOException
    {
        return toString( input, DEFAULT_BUFFER_SIZE );
    }

    /**
     * Get the contents of an <code>InputStream</code> as a String.
     * The platform's default encoding is used for the byte-to-char conversion.
     * @param bufferSize Size of internal buffer to use.
     */
    public static String toString( final InputStream input, final int bufferSize )
        throws IOException
    {
        final StringWriter sw = new StringWriter();
        copy( input, sw, bufferSize );
        return sw.toString();
    }

    /**
     * Get the contents of an <code>InputStream</code> as a String.
     * @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.
     */
    public static String toString( final InputStream input, final String encoding )
        throws IOException
    {
        return toString( input, encoding, DEFAULT_BUFFER_SIZE );
    }

    /**
     * Get the contents of an <code>InputStream</code> as a String.
     * @param encoding The name of a supported character encoding. See the
     *   <a href="http://www.iana.org/assignments/character-sets">IANA