android 读取SD卡文件

public class SDCardTest extends Activity
{
    final String FILE_NAME = "/crazyit.bin";

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        // 获取两个按钮
        Button read = (Button) findViewById(R.id.read);
        Button write = (Button) findViewById(R.id.write);
        // 获取两个文本框
        final EditText edit1 = (EditText) findViewById(R.id.edit1);
        final EditText edit2 = (EditText) findViewById(R.id.edit2);
        // 为write按钮绑定事件监听器
        write.setOnClickListener(new OnClickListener()
        {
            @Override
            public void onClick(View source)
            {
                // 将edit1中的内容写入文件中
                write(edit1.getText().toString());
                edit1.setText("");
            }
        });

        read.setOnClickListener(new OnClickListener()
        {
            @Override
            public void onClick(View v)
            {
                // 读取指定文件中的内容，并显示出来
                edit2.setText(read());
            }
        });
    }

    private String read()
    {
        try
        {
            // 如果手机插入了SD卡，而且应用程序具有访问SD的权限
            if (Environment.getExternalStorageState().equals(
                    Environment.MEDIA_MOUNTED))
            {
                // 获取SD卡对应的存储目录
                File sdCardDir = Environment.getExternalStorageDirectory();
                // 获取指定文件对应的输入流
                FileInputStream fis = new FileInputStream(
                    sdCardDir.getCanonicalPath() + FILE_NAME);
                // 将指定输入流包装成BufferedReader
                BufferedReader br = new BufferedReader(new 
                    InputStreamReader(fis));
                StringBuilder sb = new StringBuilder("");
                String line = null;
                // 循环读取文件内容                
                while ((line = br.readLine()) != null)
                {
                    sb.append(line);
                }
                // 关闭资源
                br.close();
                return sb.toString();
            }
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        return null;
    }

    private void write(String content)
    {
        try
        {
            // 如果手机插入了SD卡，而且应用程序具有访问SD的权限
            if (Environment.getExternalStorageState().equals(
                Environment.MEDIA_MOUNTED))
            {
                // 获取SD卡的目录
                File sdCardDir = Environment.getExternalStorageDirectory();
                File targetFile = new File(sdCardDir
                    .getCanonicalPath() + FILE_NAME);
                // 以指定文件创建 RandomAccessFile对象
                RandomAccessFile raf = new RandomAccessFile(
                    targetFile, "rw");
                // 将文件记录指针移动到最后
                raf.seek(targetFile.length());
                // 输出文件内容
                raf.write(content.getBytes());
                // 关闭RandomAccessFile                
                raf.close();
            }
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }
}