Android 文件操作操作时，要赋予相应的权限：
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
下面是向文件写文本的代码：
private final static String PATH = "/sdcard/lin";
private final static String FILENAME = "/test.txt";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
writeFile();
}
private void writeFile() {
//判断设备是否存在sdcard
if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
try {
Log.d("File Operation", "start!");
File path = new File(PATH);
File file = new File(PATH+FILENAME);
//如果不存在此路径，则创建此路径
if (!path.exists()) {
path.mkdir();
}
//如果不存在此文件，则创建此文件
if (!file.exists()) {
file.createNewFile();
}
//将"text message!"信息写入相应的文件
OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream(file));
osw.write("text message!");
osw.close();
Log.d("File Operation", "success!");
} catch (Exception e) {
Log.d("File Operation", "file create error");
}
}
}