ways to invoke service

Invoking web services with Java clients

http://www.ibm.com/developerworks/webservices/library/ws-javaclient/index.html

Service access

In previous sections, you saw that a JAX-RPC

ServiceFactory

acts as a factory for JAX-RPC Services. Similarly, a JAX-RPC Service
acts as a factory for proxies and stubs. Once you have instantiated a
Service, there are three methods for accessing and invoking the web
service:

Stub

Dynamic Proxy

Dynamic Invocation Interface (DII).

Stub and dynamic proxy methods use the Service Endpoint Interface
(SEI). It is basically the Java representation of the web service
operations described in the WSDL port type element. It is a Java
interface defining methods used by the Java client to interact with the
web service. The SEI is generated by a WSDL to Java mapping tool (such
as Apache Axis' Java2WSDL or IBM WSDK's WSDL2Client).

SEI

A Service Endpoint Interface (SEI) is the Java representation of a WSDL port type.

Stub

The stub method uses a platform-specific stub created before
runtime during the WSDL to Java mapping stage. Because the stub is
created before runtime, it is sometimes called a static stub
.
It is a Java class implementing the SEI. A WSDL to Java mapping tool
generates the client-side artifacts needed; basically, the tool imports
the WSDL service definition and creates the corresponding Java code. The
artifacts include an SEI, a Stub, and optionally holders, serializers,
deserializers, and utility classes. JAX-RPC recommends an instance of a
stub to be bound to a specific protocol and transport, such as a SOAP
binding stub. For the stub method, the steps to perform are:

Get a JAX-RPC Service.

Obtain a stub.

Invoke the web service's operations on the stub.

Steps 2 and 3 are shown in Listing 4
. Note that it is also possible to use the JAX-RPC

Service

's getPort method (described in the next section) to obtain a stub.

Listing 4. Accessing a web service through a stub

Hello myStub = (Hello) service.getHello(); System.out.println(myStub.getGreeting("Jane");

The advantage of this method is its simplicity. Basically, only
two lines of code are required to access and invoke a web service's
operation. However, you need to know the WSDL URL at development-time
and run your WSDL to Java mapping tool. Also, these stubs are not
portable because they depend on implementation classes and should not be
packaged as part of an application. The design of portable stubs is
out-of-scope for JAX-RPC 1.0 and 1.1.

Dynamic proxy

From a JAX-RPC

Service

, you can use a proxy to invoke
the web service's operations. The proxy is a Java class implementing
the SEI. A proxy is obtained with the JAX-RPC

Service

's
getPort() method, which takes the name of the port for the web service
you want to invoke (found in the WSDL document), as well as the SEI
implemented by the proxy. It is called dynamic
because the proxy is created at runtime. The steps for dynamic proxy clients are:

Get a JAX-RPC

Service

.

Obtain a proxy using the JAX-RPC

Service

's getPort() method in order to invoke the web service's operations.

In step 1, for unmanaged clients, a JAX-RPC

Service

is obtained from the JAX-RPC

ServiceFactory

by passing the WSDL URL as well as the web service name parameter to
the createService() method. For J2EE container-managed clients, you get a
JAX-RPC

Service

from JNDI lookup. Listing 5
shows the dynamic proxy method (step 2) to invoke the "getGreeting" operation on the web service.

Listing 5. Invoking a web Service's operation on a dynamic proxy

String namespace = "http://Hello.com"; String portName = "Hello"; QName portQN = new QName(namespace, portName); Hello myProxy = service.getPort(portQN, Hello.class); System.out.println(myProxy.getGreeting("Jane"));

This is all the code you need to write to invoke a web service
using the dynamic proxy method. The advantage of using this method is
that you write portable, vendor-independent code. However, you need to
know the WSDL URL at development-time and you need to run your WSDL to
Java mapping tool against the WSDL document before runtime. If you do
not have this information, or if the WSDL URL is likely to change, you
should use the DII method instead.

Dynamic Invocation Interface (DII)

The JAX-RPC

Call

interface supports the dynamic
invocation of a web services' operations. With this method, you do not
need to know the WSDL URL at development-time. Instead of obtaining a
proxy from the JAX-RPC

Service

, the JAX-RPC

Service

acts as a factory for instantiating JAX-RPC

Call

s. The steps for this method are:

Get a JAX-RPC

Service

.

Instantiate a JAX-RPC

Call

using JAX-RPC

Service

's createCall() method.

Configure your

Call

instance with its setter methods.

Invoke the web service's operation using the JAX-RPC Call's invoke method.

In step 1, for unmanaged clients, a JAX-RPC

Service

is obtained from the JAX-RPC

ServiceFactory

by passing only the name of the web service (not the WSDL URL) to the
createService() method. For J2EE container-managed clients, you get a
JAX-RPC

Service

from JNDI lookup. In step 3, configuration
parameters are: name of the operation, port type, address of the target
service endpoint, return type. Refer to section 8.2.4.2 of the JAX-RPC
specification for the standard set of properties (see Resources
). Steps 2 to 4 are shown in Listing 6
.

Listing 6. Invoking a web service using the DII method

String namespace = "http://Hello.com"; String portName = "Hello"; QName portQN = new QName(namespace, portName); String operationName = "getGreeting"; Call call = service.createCall(); call.setPortTypeName(portQN); call.setOperationName(new QName(namespace, operationName)); call.setProperty(Call.ENCODINGSTYLE_URI_PROPERTY, ""); call.setProperty(Call.OPERATION_STYLE_PROPERTY, "wrapped"); call.addParameter("param1", <xsd:string>,ParameterMode.IN); call.setReturnType(<xsd:string>); Object[] inParams = new Object[] {"Jane"}; String ret = (String) call.invoke(inParams);

You can reuse the Call instance to invoke other operations on the web service.

Note:
the createCall() and addParameter() methods
have other signatures. What was just described is not the only way to
invoke them. For example, it is possible to invoke createCall() with
port type name and operation name parameters.

Making DII calls through a Call object is programmatically more
complex than using a stub or dynamic proxy. However, the advantage of
using a DII

Call

interface is that a client can call a
remote procedure without development-time knowledge of the WSDL URI or
the web service operations' signatures. This makes the code easy to
modify if the web service details change. With DII clients, runtime
classes generated by WSDL to Java mapping tools (emitters) are not
required like the dynamic proxy or static stub cases. However, if you
know the web service you want to invoke is unlikely to change, you
should use dynamic proxy because configuring the

Call

instance can be complex.

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Dynamic Discovery and Invocation (DDI)

Dynamic Discovery and Invocation (DDI) is the ultimate use of web
services' flexibility where a web service client can dynamically
discover and invoke a web service without any prior knowledge of it.
Although DII clients, described in the previous section
,
do not require development-time knowledge of a web service's details,
they do not involve the process of discovering the web service. A DDI
client performs three steps:

Discovers the web service's details from UDDI: finds the
business providing the service and then the URL of the WSDL document
describing the service

Reads the WSDL document to find information on the web service: namespace, service, ports, and parameters

Invokes the service.

In step 1, the UDDI Registry Enquiry API is used to browse the
UDDI registry. In step 2, the UDDI4J API is used to parse the WSDL
document. Finally, in step 3, the DII method (described in the previous section
)
is used. For information on DDI you are encouraged to read the
developerWorks article "Dynamic Discovery and Invocation of web
services," listed in the Resources
section.