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。。。）