我发现此ADB命令可以检查键盘是否打开。

adb shell dumpsys input_method | grep mInputShown

在输出中，mInputShown=true如果键盘已打开并且mInputShown=false键盘已关闭。JAVA代码：

String cmd[] = new String[]{"adb", "shell", "dumpsys", "input_method", "|" ,"grep", "mInputShown"};
Process process = Runtime.getRuntime().exec(cmd);    
BufferedReader reader = new BufferedReader(new InputStreamReader(        
process.getInputStream()));
String output = reader.readLine();