Re: how does one talk to a web service? What makes something a web
On Sun, 28 Jun 2009, Andrew wrote:
I thought I knew what a web service was but now I am not so sure. I am
still learning java and come from a C++ background. The way people on my
project talk about web services reminds me of the C++ CORBA servants I
used to write. In which case we would use WSDL instead of OMG IDL. But I
have seen the code of some of the sruff they say is a web service and it
does not seem like a service to me. For a start, there is no WSDL. There
is a spring MVC controller responding to a URL pattern. People can go to
the URL and do admin type things from the web page. That doesnt seem
like a web service to me.
A web service is a website that has a machine-readable interface. That's
all. I could write a CGI script which would accept RSS documents via POST,
and return RSS documents translated into Esperanto, and that would be a
The conventional way to do web services is indeed virtually a straight
port of CORBA (without the sophistication, performance, richness, etc) -
an RPC mechanism with SOAP as the transport, WDSL as something like IDL,
then various other WS* and UDDI and whatnot providing facilities on top of
Another major approach is REST, which is hip but widely misunderstood.
REST basically maps URLs to objects, and uses GET, PUT and DELETE to
transfer representations of their state between client and server in some
machine-readable format like XML or JSON, or even CSV (the POST method
gets used to, but has a bit of a variable meaning). Rather than have
method calls as such, you try to factor out sub-objects which can be GOT
From what you say, it sounds like your alleged web service may be RESTful.
Although if it's human-readable, then it may not be easily
machine-readable, which would mean it's not really REST. You can still
program to it, but it will involve a lot more pain in dealing with the
I have been asked to work on a process that has to talk to such a
'service'. How would be this be done from java please? Since AFAICS it
is just a web page I would have to talk HTML, post a request and get a
response etc. That doesn't seem the right way to use a service to me. It
seems far too low level. The equivalent in my old world would be for
someone to say that I would be talking to a CORBA service and then I
find I am expected to code it using raw sockets and working directly
with the low level CORBA data transmission protocol.
There isn't the level of tool support around REST that there is around the
SOAP stack. But then it's not clear it's needed, because REST is so simple
- you form a URL, download it, stick the XML in a parser, and you're away.
If the XML is complicated, you could use JAXB to turn it into objects.
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