Transcript Knowledge Grid - VL

Web Services
Experiences
Machiel Jansen
Vrije Universiteit (VU)
Amsterdam
Building web services in Java
Prior Experience: none.
Using NetBeans IDE:
Making Webservives on the fly
IDE generates stubs and hooks
Provides container and servlets
Pro’s and cons- SUN
Pro’s:
No need to write WSDL
Write application and ”publish” it as
webservice.
Cons:
Sun webservices want the Sun Application
Server – not in GT4.
Apache Axis
Axis can be easy.
Deploy your webservice rapidly (jws):
All public methods are available
But: Not configurable
Keep to global return datatypes
Apache Axis
Two approaches:
Start building application, or class library.
Let Axis generate WSDL (?wsdl)
Write WSDL
Use WSDL2Java to generate stubs (clients)
and hooks (services)
Axis server side
More difficult side of WS
Serialize your datastructures:
Easy when you stick to:
Global types (int, double, String, array etc.)
Java beans (set and get methods)
Otherwise: write custom serializers.
Wrapping existing application
Execute application from Java.
(use runTime)
Redirect the output.
Deploy as webservice.
Wrapping existing application
public int run(String cmd, Writer out) throws IOException {
RunTime r = Runtime.getRuntime();
Process p = r.exec(cmd);
FileIO.copyFile(new InputStreamReader(p.getInputStream( )),
out, true);
try { p.waitFor( ); // wait for process to complete
} catch (InterruptedException e) {
return -1; }
return p.exitValue( );
}
WS Clients – 3 types
Stub based
(easy: use WSDL2Java)
Service endpoint is static
Dynamic proxy
Service endpoint dynamically at runtime
Dynamic Invocation Interface (DII)
Discover services at runtime then invoke
methods
Clients - DII
Axis user guide uses Call object (DII) in
examples.
WSRF and GT4 examples uses stubs.
I used a DII client – should you?
DYNAMIC BUT HARDER THAN STUBS
// Register your (un)serializer
call.registerTypeMapping(Result.class, qm, new
org.apache.axis.encoding.ser.BeanSerializerFactory(Result.class, qm),
new org.apache.axis.encoding.ser.BeanDeserializerFactory(Result.class,
qm));
call.registerTypeMapping(Result[].class, ar,
new org.apache.axis.encoding.ser.ArraySerializerFactory(),
new org.apache.axis.encoding.ser.ArrayDeserializerFactory());
WSRF and GT4
Working on it.
You can work with GT4: use the WSCore library.
http://www-128.ibm.com/developerworks/edu/gr-dw-gr-eclipseide-i.html
Note: GT4 WSRF is a little different from Apache WSRF
GT4 uses GAR files and JNDI deployment.
Eclipse has a GT4 plugin…
What we would have liked…
Use Resource aware WS’s
on different nodes to process
indexes and search queries
INDEXER/
SEARCHER
CLIENT
WS on some nodes.
Use SRB or local storage.
user and system resources.
NODE
NODE
NODE
What we would like – part 2
Scenario taken from:
Building a grid using Web services standards.
http://www-128.ibm.com/developerworks/edu/gr-dw-gr-movie1i.html?S_TACT=105AGX07&S_CMP=HP
Questions
How do we make good use of GT4 – the WS enabled part?
How do we get access to GT4?
How are WS’s (best) used in PoC infrastructure?
Why use WS’s at all?
Why can’t we use a WS outside the PoC? Does it matter?
Technical hurdles still to take:
More experience in WSRF
Writing (de)serializers for custom datatypes.