本文目录
Android文件读写概述读取raw目录文件读取assets目录文件data/data/(包名) 目录文件读写写数据读数据
sdcard文件读写申请动态权限写数据读数据sdcard文件读写完整代码
推荐阅读: Android 通过HttpURLConnection访问Http协议网络 Android SQlite数据库使用详解 Android xUtils框架最全使用详解 Android 动态权限最全解析
Android文件读写概述
在Androi中文件读写一共有以下目录
raw目录asserts目录data/data/包名sdcard目录
其中raw下的和asserts下的文件可以以资源文件的形式读取,这些目录的数据只能读取,不能写入,两者目录下的文件在打包后会原封不动的保存在apk包中,不会被编译成二进制。 data/data/包名和sdcard目录文件可读可写。其中data/data/包名目录不需要申请权限,sdcard目录需要申请权限
读取raw目录文件
Android工程默认是没有raw文件夹的在读文件前我们先把raw 文件夹以及文件建好
点中工程的res目录 右键New -> Directory -> 弹窗中输入raw点中刚刚新建的raw目录 右键New -> File -> 弹窗中输入test.txt点开刚刚新建的test.txt文件 ,往里面输入hello world 读数据方法
InputStream inputStream = null;
Reader reader = null;
BufferedReader bufferedReader = null;
try {
//得到资源中的Raw数据流
inputStream = getResources().openRawResource(R.raw.test);
reader = new InputStreamReader(inputStream);// 字符流
bufferedReader = new BufferedReader(reader); //缓冲流
StringBuilder result = new StringBuilder();
String temp;
while ((temp = bufferedReader.readLine()) != null) {
result.append(temp);
}
Log.i("MainActivity", "result:" + result);
} catch (Exception e) {
e.printStackTrace();
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (inputStream != null) {
try {
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (bufferedReader != null) {
try {
bufferedReader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
从打印的结果中我们可以看出数据读取成功 ![在这里插入图片描述](https://img-blog.csdnimg.cn/20200421150644304.png)
读取assets目录文件
Android工程默认是没有assets文件夹的,在读文件前我们先把assets 文件夹以及文件建好
点中工程 右键New -> Folder -> Assets Folder点中刚刚新建的Assets Folde目录 右键New -> File -> 弹窗中输入test.txt点开刚刚新建的test.txt文件 ,往里面输入hello world 读去assets文件中的数据方法
InputStream inputStream = null;
Reader reader = null;
BufferedReader bufferedReader = null;
try {
//得到资源中的asset数据流
inputStream = getResources().getAssets().open("test.txt");
reader = new InputStreamReader(inputStream);// 字符流
bufferedReader = new BufferedReader(reader); //缓冲流
StringBuilder result = new StringBuilder();
String temp;
while ((temp = bufferedReader.readLine()) != null) {
result.append(temp);
}
Log.i("MainActivity", "result:" + result);
} catch (Exception e) {
e.printStackTrace();
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (inputStream != null) {
try {
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (bufferedReader != null) {
try {
bufferedReader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
从打印的结果中我们可以看出数据读取成功 ![在这里插入图片描述](https://img-blog.csdnimg.cn/20200421154317498.png)
data/data/(包名) 目录文件读写
将数据以普通文件的形式保存在 /data/data/包名中,该方法不需要申请权限。 存放在数据区(/data/data/包名)的文件可以使用openFileOutput和openFileInput进行操作。 也可以直接指定文件/data/data/包名路径读写。
该目录存放文件类型规则如下:
路径功能data/data/包名/shared_prefs存放SharedPreferences数据data/data/包名/databases存放数据库数据data/data/包名/files存放普通数据data/data/包名/cache存放缓存文件
写数据
方法1:openFileOutput
FileOutputStream fileOutputStream = null;
try {
String text = "hello world";
fileOutputStream = openFileOutput("test.txt", MODE_PRIVATE);
fileOutputStream.write(text.getBytes());
} catch (Exception e) {
e.printStackTrace();
} finally {
if (fileOutputStream != null) {
try {
fileOutputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
openFileOutput方法参数详解
@Override
public FileOutputStream openFileOutput(String name, int mode)
throws FileNotFoundException {
}
name 存储文件名字mode 存储方式 其值的含义如下
参数值参数含义Context.MODE_PRIVATE指定该文件数据只能被本应用程序读、写Context.MODE_WORLD_READABLE指定该文件数据能被其他应用程序读,但不能写Context.MODE_WORLD_WRITEABLE指定该文件数据能被其他应用程序读Context.MODE_APPEND该模式会检查文件是否存在,存在就往文件追加内容,否则就创建新文件;
方法2:传统方法读写
String text = "hello world";
File file1=new File("/data/data/com.lucashu.file/","test.txt");
FileOutputStream fileOutputStream = null;
try {
fileOutputStream = new FileOutputStream(file1);
fileOutputStream.write(text.getBytes());
} catch (Exception e) {
e.printStackTrace();
}finally {
if (fileOutputStream != null) {
try {
fileOutputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
执行以后我们可以看到添加了一个文件 ![在这里插入图片描述](https://img-blog.csdnimg.cn/20200421175021142.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2h1d2VpbGl5aQ==,size_16,color_FFFFFF,t_70)
读数据
方法1:openFileInput
FileInputStream fileInputStream = null;
Reader reader = null;
BufferedReader bufferedReader = null;
try {
fileInputStream = openFileInput("test.txt");
reader = new InputStreamReader(fileInputStream);// 字符流
bufferedReader = new BufferedReader(reader); //缓冲流
StringBuilder result = new StringBuilder();
String temp;
while ((temp = bufferedReader.readLine()) != null) {
result.append(temp);
}
Log.i("MainActivity", "result:" + result);
} catch (Exception e) {
e.printStackTrace();
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (fileInputStream != null) {
try {
fileInputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (bufferedReader != null) {
try {
bufferedReader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
方法2:openFileInput
InputStream inputStream = null;
Reader reader = null;
BufferedReader bufferedReader = null;
try {
File file=new File("/data/data/com.lucashu.file/", "test.txt");
inputStream = new FileInputStream(file);
reader = new InputStreamReader(inputStream);
bufferedReader = new BufferedReader(reader);
StringBuilder result = new StringBuilder();
String temp;
while ((temp = bufferedReader.readLine()) != null) {
result.append(temp);
}
Log.i("MainActivity", "result:" + result);
} catch (Exception e) {
e.printStackTrace();
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (inputStream != null) {
try {
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (bufferedReader != null) {
try {
bufferedReader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
从打印的结果中我们可以看出数据读取成功
我们也可以用一下方法来获取改文件的路径
getFilesDir();// data/data/包名/files 目录
getFilesDir().getParent(),;// data/data/包名/ 目录
sdcard文件读写
sdcard读写的数据将数据保存在 /mnt/sdcard目录,该目录读写需要先申请动态权限,动态权限申请方法如下
申请动态权限
Android 动态权限最全解析 ![在这里插入图片描述](https://img-blog.csdnimg.cn/2020042116321052.gif#pic_center)
首先需要在manifest.xml中添加权限
如果是AndroidQ 或者更高的版本还需要在manifest.xml文件中的application节点下加入 android:requestLegacyExternalStorage="true" 申请动态权限方法:
private static final int REQUEST_EXTERNAL_STORAGE = 1;
private static String[] PERMISSIONS_STORAGE = {"android.permission.READ_EXTERNAL_STORAGE",
"android.permission.WRITE_EXTERNAL_STORAGE"};
private void checkPermission() {
//检查权限(NEED_PERMISSION)是否被授权 PackageManager.PERMISSION_GRANTED表示同意授权
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
!= PackageManager.PERMISSION_GRANTED) {
if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission
.WRITE_EXTERNAL_STORAGE)) {
Toast.makeText(this, "请开通相关权限,否则无法正常使用本应用!", Toast.LENGTH_SHORT).show();
}
//申请权限
ActivityCompat.requestPermissions(this, PERMISSIONS_STORAGE, REQUEST_EXTERNAL_STORAGE);
} else {
Toast.makeText(this, "已授权成功!", Toast.LENGTH_SHORT).show();
writeSdcard();
}
}
Activity中动态权限的回调方法
@Override
public void onRequestPermissionsResult(int requestCode,
String permissions[], int[] grantResults) {
switch (requestCode) {
case REQUEST_EXTERNAL_STORAGE: {
if (grantResults.length > 0
&& grantResults[0] == PackageManager.PERMISSION_GRANTED) {
Toast.makeText(this, "授权成功!", Toast.LENGTH_SHORT).show();
writeSdcard();
} else {
Toast.makeText(this, "授权被拒绝!", Toast.LENGTH_SHORT).show();
}
return;
}
}
}
写数据
private void writeSdcard() {
String text = "hello world";
if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
File storage = Environment.getExternalStorageDirectory();
File tmepfile = new File(storage.getPath());
if (! tmepfile.exists()) {
tmepfile.mkdirs();
}
File file1=new File(tmepfile,"test.txt");
if (!file1.exists()){
try {
file1.createNewFile();
} catch (IOException e) {
e.printStackTrace();
}
}
FileOutputStream fileOutputStream = null;
try {
fileOutputStream = new FileOutputStream(file1);
fileOutputStream.write(text.getBytes());
} catch (Exception e) {
e.printStackTrace();
}finally {
if (fileOutputStream != null) {
try {
fileOutputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
}
执行以后我们可以看到添加了一个文件 ![在这里插入图片描述](https://img-blog.csdnimg.cn/20200421172157884.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2h1d2VpbGl5aQ==,size_16,color_FFFFFF,t_70)
读数据
private void readSdcard() {
if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
InputStream inputStream = null;
Reader reader = null;
BufferedReader bufferedReader = null;
try {
File storage = Environment.getExternalStorageDirectory();
File tmepfile = new File(storage.getPath());
File file=new File(tmepfile, "test.txt");
inputStream = new FileInputStream(file);
reader = new InputStreamReader(inputStream);
bufferedReader = new BufferedReader(reader);
StringBuilder result = new StringBuilder();
String temp;
while ((temp = bufferedReader.readLine()) != null) {
result.append(temp);
}
Log.i("MainActivity", "result:" + result);
} catch (Exception e) {
e.printStackTrace();
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (inputStream != null) {
try {
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (bufferedReader != null) {
try {
bufferedReader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
}
![在这里插入图片描述](https://img-blog.csdnimg.cn/20200421172237423.png)
sdcard文件读写完整代码
package com.lucashu.file;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.widget.Toast;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.Writer;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
checkPermission();
}
private void writeSdcard() {
String text = "hello world";
if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
File storage = Environment.getExternalStorageDirectory();
File tmepfile = new File(storage.getPath());
if (! tmepfile.exists()) {
tmepfile.mkdirs();
}
File file1=new File(tmepfile,"test.txt");
if (!file1.exists()){
try {
file1.createNewFile();
} catch (IOException e) {
e.printStackTrace();
}
}
FileOutputStream fileOutputStream = null;
try {
fileOutputStream = new FileOutputStream(file1);
fileOutputStream.write(text.getBytes());
} catch (Exception e) {
e.printStackTrace();
}finally {
if (fileOutputStream != null) {
try {
fileOutputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
}
private void readSdcard() {
if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
InputStream inputStream = null;
Reader reader = null;
BufferedReader bufferedReader = null;
try {
File storage = Environment.getExternalStorageDirectory();
File tmepfile = new File(storage.getPath());
File file=new File(tmepfile, "test.txt");
inputStream = new FileInputStream(file);
reader = new InputStreamReader(inputStream);
bufferedReader = new BufferedReader(reader);
StringBuilder result = new StringBuilder();
String temp;
while ((temp = bufferedReader.readLine()) != null) {
result.append(temp);
}
Log.i("MainActivity", "result:" + result);
} catch (Exception e) {
e.printStackTrace();
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (inputStream != null) {
try {
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (bufferedReader != null) {
try {
bufferedReader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
}
private static final int REQUEST_EXTERNAL_STORAGE = 1;
private static String[] PERMISSIONS_STORAGE = {"android.permission.READ_EXTERNAL_STORAGE",
"android.permission.WRITE_EXTERNAL_STORAGE"};
private void checkPermission() {
//检查权限(NEED_PERMISSION)是否被授权 PackageManager.PERMISSION_GRANTED表示同意授权
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
!= PackageManager.PERMISSION_GRANTED) {
if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission
.WRITE_EXTERNAL_STORAGE)) {
Toast.makeText(this, "请开通相关权限,否则无法正常使用本应用!", Toast.LENGTH_SHORT).show();
}
//申请权限
ActivityCompat.requestPermissions(this, PERMISSIONS_STORAGE, REQUEST_EXTERNAL_STORAGE);
} else {
Toast.makeText(this, "已授权成功!", Toast.LENGTH_SHORT).show();
readSdcard();
}
}
@Override
public void onRequestPermissionsResult(int requestCode,
String permissions[], int[] grantResults) {
switch (requestCode) {
case REQUEST_EXTERNAL_STORAGE: {
if (grantResults.length > 0
&& grantResults[0] == PackageManager.PERMISSION_GRANTED) {
Toast.makeText(this, "授权成功!", Toast.LENGTH_SHORT).show();
readSdcard();
} else {
Toast.makeText(this, "授权被拒绝!", Toast.LENGTH_SHORT).show();
}
return;
}
}
}
}
作者:lucashu 出处:https://blog.csdn.net/huweiliyi/category_8913738.html 原创不易,欢迎转载,但未经作者同意请保留此段声明,并在文章页面明显位置给出原文链接。
|