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I've very little experience with webservices and am now faced with a tricky issue. A supplier to my organisation has exposed some of its data via a REST service(https calls following an initial https call to retrieve a token which expires following n calls or n minutes).
Most reporting in the organisation is done using SQL Reporting Services and I've been asked for help bridging the gap between SSRS and REST. The organisation may also want to use SSIS to retrieve some of the data.
I don't believe I can call the REST service easily from either of these technologies so I was thinking of wrapping the calls to the REST service in a .NET SOAP webservice, which I believe SSRS will be able to cope with.
Architecturally this seems wrong, and I'm sure there are some pitfalls waiting for me, but does this sound like an appopriate solution? (As an alternative I believe I could also write a custom data provider for SSRS but I'd then hit the same issues when I came to use SSIS)
Many Thanks,
Andrew
so I was thinking of wrapping the calls to the REST service in a .NET SOAP webservice
...
Architecturally this seems wrong, and I'm sure there are some pitfalls
waiting for me, but does this sound like an appopriate solution?
there is no problem at all.. there is no architectural restriction which forbids access to one kind of web service from another.. you may implement it in various way and if you do not feel comfortable with performing HTTP request directly from SOAP method implementation, you can wrap REST web service communication in a Proxy object and hide details from SOAP method.
I have been reading about REST and SOAP, and understand why implementing REST can be beneficial over using a SOAP protocol. However, I still don't understand why there isn't the "WSDL" equivalent in the REST world. I have seen posts saying there is "no need" for the WSDL or that it would be redundant In the REST world, but I don't understand why. Isn't it always useful to programmatically bind to a definition and create proxy classes instead of manually coding? I don't mean to get into a philosophical debate, just looking for the reason there is no WSDL in REST, or why it is not needed. Thanks.
The Web Application Description Language (WADL) is basically the equivalent to WSDL for RESTful services but there's been an ongoing controversy whether something like this is needed at all.
Joe Gregorio has written a nice article about that topic which is worth a read.
WSDL describes service endpoints. REST clients should not be coupled to server endpoints (i.e. should not be aware of in URLs in advance). REST clients are coupled on the media-types that are transfered between the client and server.
It may make sense to auto generate classes on the client to wrap around the returned media-types. However, as soon as you start to create proxy classes around the service interactions you start to obscure the HTTP interactions and risk degenerating back towards a RPC model.
RSDL aims to turn rest like a hypermedia, in other words, it has more information than a service descriptor like WSDL or WADL. For example, it has the information about navigation, like hypertext and hyperlinks.
For example, given a current resource, you have a set os links to another resources related.
However, i didn't find Rest Clients that supports this format or Rest Server Solutions with a feature to auto generate it.
I think there is a long way for a conclusion about it. See the HTML long story and W3C vs Browsers lol.
For more details about Rest like Hypermedia look it: http://en.wikipedia.org/wiki/HATEOAS
Note : Roy Fielding has been criticizing these tendencies in Rest Apis without the hypermidia approach: http://roy.gbiv.com/untangled/2008/rest-apis-must-be-hypertext-driven
My Conclusion : Now a Days, WADL is more common that Rest and Integration Frameworks like Camel CXF already supports WADL ( generate and consume ), because it is similar to WSDL, therefore most easy to understand in this migration process ( SOAP to REST ).
Let's see the next chapters ;)
Isn't it always useful to programmatically bind to a definition and
create proxy classes instead of manually coding?
Agree wholeheartedly, this is why I use Swagger.io
Swagger is a powerful open source framework backed by a large
ecosystem of tools that helps you design, build, document, and consume
your RESTful APIs.
So basically I use Swagger to describe my models, endpoints, etc, and then I use other tools like swagger-codegen to generate the proxy classes instead of manually coding it.
See also: RAML
There is an RSDL (restful service description language) which is equivalent to WSDL. The URL below describes its practice http://en.wikipedia.org/wiki/HATEOAS and http://en.wikipedia.org/wiki/RSDL.
The problem is that we have lots of tool to generate code from wsdl to java, or reverse.
But I didn't find any tool to generate code from RSDL.
WSDL is extensible to allow description of endpoints and their messages regardless of what message formats or network protocols are used to communicate
However, REST uses the network protocol by using HTTP verbs and the URI to represent an objects state.
WSDLs tell you at this place, if you send this message, you'll perform this action and get this format back as a result.
In REST, if I wanted to create a new profile I would use the verb POST with a JSON body or http server variables describing my profile to the URL /profile
POST should return a server-side generated ID, using the status code 201 CREATED and the header Location: *new_profile_id* (for example 12345)
I can then perform updates changing the state of /profile/12345 using the HTTP verb POST, say to change my email addresss or phone number. Obviously changing the state of the remote object.
GET would return the current status of the /profile/12345
PUT is usually used for client-side generated ID
DELETE, obvious
HEAD, gets the status without returning the body.
With REST it should be self-documenting through a well designed API and thus easier to use.
This is a great article on REST. It really help me understand it too.
WSDL 2.0 specification has added support for REST web services too. Best of both worlds scenario. Problem is WSDL 2.0 is not widely supported by most tools out there yet. WSDL 2.0 is W3C recommended, WSDL1.1 is not W3C recommended but widely supported by tools and developers.
Ref:
http://www.ibm.com/developerworks/library/ws-restwsdl/
The Web Application Description Language (WADL) is an XML vocabulary used to describe RESTful web services.
As with WSDL, a generic client can load a WADL file and be immediately equipped to access the full functionality of the corresponding web service.
Since RESTful services have simpler interfaces, WADL is not nearly as necessary to these services as WSDL is to RPC-style SOAP services.
To describe RESTful we can say that every resource has its own URI. Using HTTP GET, POST, PUT and DELETE, we can operate on these resources. All resources are representational. Whoever wants to use our resources can do so via a browser or REST client.
That's the main idea of a RESTful architecture. This architecture allows services on the internet. So why does this architecture need WADL? What does WADL offer that standard HTTP does not? Why does WADL need to exist?
The purpose of WADL is to define a contract. Contract specifies how one party can call another.
When you create a web application from scratch, you don't need contract and WADL.
When you integrate your system with the other system and you can communicate clearly with their development team, you don't need contract and WADL (because you can make a phone call to make things clear).
However when you integrate a complex enterprise system with several others complex enterprise systems maintained by several different companies (or federal institutions), then believe me you want to have a communication contract defined as strictly as possible. Then you need WADL or Open Specification. Need it badly.
People with weak enterprise background tend to see entire IT as a collection of separated web applications developed independently. But enterprise reality is sometimes tough. Sometimes you can't even call or write to the people developing the application you have to integrate with. Sometimes you communicate with a legacy application that is no longer maintained--it just runs and you need to figure out how to communicate with it properly. In such conditions you need a contract because it saves your ass.
Actually client generation is the minor feature of the contract definition. It's just a toy. Contract enforces bad communicators to communicate integration rules clearly. This is the main reason to use WADL or Open Specification or whatever.
Using WADL implies that you just might be gracious enough to actually define the data / documents you are passing back and forth. Say you are passing some XML fragments, they might actually be part of a defined schema.
Whether or not you use the DL to generate code is not very important to me. What matters, in my subjective opinion, is that it is important to have a formal agreement on interfaces between business partners. Even if what is passed is obvious, it helps to identify who has to fix what later if somebody changes the previous interface.
Data format is just as much a part of an interface as verb names.
WADL appeals to people coming from the SOAP world where it is common to use a code generator to create client side code based on the WSDL. I don't think that mechanism is useful in REST as it creates client code that is coupled to server endpoints.
I believe that if you properly define your media-types and use hypermedia within those media-types, then it is not necessary to have WADL. The description of the available end-points is contained within the media-type definitions themselves. And if you are now saying to yourself, but application/xml doesn't contain any information about available hyperlinks, then I say BINGO. That's why I don't think application/xml and application/json are appropriate media-types for REST. I'm not saying don't use XML or JSON, just don't use the generic media type name.
The other appeal of WADL is for the purpose of documenting REST services. Unfortunately, it leads developers down the wrong path as WADL attempts to document server-side end points. Documenting a REST services should focus primarily on the media-types. A client developer should be able to write a REST client without knowing any url other than the root url.
WADL allows you to generate code, tests and documentation. Actually there are few very useful tools utilizing WADL, you can see some examples here. The problem with the "pure" REST, as described in Fielding's dissertation, is writing clients supporting Hypermedia (imagine writing Java Swing-based client application for example). With WADL this task is completely automated, and it's a huge advantage in my view. Testing becomes a way easier too.
Before I give my explanation, let me say that most pure REST extremists will deride it to the ends of the earth. I don't agree with them, as i'd rather get something done, but just so you know.
WADL is a description of a web service API, a little like WSDL is for SOAP type web services, that is designed to be more in tune with RESTful interfaces (something WSDL is poor at).
It's primary usage in my experience is to allow you to generate client code that can call the service (handy if it's a very large API, which literally saves hours of work). It also serves the purpose of documenting a REST-like interface.
REST specifies nothing about WADL.
When you want to expose the REST services ,the best way is to generate WADL and share with consumer(similar to WSDL in SOAP based web services).WADL is used to describe service all in on place.
WADL is not necessary to use. But, If you are working with complex existing application and you want to implement REST service call by replacing the EJB/SOAP service call, Then it is very safe and good practice that you use WADL. By using WADL generate client side java stubs you will be in sync with the service.
You can generate client side java stub using WADL file with help of wadl2java maven plugin.
I'm trying to get a handle on web services and was wondering if I get some help from the SO community. In particular, a I'm trying to get a handle on WSDL, UDDI, SOAP AND JAX-P, because I'm most familiar with Java.
Edit:
Please tell me if I'm right or wrong on these definitions:
WSDL: This is a schema to describe what kind of XML documents can be passed to and from the WS.
UDDI: This is the most confusing to me ATM and don't really have a good def.
SOAP: Basic protocol used.
JAX-p: This is used for parsing the XML documents.
As an alternative to the SOAP path you might also want to consider looking into REST-based (or RESTful) web services, for Java in particular JAX-RS: The Java API for RESTful Web Services.
That's a very broad question. At a high level, SOAP refers to the XML protocol of the messages that travel back and forth. WSDL is another XML protocol that defines the format of the SOAP messages (very useful for tools that translate SOAP requests and responses for you). Typically a SOAP service endpoint will also have a way to access the static WSDL document about that service (e.g. if a service is hosted at http://myservice.com/services/MyService, the WSDL will usually be served from http://myservice.com/services/MyService?WSDL in most implementations). UDDI is yet another XML protocol that describes queries to a registry asking for information about SOAP services stored there.
Learn SOAP and WSDL first. UDDI is not all that widely used (although getting more so slowly). JAXR is the Java API around UDDI, which means that you probably should never need to write a raw UDDI query yourself.
JAXP is just a Java XML parser API. It can be used for lots of things, not just SOAP and WSDL. Apache Axis is a good Java SOAP client tool, and wsdl4j is a good WSDL parsing tool, although Axis will also autogenerate SOAP requests and responses from Java objects for you by parsing WSDL. Optimally, you should never need to parse a WSDL document yourself, but you often have to in practice when the tool doesn't quite do what you want.
If you want a practical introduction, do the Spring Web Services tutorial: http://static.springframework.org/spring-ws/sites/1.5/reference/html/tutorial.html
Web Services messages are defined according to the WSDL schema. Some parts will define where the message is supposed to go, and some parts will define the message contents.
Good Thomas Erl introduction to whats in the WSDL
They can be embedded in SOAP messages for transmission.
UDDI is like a look up directory to find web services you might use / consume. If you're trying to tie two specific systems together as opposed to broadcast the offering of some services, its probably irrelevant to you.
In Java, you can use a web services containers like Apache Axis to comprise your web services. JaxP could be used to parse XML documents for transmission etc.
You should read some overviews from the web and then post some more specific questions :-) Maybe if you described what you were trying to achieve, some readers would have experience with similar requirements.
I mean, really, what is the point of SOAP?
Web services have been around for a while, and for a while it seemed that the terms 'SOAP' and 'Web service' were largely interchangeable. However SOAP always seemed unwieldy and massively overcomplicated to me.
Then REST came along, and suddenly web services made sense.
As Joel Spolsky says, give a programmer a REST URL, and they can start playing with the service right away, figuring it out.
SOAP is obfuscated behind WSDLs and massively verbose XML, and despite being web based, you can't do anything as simple as access a SOAP service with a web browser.
So the essence of my question is:
Are there any good reasons to ever choose SOAP over REST?
Are you working with SOAP now? Would it be better if the interface was REST?
Am I wrong?
As Joel Spolsky says, give a programmer a REST URL, and they can start playing with the service right away, figuring it out.
Whereas if the service had a well specified, machine readable contract, then the programmer wouldn't have to waste any time figuring it out.
(not that WSDL/SOAP is necessarily an example of good implementation of a well specified contract, but that was the point of WSDL)
Originally, SOAP was a simple protocol which allowed you to add a header to a message, and had a standardized mapping of object instances to XML structures. Putting the handling metadata in the message simplified the client code, and meant you could very simply persist and queue messages.
I never needed the header processing details when I built SOAP services back in 2001. This was pre-WSDL, and it was then normal to use GET for getting information and queries (no different to most applications which claim to be REST; REST has more in terms of using hyperlinks for service discovery) and POST with a SOAP payload to perform actions. Those actions which created resources would return the URL of the created resource to the client, and the client could then GET the resource. I think it's the fact that WSDL made it easy to think only in terms of RPC rather than actions which create resources which made SOAP lose the plot.
The way I see it, SOAP might be more "flexible", but as a result it's just way too complicated (you mentioned the WSDL, which is always a stumbling block to me personally).
I get REST. It's simple. The only downside I might see is that you are limiting yourself to those 4 basic actions against a single resource, which might not exactly fit the way you view your data.
The topic is well-discussed in Why is soap considered to be thick.
While doing some research to understand some of the answers here (especially John Saunders') I found this post http://harmful.cat-v.org/software/xml/soap/simple
SOAP is more insane than I thought...
The point of WSDL was auto-discovery. The idea was that you wouldn't have to write client code, it would be auto-generated.
BTW. next step beyond WSDL are Semantic Web Services.
If you don't need the features of the WS-* series of protocols; if you don't need self-describing services; if your service cannot be completely described as resources, as defined by the HTTP protocol; if you don't like having to author XML for every interaction with the service, and parse it afterwards; then you need SOAP.
Otherwise, sure, use REST.
There's been some question about the value of a self-describing service. My imagination fails me when it comes to imagining how anyone could fail to understand this. That's on me. Still, I have to think that anyone who has ever used a service much more complicated than "Hello, world" would know why it is valuable to have someone else write the code that accepts parameters, creates the XML to send to the service, sends it, receives the response, then turns that back into objects.
Now, I suppose this might not be necessary when using a RESTful service; at least not with a RESTful service that does not process complex objects. Even with a relatively simple service like http://www.earthtools.org/webservices.htm (which I've used as an example of calling a RESTful service), one benefits from understanding the structure of the returned data. Even the above service provides an XML Schema - it unfortunately doesn't describe the entire response. Given that schema one still has to manually process the XML, or else use a tool to produce serializable classes from the schema.
All of this happens for you when the service is described in a WSDL, and you use a tool like "Add Service Reference" in Visual Studio, or the svcutil.exe program, or I-forget-what-the-command-is-in-Eclipse.
If you want examples, start with the EarthTools services, and go on to any other services with more complicated messaging.
BTW, another thing that requires self-description is description of the messaging patterns and protocols supported by the service. Perhaps that's not required when the only choices are HTTP verbs over HTTP or HTTPS. Life gets more complicated if you're using WS-Security and friends.
I find that SOAP fits in most appropriately when there is a high probability that a service will be consumed by corporate off the shelf (COTS) software. Because of the well specified contract employed by SOAP/WSDL most COTS packages have built in functionality for consuming such services. This can make it easy for BPM/workflow tools etc. to simply consume defined services without customization. Beyond that service use case REST tends to be my goto web service implementation for applications.
Well it appears now that the WSI agree that SOAP no longer has a point as they have announced they will cease to exist as an independent entity.
Interesting article about the announcement and some commentary here: http://blogs.computerworlduk.com/simon-says/2010/11/the-end-of-the-road-for-web-services/index.htm
Edited to be completely accurate in response to John Saunders.
I think SOAP appeals to the Java and .net crowd who may be more familiar with the old CORBA and COM and less familiar with internet technologies.
REST also has one major drawback: there is very little guidance on how to actually implement such a system. You will find significant variations on how many of the public RESTful APIs have been designed. In fact many violate key aspects of REST (such as using GET for manipulation or POST for retrieval) and there are disagreements over fundamental usage (POST/GET vs POST/GET/PUT/DELETE).
Am I wrong?
"You're not wrong, Walter, you're just... :)"
Are there any good reasons to ever choose SOAP over REST?
SOAP, to my understanding adheres to a contract, thus can be type checked.
SOAP is a lightweight XML based structured protocol specification to be used in the implementation of services . It is used for exchanging
structured information in a decentralized, distributed environment. SOAP uses XML technologies for exchanging of information over any transport layer protocol.
It is independent of any particular programming model and other implementation specific semantics. Learn More about XML
SOAP Messaging Framework
XML-based messaging framework that is
1) Extensible : Simplicity remains one of SOAP's primary design goals. SOAP defines a communication framework that allows for features such as security, routing, and
reliability to be added later as layered extensions
2) Inter operable : SOAP can be used over any transport protocol such as TCP, HTTP, SMTP. SOAP provides an explicit binding today for HTTP.
3) Independent : SOAP allows for any programming model and is not tied to Remote procedure call(RPC). SOAP defines a model for processing individual, one-way messages.
SOAP also allows for any number of message exchange patterns (MEPs) .Learn more about SOAP