I have been working on a mobile app that sends an ajax call to the server and waits for a response from the server in json format.
I am wondering from the server side, how to respond to an ajax call? Could someone give me an example in code?
I check the server code of my project (written by other members of the team) and could not understand it. I can only see it is written in java and also some keywords such as apache, springframework, etc pop up. I am a total newbie for server side programming and I want to learn more about it. Could someone give me some tips on how to get started with those as well? How does a server work? Is it just like responding to various request? What language could you use to build it and what is Apache? I know this looks like a lot of questions so probably I need to get some basic knowledge first. Any help/tips/suggestions on readings is appreciated.
This is kind of a broad question, as there are a lot of different server-side technologies that can handle server side AJAX requests, but if you want to go the Java route, using Spring Framework makes it very easy.
Spring Framework is a large open-source Enterprise Java framework that has a variety of features which entire books rarely even cover.
(Apache is an open-source project that contains over a hundred different sub-projects, the most popular being a web server.)
Spring does have some specific tools to handle REST calls. Assuming your AJAX is making a REST call (which is what it sounds like), and your project is already using Spring framework, it is fairly straightforward (assuming you already know Java). The Spring framework handles all the hard stuff for you. There are a few different ways to do this using Spring, but check out this link for creating a simple REST service:
https://spring.io/guides/gs/rest-service/
Another route would be to look into PHP, which is a server-side scripting language. With PHP, you can handle AJAX requests without the need for an application server (most basic web servers speak PHP). There are plenty of good resources for this, but one of my favorites is http://www.tutorialspoint.com/php/
BTW - the TutorialsPoint site is great for Java and Spring as well
Related
Let's say I wanted to create a collaborative web application where users can simultaneously work on e.g. a diagram. I have my interactive web site (HTML/CSS/JavaScript) on the client side, and let's say a Java application synchronizing a centralized model on the server side. How would client and server exchange messages? To get a better idea of how the system is supposed to work like, here are some details and a small illustration:
Requirements
The underlaying technology should support authorized communication to show/hide sensitive information.
The model of the diagram should only exist on the server (centralized model, no copies), whereby changes should be broadcasted to other users (other browsers who are currently editing the same document).
After receiving changes to the model, the server shall perform computationally higher demanding tasks such as consistency checks and inform the user if e.g. an action is invalid.
Constraints
The system must not poll or set flags (it should be a direct communication).
The website must not be reloaded during use.
Software running on the client must be restricted to JavaScript.
Technology I've found
Here are some of the solutions I've looked at, ranked from (imho) most suitable to least, whereby I'm not sure if the list is even complete and all my assumptions are correct.
Java Web Service using javax.jws - The service would offer an API described by WSDL and be capable of responding with SOAP messages using the HTTP protocol, but can JavaScript process these messages?
Servlets & Java Server Pages (JSPs) - Would, as far as I know, require a page reload to fetch new content (isn't this pretty much the same as PHP? Both are executed on the server to generate HTML pages..)
I've already found this question which, however, does not provide concrete technologies in the answer. Thank you for any hints and clarification, I dearly appreciate it!
As you have already found out, there are many approaches to this common problem.
SOAP (sometimes called "Web Services" or "WS*") is a standard that was developed for application to application communication. It's strengths are precise specifications (and therefore many good libraries), interface sharing for client and server (through WSDL), and discoverability.
However, SOAP has very limited -if any- support in Browsers.
The most common modern approach is probably RESTful web services based on XML or JSON. When used in a browser as client, JSON is preferred, as the unmarshalling is trivial in JavaScript. Many frameworks and libraries like Angular and jQuery take on the tedious cross-browser AJAX request crafting. Some boilerplate is required to wrap the data in HTML, however. This downside can also be an upside if you consider the cleaner architecture and maintainability.
Since you're using Java on your server, you might also want to look into JSFs AJAX capabilities. It doesn't really use REST (no well-defined resources), but loads server-side rendered chunks of your HTML page asynchronously (read: AJAX) and re-renders them in the DOM. This can be seen as a compromise between real REST and full page reloading. The good side of it is you don't have to define any resources but your backing beans. The downsides are: possible overhead, since you're downloading HTML instead of pure data; and bad testability since you cannot access the rendered chunks outside the JSF context.
Wholly different issues are 1. the synchronization of concurrent requests and 2. communication with clients from server. For the latter you can either look into Web Sockets (the next big thing) or the good-old polling.
If concurrent edits of the same data are a concern to you, you'll have to implement a sort of strategy to tell whether edits can be merged or whether one has to be declined. The client will need to handle such situations and offer the user reviewing, overriding or reverting etc.
EDIT: more on Java servlets and JSP
Servlets are nothing but Java classes that handle specific HTTP requests, usually bound to certain URL paths. They're comparable to PHP pages: In PHP the web server gets a request and searches for a corresponding PHP file. Then it parses the PHP script and returns the response. Servlets do the same, only the syntax is very different. JSP is mostly a try at bringing more PHP-ish syntax to Java. Behind the curtains, they're rendered to pure Java servlets.
Java servlets have a long history which is older than AJAX, but many frameworks have taken on the challenge of implementing flexible resource handling on the server. Most notably Jersey and RESTEasy, which are implementations of the Java EE standard JAX-RS; and Spring, which is a request-based framework that competes well against Java EE standards. Then there is also JSF, which is sometimes called a successor of JSP. To the user it's little different than JSP, but the syntax is nicer and IMHO it is more feature-rich than JSP. Especially considering extensions like PrimeFaces. In contrast to JSP, JSF embraces AJAX and many built-in components are capable of communicating with the server using AJAX, including calling Java functions and re-rendering parts of the page.
I would recommend you try websockets since connections will be persistent between clients and server and any of them can send a message at any time.
You could implement a websocket server in Java on the server and use Javascript's built in websockets functionallity on the clients.
Take a look at https://www.websocket.org/ to learn more about websockets.
Consider a ClojureScript web application using reagent where the reagent components are subscribed to a single db atom containing a vector of maps. The contents of this vector is different for each user and has to be queried from a mongo database ( which is updated with regular intervals ). The database might be hosted by a third party. Considering that CongoMongo, Karras and Monger are Clojure ( not ClojureScript ) libraries what would be the best way to connect to MongoDB from a single page ClojureScript/React.js using Ajax?
This “answer” is more of a comment but here goes.
If you don't absolutely need a Clojure backend, I'd recommend having a ClojureScript-only single-page app without any Clojure wrapper to Mongo (so no need for Sente either). As Timothy Baldridge (of Cognitect, so he knows a thing or two about this 😛) pointed out, your ClojureScript app can just make HTTP REST requests to the database.
cljs-http is a ClojureScript project that uses Clojure's core.async library to make HTTP requests and is perfect for interacting with REST APIs if you know or can learn core.async.
A more conventional (i.e., callbacks) approach, but still very ClojureScript-friendly, is to use Google Closure's goog.net.XhrIo library. I have an example here of connecting to a public REST API using XhrIo and re-frame (built on top of reagent, and highly recommended) that may help show how to get started.
Using either of these ClojureScript/JS libs, you can make requests directly from the ClojureScript browser app to the database, get replies, parse the JSON with (js->clj (js/JSON.parse json-string)) or with transit-cljs, and do something with the result.
Since Mongo has a fairly simple REST interface (https://docs.mongodb.org/ecosystem/tools/http-interfaces/#simple-rest-api), I'd be tempted to just write my own CLJS code that calls the Mongo server. Depends on your security requirements. But writing the CLJS code would be no different than any other remote request. Just a bit of string concatenation and parameter serialization.
You could use sente to get communication going between the Reagent application and your web server. This SO answer references an example client/server application that consists of a web server with browser access, giving you some buttons to press that return information from the server. It is not Reagent - but you can substitute what they use. It is a starting point example that works out of the box.
Then build up the example's web server so that it communicates with the three Clojure libraries rather than just returning static text as it does.
My first post.
I have experience of basic java servlet and jsp and have got my webpage implemented in tomcat7.
Regarding Websocket, I am finding difficult to build understanding of how to implement it, i want to use tomcat8 implementation of websocket api and uplift my webpage (jsp, java, jquery, tomcat7) to use the websocket features, have not been able to find the the tutorial that can guide me through, something like hello world example. any pointers (sample codes, tutorials)?
have tried to understand tomcat8 examples but not understanding them at all
You need to understand that you don't just "add" WebSocket to an existing web application.. to make it faster, better, cheaper, more scalable, etc. Instead, you have to completely re-architect the web-layer of the application to take advantage of its capabilities.
I suggest that you first read a lot about WebSocket and what the whole idea is before you try to write any code, using Tomcat or any other WebSocket-capable server.
Nick Williams has a forthcoming book that appears to cover everything in the web application world, and as I understand it, will have a great deal of information about WebSocket-based code. You will unfortunately have to wait until March 2013 (at least) to use that particular book.
I'm sure there are similar books available, or even online tutorials to help get you started using WebSocket. Just be aware that switching to WebSocket isn't some simple configuration option: it's a very disruptive change to any existing web application.
I'm a CS student trying to do some side projects during this summer. One of my aims to is create a chat app which will be ultimately hosted on GAE. I am new to web development so I'm trying to shoot around in the dark hoping to hit the target but I guess it will be a major waste of my time. The rationale for using servlets and JSP is that GAE requires Java for the backend. I hope to use AJAX to do the front-end.
However it is hard for me to put all the technologies together to make it work. I am having trouble with the design. I don't need any codes, but rather help with the design patterns.
I am confused with how GAE works. Since GAE requires Java/PHP/Python etc, is it possible to deploy the client coded in AJAX using GAE? Do I require two GAEs, one for the client and one for the server which is coded in Java?
I am also quite lost with how to connect the AJAX technologies with the Servlet & JSP technologies. I'd appreciate it very much if you guys can provide a step by step instruction on the design pattern. Links to online tutorials will be very much appreciated. My style is to learn as I go.
Ultimately, my aim is to get an chat app (very simple one where all users can see each other messages) up and running on GAE to get a feel of the whole web development process (code, run, deploy).
Just a side note, I don't know any PHP/MySQL (but will learn later if I get the whole web dev thingy down to include database features).
Thank you all.
There's a LOT of stuff available out there to read if you just search for Google App Engine. Start with the documentation and work through the tutorials. It's not a waste of your time to learn, since you don't already understand it.
Google App Engine is essentially a distributed web server + database. AJAX on App Engine is no different from AJAX anywhere else - the server serves HTML+Javascript which runs on a web browser, and communicates back to the server.
I would like to create a web page which would allow multiple users to work together on a page, Imagine a web based editor that allowed to users to change the documents as an example of this type of feature.
How would more experienced programmers go about implementing this as i really cant seem to formulate any way to even begin going about this task. Would there be any programming librarys that make implementing this feature easier or is it just too complex to even think about?
I am creating this webapp primarily using GWT and SmartGWT if that helps.
Thanks for any input you may have.
There is indeed a cometd-like library for gwt - http://code.google.com/p/gwteventservice/
Wiki:
In web development, Comet is a neologism to describe a web application model in which a long-held HTTP request allows a web server to push data to a browser, without the browser explicitly requesting it. Comet is an umbrella term for multiple techniques for achieving this interaction. All these methods rely on features included by default in browsers, such as JavaScript, rather than on non-default plugins.
In practice:
In normal way client can receive resources by request->responce. It is no possible to send data directly to client without request. With comet you can hold realtime connection between client and server and exchange data in realtime.
Check out: docs.google.com. They are using comet.
Etherpad.com is a service that used to do this. It has been since bought by Google, and the code released as open-source. You can see several links on the etherpad.com page for the source download and related information.