resettablefileinputstream.java

java 开发的邮件服务器平台。支持以下协议。 协议可以修改为自己的专门标识

/***********************************************************************
 * Copyright (c) 2000-2004 The Apache Software Foundation.             *
 * All rights reserved.                                                *
 * ------------------------------------------------------------------- *
 * 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.james.mailrepository.filepair;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 */
public class ResettableFileInputStream
    extends InputStream
{
    protected static final int DEFAULT_BUFFER_SIZE = 1024;

    protected final String m_filename;
    protected int m_bufferSize;
    protected InputStream m_inputStream;
    protected long m_position;
    protected long m_mark;
    protected boolean m_isMarkSet;

    public ResettableFileInputStream( final File file )
        throws IOException
    {
        this( file.getCanonicalPath() );
    }

    public ResettableFileInputStream( final String filename )
        throws IOException
    {
        this( filename, DEFAULT_BUFFER_SIZE );
    }

    public ResettableFileInputStream( final String filename, final int bufferSize )
        throws IOException
    {
        m_bufferSize = bufferSize;
        m_filename = filename;
        m_position = 0;

        m_inputStream = newStream();
    }

    public void mark( final int readLimit )
    {
        m_isMarkSet = true;
        m_mark = m_position;
        m_inputStream.mark( readLimit );
    }

    public boolean markSupported()
    {
        return true;
    }

    public void reset()
        throws IOException
    {
        if( !m_isMarkSet )
        {
            throw new IOException( "Unmarked Stream" );
        }
        try
        {
            m_inputStream.reset();
        }
        catch( final IOException ioe )
        {
            try
            {
                m_inputStream.close();
                m_inputStream = newStream();
                m_inputStream.skip( m_mark );
                m_position = m_mark;
            }
            catch( final Exception e )
            {
                throw new IOException( "Cannot reset current Stream: " + e.getMessage() );
            }
        }
    }

    protected InputStream newStream()
        throws IOException
    {
        return new BufferedInputStream( new FileInputStream( m_filename ), m_bufferSize );
    }

    public int available()
        throws IOException
    {
        return m_inputStream.available();
    }

    public void close() throws IOException
    {
        m_inputStream.close();
    }

    public int read() throws IOException
    {
        m_position++;
        return m_inputStream.read();
    }

    public int read( final byte[] bytes, final int offset, final int length )
        throws IOException
    {
        final int count = m_inputStream.read( bytes, offset, length );
        m_position += count;
        return count;
    }

    public long skip( final long count )
        throws IOException
    {
        m_position += count;
        return m_inputStream.skip( count );
    }
}