Java Web Service Tutorial (WSDL & XSD ) - Part 04

WSDL :


WSDL stands for Web Services Description Language

WSDL is an XML based protocol for information exchange in decentralized and distributed environments.

WSDL is the standard format for describing a web service.

WSDL is an interface provided by the webservice publisher to the clients .Using this interface client can understands what are they type of operation the webservice is offering.

WSDL is declard as a  part of UDDI  while registering the webservice in UDDI.

WSDL Elements:

Three major elements of WSDL that can be defined separately and they are:

a.Types - It contains all the datatypes specification what type of values methods accepts.

b.Operations - Define the Methods provided by the Webservice and it's input parameters and it's result.

c.Binding - Contains the end point URL of  the webservice .

Apart from these WSDL also have other elements.

Definition: This element must be the root element of all WSDL documents. It defines the name of the web service, declares multiple namespaces used throughout the remainder of the document, and contains all the service elements described here.

Data types(xsd): the data types - in the form of XML schemas(xsd) or possibly some other mechanism - to be used in the messages. This can define inside the WSDL or can refer from external location.

Message: an abstract definition of the data, in the form of a message presented either as an entire document or as arguments to be mapped to a method invocation.

Operation: the abstract definition of the operation for a message, such as naming a method, message queue, or business process, that will accept and process the message

Port type : an abstract set of operations mapped to one or more end points, defining the collection of operations for a binding; the collection of operations, because it is abstract, can be mapped to multiple transports through various bindings.

Binding: the concrete protocol and data formats for the operations and messages defined for a particular port type.

Port: a combination of a binding and a network address, providing the target address of the service communication.

Service: a collection of related end points encompassing the service definitions in the file; the services map the binding to the port and include any extensibility definitions.

In addition to these major elements, the WSDL specification also defines the following utility elements:

Documentation: element is used to provide human-readable documentation and can be included inside any other WSDL element.

Import: element is used to import other WSDL documents or XML Schemas.

Ex:

<?xml version="1.0" encoding="utf-8"?>
<wsdl:definitions xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:tm="http://microsoft.com/wsdl/mime/textMatching/" xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/" xmlns:mime="http://schemas.xmlsoap.org/wsdl/mime/" xmlns:tns="http://tempuri.org/" xmlns:s="http://www.w3.org/2001/XMLSchema" xmlns:soap12="http://schemas.xmlsoap.org/wsdl/soap12/" xmlns:http="http://schemas.xmlsoap.org/wsdl/http/" targetNamespace="http://tempuri.org/" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/">
<wsdl:types>
<s:schema elementFormDefault="qualified" targetNamespace="http://tempuri.org/">
<s:element name="FahrenheitToCelsius">
<s:complexType>
<s:sequence>
<s:element minOccurs="0" maxOccurs="1" name="Fahrenheit" type="s:string" />
</s:sequence>
</s:complexType>
</s:element>
<s:element name="FahrenheitToCelsiusResponse">
<s:complexType>
<s:sequence>
<s:element minOccurs="0" maxOccurs="1" name="FahrenheitToCelsiusResult" type="s:string" />
</s:sequence>
</s:complexType>
</s:element>
<s:element name="CelsiusToFahrenheit">
<s:complexType>
<s:sequence>
<s:element minOccurs="0" maxOccurs="1" name="Celsius" type="s:string" />
</s:sequence>
</s:complexType>
</s:element>
<s:element name="CelsiusToFahrenheitResponse">
<s:complexType>
<s:sequence>
<s:element minOccurs="0" maxOccurs="1" name="CelsiusToFahrenheitResult" type="s:string" />
</s:sequence>
</s:complexType>
</s:element>
<s:element name="string" nillable="true" type="s:string" />
</s:schema>
</wsdl:types>
<wsdl:message name="FahrenheitToCelsiusSoapIn">
<wsdl:part name="parameters" element="tns:FahrenheitToCelsius" />
</wsdl:message>
<wsdl:message name="FahrenheitToCelsiusSoapOut">
<wsdl:part name="parameters" element="tns:FahrenheitToCelsiusResponse" />
</wsdl:message>
<wsdl:message name="CelsiusToFahrenheitSoapIn">
<wsdl:part name="parameters" element="tns:CelsiusToFahrenheit" />
</wsdl:message>
<wsdl:message name="CelsiusToFahrenheitSoapOut">
<wsdl:part name="parameters" element="tns:CelsiusToFahrenheitResponse" />
</wsdl:message>
<wsdl:message name="FahrenheitToCelsiusHttpPostIn">
<wsdl:part name="Fahrenheit" type="s:string" />
</wsdl:message>
<wsdl:message name="FahrenheitToCelsiusHttpPostOut">
<wsdl:part name="Body" element="tns:string" />
</wsdl:message>
<wsdl:message name="CelsiusToFahrenheitHttpPostIn">
<wsdl:part name="Celsius" type="s:string" />
</wsdl:message>
<wsdl:message name="CelsiusToFahrenheitHttpPostOut">
<wsdl:part name="Body" element="tns:string" />
</wsdl:message>
<wsdl:portType name="TempConvertSoap">
<wsdl:operation name="FahrenheitToCelsius">
<wsdl:input message="tns:FahrenheitToCelsiusSoapIn" />
<wsdl:output message="tns:FahrenheitToCelsiusSoapOut" />
</wsdl:operation>
<wsdl:operation name="CelsiusToFahrenheit">
<wsdl:input message="tns:CelsiusToFahrenheitSoapIn" />
<wsdl:output message="tns:CelsiusToFahrenheitSoapOut" />
</wsdl:operation>
</wsdl:portType>
<wsdl:portType name="TempConvertHttpPost">
<wsdl:operation name="FahrenheitToCelsius">
<wsdl:input message="tns:FahrenheitToCelsiusHttpPostIn" />
<wsdl:output message="tns:FahrenheitToCelsiusHttpPostOut" />
</wsdl:operation>
<wsdl:operation name="CelsiusToFahrenheit">
<wsdl:input message="tns:CelsiusToFahrenheitHttpPostIn" />
<wsdl:output message="tns:CelsiusToFahrenheitHttpPostOut" />
</wsdl:operation>
</wsdl:portType>
<wsdl:binding name="TempConvertSoap" type="tns:TempConvertSoap">
<soap:binding transport="http://schemas.xmlsoap.org/soap/http" />
<wsdl:operation name="FahrenheitToCelsius">
<soap:operation soapAction="http://tempuri.org/FahrenheitToCelsius" style="document" />
<wsdl:input>
<soap:body use="literal" />
</wsdl:input>
<wsdl:output>
<soap:body use="literal" />
</wsdl:output>
</wsdl:operation>
<wsdl:operation name="CelsiusToFahrenheit">
<soap:operation soapAction="http://tempuri.org/CelsiusToFahrenheit" style="document" />
<wsdl:input>
<soap:body use="literal" />
</wsdl:input>
<wsdl:output>
<soap:body use="literal" />
</wsdl:output>
</wsdl:operation>
</wsdl:binding>
<wsdl:binding name="TempConvertSoap12" type="tns:TempConvertSoap">
<soap12:binding transport="http://schemas.xmlsoap.org/soap/http" />
<wsdl:operation name="FahrenheitToCelsius">
<soap12:operation soapAction="http://tempuri.org/FahrenheitToCelsius" style="document" />
<wsdl:input>
<soap12:body use="literal" />
</wsdl:input>
<wsdl:output>
<soap12:body use="literal" />
</wsdl:output>
</wsdl:operation>
<wsdl:operation name="CelsiusToFahrenheit">
<soap12:operation soapAction="http://tempuri.org/CelsiusToFahrenheit" style="document" />
<wsdl:input>
<soap12:body use="literal" />
</wsdl:input>
<wsdl:output>
<soap12:body use="literal" />
</wsdl:output>
</wsdl:operation>
</wsdl:binding>
<wsdl:binding name="TempConvertHttpPost" type="tns:TempConvertHttpPost">
<http:binding verb="POST" />
<wsdl:operation name="FahrenheitToCelsius">
<http:operation location="/FahrenheitToCelsius" />
<wsdl:input>
<mime:content type="application/x-www-form-urlencoded" />
</wsdl:input>
<wsdl:output>
<mime:mimeXml part="Body" />
</wsdl:output>
</wsdl:operation>
<wsdl:operation name="CelsiusToFahrenheit">
<http:operation location="/CelsiusToFahrenheit" />
<wsdl:input>
<mime:content type="application/x-www-form-urlencoded" />
</wsdl:input>
<wsdl:output>
<mime:mimeXml part="Body" />
</wsdl:output>
</wsdl:operation>
</wsdl:binding>
<wsdl:service name="TempConvert">
<wsdl:port name="TempConvertSoap" binding="tns:TempConvertSoap">
<soap:address location="http://www.w3schools.com/webservices/tempconvert.asmx" />
</wsdl:port>
<wsdl:port name="TempConvertSoap12" binding="tns:TempConvertSoap12">
<soap12:address location="http://www.w3schools.com/webservices/tempconvert.asmx" />
</wsdl:port>
<wsdl:port name="TempConvertHttpPost" binding="tns:TempConvertHttpPost">
<http:address location="http://www.w3schools.com/webservices/tempconvert.asmx" />
</wsdl:port>
</wsdl:service>
</wsdl:definitions>

The following wsdl is obtained from the webservice TempConvert of w3schools.com
URL : http://www.w3schools.com/webservices/tempconvert.asmx?WSDL
Now,examine this WSDL closely.

wsdl definition- This contains lot of name space we don't need to care about this,these are all can be added/generated by tools. Generally a WSDL is generated by Tools.But we need to understand it content which help us to write the client code.

wsdl types : This contains the in-built xsd(Xml Schema Definition)for the types methods accept.We will discuss about XSD in detail in next part.

wsdl message : This contains the message name which can refer at various place for mention the types of input and output parameters for webservice methods.

wsdl operation : It contains the Methods provided by the webservice.

wsdl input/output : It contains the Methods inputs and output parameter name and it's type.Normally in big WSDL it being refer in external xsd's.

Other elements we actually no need to worry.Since once we obtained the WSDL ,next thing we have to do is generate java classes from it .It can done by tools.Once we obtained the java classes we can write the client code easily and  make a request to the webservice.

In the next part we will in detail about xsd, because it is important to understand what type of data a method accept. Please provide your comments.


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