package com.rwfile.main; 
 
import java.io.BufferedReader; 
 
import java.io.BufferedWriter; 
 
import java.io.File; 
 
import java.io.FileInputStream; 
 
import java.io.FileOutputStream; 
 
import java.io.InputStreamReader; 
 
import java.io.OutputStreamWriter; 
 
import android.os.Environment; 
 
public class RWFile { 
 
/** 
 
* 判断sdcard是否存在 
 
* 
 
* @return 
 
*/ 
 
public static boolean isSdcard() { 
 
String status = Environment.getExternalStorageState(); 
 
if (status.equals(Environment.MEDIA_MOUNTED)) { 
 
return true; 
 
} else { 
 
return false; 
 
} 
 
} 
 
/** 
 
* 读取文件内容 
 
* 
 
* @param filePathAndName 
 
* @return 
 
*/ 
 
public static String readFile(String filePathAndName) { 
 
String fileContent = null; 
 
try { 
 
File f = new File(filePathAndName); 
 
if (f.isFile() && f.exists()) { 
 
fileContent = ""; 
 
InputStreamReader read = new InputStreamReader( 
 
new FileInputStream(f), "UTF-8"); 
 
BufferedReader reader = new BufferedReader(read); 
 
String line; 
 
while ((line = reader.readLine()) != null) { 
 
fileContent += line; 
 
} 
 
read.close(); 
 
} 
 
} catch (Exception e) { 
 
e.printStackTrace(); 
 
return null; 
 
} 
 
return fileContent; 
 
} 
 
/** 
 
* 写入文件内容 
 
* 
 
* @param filePathAndName 
 
* @param fileContent 
 
*/ 
 
public static boolean writeFile(String filePathAndName, String fileContent) { 
 
try { 
 
File f = new File(filePathAndName); 
 
if (!f.exists()) { 
 
f.createNewFile(); 
 
} 
 
// 覆盖文件 
 
OutputStreamWriter write = new OutputStreamWriter( 
 
new FileOutputStream(f), "UTF-8");// 覆盖文件 
 
// 追加文件 
 
// OutputStreamWriter write = new OutputStreamWriter( 
 
// new FileOutputStream(f, true), "UTF-8"); // 追加文件 
 
BufferedWriter writer = new BufferedWriter(write); 
 
writer.write(fileContent); 
 
writer.close(); 
 
} catch (Exception e) { 
 
e.printStackTrace(); 
 
return false; 
 
} 
 
return true; 
 
} 
 
} 

package com.rwfile.main; 
 
import java.io.File; 
 
import android.os.Bundle; 
import android.os.Environment; 
import android.app.Activity; 
import android.view.Menu; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.TextView; 
import android.widget.Toast; 
 
public class MainActivity extends Activity { 
 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
setContentView(R.layout.activity_main); 
 
final EditText input = (EditText) findViewById(R.id.input); 
final TextView content = (TextView) findViewById(R.id.content); 
Button write = (Button) findViewById(R.id.write); 
 
write.setOnClickListener(new OnClickListener() { 
 
@Override 
public void onClick(View arg0) { 
// TODO Auto-generated method stub 
if (!RWFile.isSdcard()) { 
Toast.makeText(MainActivity.this, "无法找到sdcard卡", 
Toast.LENGTH_LONG).show(); 
} else { 
String sdcard = Environment.getExternalStorageDirectory() 
.toString() + File.separator; 
System.out.println("write path:" + sdcard + "test.txt"); 
RWFile.writeFile(sdcard + "test.txt", input.getText() 
.toString()); 
 
} 
} 
}); 
Button read = (Button) findViewById(R.id.read); 
 
read.setOnClickListener(new OnClickListener() { 
 
@Override 
public void onClick(View arg0) { 
// TODO Auto-generated method stub 
if (!RWFile.isSdcard()) { 
Toast.makeText(MainActivity.this, "无法找到sdcard卡", 
Toast.LENGTH_LONG).show(); 
} else { 
String sdcard = Environment.getExternalStorageDirectory() 
.toString() + File.separator; 
System.out.println("read path:" + sdcard + "test.txt"); 
String str = RWFile.readFile(sdcard + "test.txt"); 
if (str == null) 
Toast.makeText(MainActivity.this, "无法找到test.txt文件", 
Toast.LENGTH_LONG).show(); 
else { 
content.setText(str); 
} 
} 
} 
}); 
 
} 
 
@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
// Inflate the menu; this adds items to the action bar if it is present. 
getMenuInflater().inflate(R.menu.activity_main, menu); 
return true; 
} 
 
} 

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
 
xmlns:tools="http://schemas.android.com/tools" 
 
android:layout_width="match_parent" 
 
android:layout_height="match_parent" 
 
android:orientation="vertical" 
 
tools:context=".MainActivity" > 
 
<TextView 
 
android:layout_width="wrap_content" 
 
android:layout_height="wrap_content" 
 
android:text="@string/input" /> 
 
<EditText android:id="@+id/input" 
 
android:layout_width="match_parent" 
 
android:layout_height="wrap_content" 
 
android:hint="@string/chinese" 
 
android:text="@string/chinese"/> 
 
<Button android:id="@+id/write" 
 
android:layout_width="wrap_content" 
 
android:layout_height="wrap_content" 
 
android:text="@string/write"/> 
 
<Button android:id="@+id/read" 
 
android:layout_width="wrap_content" 
 
android:layout_height="wrap_content" 
 
android:text="@string/read"/> 
 
<TextView android:id="@+id/content" 
 
android:layout_width="wrap_content" 
 
android:layout_height="wrap_content" 
 
/> 
 
</LinearLayout> 

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