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。。。）