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SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by downstream projects in the SciJava ecosystem, such as ImageJ and SCIFIO.
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package org.scijava.io.nio;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;
import org.scijava.log.LogService;
import org.scijava.plugin.Parameter;
import org.scijava.plugin.Plugin;
import org.scijava.service.AbstractService;
import org.scijava.service.Service;
/**
* Default service for working with the {@link java.nio} package, particularly
* NIO {@link ByteBuffer} objects.
*
* @author Chris Allan
* @author Curtis Rueden
*/
@Plugin(type = Service.class)
public class DefaultNIOService extends AbstractService implements NIOService {
// -- Fields --
@Parameter
private LogService log;
/** Whether or not we are to use memory mapped I/O. */
private final boolean useMappedByteBuffer = Boolean.parseBoolean(System
.getProperty("mappedBuffers"));
// -- NIOService API methods --
@Override
public ByteBuffer allocate(final FileChannel channel, final MapMode mapMode,
final long bufferStartPosition, final int newSize) throws IOException
{
log.debug("NIO: allocate: mapped=" + useMappedByteBuffer + ", start=" +
bufferStartPosition + ", size=" + newSize);
if (useMappedByteBuffer) {
return allocateMappedByteBuffer(channel, mapMode, bufferStartPosition,
newSize);
}
return allocateDirect(channel, bufferStartPosition, newSize);
}
// -- Helper methods --
/**
* Allocates memory and copies the desired file data into it.
*
* @param channel File channel to allocate or map byte buffers from.
* @param bufferStartPosition The absolute position of the start of the
* buffer.
* @param newSize The buffer size.
* @return A newly allocated NIO byte buffer.
* @throws IOException If there is an issue aligning or allocating the buffer.
*/
private ByteBuffer allocateDirect(final FileChannel channel,
final long bufferStartPosition, final int newSize) throws IOException
{
final ByteBuffer buffer = ByteBuffer.allocate(newSize);
channel.read(buffer, bufferStartPosition);
return buffer;
}
/**
* Memory maps the desired file data into memory.
*
* @param channel File channel to allocate or map byte buffers from.
* @param mapMode The map mode. Required but only used if memory mapped I/O is
* to occur.
* @param bufferStartPosition The absolute position of the start of the
* buffer.
* @param newSize The buffer size.
* @return A newly mapped NIO byte buffer.
* @throws IOException If there is an issue mapping, aligning or allocating
* the buffer.
*/
private ByteBuffer allocateMappedByteBuffer(final FileChannel channel,
final MapMode mapMode, final long bufferStartPosition, final int newSize)
throws IOException
{
return channel.map(mapMode, bufferStartPosition, newSize);
}
}