Become familiar with Javascript, Jquery, Ajax solve !

Ajax has a method , such as:

  $.ajax({
  		type:"POST",
  		url:"ceremony/awardsAction!getTheGold?awardsId="+awardsId,
  		data:"json",
  		success:function(obj){
  			if(obj!=null){                //问题出在这一行，逻辑问题
  			      alert("not null");
  			}
  		}
  	});
  

here obj sometimes returns null, not null when I want the output to determine if obj is not equal to null.

I should ask how big God judge ?

even if it is null into ( judgment condition is not null to get into ) the following two will not work :

if (obj! = "null") tried ( if it returns null), it will enter .

if (obj! = null) tried ( if it returns null), it will enter .
------ Solution ---------------------------------------- ----
return in the end you do not know what it was changed to try this
if (obj && obj! = null && obj! = "null") {
alert ("not null");
}
------ For reference only --------------------------------- ------


is an object Object, but sometimes it is null.
------ For reference only --------------------- ------------------


or not, it is null which will enter judgment .
------ For reference only -------------------------------------- -
you see in the end is used firebug to debug what value is null or undefined
if (obj! = undefined && obj && obj! = null && obj! = "null") { ;
alert ("not null");
}
------ For reference only --------------------------------- ------


seen, is null, String type. But if (obj! = "null") {} is wrong ( as null also entered ) .
------ For reference only -------------------------------------- -

  
seen, is null, String type. But if (obj! = "null") {} is wrong ( as null also entered ) .  
If a string is "null" main floor, see if there are spaces and line breaks , if you look at the value of the case is invisible behind the hidden \ r \ n or spaces
------ For reference only ---------------------------------------

    
seen, is null, String type. But if (obj! = "null") {} is wrong ( as null also entered ) .          
If a string is "null" main floor, see if there are spaces and line breaks , if you look at the value of the case is invisible behind the hidden \ r \ n or spaces  
If there are spaces or line breaks with $ trim (obj) = "null";.!
------ For reference only -------------- -------------------------

      
seen, is null, String type. But if (obj! = "null") {} is wrong ( as null also entered ) .                
If a string is "null" main floor, see if there are spaces and line breaks , if you look at the value of the case is invisible behind the hidden \ r \ n or spaces          
If there are spaces or line breaks with $ trim (obj) = "null".!;  

trouble , or not ~
------ For reference only ---------------------------------------

        
seen, is null, String type. But if (obj! = "null") {} is wrong ( as null also entered ) .                      
If a string is "null" main floor, see if there are spaces and line breaks , if you look at the value of the case is invisible behind the hidden \ r \ n or spaces                
If there are spaces or line breaks with $ trim (obj) = "null".!;          
  
trouble , or not ~     
Please firebug when his landlord see, I can not know
------ For reference only your business and data -------------- -------------------------

          
seen, is null, String type. But if (obj! = "null") {} is wrong ( as null also entered ) .                            
If a string is "null" main floor, see if there are spaces and line breaks , if you look at the value of the case is invisible behind the hidden \ r \ n or spaces                      
If there are spaces or line breaks with $ trim (obj) = "null".!;                
    
trouble , or not ~               
Please firebug when his landlord see, I can not know your business and data  
------ For reference only ----- ----------------------------------


finally did get out , but then I get a compromise .

Solution:
I judge from backstage :

  if(object!=null){
      out.println(jsonObj);
  } 
  

If the object is not equal to null the output format json object , the object is equal to null if nothing is output, foreground Js will return an empty string "", foreground Js may determine:

  ......
  success:function(obj){
       if(obj != ""){
                ......
       }
  }
  ......