fileregionwritefilter.java

mina是以Java实现的一个开源的网络程序框架

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 *  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
 *
 *    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
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package org.apache.mina.filter.stream;

import java.io.IOException;

import org.apache.mina.core.buffer.IoBuffer;
import org.apache.mina.core.file.FileRegion;
import org.apache.mina.core.filterchain.IoFilter;
import org.apache.mina.core.session.IoSession;
import org.apache.mina.core.write.WriteRequest;

/**
 * Filter implementation that converts a {@link FileRegion} to {@link IoBuffer}
 * objects and writes those buffers to the next filter. When end of the
 * {@code FileRegion} has been reached this filter will call
 * {@link IoFilter.NextFilter#messageSent(IoSession,WriteRequest)} using the
 * original {@link FileRegion} written to the session and notifies
 * {@link org.apache.mina.core.future.WriteFuture} on the original
 * {@link org.apache.mina.core.write.WriteRequest}.
 * <p>Normall {@code FileRegion} objects should be handled by the
 * {@link org.apache.mina.core.service.IoProcessor} but this is not always possible
 * if a filter is being used that needs to modify the contents of the file
 * before sending over the network (i.e. the
 * {@link org.apache.mina.filter.ssl.SslFilter} or a data compression filter.)
 * </p>
 * <p> This filter will ignore written messages which aren't {@link FileRegion}
 * instances. Such messages will be passed to the next filter directly.
 * </p>
 * <p><b>NOTE:</b> this filter does not close the file channel in
 * {@link FileRegion#getFileChannel()} after the data from the file has been
 * written.  The {@code FileChannel} should be closed in either 
 * {@link org.apache.mina.core.service.IoHandler#messageSent(IoSession,Object)}
 * or in an {@link org.apache.mina.core.future.IoFutureListener} associated with the
 * {@code WriteFuture}.
 * </p>
 *
 * @author The Apache MINA Project ([e-mail])
 * @version $Rev$, $Date$
 * @org.apache.xbean.XBean
 */
public class FileRegionWriteFilter extends
        AbstractStreamWriteFilter<FileRegion> {

    @Override
    protected Class<FileRegion> getMessageClass() {
        return FileRegion.class;
    }

    @Override
    protected IoBuffer getNextBuffer(FileRegion fileRegion) throws IOException {
        // If there are no more bytes to read, return null
        if (fileRegion.getRemainingBytes() <= 0) {
            return null;
        }
        
        // Allocate the buffer for reading from the file
        final int bufferSize = (int) Math.min(getWriteBufferSize(), fileRegion.getRemainingBytes());
        IoBuffer buffer = IoBuffer.allocate(bufferSize);

        // Read from the file
        int bytesRead = fileRegion.getFileChannel().read(buffer.buf(),
                fileRegion.getPosition());
        fileRegion.update(bytesRead);

        // return the buffer
        buffer.flip();
        return buffer;
    }

}