Does SOAP always need WSDL or can it work without WSDL? I've been doing some reading on the internet and it's making me confused.
From what I can see, SOAP request can contain the message in the XML: http://www.w3schools.com/soap/soap_example.asp. Then why do I need WSDL? Or does it depend on how the SOAP service is set up in the server end?
WSDL is a description of the service (Web Service Description Language). It is mainly used to a) describe the service in a non-ambiguous way, and b) allow tools to generate client and/or server code, which make building, and interacting with, the service easier.
You can certainly implement, or interact with, a SOAP service "by hand" but you wouldn't want to.
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I have done a few use cases on WSO2-ESB including protocol mediation with transformation and service-chaining.
In all of them I had to manually write the wsdl for the proxy service. Having experienced other vendor products including Oracle and Tibco where wsdl generation is done by the tool.
Would it be right to assume in WSO2 ESB one needs to manually write the wsdl file to expose a proxy service on any protocol, do not see any documents calling that out.
Considering the usage of wsdl in practical use cases.
I have seen posts stating "you can give the WSDL available at your Axis2 service" but most of real time use cases would not be pass through and have custom request and response.
Thanks,
Wajid
I'm also confused with manual wsdl creation. As far as I can see there are gaps in wsdl proxy description. When I do wsdl proxy with WSO2 I have to indicate wsdl to expose
its either as:
"none" and I have only mediate function exposed
"same contract" and this breaks the whole idea of proxy because after that clients read original wsdl and go straight to original server access point.
or and I have several options to make my own wsdl.
With rich SOAP API (hundreds of methods) none of above work well, considering that manual support of exposed WSDL is rather cumbersome.
I wonder if there is more adequate way for proxying WSDL?
You can use java2wsdl generator tool to achieve the WSDL generation.
For the proxies, if you try to restrict access for some operations in your backend service, you can attach customized wsdl to the proxy.
The customization has to be done by yourself and it is simple..
If you want to generate a wsdl fro your service, jsut deploy the service in wso2as, and check the service dashboard, wsdl option to view the wsdls.
I've started learning about webservices recently. Have few question about that:
For webservice, is it always necessary that source should provide wsdl or any other way possible to consume it without needing wsdl?
Till a while ago, I was doing server side XMLhttp post in classic ASP to do modifications in external application & to push data in my application from external application. I'm confused - is that very different from webservice or can be called a sort of webservice(ofcourse without based on SOAP). Any major difference or it is just protocol difference bw webservice and server side XMLhttp post?
Web services can be made asynchronous?(Something like AJAX call through javascript)
Are there any different types of webservices ? (for e.g is there difference bw, webservice providing stock quotes and webservice provided by google)
1.For webservice, is it always necessary that source should provide wsdl or any other way possible to consume it without needing wsdl?
WSDL is a document that publishes an interface. As long as a client complies to the inteface, it is guaranteed to be able to "talk" to the web service. Having said that WSDL is a formal way for a specification when there are many stakeholders. You can proceed without one, as long as you somehow know what the web service expects. Just wrap the application data in a SOAP envelope and send it to the web service. As long as you send what the web service expects (in the SOAP envelope or the application data) and in the way they are expected e.g. transport HTTP etc. it does not matter for the WS if you have used a WSDL or not.
2.Till a while ago, I was doing server side XMLhttp post in classic ASP to do modifications in external application & to push data in my
application from external application. I'm confused - is that very
different from webservice or can be called a sort of
webservice(ofcourse without based on SOAP). Any major difference or it
is just protocol difference bw webservice and server side XMLhttp
post?
In very simple terms web service is XML over some application protocol (usually HTTP). Could be SOAP based or REST. To understand more on this you should read about Service Oriented Applications
3.Web services can be made asynchronous?(Something like AJAX call through javascript)
They could but it is more complicated than that.
4.Are there any different types of webservices ? (for e.g is there difference bw, webservice providing stock quotes and webservice
provided by google)
Not sure what you ask here. Each web service offers something.
I will try to be very simple here:
The W3C defines a "Web service" as "a software system designed to
support interoperable machine-to-machine interaction over a network".
That means first requisite for any software to be web-service is that it should not depend upon platform or software i.e a web service made on java stack can be consumed by client in .net stack on windows or java stack on android.
If your server side implementation XMLhttp post suffice this ,its a
web service.
Types of Web services
Actually, there is no overall and clear categorization on types of web services. But two most popular are :
SOAP based web services. :It use XML messages that follow the Simple Object Access Protocol (SOAP) standard, an XML language defining a message architecture and message formats(WSDL).
REST based web services. With evolution of WEb 2.0 emphasis has been moving away from SOAP based services towards representational state transfer (REST) based communications.[3] REST services do not require XML, SOAP, or WSDL service-API definitions.Read here to get a easy explanation of REST
Need of WSDL to consume SOAP web services?
To consume a SOAP service we only require SOAP endpoint and XML message format. WSDL is a pre-requisite for automatic client side code generation through Java and .NET SOAP frameworks.
Asynchronous web services
Making web services asynchronous is possible.But complexity depends upon frameworks used, for example AXIS2 in JAVA has easy implementation of this.
If I need a web service to pass back and forth a complex object, is there a reason I should prefer SOAP over REST? Here is an example of the possible SOAP message:
<soap:Envelope>
<soap:Header>
<Credentials>
<User>Joe</User>
<Password>abc123</Password>
</Credentials>
</soap:Header>
<soap:Body>
<MyComplexBusinessObject>
<Search>
<First>Joe</First>
<Last>Smith</Last>
</Search>
...
...
</MyComplexBusinessObject>
</soap:Body>
</soap:Envelope>
Using REST, I would be asking the client to POST the following xml and authenticate using Basic Authentication:
<MyComplexBusinessObject>
<Search>
<First>Joe</First>
<Last>Smith</Last>
</Search>
...
...
</MyComplexBusinessObject>
The SOAP message is slightly more complicated, but not by much. They are still both XML, but SOAP comes with a WSDL and most programming environments will generate proxy classes for you. However, most people I talk to say I should use REST instead because it's easier to use. But I don't see how SOAP is any harder to use.
Am I missing something?
Your first requirement of "passing back and forth a complex object" constrains your architecture to eliminate many of the benefits of REST. SOAP is designed for accessing remote objects, REST is not. REST supports passing media-types as simple as text/plain, which is far more primitive than dealing with an object.
If you haven't seen it already, this question and its answers cover most of the REST vs SOAP issues.
One major benefit of REST is that all you need to call and use it is a browser and a HTTP stack - pretty much every device and machine has that. So if ease of use and reach are you main goal - use REST.
One of the major benefits of SOAP is that you have a WSDL service description and you can pretty much discover the service automatically, and generate a useable client proxy from that service description (generate the service calls, the necessary data types for the methods and so forth).
So if discoverability and a strict, formal service description are more important to you, use SOAP (with the downside that you need a full-fledged SOAP client to call your service - your web browser won't be sufficient).
SOAP isn't harder to use - but it's just not quite as "pervasive" in terms of being available - any browser can call a REST service and get an answer - but then it needs to parse and interpret that response. SOAP gets nice data structure, but you need a SOAP client for this.
I view SOAP and REST as orthogonal APIs, designed to do different things.
SOAP is basically a fancy RPC, so if you want to send a computation request over to the server and get the result back, you use SOAP. If it would be local, it would be a method call to an object instance.
REST is a way to create, retrieve, update and delete remote objects, not in the sense of POO, using a uniform API. If it would be local, it would be like working with a file.
So they actually respond to different needs. You can bastardize one to do the work of the other, but you mangle the meanings.
If you develop both the service and the client, using SOAP is as easy as REST (actually easier).
You may prefer SOAP over REST if these conditions meet:
The entire service API is complex, not just one object.
The service is used within a relatively small network, and performance is not an important requirement.
You decide to spend the minimum amount of time to develop both the service and the API documentation.
What is WSDL? How is it related to SOAP? Where does REST fit in all of that?
A WSDL is an XML document that describes a web service. It actually stands for Web Services Description Language.
SOAP is an XML-based protocol that lets you exchange info over a particular protocol (can be HTTP or SMTP, for example) between applications. It stands for Simple Object Access Protocol and uses XML for its messaging format to relay the information.
REST is an architectural style of networked systems and stands for Representational State Transfer. It's not a standard itself, but does use standards such as HTTP, URL, XML, etc.
Example: In a simple terms if you have a web service of calculator.
WSDL: WSDL tells about the functions that you can implement or exposed to the client. For example: add, delete, subtract and so on.
SOAP: Where as using SOAP you actually perform actions like doDelete(), doSubtract(), doAdd(). So SOAP and WSDL are apples and oranges. We should not compare them. They both have their own different functionality.
Why we use SOAP and WSDL: For platform independent data exchange.
EDIT: In a normal day to day life example:
WSDL: When we go to a restaurant we see the Menu Items, those are the WSDL's.
Proxy Classes: Now after seeing the Menu Items we make up our Mind (Process our mind on what to order): So, basically we make Proxy classes based on WSDL Document.
SOAP: Then when we actually order the food based on the Menu's: Meaning we use proxy classes to call upon the service methods which is done using SOAP. :)
Every time someone mentions SOAP/WSDL, I think of objects and classes defined in xml...
"You use SOAP just the same way that you would any PHP class. However, in this case the class does not exist in the local applications file system, but at a remote site accessed over http."
...
"If we think of using a SOAP service as just another PHP class then the WSDL document is a list of all the available class methods and properties. "
http://www.doublehops.com/2009/07/07/quick-tutorial-on-getting-started-with-soap-in-php/comment-page-1/
..and whenever someone talks about REST I think of HTTP's commands (request methods) like POST, GET and DELETE
SOAP -> SOAP(Simple object access protocal) is the application level protocal created for machine to machine interaction. Protocol defines standard rules. All the parties who are using the particular protocol should adhere to the protocol rules. Like TCP, It unwinds at transport layer, The SOAP protocol will be understood by Application layer( any application which supports SOAP - Axis2, .Net).
WSDL -> SOAP message consist of SoapEnevelope->SoapHeader and SoapBody. It doesn't define what would be message format? what are all the transports(HTTP,JMS) it supports? without this info, It is hard for any client who wants to consume the particular web service to construct the SOAP message. Even if they do, they won't be sure, it'll work all the time. WSDL is the rescue. WSDL (Web Service description Language) defines the operations, message formats and transport details for the SOAP message.
REST -> REST(Representational state transfer) is based on the Transport. Unlike SOAP which targets the actions, REST concerns more on the resources. REST locates the resources by using URL (example -http://{serverAddress}/employees/employeeNumber/12345) and it depends on the transport protocol( with HTTP - GET,POST, PUT, DELETE,...) for the actions to be performed on the resources. The REST service locates the resource based on the URL and perform the action based on the transport action verb. It is more of architectural style and conventions based.
You're not going to "simply" understand something complex.
WSDL is an XML-based language for describing a web service. It describes the messages, operations, and network transport information used by the service. These web services usually use SOAP, but may use other protocols.
A WSDL is readable by a program, and so may be used to generate all, or part of the client code necessary to call the web service. This is what it means to call SOAP-based web services "self-describing".
REST is not related to WSDL at all.
SOAP stands for Simple (sic) Object Access Protocol. It was intended to be a way to do Remote Procedure Calls to remote objects by sending XML over HTTP.
WSDL is Web Service Description Language. A request ending in '.wsdl' to an endpoint will result in an XML message describing request and response that a use can expect. It descibes the contract between service & client.
REST uses HTTP to send messages to services.
SOAP is a spec, REST is a style.
Wikipedia says "The Web Services Description Language is an XML-based language that provides a model for describing Web services". Put another way, WSDL is to a web service, as javadoc is to a java library.
The really sweet thing about WSDL, though, is that software can generate a client and server using WSDL.
Some clear explanations (for SOAP and WSDL) can be found here as well.
Difference between a SOAP message and a WSDL?
REST is light-weight in terms of encoding, much more useful for light weight devices i.e. non strict APIs.
REST is format independent. XML, HTML, JSON all options are available.
REST provides abilities for on 2 point message transfer (not surprising since REST stands for REpresentational State Transfer) where WSDL/SOAP interaction is multiple point message interaction.
REST does not require a new extension for XML messages, where in WSDL/SOAP this is the case.
WSDL/SOAP uses multiple transport protocols, REST relies on only HTTP. Therefore WSDL/SOAP can be used like a RESTful way, however simple requests can be overly complicated/heavy weighted.
A simple analogy: REST is like a motoboy delivers your food easy and quick. XML extended WSDL/SOAP more like UPS delivery, more structured and serious stuff but comes with a cost.
A WSDL document describes a webservice. It specifies the location of the service and the methods of the service using these major elements:
data types using in webservice
data elements for each operation
describe the operations that can be performed and the messages envolved
SOAP (Simple Object Access Protocol) is a messaging protocol that allows programs that run on disparate operating systems to communicate using http and xml.
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.