在这种情况下使用异步请求是一种好习惯吗？

Question

I have a scenario that I have a button in JSP page which sends an email, the request is send to servlet asynchronously using jQuery Ajax and JSON, servlet searches in DB, if the user has an email, it returns the email address and sends an email to it, then forwards to the result page with success or fail of sending the email, but in a case that the user doesn't have an email, it returns false values using JSON to JSP and then a JSP form appears to the user to enter his email.

Is it good practice to use Ajax and I know that not each time there's a return value to the user or send request to servlet using get method which return a parameter in a case that the user doesn't have an email?

Answer 1

Using ajax is in practically all cases very good for User Experience . With ajax, the user will experience instant feedback without the need to face an annoying "flash of content" or a (partially) empty page because the whole HTML response needs to be generated/buffered by the server first. This is really a huge plus of using JS/ajax.

Using JSON is generally favorable above XML, HTML or even plain text. But there is no "best practice" with regard to the ajax data exchange format between client and server. Just pick whatever suits the requirement the best. JSON is perfectly fine for this case. jQuery understands it out-the-box and in Java you have choice of a plethora of easy-to-use JSON parsers.

However, when developing an ajax-enabled webapplication, you really need to take into account that the core functionality does not break when the client has JS disabled . This is called Unobtrusive JavaScript . Most of the searchbots, mobile browsers and textbased browsers don't use JS. You should try to use JS only for Progressive Enhancements . To test this yourself, in Firefox you can use for example the Web Developer Toolbar to easily enable/disable JS support. Run your website with JS disabled and observe if the core functionality is maintained as well.

The best way to achieve this is to start developing the website without any single line of JS code, even without a single onclick , onsubmit , onwhatever attribute on the HTML elements. Once you get the core functionality to work, then you can start adding JS in flavor of a script which executes during document ready and attachs functions to the HTML elements of interest (even here, you should not change the original HTML code!). Let the JS functions fire ajax requests on the same URL or maybe a different one, depending on the requirement. You can in the Servlet distinguish between an ajax and normal request as follows:

if ("XMLHttpRequest".equals(request.getHeader("X-Requested-With"))) {
    // Handle ajax request. Return JSON response here.
} else {
    // Handle normal request. Return normal HTML response here (by JSP).
}

See also:

• Simple calculator in JSP - contains unobtrusive JSP/Servlet/jQuery example

Answer 2

Json is just a data-interchange format. Using Json or not has nothing to do with using asynchronous communication or not... You can do both communication types using Json (or XML, or serialized objects, it doesn't matter).

Now, in your problem, it looks like you just want to use Asynchronous communication to improve the user experience (it will not flick the user's browser). If that's the case, Asynchronous communication is the way to go!

Answer 3

I don't think you need ot use AJAX in this. The main idea of the ajax is to render server response without postback and in your case you are redirecting page after you get some kind of result.

In my opinion you shoul choose on of these two ways.

1) Use AJAX, send data to servlet and then render response from server wether the mail is sent or not.

2) Submit your form to servlet and sent email and then redirect to jsp with the success/fail result.

Hope it helps.