Android测试读写sd卡文件与写sd卡文件耗时

　　测试从sd卡读1k大小的文件，再写1k大小的文件，由于处理耗时很短，所以循环500次，查看耗时；测试写1k大小的文件，直接在内存构造一个1k的buffer，将这个buffer直接写到文件，同样循环500次，查看耗时。

　　思路：首先读写文件，建立文件输入输出流，然后将读取的数据直接写入文件，打印时间戳，查看耗时；只写文件，新建一个1k的buffer，然后用文件输出流写入文件，打印时间戳，查看耗时。

　　直接上代码：

　　

package com.example.ghimtim.myapplication;

import android.Manifest;
import android.content.Context;
import android.content.pm.PackageManager;
import android.os.Environment;
import android.os.SystemClock;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class MainActivity extends AppCompatActivity implements ActivityCompat.OnRequestPermissionsResultCallback{

    private static final int MY_PERMISSIONS_REQUEST = 10000;

    private Button bt_wr;
    private Button bt_w;
    private TextView tv_wr;
    private TextView tv_w;
    private EditText et_time;
    private File sdcard;

    private Context mContext;

    int Fortime = 1000;
    char[] buffer = new char[1024];
    long time;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mContext = this;
        requestpermisson();
        sdcard= Environment.getExternalStorageDirectory();
        initData();
        initView();
    }

    private void initData() {
        for(int i = 0 ; i < 1024;i++){
            buffer[i] = 'b';
        }
    }

    private void requestpermisson() {
        ActivityCompat.requestPermissions(this,
            new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
                MY_PERMISSIONS_REQUEST);

    }

    @Override
    public void onRequestPermissionsResult(int requestCode,
                                           String permissions[], int[] grantResults) {
        switch (requestCode) {
            case MY_PERMISSIONS_REQUEST: {
                // If request is cancelled, the result arrays are empty.
                if (grantResults.length > 0
                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {

                    // permission was granted, yay! Do the
                    // contacts-related task you need to do.

                } else {
                  Toast.makeText(this,"no permission!",Toast.LENGTH_LONG).show();
//                    this.finish();
                    // permission denied, boo! Disable the
                    // functionality that depends on this permission.
                }
                return;
            }
        }
    }

    private void initView() {
        bt_wr = (Button) findViewById(R.id.write_read_sd_file);
        bt_w = (Button) findViewById(R.id.write_sd_file);
        tv_wr = (TextView) findViewById(R.id.write_read_sd_file_time);
        tv_w = (TextView) findViewById(R.id.write_sd_file_time);
        et_time = (EditText) findViewById(R.id.for_time);
        et_time.setText(String.valueOf(Fortime));
        bt_wr.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(!et_time.getText().toString().equals("")){
                    Fortime =  Integer.parseInt(et_time.getText().toString());
                }
                time = System.currentTimeMillis();
                writeAndReadForTime();

            }
        });
        bt_w.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(!et_time.getText().toString().equals("")){
                    Fortime =  Integer.parseInt(et_time.getText().toString());
                }
                time = System.currentTimeMillis();
                ReadFileForTime();
            }
        });
    }

    private void ReadFileForTime() {
        for(int i =0;i<Fortime;i ++){
            ReadFile();
        }
        time = System.currentTimeMillis() - time;
        tv_w.setText(String.valueOf(time));
    }

    private void writeAndReadForTime() {
        for(int i =0;i<Fortime;i ++){
            writeAndRead();
        }
        time = System.currentTimeMillis() - time;
        tv_wr.setText(String.valueOf(time));
    }

    private void ReadFile() {
        File file2 =  new File(sdcard,"c.txt");
        if(!sdcard.exists()){
            return;
        }
        try{
//            file2.createNewFile();
            FileOutputStream fos=new FileOutputStream(file2);
            OutputStreamWriter osw=new OutputStreamWriter(fos);
            String str = new String(buffer);
            osw.write(str);
            osw.flush();
            osw.close();
            fos.close();
        }catch (Exception e){
            e.printStackTrace();
        }
    }

    private void writeAndRead() {
        File file1 = new File(sdcard,"a.txt");
        File file2 =  new File(sdcard,"b.txt");
        if(!sdcard.exists()){
            return;
        }
        try{
//            file2.createNewFile();
            FileInputStream fis = new FileInputStream(file1);
            InputStreamReader isr = new InputStreamReader(fis,"UTF-8");
            FileOutputStream fos=new FileOutputStream(file2);
            OutputStreamWriter osw=new OutputStreamWriter(fos);
            char[] input =  new char[fis.available()];
            isr.read(input);
            String str = new String(input);
            osw.write(str);
            osw.flush();
            isr.close();
            fis.close();
            osw.close();
            fos.close();
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}

　　还有一个注意的地方，读写sd卡，在Android6.0以后需要动态申请读写外部存储的权限！

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

　　（编码时粗心地将uses-permission写进application标签里面= =，这个uses-permission是应该要和application同级的。。。）