/**
* 向sdcard中写入文件
* @param filename 文件名
* @param content 文件内容
*/
public void saveToSDCard(String filename,String content) throws Exception{
  File file=new File("/mnt/sdcard", filename);
  OutputStream out=new FileOutputStream(file);
  out.write(content.getBytes());
  out.close();
}

/**
* 向sdcard中写入文件
* @param filename 文件名
* @param content 文件内容
*/
public void saveToSDCard(String filename,String content) throws Exception{
  File file=new File(Environment.getExternalStorageDirectory(), filename);
  OutputStream out=new FileOutputStream(file);
  out.write(content.getBytes());
  out.close();
}

<!-- 在SDCard中创建于删除文件的权限 -->
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
<!-- 往SDCard中写入数据的权限 -->
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

//向SDCard中保存
String en=Environment.getExternalStorageState();
//获取SDCard状态,如果SDCard插入了手机且为非写保护状态
if(en.equals(Environment.MEDIA_MOUNTED)){
 try {
  service.saveToSDCard(filename, content);
  Toast.makeText(getApplicationContext(), "保存成功", 1).show();
 } catch (Exception e) {
  Toast.makeText(getApplicationContext(), "保存失败", 1).show();
 }
}else{
 //提示用户SDCard不存在或者为写保护状态
 Toast.makeText(getApplicationContext(), "SDCard不存在或者为写保护状态", 1).show();
}