用java快速写入/读取float数组

Question

我试图用java代码在Android设备中编写和读取浮点数组(实际上相当大,640*480).喜欢这个

    DataOutputStream out = ...;
for (int i=0; i<floatarray.length; ++i)
    out.writeFloat(floatarray[i]);

非常慢,我已经尝试过了.

写:

            float[] test=new float[3];
        test[0]=1.0f;
        test[1]=1.2f;
        test[2]=1.5f;
        //long timeBeforeWrite = System.nanoTime();
        try {
            BufferedOutputStream  dataOut = new BufferedOutputStream (
                    new FileOutputStream("/sdcard/DCIM/Camera/Dual/demo.bin"));

            byte buf[]=new byte[4*test.length];

            long timeBeforeWrite = System.nanoTime();

            for (int i=0; i<test.length; ++i)
            {
                int val = Float.floatToRawIntBits(test[i]);
                buf[4 * i] = (byte) (val >> 24);
                buf[4 * i + 1] = (byte) (val >> 16) ;
                buf[4 * i + 2] = (byte) (val >> 8);
                buf[4 * i + 3] = (byte) (val);
            }



            dataOut.write(buf);

            long ct_write = System.nanoTime();
            long offset_write = ct_write - timeBeforeWrite;
            float mOffsetInMs_write = (float)(offset_write)/1000000;
            Log.e("ETA", "write float[]  " + Float.toString(mOffsetInMs_write));

            dataOut.flush();
            dataOut.close();
        } catch (IOException ex) {
            System.err.println(ex.getMessage());
        }

读:

            float[] read=new float[3];

        try{
            BufferedInputStream  dataIn=new BufferedInputStream (new FileInputStream("/sdcard/DCIM/Camera/Dual/demo.txt"));
            byte buf[]=new byte[4*read.length];
            long timeBeforeWrite = System.nanoTime();

            dataIn.read(buf);

            for (int i=0; i<read.length; ++i)
            {
                    int val;
val = buf[4 * i] << 24;
                    val += buf[4 * i + 1] << 16;
                    val += buf[4 * i + 2] << 8;
                    val += buf[4 * i + 3];

                read[i]=Float.valueOf(Integer.toBinaryString(val));

                //int val = Float.floatToRawIntBits(disparityMap[i]);

            }

            long ct_write = System.nanoTime();
            long offset_write = ct_write - timeBeforeWrite;
            float mOffsetInMs_write = (float)(offset_write)/1000000;
            Log.e("ETA", "read float[]  " + Float.toString(mOffsetInMs_write));

            dataIn.close();

        }catch (IOException ex) {
            System.err.println(ex.getMessage());
        }

回读的东西是非常奇怪的浮点值,这有什么问题？BTW,回读运行速度很慢,不知道为什么.或者快速读/写浮点数组的任何其他好主意？

谢谢!

//感谢Larry,我尝试了一下bytebuffer.asfloatbuffer()方式:

//WRITE
    float[] test = new float[3];
    test[0]=1.1f;
    test[1]=1.2f;
    test[2]=1.5f;
    try{
        RandomAccessFile aFile = new RandomAccessFile("/sdcard/demo.data", "rw");
        FileChannel outChannel = aFile.getChannel();

        //one float 3 bytes
        ByteBuffer buf = ByteBuffer.allocate(12);
        buf.clear();
        buf.asFloatBuffer().put(test);

        //while(buf.hasRemaining()) 
        {
            outChannel.write(buf);
        }

        outChannel.close();

    }
    catch (IOException ex) {
        System.err.println(ex.getMessage());
    }

    //READ
    float[] readback=new float[3];
    try{


        RandomAccessFile rFile = new RandomAccessFile("/sdcard/demo.data", "rw");
        FileChannel inChannel = rFile.getChannel();
        ByteBuffer buf_in = ByteBuffer.allocate(12);
        buf_in.clear();

        inChannel.read(buf_in);

        buf_in.asFloatBuffer().get(readback);

        inChannel.close();

    }
    catch (IOException ex) {
        System.err.println(ex.getMessage());
    }

并且程序在buf_in.asFloatBuffer().get(readback); 任何想法中崩溃,并且在java中有商品进入和调试的内容,抱歉在java世界中全新.再次感谢

Answer 1

感谢Larry,我只是分享我的代码,希望它可以帮助其他人.

我只想弄清楚,我们需要在读/写文件通道后回放到缓冲区.以下代码正常运行,运行速度非常快.

float[] disparity=new float[640*480];

    disparity[1]=1.5f;
    disparity[2]=4.566f;

//WRITE
    try{
        RandomAccessFile aFile = new RandomAccessFile("/sdcard/demo.data", "rw");
        FileChannel outChannel = aFile.getChannel();

        //one float 4 bytes
        ByteBuffer buf = ByteBuffer.allocate(4*640*480);
        buf.clear();
        buf.asFloatBuffer().put(disparity);

        //while(buf.hasRemaining()) 
        {
            outChannel.write(buf);
        }

        //outChannel.close();
        buf.rewind();

        float[] out=new float[3];
        buf.asFloatBuffer().get(out);

        outChannel.close();

    }
    catch (IOException ex) {
        System.err.println(ex.getMessage());
    }

    //READ
    float[] readback=new float[640*480];
    try{

        RandomAccessFile rFile = new RandomAccessFile("/sdcard/demo.data", "rw");
        FileChannel inChannel = rFile.getChannel();
        ByteBuffer buf_in = ByteBuffer.allocate(640*480*4);
        buf_in.clear();

        inChannel.read(buf_in);

        buf_in.rewind();
        buf_in.asFloatBuffer().get(readback);

        inChannel.close();

    }
    catch (IOException ex) {
        System.err.println(ex.getMessage());
    }

再次感谢.

Answer 2

尝试使用FileChannel文件访问和ByteBuffer数据.您可以将数据放入ByteBuffer使用ByteBuffer.putFloat()方法并将其写出来FileChannel.write().当你回读它时,你可以调用FileChannel.read()以获取表示数据的ByteBuffer,然后调用ByteBuffer.asFloatBuffer()以获得FloatBuffer表示可以用来获取数据的数据float[].