JSON concatenation string must be __js with double quotes

Action

Long num = 10L;
String jsonstr = "{\" long\ ":" + num + "}";
Outputjson (JSONSTR);
The JSONSTR string is output to the foreground, which is parsed by the foreground in JSON format.

If it's a string,

String result = "XY";

String jsonstr = "{\" long\ ": \" "+ num +" \ "}";

JSP

$.ajax ({
URL: "...",
datatype: "JSON",
Success:function (data) {
alert (Data.long);
}
});

Note the point:

Watch out for one.
Cannot use single quotation mark "{' Long '" + num +} ", the foreground cannot parse.

Pay attention to two.
When using $.ajax to accept JSON, don't forget to write Datatype:json. I used to be used to $.getjson, so I sometimes forget to add.