java - Android IO 慢？

Question

这应该显示内部和外部内存速度，但不幸的是它说是 0.02 或 0.04 MB/s？这是 Android 中效率低下的表现，还是编码错误？

findViewById(R.id.buttonStorageSpeed).setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View arg0) {
                double SDSpeed = MBPSTest(getExternalCacheDir()); // /sdcard
                double MemSpeed = MBPSTest(getCacheDir());        // /data/data
                final AlertDialog dialog = new AlertDialog.Builder(thisContext)
                .setTitle("Memory speed")
                .setMessage( "Internal:"+String.valueOf(MemSpeed) + "\n"  + "SD:"+String.valueOf(SDSpeed))
                .create();
                dialog.show();
            }
        });




/**
     * Test MB/s write speed in some directory.
     * Writes 4MB, deletes it after.
     * @param outdir
     * @return
     */
    private double MBPSTest(File outDir) {

        long start = System.currentTimeMillis();
        try {
            for (int fnum = 0; fnum < 1024; fnum++) {
                File out = new File(outDir,"TESTspeed"+String.valueOf(fnum));
                FileOutputStream fos = new FileOutputStream(out);

                //Write 4k files
                for (int i=0; i < 1024; i++) {
                    fos.write(65);//A
                    fos.write(69);//E
                    fos.write(73);//I
                    fos.write(79);//O
                }
                fos.flush();
                fos.close();
                //System.out.println("Wrote file.");
            }
            //Wrote 4MB

            //Toast.makeText(getApplicationContext(), "Wrote External at: "+String.valueOf(4.0 / (elapsed/1000.0) )+" MB/S", Toast.LENGTH_LONG).show();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
            return 0;
        } catch (IOException e) {
            e.printStackTrace();
            return 0;
        }

        long elapsed = System.currentTimeMillis() - start;

        //Clean up:
        for (int fnum = 0; fnum < 1024; fnum++) {
            File out = new File(outDir, "TESTspeed"+String.valueOf(fnum));
            out.delete();
        }
        // 4 MB / (seconds)
        return 4.0 / (elapsed/1000.0);
    }

Answer 1

除了 Jonathon 提到的频繁打开和关闭文件的开销之外，您还调用 write(int)对于每个字节。

使用write(byte[])使用大缓冲区，或使用 BufferedOutputStream包裹 FileOutputStream 。 FileOutputStream 中可能有一些缓冲已经存在，但同样也可能没有。您可能会发现，一旦写入操作较少(但数据量仍然相同)，速度就会快得多。