Oracle Application Server 10g Essentials [Electronic resources] نسخه متنی

11.3 Service Provider

As mentioned earlier, Oracle provides two implementations for

Web Services on Oracle Application
Server:
OracleAS SOAP
and OC4J Web Services. Oracle's official stand on
OracleAS SOAP, an enhanced version of the Apache
organization's Java-based SOAP implementation, is
that it is in maintenance mode. In other words, Oracle will continue
to maintain OracleAS SOAP for the time being, but you are strongly
encouraged to use OC4J Web Services instead. For that reason, we
cover only OC4J Web Services and its tools in the remainder of this
chapter.

11.3.1 OC4J Web Services Agents

Web Services are implemented in
OC4J by
seven servlets for the following seven types of service objects:

A stateless Java class

Using an RPC-style XML message

A stateless Java class

Using a document-style XML message

A stateful Java class

Using an RPC-style XML message

A stateful Java class

Using a document-style XML message

A stateless session EJB

Using an RPC-style XML message

A stateless PL/SQL stored procedure

Using an RPC-style message

Java Message Service (JMS)

Using a document-style XML message

As demonstrated in Figure 11-4, an OC4J Web Services
servlet is responsible for parsing an incoming request in the form of
an XML message, calling the appropriate service, encoding the result
into an XML document, and then sending the XML document back to the
requester through the Oracle HTTP Server.

Figure 11-4. OC4J Web Service architecture

By creating seven different servlets for these seven different
service types, Oracle has simplified the process of creating a Web
Service so that it consists only of programming the service method,
configuring the service via an XML file, and then generating a
deployment Enterprise Application Archive file. The resultant EAR
file is then deployed on Oracle Application Server using Application
Server Control. In addition, a different servlet for each service
type makes the servlet's code base smaller and more
efficient, which leads to better performance.

11.3.1.1 RPC-style versus document-style

Two styles of Web Services calls are
supported:

Remote procedure calls

As mentioned earlier, an RPC is a parameterized encoding in which the
parameters for a service are encoded with elements in the XML message
sent to and received from the service.

Document (literal)

The document or literal style
doesn't encode parameters. Instead, it sends an
entire encapsulated XML document as the message payload.

11.3.1.2 Stateless Java class services

Stateless Java class services, whether
they are RPC- or document-style, are provided by a Java class that
has one or more public methods. Each public method is exposed as a
service. An RPC-style service can use one of the many default
datatypes specified in the SOAP schema. In contrast, the
document-style service must receive, return, or receive and return an
XML document passed as an instance of Java class
org.w3c.dom.Element. OC4J maintains a cache of
instances of each stateless service for reuse to increase
performance.

11.3.1.3 Stateful Java class services

Stateful Java class services, whether
they are RPC- or document-style, are provided by a Java class that
has one or more public methods and maintains one or more instance
variables. Instances of stateful services aren't
cached by OC4J. Instead, they are stored in the HTTP session object
for each user's session.

11.3.1.4 Stateless session EJB services

Any stateless session EJB can be used as
an RPC-style service. The public methods exposed by the
EJB's remote interface are accessible as services.
As with stateless Java classes, instances of stateless session EJBs
are cached by OC4J for reuse.

11.3.1.5 Java Message Service services

Oracle Application Server Java Message Service and Oracle Advanced Queuing, as well
as any desired third-party messaging systems, are supported by OC4J
Web Services. JMS Web Services expose JMS sends and receives as
services, for both queues and topics. A JMS Web Services client can
act as producer or consumer.

11.3.1.6 Stateless PL/SQL services

Any Oracle
PL/SQL stored procedure that is part
of a PL/SQL package can be used as an RPC-style service. Both PL/SQL
procedures and functions declared in a package's
specification are exposed as services. These services are executed
through a dedicated servlet that uses a JDBC data source to access
the host database.

11.3.2 Web Services Assembler

Oracle Application Server provides a

command-line tool written in Java
called WebServicesAssembler.jar that packages
services into a Web Services EAR file for deployment on Oracle
Application Server. Using the Web Services Assembler, Web Service
development becomes a matter of doing the following:

Creating a JavaBean, EJB, or stored procedure to provide service
methods

Editing the Web Services Assembler configuration file, adding
directives required for the type and style of service

Executing the Web Services Assembler to create a deployment EAR file

Deploying the EAR file using Application Server Control