// In project_root/Application.php:
        $this->addPlugin('JsonTools');

[
    'error' => false,
    'field_errors' => [],
    'message' => '',
    '_redirect' => false,
    'content' => null,
];

// All Json actions where you want to use this component should have one of the following lines

/**
* The most basic priming. Will set the boiler-plate variables (see below) that can be processed by ResponseHandler
* should there be a json request. If the request is not XHR/JSON, then this method would not have an effect.
*/
$this->Json->prepareVars();


/**
* Will return true if is Json and is POST/PUT, otherwise false
* Can replace something like $this->getRequest()->is(['post', 'put']) that is often used to check if form is submitted.
* You don't need to run prepareVars() if you use this line
*/
if($this->Json->isJsonSubmit()){}


/**
* Will force the output to be Json regardless of HTTP request headers
* You don't need to run prepareVars() if you use this line
*/
$this->Json->forceJson(); // will force the output to be Json regardless of HTTP request headers


/**
* Throw exception if request is not Json or not POST/PUT
* You don't need to run prepareVars() if you use this line
*/
$this->Json->requireJsonSubmit(); // throw exception if request is not Json or not POST/PUT

$this->Json->set('data', $data); // add a new key called data
$this->Json->set('field_errors', $errors); // replace a key
$this->Json->setMessage('Great'); // shortcut to replace message
$this->Json->setError('Bad input'); // sets error to true and message to 'Bad Input' (can be configured to set error to string 'Bad Input' rather than bool true
$this->Json->redirect(['action' => 'index']); // sets _redirect key to a URL (for javascript client to handle the redirect)
$this->Json->entityErrorVars($user); // change the Json output to error: true, and message: a list of validation errors as a string (e.g. Username: Too long, Email: Incorrect email address)

// UsersController.php
    public function ajaxUpdateUser()
    {
        /*
        Json->requireJsonSubmit() will throw exception if not Json and a Post/Put request and also
        It will also prepare boiler plate variables that can be handled by RequestHandler
                    'error' => false,
                    'field_errors' => [],
                    'message' => '',
                    '_redirect' => false,
                    'content' => null,
        In other words, the action output will be {"error": false, "field_errors": {}, "message": "OK", "_redirect": false, "content": false }
        All of these variables can be overridden in the action if errors do develop or example
        */
        $this->Json->requireJsonSubmit();
        if(!$user = $this->Users->save($this->getRequest()->getData()) {
            // Json->entityErrorVars($entity) will change the Json output to error: true, and message: a list of validation errors as a string (e.g. Username: Too long, Email: Incorrect email address)
            $this->Json->entityErrorVars($user);
        } else {
            // will make the Json output _redirect key into a URL. If you use this, your javascript needs to recognise this (see example javascript)
            $this->Flash->success("Saved");
            $this->Json->redirect(['action' => 'view', $user->id]);
        }
    }

    public ajaxGetUser($user_id) {
        $user = $this->Users->get($user_id);
        $this->Json->forceJson(); // output will be Json. As of this line, the Json output will be the boilerplate output (error: false, message: OK etc.)
        $this->Json->set('data', $user); // the output will now have a data field containing the user object
    }

    public userCard($user_id) {
        $user = $this->Users->get($user_id);
        $this->Json->forceJson(); // output will be Json. As of this line, the Json output will be the boilerplate output (error: false, message: OK etc.)
        $this->set(compact('user')); // for use by the template. don't use $this->Json->set so that the user object does not get send in the output 
        $this->Json->sendContent('element/Users/card'); // the Json output will have a 'content' key containing Html generated by the template
    }

    public otherExamples() {
        // Configuration
        $this->Json->setErrorMessageInErrorKey(true); // (default false)
            // true: if $this->Json->setError('error message') is called, the error key and the message key will contain the error message
            // false:  if $this->Json->setError('error message') is called, the error message will be in the message key and the error key will be true and
        $this->Json->setHttpErrorStatusOnError(true); // (default false)
            // by default, the HTTP response is always 200 even in error situations
        $this->Json->setMessage('Great, all saved'); // shortcut to set the message key
        $this->Json->set('count', 5); // set any other json output keys you want to output
    }