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：
1 package com.example.ghimtim.myapplication;
2
3 import android.Manifest;
4 import android.content.Context;
5 import android.content.pm.PackageManager;
6 import android.os.Environment;
7 import android.os.SystemClock;
8 import android.support.v4.app.ActivityCompat;
9 import android.support.v4.content.ContextCompat;
10 import android.support.v7.app.AppCompatActivity;
11 import android.os.Bundle;
12 import android.view.View;
13 import android.widget.Button;
14 import android.widget.EditText;
15 import android.widget.TextView;
16 import android.widget.Toast;
17
18 import java.io.File;
19 import java.io.FileInputStream;
20 import java.io.FileOutputStream;
21 import java.io.InputStreamReader;
22 import java.io.OutputStreamWriter;
23
24 public class MainActivity extends AppCompatActivity implements ActivityCompat.OnRequestPermissionsResultCallback{
25
26 private static final int MY_PERMISSIONS_REQUEST = 10000;
27
28 private Button bt_wr;
29 private Button bt_w;
30 private TextView tv_wr;
31 private TextView tv_w;
32 private EditText et_time;
33 private File sdcard;
34
35 private Context mContext;
36
37 int Fortime = 1000;
38 char[] buffer = new char[1024];
39 long time;
40
41
42 @Override
43 protected void onCreate(Bundle savedInstanceState) {
44 super.onCreate(savedInstanceState);
45 setContentView(R.layout.activity_main);
46 mContext = this;
47 requestpermisson();
48 sdcard= Environment.getExternalStorageDirectory();
49 initData();
50 initView();
51 }
52
53 private void initData() {
54 for(int i = 0 ; i < 1024;i++){
55 buffer[i] = ‘b‘;
56 }
57 }
58
59 private void requestpermisson() {
60 ActivityCompat.requestPermissions(this,
61 new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
62 MY_PERMISSIONS_REQUEST);
63
64 }
65
66 @Override
67 public void onRequestPermissionsResult(int requestCode,
68 String permissions[], int[] grantResults) {
69 switch (requestCode) {
70 case MY_PERMISSIONS_REQUEST: {
71 // If request is cancelled, the result arrays are empty.
72 if (grantResults.length > 0
73 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
74
75 // permission was granted, yay! Do the
76 // contacts-related task you need to do.
77
78 } else {
79 Toast.makeText(this,"no permission!",Toast.LENGTH_LONG).show();
80 // this.finish();
81 // permission denied, boo! Disable the
82 // functionality that depends on this permission.
83 }
84 return;
85 }
86 }
87 }
88
89 private void initView() {
90 bt_wr = (Button) findViewById(R.id.write_read_sd_file);
91 bt_w = (Button) findViewById(R.id.write_sd_file);
92 tv_wr = (TextView) findViewById(R.id.write_read_sd_file_time);
93 tv_w = (TextView) findViewById(R.id.write_sd_file_time);
94 et_time = (EditText) findViewById(R.id.for_time);
95 et_time.setText(String.valueOf(Fortime));
96 bt_wr.setOnClickListener(new View.OnClickListener() {
97 @Override
98 public void onClick(View v) {
99 if(!et_time.getText().toString().equals("")){
100 Fortime = Integer.parseInt(et_time.getText().toString());
101 }
102 time = System.currentTimeMillis();
103 writeAndReadForTime();
104
105 }
106 });
107 bt_w.setOnClickListener(new View.OnClickListener() {
108 @Override
109 public void onClick(View v) {
110 if(!et_time.getText().toString().equals("")){
111 Fortime = Integer.parseInt(et_time.getText().toString());
112 }
113 time = System.currentTimeMillis();
114 ReadFileForTime();
115 }
116 });
117 }
118
119 private void ReadFileForTime() {
120 for(int i =0;i<Fortime;i ++){
121 ReadFile();
122 }
123 time = System.currentTimeMillis() - time;
124 tv_w.setText(String.valueOf(time));
125 }
126
127 private void writeAndReadForTime() {
128 for(int i =0;i<Fortime;i ++){
129 writeAndRead();
130 }
131 time = System.currentTimeMillis() - time;
132 tv_wr.setText(String.valueOf(time));
133 }
134
135 private void ReadFile() {
136 File file2 = new File(sdcard,"c.txt");
137 if(!sdcard.exists()){
138 return;
139 }
140 try{
141 // file2.createNewFile();
142 FileOutputStream fos=new FileOutputStream(file2);
143 OutputStreamWriter osw=new OutputStreamWriter(fos);
144 String str = new String(buffer);
145 osw.write(str);
146 osw.flush();
147 osw.close();
148 fos.close();
149 }catch (Exception e){
150 e.printStackTrace();
151 }
152 }
153
154 private void writeAndRead() {
155 File file1 = new File(sdcard,"a.txt");
156 File file2 = new File(sdcard,"b.txt");
157 if(!sdcard.exists()){
158 return;
159 }
160 try{
161 // file2.createNewFile();
162 FileInputStream fis = new FileInputStream(file1);
163 InputStreamReader isr = new InputStreamReader(fis,"UTF-8");
164 FileOutputStream fos=new FileOutputStream(file2);
165 OutputStreamWriter osw=new OutputStreamWriter(fos);
166 char[] input = new char[fis.available()];
167 isr.read(input);
168 String str = new String(input);
169 osw.write(str);
170 osw.flush();
171 isr.close();
172 fis.close();
173 osw.close();
174 fos.close();
175 }catch (Exception e){
176 e.printStackTrace();
177 }
178 }
179 }
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！
1 <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。。。）
时间： 2024-10-11 04:04:45