I am new to RESTful webservice. Whatever I have read over the internet about RESTful webservice, I came to know that REST works similar to servlet + webservice.
Our traditional webservice looks like JSP-> Servlet -> Service -> DAO -> Database.
Will REST replace Servlet in this heirarchy?
My ultimate goal is that my web application should support mobile application and normal browser also. Is it good idea to use REST in that case. If not, in what situation we should use REST?
I hope my question is clear.
Please help me.
Thanks in advance.
There are many ways we can achieve Machine to Machine communication.
Web services also helps communicating between applications made in different platforms.
For example a .net GUI can call a java server side program for data.
REST is one of that kind, based on HTTP protocol.
SOAP web service is heavy weight (using lots of XML) where as REST is simple and you can expose any of your APIS simply using REST.
A services exposed as REST services can be invoked by a client using on of the HTTP verbs GET, POST, PUT, and DELETE with their meaning same as in HTTP.
RESTful Web Services expose the state of its resources.
An 'Employee' data can be queried and represented in any format (Json, XML ...) using REST.
Rest won't replace the Servlet in your hierarchy, actually the HTTP based REST methods are written on this servlets.
Please go through this URL : http://docs.oracle.com/javaee/6/tutorial/doc/gijqy.html
Using REST is not related to browser experience on mobile or other devices. It totally depends on the client side technology used and your browser compatibility with those technologies.
Using REST is a good idea to access data at client side using simple AJAX calls.
REST means Representational State Transfer. It is a way of thinking about architecting network communication between client and server, with the focus being on transferring a resource from server to client and back again.
To understand the significance of this first consider a different architecture, Remote Procedure Call. This is where the client calls a function on the server as if the function existed on the client.
So you want to edit a photo that exists on the server. Your client is a photo editing app that uses RPC to achieve this. You want to blur the photo so your client calls the blur() function using RPC, and the server blurs the image and sends back the updated image. Then you want to rotate the image, so your client calls the rotate() function and the server rotates the image and sends the rotated image to your client.
You might have noticed two issues. Firstly, every time you carry out an action on the photo the server needs to do some work and send you back the updated image. This uses a lot of bandwidth.
Secondly what happens if tomorrow the server developers (who might be nothing to do with the client developers) decide that rotate() is the wrong function name, it should really be rotate_image(), and they update the server. Your client continues to call rotate() but this now fails because such a function doesn't exist on the client.
REST is an alternative way of thinking about client/server communication. Instead of telling the server to carry out an action on the resource (eg rotate the photo), why doesn't the client not just get a representation of the resource and carry out all the actions it wants to (blur, rotate etc) and then send the new state of the resource back to the server.
If you did it this way the protocol to communicate between client and server can be kept very simple and will require very few updates. All you need is functions for the client to get the resource and functions to put it back on the server. The client will have to know how to blur the image and rotate the image, but it doesn't need to know how to tell the server to do this, it just needs a way of telling the server to save the updated image.
This means that the developers of the client can work away implementing new features independently to the developers of the server. Very handy if the developers of the client are nothing to do with the server (the developers of Firefox have nothing to do with the New York Times website and vice versa)
HTTP is one such protocol that follows this architecture pattern and it allows the web to grow as it has. There are a small set of verbs (functions) in HTTP and they are concerned only with transferring a representation of the resource back and forth between client and server.
Using HTTP your photo client simply sends a GET message to the server to get the photo. The client can then do everything it wants to to the photo. When it is finished it sends the PUT message with the updated photo to the server.
Because there are not domain specific actions in the protocol (blur, rotate, resize) this protocol can also be used for any number of resources. HTTP doesn't care if the resource is a HTML document, a WAV file, a Javascript script, a PNG image. The client obviously cares because it needs to understand the resource it gets, and the server might care as well. But the protocol between the client and server doesn't need to care. The only thing HTTP knows is that there is a variable Content-Type in the HTTP header where the server can tell the client what type of resource this is.
This is powerful because it means you can update your client independently to updating your server without updating the transfer protocol. HTTP hasn't been updated in years. HTML on the other hand is updated constantly, and web servers and web browser are updated constantly (Chrome is on version 33). These updates can happen independently to each other because HTTP never (rarely) changes.
A web browser from 10 years ago can still communicate with a modern web server over HTTP to get a resource. The browser might not understand the resource, say it gets a WebM video that it can't understand, but it can still get this resource without the network communication failing.
Contrast that with the example of RPC above where the client server communication will break if the server changes rotate() to rotate_image(). Every single client will have to be updated with this new function or they will crash when trying to talk to the server.
So REST is a way of thinking about client server communication, it is an architecture design/pattern. HTTP is a protocol that works under this way of thinking that focuses on simply transferring state of a resource between server and client.
Now it is important to understand that historically a lot of people, including web developers, didn't get this. So you got things like developers putting verbs into resource names to try and simulate Remote Procedure Call over HTTP. Things like
GET http://www.mywebsite.com/image/blur_image
And they would hard code the URI /image/blur_image into their client and then try and make sure the guys developing the server never changed the URI blur_image. You get back to all problems of RPC. As soon as the server guys move the resource blur_image (which is not really a resource to start with) to /image/blur_my_image the client falls over because it has that hard coded as an action to perform, rather than simply getting /image and doing what ever it wants to it.
So there are lot of examples on the web of doing REST wrong. Anything that tightly couples client and server communication is doing REST wrong. Your client should be able to survive URIs changing, or Content-Types being updated, without falling over. It can complain it doesn't understand a resource (eg Netscape Navigator 2.0 complaining it has no idea what a HTML5 document is), but it should complain that a URI has changed. This is the discoverability aspect of REST, which I haven't gone into too much, but basically your client should be able to start at the root of the server http://www.mywebsite.com and if it understand the content types it should be able to continue on to the resource it wants. You should never need to hard code a URI into your client other than the root of the server.
I could write a book about this stuff (and many have), but I hope that serves as a good introduction about what REST actually is.
#javafan I just checked the mykong example you provided. Please note that that is not standard http servlet implementation, it is a Jersy way of implimentinmg rest. So when you map all your URIs goes through this servlet com.sun.jersey.spi.container.servlet.ServletContainer and you write classes with annotation #path etc the Jersy runtime environment will do the necessary processing for you like converting the input and output objects to necessary formats (json, xml etc) depending on your configuration. You can write a simple servlet and add methods in it with #path annotation in it and that will be invoked inturn when you make the corresponding request. but the doGet and doPost methods are standard servlet methods that processes GET and POST method by default. You can ad another methods to the same servlet and add more qualifiers to process your request.
#GET, #Produces("xml") etc.
I hope this helps.
Related
I will be happy to get advice from more experienced developers about adding Web Sockets into my HTTP-based project.
That’s the thing. I have developed the REST API based service. Everything works well enough, but… In some special cases my server needs a long time to serve client requests. It may be from 1 minute to several hours (and even days)! I implement some not-so-good algorithm to address this issue:
Client sends HTTP request
Server replies about registering request
Client starts sending HTTP requests to get necessary data (if response does not have needed information the client sends another request and so on)
That is all in a nutshell.
And it seems to be a bad scenario and I am trying to integrate web sockets for adding duplex-channels in this architecture. I hope that my API will be able to send info about updated data as soon as possible without the necessity of many requests from the client.
But I am a bit confused in choosing one of two ways to use web socket (WS).
Variant A.
The server only tells the client via WS that data is ready. And the client gets data by standard request-response HTTP method from REST API.
Variant B.
The server sends all data to the client via WS without HTTP at all.
What variant is more suitable? Or maybe some other variants?
I do not want to remove HTTP at all. I just try to implement WS for a particular kind of end-points.
Variant A would be more suitable and easy to implement. You can send message to the client after the data is ready, and he can then send request for the data. It will be like a simple chat websocket, and will serve your purpose.
I have a website that is that is architected using an n-layer approach. The problem I have is that I need the client to make a call to the application layer, one of the other layers will then make a call to another web service somewhere in the world. The other web service could take some time to come back so what I would like to do, if possible, something along the lines of the following using async requests:
The client is HTML & JavaScript, the server layers are written in C# (.NET 4.5), the 3rd party web services are just web services I need to consume
How would you go about writing this?
Any help will be much appreciated
It doesn't look like the server-side code needs to call the external service asynchronously. I'm not seeing an advantage in doing that.
The client-side code would call the server-side code asynchronously, of course. (An AJAX request, using jQuery for example.) And it would await the response form that service in an asynchronous manner before handling that response. But since the server-side code in this request is only serving that one request, it can do so synchronously.
Indeed, if the server-side code were itself also asynchronous then it would return control to the client-side code immediately before it has anything useful to give it. Which means the client-side asynchronous handler can't do anything. Instead, when the server-side code gets a response from the external service, it would need to push that response to the client-side code. Which is possible with websockets and whatnot, but probably a lot more complex than this situation requires.
Only the first link in the chain needs to be asynchronous in order to provide the user experience of asynchronicity, the rest of the system doesn't need to be.
Whenever you have a "client/server" boundary, you have the option of making the server asynchronous as well as the option of making the client asynchronous. Those decisions are independent.
I'll make the assumption that your third-party webservice is scalable, or that your server has other things to do besides just this one request. In that case, I'd recommend that your server be asynchronous.
Asynchronous programming is natural with async/await in ASP.NET 4.5. Depending on your third-party service, you may want to use HttpClient or the async-compatible WCF or webservice proxies. Both ASP.NET MVC and WebAPI support asynchronous calls for your service.
On the client side, you have no choice; JavaScript in the browser must be asynchronous.
I am not sure if this is the correct place to ask but since there are a lot of questions of this kind i ll go ahead and ask.
A year ago i developed an iOS application that was connecting to a server with HTTP requests exchanging JSON files etc. I was told at that time that the server was a web (REST) service. I didnt care much since for me was just a black box.
The last months i am developing a hybrid mobile application where i use native code + jquery mobile for the front end part and php + mysql for the back end part. The application is about registering new users to the data base , having users to subscribe in various kinds of events , get notifications on them etc. So for all the communication between the front ent(client) and back end(server) i make http requests(POST) , ajax calls using json files.
Is this a RESTfull Web Service? I am a bit confused on the definition of REST. According to wikipedia REST is :
REST-style architectures conventionally consist of clients and servers. Clients initiate requests to servers; servers process requests and return appropriate responses.
So is what i am building a Restfull Web Service? Also do we call Rest only the server part or in general the client-server architecture?
Is it just a web Service? And if yes what kind of web service?
there is no difference when you invoke a controller (aka web service) from browser through http or from a client code (java, .NET or any language). when you want to invoke a service from outside world from your code.. you have choice of soap or rest .. soap is protocol, where as REST is an architecture style.. so REST is methodology of calling a service (which is simple http POST or GET call) from outside world .. not necessarily from a browser .. it may from client code which acts as browser to get response from outside world service..this is based on my experience..
I feel the term "webserver communication" is not right when it comes to just accessing an server to retrieve information.
Example:
iPhone connects to http://foobar.foo/bar.php?foo=bar&bar=foo and receives an XML. XML is parsed on the iPhone.
iPhone connects to some server and sends some instructions + data to store some stuff there. Lets say XML-RPC or something like that. Server processes that stuff, saves it and sends a response like "OK".
You get it...iPhone talks to server, server talks to iPhone. For me, Webservice and Webserver is the same thing, both are called with an URL and both respond something.
So waht's the correct term when I wanted to mention this sort of thing when talking to a computer scientist (studied)?
"Webservice communcation"?
"Webserver communication"?
"Call"? ... i mean... yeah you know what I mean. I hope so ;)
note:
1) my english is bad
2) never studied cs
That would be a Web Service Call.
A Web Service is a Service (that serves data) and it runs on a Web Server (the actual hardware running the software).
Well I don't know any better way to describe it as a Web Service...
What you have described is a classic case of a 'Web Service'... Just because you don't like calling a sheep a sheep doesn't stop it from being a sheep.
Also imho a web service is very different to a web server.
I think any of these would be fine:
Web request (if it's HTTP, FTP, other "web protocol")
Network call/request (more generic)
HTTP request (if you want to be specific about HTTP)
Web service call (web services are associated with SOAP/XML a lot of times, but the term applies to any web-base service call)
For generic cases, I usually use transmit or receive when I need to be more specific than saying communicate.
The term you are looking for is HTTP request.
The specific technique you are using (javascript/xml through the browser) is called AJAX.
I've heard/used:
Web Services (generically)
XML over HTTP (based on your specific description)
Other paradigms pertain to implementation of Web Services using specific technologies/protocols such as:
SOAP
XML-RPC
REST
What you've described here may actually be one of these specific technologies, but there's not enough information to determine this based on your post.
I'm looking to add a web services interface to an existing server application. The set of services to expose is not known at compile time and can change over the runtime life of the server.
From a tech standpoint all the server/web services endpoints will be on Windows.
In our server app a user will have the option to register workflows as 'web services callable'. This will create the WSDL defining this particular workflow service.
For the calling endpoint I'm thinking of an HttpModule that accepts the inbound web service request, unpacks the request and converts the XML data types into our server applications "domain", calls the server and finally converts the server outputs back into XML for return down the http connection.
Does that make sense?
Critical comments welcomed.
In effect writing your own WS engine. Clearly doable, but quite a bit of work to get right from scratch. I guess if you find some open source implementation, then adapting it should be possible.
A rather dirtier alternative, but one I've seen applied in another context, is to go for a simgle WS interface
String call( String workkFlowName, String payload)
The payload and response are both Strings containing any XML. So the caller needs to undestand the schemas for those XMLs. From the client's perspective the amount of coding effort is not much different. Your coding effort would I think be significantly redcued.
an HttpModule that accepts the inbound
web service request, unpacks the
request and converts the XML data
types into our server applications
"domain", calls the server and finally
converts the server outputs back into
XML for return down the http
connection.
That is what all web service frameworks do (e.g. Metro, Axis). So I can't see your problem. What's your concern with this approach?
The downside for the client is that, as far as I understand it, availability of your services may change over time. So you should consider a way to inform the client if the service is available (other than getting a time out error because it is not there), e.g. WS-ResourceLifetime or UUDI.
I ended up creating a C# class that implements the IHttpHandler interface. The implementation serves up the WSDL of the services exposed from our app and accepts SOAP posts to invoke the services. In the end most of the work went on converting SOAP types to our types and vice versa.