Agi can not get xml variable

hi, recently i doing asr test.
i use agi in java .

here is java agi:
String prompt = “welcome,please say something”;
String welcomeIVR = prompt + “,builtin:grammar/number,t=5000&b=1&ct=0.7&spl=zh-CN”;
channel.exec(“SynthAndRecog”, welcomeIVR);

    	String status = channel.getVariable("RECOG_STATUS");
    	System.out.println("status:" +status );
    	
    	String result = channel.getVariable("RECOG_RESULT");
    	System.out.println("result:" + result );

the console result is below:
status:OK
result:null

but asterisk cli output line print result like:
[2019-08-07 15:42:26] VERBOSE[19017][C-00078f29] app_verbose.c:

<?xml version="1.0" encoding="UTF-8" ?>
 <result>
     <asr confidence="100">hello</asr>
     <ext>
         <logid>e3894f5eb8e611e9_0</logid>
     </ext>
 </result>

why java agi can not get the variable?

any good idea?
or please give something to list