Why use XML(SOAP) when JSON so simple and easy to handle?

Question

Receiving and sending data with JSON is done with simple HTTP requests. Whereas in SOAP, we need to take care of a lot of things. Parsing XML is also, sometimes, hard. Even Facebook uses JSON in Graph API. I still wonder why one should still use SOAP? Is there any reason or area where SOAP is still a better option? (Despite the data format)

Also, in simple client-server apps (like Mobile apps connected with a server), can SOAP give any advantage over JSON?

I will be very thankful if someone can enlist the major/prominent differences between JSON and SOAP considering the information I have provided(If there are any).

Answer 1

I have spent several years writing SOAP web services (with JAX WS). They are not hard to write. And I love the idea of a single endpoint and single HTTP method (POST). For me, REST is too verbose.

But as a data container, JSON is simpler, smaller, more readable, more flexible, looks closer to programming languages.

So, I reinvented the wheel and created my own approach to writing backends for AJAX requests. In comparison:

REST:

• get user: method GET https://example.com/users/{id}
• update user: method POST https://example.com/users/ (JSON with User object in request body)

RPC:

• get user: method GET https://example.com/getUser?id=1
• update user: method POST https://example.com/updateUser (JSON with User object in the request body)

My way (the proposed name is JOH - JSON over HTTP):

• get user: method POST https://example.com/ (JSON specifies both user ID and class/method responsible for handling request)
• update user: method POST https://example.com/ (JSON specifies both user object and class/method responsible for handling request)

Answer 2

I think there is a lot of basic misinformation on this thread. SOAP, REST, XML, and JSON concepts seem to be mixed up in the responses.

Here is some clarification -

XML and JSON (an others) are encodings of information. SOAP is a communications protocol REST is an (Architecture) style

each is used for something different although you might use more than one of these things together.

Lets start with encoding data structures as XML vs JSON:

Everything JSON currently supports can be done in XML, but not the other way around. JSON will eventually adopt all the features that XML has, but its proponents haven't encountered all of the problems yet, once they get more experience things will be added on to close the gap. for example JSON didn't start out with Schemas and binary formats.

SOAP is a communication protocol for calling an operation. It runs on top of things like, HTTP, SMTP, etc. Aside from many other features, SOAP messages can span multiple "application" layer protocols. i.e. i can sent a SOAP message by HTTP to a service endpoint which then puts it on a message queue for another system. SOAP solves the problem of maintaining authentication, message authenticity, etc. as the requested moved between different parts of a distributed system.

JSON and other data formats canbe sent via SOAP. I work with some systems that sent binary fixed-width encoded objects via SOAP, its not a problem.

The analogy is that - if only the postman is allowed to send you a letter, then it is just HTTP, but if anyone can send you a letter, then you want SOAP. (i.e. message transport security vs message content security)

the 6 REST constraints are architectural style. Interestingly the first several years of REST the examples were in SOAP. (there is no such thing as REST or SOAP they are not opposites)

A "heavyweight bloated, etc.etc." SOA SOAP system might have monoliths with operations like GET, PUT, POST instances of a single entity. SOAP doesn't have those operations predefined, but that is typically how it is used.

Consider that if you built a "REST" service on HTTP alone with an SSL/TLS terminating proxy, then you may have violated the 4th constraint of REST.

So for your software development today, you wouldn't normally interact with any of these directly. Just as if you were written a graphics program you wouldn't directly work with HDMI vs. DisplayPort typically.

The question is do you understand architecturally what your system needs to do and configure it to use the mechanism that does that job. (for example, all the challenges of applying today's microservices to general systems are old problems previously solved by SOAP, CORBA and the old protocols)

Answer 3

I found the following on advantages of SOAP:

• There is one big reason everyone sticks with SOAP instead of using JSON. With every JSON setup, you're always coming up with your own data structure for each project. I don't mean how the data is encoded and passed, but how the data formatted format is defined, the data model.
• SOAP has an industry-mature way of specifying that data will be in a certain format: e.g. "Cart is a collection of Products and each Product can have these attributes, etc." A well put together WSDL document really has this nailed. See W3C specification: Web Services Description Language
• JSON has similar ways of specifying this data structure — a JavaScript class comes to mind as the most common way of doing this — but a JavaScript class isn't really a data structure used for this purpose in any kind of agnostic, well established, widely used way.

In short, SOAP has a way of specifying the data structure in a maturely formatted document (WSDL). JSON doesn't have a standard way of doing this.

If you are creating a client application and your server implementation is done with SOAP then you have to use SOAP in client side.

Also, see: Why use SOAP over JSON and custom data format in an “ENTERPRISE” application? [closed]

Answer 4

I disagree a bit on the trend of JSON I see here. Although JSON is an order maginitude easier, I'd venture to say it's quite limited. For example, SOAP WS is not the last thing. Indeed, between soap client/server you now have enterprise services bus, authentification scheme based on crypto, user management, timestamping requests/replies, etc. For all of this, there're some huge software platforms that provide services around SOAP (well, "web services") and will inject stuff in your XML. So although JSON is probably enough for small projects and an order of magnitude easier there, I think it becomes quite limited if you have decoupled transmission control and content (ie. you develop the content stuff, the actual server, but all the transmission is managed by another team, the authentification by one more team, deployment by yet another team). I don't know if my experience at a big corp is relevant, but I'd say that JSON won't survive there. There are too many constraints on top of the basic need of data representation. So the problem is not JSON RPC itself, the problem is it misses the additional tools to manage the complexity that arises in complex applications (not to say that what you do is not complex, it's just that the software reflects the complexity of the company that produces it)

Answer 5

Nowadays SOAP is a complete overkill, IMHO. It was nice to use it, nice to learn it, and it is beautiful we can use JSON now.

The only difference between SOAP and REST services (no matter whether using JSON) is that SOAP WS always has it's own WSDL document that could be easily transformed into a self-descriptive documentation while within REST you have to write the documentation for yourself (at least to document the data structures). Here are my cons'&'pros for both:

REST

Pros

• lightweight (in all means: no server- nor client-side extensions needed, no big chunks of XML are needed to be transfered here and there)
• free choice of the data format - it's up on you to decide whether you can use plain TXT, JSON, XML, or even create you own format of data
• most of the current data formats (and even if used XML) ensures that only the really required amount of data is transfered over HTTP while with SOAP for 5 bytes of data you need 1 kB of XML junk (exaggerated, ofc, but you got the point)

Cons

• even there are tools that could generate the documentation from docblock comments there is need to write such comments in very descriptive way if one wants to achieve a good documentation as well

SOAP

Pros

• has a WSDL that could be generated from even basic docblock comments (in many languages even without them) that works well as a documentation
  • even there are tools that could work with WSDL to give an enhanced try this request interface (while I do not know about any such tool for REST)
• strict data structure

Cons

• strict data structure
• uses an XML (only!) for data transfers while each request contains a lot of junk and the response contains five times more junk of information
• the need for external libraries (for client and/or server, though nowadays there are such libraries already a native part of many languages yet people always tend to use some third-party ones)

To conclude, I do not see a big reason to prefer SOAP over REST (and JSON). Both can do the same, there is a native support for JSON encoding and decoding in almost every popular web programming language and with JSON you have more freedom and the HTTP transfers are cleansed from lot of useless information junk. If I were to build any API now I would use REST with JSON.