在Sd卡中新建chen文件夹前后：
前
后
新建FileService.java的代码：
package cn.example.cx9_6_datasavesdcard; import java.io.File; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import android.os.Environment; public class FileService { public boolean saveFileToSdcard(String filename, byte[] data) throws IOException { String state = Environment.getExternalStorageState(); // 判断sdcard的状态 FileOutputStream outputStream = null; // 表示sdcard卡挂在手机上 并且可以读写 File root = Environment.getExternalStorageDirectory(); // 获得sdcard的根目录 if (state.equals(Environment.MEDIA_MOUNTED)) { File file = new File(root, filename); try { outputStream = new FileOutputStream(file); outputStream.write(data, 0, data.length); } catch (FileNotFoundException e) { e.printStackTrace(); } finally { if (outputStream != null) { try { outputStream.close(); } catch (IOException e) { e.printStackTrace(); } } } } return false; } }Mainactivity.java的代码不需改变；
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新建测试类Mytext.java的代码：
package cn.example.cx9_6_datasavesdcard; import java.io.IOException; import android.test.AndroidTestCase; public class Mytext extends AndroidTestCase { public void save() throws IOException { FileService service = new FileService(); service.saveFileToSdcard("chen.text", "nihaoaniazainalia".getBytes()); } } 选中save()右击选择测试。