How to use google app engine with ajax (json)?

Question

How to use google app engine with ajax (json)?

Now I have this but I got this error:

raise ValueError("No JSON object could be decoded")
ValueError: No JSON object could be decoded


from google.appengine.ext import webapp
from google.appengine.ext.webapp.util import run_wsgi_app
import simplejson as json

class AjaxHandler(webapp.RequestHandler):
    def post(self):
        args = json.loads(self.request.body)
        self.response.headers['Content-Type'] = 'application/json'
        self.response.out.write('Hello, webapp World!')





application = webapp.WSGIApplication(
                                     [('/AJAX', AjaxHandler)],
                                     debug=True)

def main():
    run_wsgi_app(application)

if __name__ == "__main__":
    main()

and javascript + jquery:

var Server = function() {
};
Server.prototype = {
    init: function(ajaxTargetUrl) {
        this.ajaxTargetUrl = ajaxTargetUrl;
    },
    request: function(service, data) {
        $.ajax({
            url: this.ajaxTargetUrl,
            context: document.body,
            success: function(data) {
                $('body').append('<p>'+data+'</p>');
            },
            error: function(){
                $('body').append('<p>error</p>');
            },
            data: data,
            type: 'POST',
            dataType: 'json'
        });
    }
};

var APP = ( function() {
    var server = new Server();
    server.init('http://localhost:9999/AJAX');
    server.request('questions.all', {test:'hey', y:99});
}());

my self.request.body = str: test=hey&y=99

Answer 1

1. as long as I know self.request.body wouldn't return anything. There's no argument named 'body' in your query-string, but I might be wrong. So, if it returns something, this something is a STRING. So simplejson.dumps() cannot turn it into a valid JSON.

   If you need a 'list' of all arguments you have sent to the server, use self.request.arguments()

2. self.response.out.write('Hello, webapp World!') do not send a valid JSON back to client. It sends a string with "application/json" header instead of "plain/text". Try to create a python dictionary. For example:

   my_response = {'ajax_resp':'Hello, webapp World!'}
json = json.dumps(my_resposne)

   and then

   self.response.headers.add_header('content-type', 'application/json', charset='utf-8')
self.response.out.write(json)

3. On the client side I would suggest you to use console.log() (debugging tool) for testing your responses.

   you can just try:

   $.ajax({
      type: 'GET',
      url: '/AJAX', // or your absolute-path
      data : name=totty&age=20,
      dataType : 'json',
      success : function(resp) 
                {
                console.info("Ajax Response is there.....");
                console.log(resp);
                }
      });

Answer 2

Your JavaScript is not sending JSON data to App Engine (test=hey&y=99 is a urlencoded string). Your App Engine page is not returning JSON data (Hello, webapp World! will just be received as a naked string).