android蓝牙开发read failed, socket might closed or timeout, read ret: -1

read failed, socket might closed or timeout, read ret: -1

这个问题的原因有很多种可能。

一、如果设备1没开启接收服务，设备2连接它理所当然会连接失败，此时当设备1开启服务，设备2再连接也可能会失败，
http://stackoverflow.com/questions/18657427/ioexception-read-failed-socket-might-closed-bluetooth-on-android-4-3
原因：well, i had the same problem with my code, and it's because since android 4.2 bluetooth stack has changed. so my code was running fine on devices with android < 4.2 , on the other devices i was getting the famous exception "read
failed, socket might closed or timeout, read ret: -1"

The problem is with the 

socket.mPort

 parameter.
When you create your socket using 

socket
= device.createRfcommSocketToServiceRecord(SERIAL_UUID);

 , the 

mPort

 gets
integer value "-1", and this value seems doesn't work for android >=4.2 , so you need to set it to "1". The bad news is that 

createRfcommSocketToServiceRecord

 only
accepts UUID as parameter and not 

mPort

 so
we have to use other aproach. The answer posted by @matthes also worked for me, but i simplified it: 

socket
=(BluetoothSocket) device.getClass().getMethod("createRfcommSocket", new Class[] {int.class}).invoke(device,1);

. We need to use both socket attribs , the second one as a fallback.

So the code is (for connecting to a SPP on an ELM327 device):

解决方法：

try {
socket.connect();
Log.e("","Connected");
} catch (IOException e) {
Log.e("",e.getMessage());
try {
Log.e("","trying fallback...");

socket =(BluetoothSocket) device.getClass().getMethod("createRfcommSocket", new Class[] {int.class}).invoke(device,1);
socket.connect();

Log.e("","Connected");
}
catch (Exception e2) {
Log.e("", "Couldn't establish Bluetooth connection!");
}
}

通过反射把端口改成1

二、服务器监听端口可能不是1
http://simonlei.iteye.com/blog/1522196
解决方法：

Method listenMethod = btClass.getMethod("listenUsingRfcommOn", new Class[]{int.class});

BluetoothServerSocket returnValue = ( BluetoothServerSocket) listenMethod.invoke(btAdapter, new Object[]{ 29});

三、设备1在搜索的时候设备2连接它会失败