resettablefileinputstream.java

来自「java mail,java mailjava mailjava mailjav」· Java 代码 · 共 142 行

/****************************************************************
 * 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   *
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 * 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.                                           *
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package org.apache.james.util.io;

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

/**
 * @author  Federico Barbieri <[e-mail]>
 */
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 );
    }
}