created where necessary.
is functionality that can be provided by
Running a JAX-RPC-compliant, WSDL-
the ESB itself and is typically common to
generation tool over this kind of a Java
• portTypes should have a small number of
all services.
interface results in the WSDL in Listing
operations that reflect the business tasks.
These features can also be described
by the WSDL or by policy statements in-
cluded within the WSDL; see Figure 2.
This step in the project lifecycle can be
considered the point at which the WSDL
changes from being a description of the
API to becoming a contract between the
service and its clients. The additional fea-
tures provided by the ESB, such as secu-
rity, management capabilities, auditing,
logging, or even custom features can be
added. These can be added across the dif-
ferent services implemented using an in-
terceptor or message-handler framework.
This is an area where you can expect an
ESB to provide components that can be
easily combined with the services you
have built.
Building Business Processes
With services that reflect business func-
tions in place on the ESB, new services
that model complete business process-
es can be created. Business Process Ex-
Figure 2: Implementing the service policy.
ecution Language (BPEL) is a language
28
Dr. Dobb’s Journal, February 2005
http://www.ddj.com
designed for just this purpose. A BPEL
solve integration issues. These should be
requires a good understanding of the prin-
editor should be provided to enable the
solved in the lower layers.
cipals of SOA to evaluate the output of
existing services to be combined into
the tools provided by the ESB. The effort
processes. The ease with which new
Conclusion
put into the design of individual services
business processes can be developed de-
An ESB provides effective tools and ser-
exposed on the ESB results in benefits
pends in part on how successful the de-
vices that can be used to construct an
when the task of business-process mod-
sign of the business services has been.
SOA. However, careful thought and plan-
eling is performed.
BPEL is a language designed to model
ning is required in order to ensure that
business processes — it is not a place to
the resulting system is truly an SOA. This
DDJ
Listing One
<input message="tns:processApplication"/>
<output message="tns:processApplicationResponse"/> public class CustomerDetails {
</operation>
public String name;
<operation name="setCarDetails">
public String street;
<input message="tns:setCarDetails"/>
public String city;
<output message="tns:setCarDetailsResponse"/> public String state;
</operation>
}
</portType>
public class CarDetails {
</definitions>
public String make;
public String model;
}
Listing Three
public class BillingInfo {
public String creditCardNumber;
<?xml version="1.0" encoding="UTF-8"?> public String exprityDate;
<wsdl:definitions name="InsuranceService"
}
targetNamespace="http://capeclear.com/CarInsurance.wsdl"
public interface InsurancePortType {
xmlns="http://schemas.xmlsoap.org/wsdl/"
public String createApplication( CustomerDetails customer ); xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"
public void setCarDetails( String reference, CarDetails details ); xmlns:tns="http://capeclear.com/CarInsurance.wsdl"
public Decimal calculateQuote( String reference );
xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/"
public void processApplication( String reference, BillingInfo info ); xmlns:xsd="http://www.w3.org/2001/XMLSchema"
}
xmlns:xsd1="http://capeclear.com/CarInsurance.xsd">
<wsdl:types>
<xsd:schema targetNamespace="http://capeclear.com/CarInsurance.xsd"> Listing Two
<xsd:element name="InsuranceApplication">
<xsd:complexType>
<?xml version="1.0" encoding="UTF-8"?>
<xsd:sequence>
<definitions name="Insurance"
<xsd:element name=
targetNamespace="http://capeclear.com/CarInsurance.wsdl"
"CustomerDetails" type="xsd1:CustomerDetails"/> xmlns="http://schemas.xmlsoap.org/wsdl/"
<xsd:element name=
xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"
"CarDetails" type="xsd1:CarDetails"/> xmlns:tns="http://capeclear.com/CarInsurance.wsdl"
<xsd:element name=
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
"BillingInformation" type="xsd1:BillingInformation"/> xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/"
</xsd:sequence>
xmlns:xsd1="http://capeclear.com/CarInsurance.xsd">
</xsd:complexType>
<types>
</xsd:element>
<xsd:schema targetNamespace="http://capeclear.com/CarInsurance.xsd">
<xsd:complexType name="BillingInformation">
<xsd:complexType name="BillingInformation">
<xsd:sequence>
<xsd:sequence>
<xsd:element name="creditCardNumber" type="xsd:string"/>
<xsd:element name="creditCardNumber" type="xsd:string"/>