Android开发进阶之NIO非阻塞包(七) Android开发技术

  今天我们继续就Android DDMS源码一起分析NIO非阻塞通讯方式，Android123也会给大家分享下手机和PC互通中的一些技术。在NIO中有关SocketChannel和ByteBuffer的使用细节，可以在今天文章中

   static void read(SocketChannel chan, byte[] data, int length, int timeout)
            throws TimeoutException, IOException {
        ByteBuffer buf = ByteBuffer.wrap(data, 0, length != -1 ? length : data.length); //从字节数组中实例化ByteBuffer
        int numWaits = 0;

        while (buf.position() != buf.limit()) {  //循环接收数据
            int count;

            count = chan.read(buf);
            if (count < 0) {
                    throw new IOException("EOF"); //读到末尾
            } else if (count == 0) {
                if (timeout != 0 && numWaits * WAIT_TIME > timeout) {
                    throw new TimeoutException();
                }
                 try {
                    Thread.sleep(WAIT_TIME);
                } catch (InterruptedException ie) {
                }
                numWaits++;
            } else {
                numWaits = 0;
            }
        }
    }

    有关SocketChannel的写操作，就是发送数据代码如下:

  static void write(SocketChannel chan, byte[] data, int length, int timeout)
            throws TimeoutException, IOException {
        ByteBuffer buf = ByteBuffer.wrap(data, 0, length != -1 ? length : data.length);
        int numWaits = 0;

        while (buf.position() != buf.limit()) {
            int count;

            count = chan.write(buf); //发送数据从ByteBuffer中
            if (count < 0) {
                       throw new IOException("channel EOF");
            } else if (count == 0) {
                             if (timeout != 0 && numWaits * WAIT_TIME > timeout) {
                            throw new TimeoutException();
                }
                 try {
                    Thread.sleep(WAIT_TIME);
                } catch (InterruptedException ie) {
                }
                numWaits++;
            } else {
                numWaits = 0;
            }
        }
    }

   有关ADB如何选择一个具体的设备，可以使用 setDevice 方法，这样当电脑中有模拟器或链接了多个手机，可以通过设备序列号，选择需要通讯的设备。

  static void setDevice(SocketChannel adbChan, IDevice device)
            throws TimeoutException, AdbCommandRejectedException, IOException {
        // if the device is not -1, then we first tell adb we’re looking to talk
        // to a specific device
        if (device != null) {
            String msg = "host:transport:" + device.getSerialNumber(); // 最后的获取序列号，android123提示大家在adb命令中是adb get-serialno

            byte[] device_query = formAdbRequest(msg);

            write(adbChan, device_query);

            AdbResponse resp = readAdbResponse(adbChan, false /* readDiagString */);
            if (resp.okay == false) {
                throw new AdbCommandRejectedException(resp.message,
                        true/*errorDuringDeviceSelection*/);
            }
        }
    }

    通过PC控制手机重启的代码，当然这里需要Root权限才能执行

   public static void reboot(String into, InetSocketAddress adbSockAddr,
            Device device) throws TimeoutException, AdbCommandRejectedException, IOException {
        byte[] request;
        if (into == null) {
            request = formAdbRequest("reboot:"); //$NON-NLS-1$
        } else {
            request = formAdbRequest("reboot:" + into); //$NON-NLS-1$
        }

        SocketChannel adbChan = null;
        try {
            adbChan = SocketChannel.open(adbSockAddr);
            adbChan.configureBlocking(false);

            // if the device is not -1, then we first tell adb we’re looking to talk
            // to a specific device
            setDevice(adbChan, device);

            write(adbChan, request);
        } finally {
            if (adbChan != null) {
                adbChan.close();
            }
        }
    }

  我们可以看到基本上，每个命令的执行，都是用了单独SocketChannel通过非阻塞方式执行，这样大大加强了并发，所以DDMS可以一边处理Logcat打印，显示堆信息，处理文件管理等等，有关NIO服务器的内容，Android开发网将着重分析MonitorThread.java这个文件，一起说下NIO的框架。