将FloatBuffer转换为ByteBuffer

Question

ByteBuffer提供asFloatBuffer()功能。但是，没有等效的FloatBuffer.asByteBuffer()。

我想做的是：

float[] array = ...
try( ByteChannel channel = Files.newByteChannel( path, WRITE, CREATE, TRUNCATE_EXISTING ) ) {
    channel.write (FloatBuffer.wrap (array) .asByteBuffer());
}

是否有一种有效地这样做的方法，或者我是否必须像以下所示那样分配一个ByteBuffer：

ByteBuffer buffer = ByteBuffer.allocate( array.length * 4 );
buffer .asFloatBuffer() .put (array);
channel.write (buffer);

Answer 1

对于HeapFloatBuffer (由FloatBuffer.allocate或FloatBuffer.wrap创建)，没有简单的解决方案。需要编写扩展ByteBuffer的自定义类。

对于HotSpot 8中的直接缓冲区，这将在简单的情况下起作用：

FloatBuffer floatBuffer = ByteBuffer.allocateDirect (...).asFloatBuffer();
ByteBuffer byteBuffer = (ByteBuffer) ((sun.nio.ch.DirectBuffer)floatBuffer).attachment();

对于其他情况，请使用以下方法。注意，这个类是在包java.nio中声明的。这也可能只适用于HotSpot 8。

package java.nio;

/**
 *
 * @author Aleksandr Dubinsky
 */
public class BufferUtils {

      public static ByteBuffer
    asByteBuffer (FloatBuffer floatBuffer) {

            if (floatBuffer instanceof DirectFloatBufferU)
            {
                DirectFloatBufferU buffer = (DirectFloatBufferU) floatBuffer;
                return (ByteBuffer) new DirectByteBuffer (buffer.address(), floatBuffer.capacity() * Float.BYTES, buffer)
                                            .position (floatBuffer.position() * Float.BYTES)
                                            .limit (floatBuffer.limit() * Float.BYTES);
            }
            else if (floatBuffer instanceof DirectFloatBufferS)
            {
                DirectFloatBufferS buffer = (DirectFloatBufferS) floatBuffer;
                return (ByteBuffer) new DirectByteBuffer (buffer.address(), floatBuffer.capacity() * Float.BYTES, buffer)
                                            .position (floatBuffer.position() * Float.BYTES)
                                            .limit (floatBuffer.limit() * Float.BYTES);
            }
            else if (floatBuffer instanceof ByteBufferAsFloatBufferB)
            {
                ByteBufferAsFloatBufferB buffer = (ByteBufferAsFloatBufferB)floatBuffer;
                return (ByteBuffer) ((ByteBuffer) buffer.bb
                                                        .duplicate()
                                                        .position (buffer.offset)
                                                        .limit (buffer.offset + buffer.capacity() * Float.BYTES))
                                                        .slice()
                                                        .position (buffer.position() * Float.SIZE)
                                                        .limit (buffer.limit() * Float.BYTES);
            }
            else if (floatBuffer instanceof ByteBufferAsFloatBufferL)
            {
                ByteBufferAsFloatBufferL buffer = (ByteBufferAsFloatBufferL)floatBuffer;
                return (ByteBuffer) ((ByteBuffer) buffer.bb
                                                        .duplicate()
                                                        .position (buffer.offset)
                                                        .limit (buffer.offset + buffer.capacity() * Float.BYTES))
                                                        .slice()
                                                        .position (buffer.position() * Float.SIZE)
                                                        .limit (buffer.limit() * Float.BYTES);
            }
            else
                throw new IllegalArgumentException ("Unsupported implementing class " + floatBuffer.getClass().getName());
        }

}