Transcript Object Models for Distributed Systems

Presentation:
Advanced AXIS:
Deployment Descriptors and
Advanced Types
Outline
• So far with AXIS
– Installation of Apache Tomcat and AXIS
– Easy deployment of .java with .jws
– Using Dynamic Call Interface for the Client to .jws
• Rather tedious work – and pretty error-prone
– WSDL2Java Client generation
• This time
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Use of.wsdd deployment files in AXIS (server specific)
Types allowed in Java/WSDL mappings (client/server)
Use of Arrays and Objects (client/server)
Custom Objets (client/server)
Use of the WSDL2Java stubgeneration tool (client)
Scope (client/server)
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Using Axis Web Service Deployment
Descriptor
• Easy to use .jws
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But not nice deployment
Only source code (.java) no bytecode (.class)
How to undeploy?
Problems with accessing outside classes (no suppot for packages)
Not possible to use custom objects
• Alternative: Using the deployment tool in Axis with Web
Service Deployment Descriptor (.wsdd) files
– % java org.apache.axis.client.AdminClient deploy.wsdd
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Use of AdminClient
• AdminClient may be used as console application taking a deployment
file as argument (as shown on the previous slide)
• Or may be adopted into a deployment program or software-tool if
needed for better deployment control:
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List of deployed services with AdminClient
Using the “list” argument with AdminClient
Results in a complete list of deployed services
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Using Axis Web Service Deployment
Descriptor II – into the .wsdd
• Web Service Deployment Descriptor (.wsdd) is
XML for defining characteristics of a Web service
– The service name and the provider
<service name="HelloWorld" provider="java:RPC">
– The (packaged) class that provides the service
<parameter name="className" value=“hello.
HelloWorld"/>
– Which of the class methods are to be exposed (all or
limited)
<parameter name="allowedMethods" value="*"/>
<parameter name="allowedMethods"
value="getHelloWorldMessage
someOtherMethod"/>
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Using Axis Web Service Deployment
Descriptor III – provider style
• Much higher degree of deployment control
• Also needed when dealing with non RPC
java:RPC = ”object-oriented middleware style”
- others include:
- Document services
- Wrapped services &
- Message services
- these are not an integral part of the curriculum
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Using Axis Web Service Deployment
Descriptor IIII
• Web service scope specifies the lifetime/management of
the service class.
– Specify scope of the Web service (request, application or session)
in wsdd
<parameter name="scope" value="request"/>
– request - is the default scope; each request causes a new service
object to be created to handle the request
– session - conceptually, all requests by a single client are handled
by a single object (implemented with cookies)
– application - a singleton web service. A single object serves all
clients.
• More on scope later
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Parameter Types for Web Services and
Clients in AXIS
• The primitive types are mapped as shown below:
• These types can be used as either parameter or return types
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Value Objects
• Allowed objects are:
– Objects listed in the preceding slide
– Objects that conforms to the Java Bean Standard
• Custom objects – rolling your own
– Normally one would like to use ones own objects as parameters and
return values
– This may be done using the BeanSerializer
– Beans MUST conform to the Java Bean Standard
• This means empty constructor and accessor (getter/setter) methods
– More on this later
• Collections SHOULD NOT BE USED if interoperability is needed (e.g.
with C# og C++) as this is under-specified
– Instead use regular Arrays (Object[] and typecast)
– At least until next version of the specification
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Using Custom Objects
• Axis supports passing user-defined class objects that are Java Beans
– get and set methods are defined for every class attribute
– no-argument constructor
– the class is Serializable
• Marshalling and Unmarshalling parameters and return-values
• Suppose a Web Service returns a user-defined SomeClass object.
– On the server, deploy with a .wsdd element associating the user-defined
class (SomeClass ) with the Axis provided BeanService as:
– <beanMapping qname="msgNS:SomeClass"
xmlns:msgNS="urn:BeanService"
languageSpecificType="java:onk1Package.SomeClass"/>
• On the client side, WSDL2Java creates a BeanService. SomeObject
class
– The wsdl for the corresponding Web Service includes xml for SomeClass.
– The proxy unmarshals a returned Message object to a BeanService.
SomeClass object.
• This is integral for the support of the Data Transfer Object pattern (also
known as Replicating Objects pattern)
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Example WSDD
•TV-Program Web service (TVPSService.class):
•Java Server
•C# Client (Pocket PC .NET CF)
•Java Client (UNIX, LINUX, Windows)
<deployment xmlns="http://xml.apache.org/axis/wsdd/"
xmlns:java="http://xml.apache.org/axis/wsdd/providers/java">
<service name="TVPSService" provider="java:RPC">
<parameter name="className" value="tvps.TVPSService"/>
<parameter name="allowedMethods" value="*"/>
<beanMapping qname="myNS:Programme" xmlns:myNS="urn:BeanService"
languageSpecificType="java:tvps.Programme"/>
</service>
</deployment>
•Key elements:
•Package of service = tvps
•Class of service = tvps.TVPSService
•Allowed methods = all (*)
•Custom class (return parameter) = tvps.Programme
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Client side – using WSDL2Java
• The deployment is purely server side
• Lets now take a look at the client side
• We have already seen dynamic clients
• If we would like to generate static Client proxy
stubs for a WSDL service – we could use:
– C:\dev-axis\java org.apache.axis.wsdl.WSDL2Java
http://localhost:8080/axis/Calculator.jws?wsdl -p calc
• Which would generate a package ”calc”
containing all the Proxy code needed for building
a Client
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Result of WSDL2Java
WSDL clause
Java class(es) generated
For each entry in the type section
A java class (as in Java RMI & CORBA)
A holder if this type is used as an inout/out parameter
(as in CORBA)
For each portType
A java interface (as in Java RMI & CORBA)
For each binding
A stub class (as in Java RMI & CORBA)
For each service
A service interface
A service implementation (the locator)
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Building a Client
•Lets start by generating the Clients stub given the WSDL (-p = destination package = hello):
•java org.apache.axis.wsdl.WSDL2Java http://localhost:8080/axis/HelloWorld.jws?wsdl –p hello
package hello;
public class HelloWorldClient {
public static void main (String args[]) throws Exception {
// Make a service
HelloWorldService service = new HelloWorldServiceLocator();
//Now use the service to get a stub which implements the SDI
HelloWorld stub = (HelloWorld) service.getHelloWorld();
String text = stub.getHelloWorldMessage("Test af OO indpakning");
System.out.println(”Recieved from server: "+text);
}
}
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HelloWorld.java – the interface
• Generated by the WSDL2Java tool
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HelloWorldService.java – service interface
• Generated by the WSDL2Java tool
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HelloWorldServiceLocator.java part 1
implementation of the interface
Hot wired address – from where?
standard getHelloWorld impl takes hot wired address
Calls the getHelloWorld(endpoint)
More code to follow
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HelloWorldServiceLocator.java part 2
If you want to implement a naming service a different accessor is provided
It returns a proxy stub – which is also generated – the HelloWorldSoapBindingStub
The remaining code is not commented further – take a closer look for yourself
More code is generated – but not shown here
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HelloWorldSoapBindingStub.java – the stub part 1
Extending stub and implementing the interface
Only excerpts of the code have been shown on these slides
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HelloWorldSoapBindingStub.java – the stub part 2
Implementing the marshalling – compare this to the dynamic client we made
earlier on, or your UDP assignment!
We are using the call object
To invoke the method on the server
Only excerpts of the code have been shown on these slides
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Axis Life-Cycle Management for Web
Services
• Web service scope specifies the lifetime/management of
the service class.
– request - has the same effect as if a new service object is created
to handle each method call.
– Request is the default scope - provides scalability in highcapacity load-balanced applications. Connections and/or server
objects can be pooled.
– session - conceptually, all requests from a single client are
handled by a single object. Implemented with cookies, and
requires client support.
– application - a singleton web service. A single object serves all
clients.
• Using application scope for a Java Web Service and
Client
– The deploy.wsdd specifies application scope for the Web Service
<parameter name="scope" value="application"/>
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Using Session Scope with Axis
• Using the session scope for a Java Web Service and
Client
– For example, count all calls made to a service by a single client.
– Each client has its own call count -- in effect, has its own service
object.
– The deploy.wsdd specifies session scope for the Web Service
<parameter name="scope" value="session"/>
• For session scope to work, the web service client must
also specify a session mechanism
– In C# as: tcs.CookieContainer = new
System.Net.CookieContainer();
– Java Proxy as:
((MyWSServiceLocator)tcs).setMaintainSession(true);
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