java - 如何将短数组转换为字节数组

Question

我找到了 converting a short to byte array , 和 byte array to short array ，但不是短数组到字节数组。

这是导致转换的代码

while(!stopped)
        { 
            Log.i("Map", "Writing new data to buffer");
            short[] buffer = buffers[ix++ % buffers.length];

            N = recorder.read(buffer,0,buffer.length);
            track.write(buffer, 0, buffer.length);

            byte[] bytes2 = new byte[N];

我试过了

              int i = 0;
              ByteBuffer byteBuf = ByteBuffer.allocate(N);
              while (buffer.length >= i) {
                  byteBuf.putShort(buffer[i]);
                  i++;
        }

bytes2 = byteBuf.array();

和

    ByteBuffer.wrap(bytes2).order(ByteOrder.LITTLE_ENDIAN).asShortBuffer().put(buffer);

但是我在两者上都收到此错误(错误如果不完全相同但两者非常相似):

05-29 13:41:12.021: W/AudioTrack(9758): obtainBuffer() track 0x30efa0 disabled, restarting

05-29 13:41:12.857: W/AudioWorker(9758): Error reading voice AudioWorker

05-29 13:41:12.857: W/AudioWorker(9758): java.nio.BufferOverflowException

05-29 13:41:12.857: W/AudioWorker(9758): at java.nio.ShortBuffer.put(ShortBuffer.java:422)

05-29 13:41:12.857: W/AudioWorker(9758): at java.nio.ShortToByteBufferAdapter.put(ShortToByteBufferAdapter.java:210)

05-29 13:41:12.857: W/AudioWorker(9758): at java.nio.ShortBuffer.put(ShortBuffer.java:391)

05-29 13:41:12.857: W/AudioWorker(9758): at com.avispl.nicu.audio.AudioWorker.run(AudioWorker.java:126)

这里只是为了提供尽可能多的信息，这是使用字节数组之后的代码

Log.i("Map", "test");
                //convert to ulaw
                read(bytes2, 0, N);

                //send to server
                os.write(bytes2,0,bytes2.length);

                System.out.println("bytesRead "+buffer.length);
                System.out.println("data "+Arrays.toString(buffer));
            }

Answer 1

我发现 ByteBuffer 是我分析过的三种转换方法中最慢的。见下文...

平台:Nexus S，Android 4.1.1，无 SIM 卡

方法 #1:使用 ByteBuffer

byte [] ShortToByte_ByteBuffer_Method(short [] input)
{
  int index;
  int iterations = input.length;

  ByteBuffer bb = ByteBuffer.allocate(input.length * 2);

  for(index = 0; index != iterations; ++index)
  {
    bb.putShort(input[index]);    
  }

  return bb.array();       
}

方法#2:直接旋转钻头

byte [] ShortToByte_Twiddle_Method(short [] input)
{
  int short_index, byte_index;
  int iterations = input.length;

  byte [] buffer = new byte[input.length * 2];

  short_index = byte_index = 0;

  for(/*NOP*/; short_index != iterations; /*NOP*/)
  {
    buffer[byte_index]     = (byte) (input[short_index] & 0x00FF); 
    buffer[byte_index + 1] = (byte) ((input[short_index] & 0xFF00) >> 8);

    ++short_index; byte_index += 2;
  }

  return buffer;
}

方法#3:通过 JNI 使用 C

TypeCast.java

package mynamespace.util;

public class TypeCast
{
  public static native byte [] shortToByte(short [] input);

  static
  {
    System.loadLibrary("type_conversion");
  }
}

native.c

#include <jni.h>
#include <string.h>

jbyteArray Java_mynamespace_util_TypeCast_shortToByte(JNIEnv *env, jobject obj, jshortArray input)
{
  jshort     *input_array_elements;
  int         input_length;

  jbyte      *output_array_elements;
  jbyteArray  output;

  input_array_elements = (*env)->GetShortArrayElements(env, input, 0);
  input_length         = (*env)->GetArrayLength(env, input);

  output                = (jbyteArray) ((*env)->NewByteArray(env, input_length * 2));
  output_array_elements = (*env)->GetByteArrayElements(env, output, 0);

  memcpy(output_array_elements, input_array_elements, input_length * 2);

  (*env)->ReleaseShortArrayElements(env, input, input_array_elements, JNI_ABORT);
  (*env)->ReleaseByteArrayElements(env, output, output_array_elements, 0);

  return output;
}

结果:

对于一个百万元素的输入数组，执行时间如下:

方法#1 字节缓冲区:865 毫秒

方法#2 转动:299 毫秒

方法#3 C:39 毫秒