Android 读取用户logcat日志

在一个服务中开启logcat程序，然后读取

public void onCreate() {
        super.onCreate();
        new Thread(){
            public void run() {
                try {
                    File file = new File(Environment.getExternalStorageDirectory(),"log.txt");
                    FileOutputStream fos = new FileOutputStream(file);
                    Process process = Runtime.getRuntime().exec("logcat");
                    InputStream is = process.getInputStream();
                    BufferedReader br = new BufferedReader(new InputStreamReader(is));
                    String line;
                    while((line = br.readLine())!=null){
                        if(line.contains("I/ActivityManager")){
                            fos.write(line.getBytes());
                            fos.flush();
                        }
                    }
                    fos.close();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            };
        }.start();
    }