Android手机内存，SD卡读写

//保存文件到手机内存
public void save(String fileName,String content) throws IOException{
　　FileOutputStream fos = context.openFileOutput("a.txt", Context.MODE_PRIVATE);
　　fos.write(content.getBytes());
　　fos.close();
}

// 从手机内存读取文件
public String read(String fileName) throws IOException {
　　ByteArrayOutputStream baos = new ByteArrayOutputStream(); // 向内存输入字节数据的流
　　FileInputStream fis = context.openFileInput(fileName);
　　byte[] buffer = new byte[1024];
　　int len = 0;
　　while ((len = fis.read(buffer)) != -1) {
　　　　baos.write(buffer, 0, len);
　　}
　　byte[] data = baos.toByteArray();
　　return data.toString();
}

// 判断SD卡状态，插入可读写
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
　　service.saveToSDCard(fileName, content);
} else {
　　// sdcard不存在时，保存到手机内存
　　service.save(fileName, content);
}

//保存文件到SD卡
public void saveToSDCard(String fileName, String content) throws IOException{
　　File file = new File(Environment.getExternalStorageDirectory(),fileName);
　　FileOutputStream fos = new FileOutputStream(file);
　　fos.write(content.getBytes());
　　fos.close();
}

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