Tutorial on Web Services HY559 Infrastructure Technologies for - - PowerPoint PPT Presentation

Tutorial on Web Services

HY559 Infrastructure Technologies for Large- Scale Service-Oriented Systems Jason Polakis polakis@csd.uoc.gr

Required Software

• Eclipse IDE for Java developers EE

http://www.eclipse.org/downloads/

• Netbeans IDE

http://netbeans.org/downloads/

• Apache Tomcat
• Apache Tomcat

http://tomcat.apache.org/

• Apache AXIS2

http://axis.apache.org/axis2/java/core/download.cgi

• Apache JUDDI

http://juddi.apache.org/releases.html

Getting Software

• Either directly from given links, or:
• In Ubuntu (as root)
• To search for software

– apt-cache search <program name> – Returns list of <packages> with short description

• To install software

– apt-get install <package> – Installs software, as well as dependencies

Web Services

“Any piece of software that makes itself available

• ver the Internet and uses a standardized XML

messaging system”

• Extremely available
• Language and platform independent
• Distributed application components
• Discoverable via a simple find mechanism
• Components of Web Services

– SOAP (Simple Object Access Protocol) – WSDL (Web Services Description Language) – UDDI (Universal Description, Discovery and Integration)

Web Service Architecture

• Web Service Protocol Stack

–Service transport (transport messages between applications)

• HTTP, SMTP, FTP

–XML messaging (encode messages in common XML format ) –XML messaging (encode messages in common XML format )

• XML-RPC, WS-Addressing, and SOAP

–Service description (describe public interface of service) –Service discovery (centralize services into common registry)

• Programming models:

–REST-based web services –SOAP-based web services

SOAP-based Services

• Use SOAP

–protocol for exchanging structured information

• Use WSDL

–xml-based language for describing Web services

• WSDL file

–created based on the JAVA code in the service –created based on the JAVA code in the service –exposed on the net

• To use service, must create a client

–based on WSDL info

• Messages exchanged in SOAP
• Java API for XML Web Services (JAX-WS) model also used for SOAP
• services. Can use instead of AXIS2.

WSDL example

• Web service
• Single publicly available function sayHello

–argument: string –return value: string

WSDL Definitions element

<definitions name="HelloService" targetNamespace="http://www.examples.com/wsdl/HelloService.wsdl" xmlns="http://schemas.xmlsoap.org/wsdl/" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:tns="http://www.examples.com/wsdl/HelloService.wsdl" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> ................................................

• container of all other elements
• specifies that this document is the HelloService
• Namespace: abstract container providing context -> logical grouping of code
• specifies a targetNamespace attribute (XML convention) → enables self reference
• specifies a default namespace
• specifies numerous namespaces that will be used

................................................ </definitions>

WSDL types

• Describes data types used

between client and server

• Uses W3C XML Schema

specification as default

<types> <schema targetNamespace="http://example.com/stockquote.xsd" xmlns="http://www.w3.org/2000/10/XMLSchema"> <element name="TradePriceRequest"> <complexType> <all> <element name="tickerSymbol" type="string"/>

specification as default choice to define data types

• If the service uses only XML

Schema built-in simple types, such as strings and integers, then types element is not required

</all> </complexType> </element> <element name="TradePrice"> <complexType> <all> <element name="price" type="float"/> </all> </complexType> </element> </schema> </types>

WSDL message

• <message name="SayHelloRequest">

<part name="firstName" type="xsd:string"/> </message> <message name="SayHelloResponse"> <part name="greeting" type="xsd:string"/> </message>

• <message>: describes the data exchanged between service providers and consumers
• Each Web Service has two messages: input and output
• Input: parameters for the Web Service
• Output: return data from the Web Service
• Each message contains zero or more <part> parameters, one for each parameter of

the function

• Each <part> parameter associates with a concrete type defined in the <types>

container element

WSDL portType element

• <portType name="Hello_PortType">

<operation name="sayHello"> <input message="tns:SayHelloRequest"/> <output message="tns:SayHelloResponse"/> </operation> </portType>

• Basically, defines an interface: how unrelated objects communicate with

each other

• "portType“ used to define one or multiple operations
• Operation: a sequence of messages to form an input-output pattern
• WSDL supports four basic patterns of operation

–One-way (input) –Request-response (input, output) –Solicit-response (output, input) –Notification (output)

• Is an abstract definition

WSDL Binding Element

• Concrete implement. of

portType

• How portType operation will

be transmitted

• Where service is located
• name attribute defines the

<binding name="Hello_Binding" type="tns:Hello_PortType"> <soap:binding style="rpc" transport="http://schemas.xmlsoap.org/soap/http"/> <operation name="sayHello"> <soap:operation soapAction="sayHello"/> <input> <soap:body encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"

name of the binding

• type attribute points to the

port for the binding

• Binding: format of messages,

transport type (http)

• Operation: specifies that

soapAction HTTP header identifies the service

• Body: specify the details of

the input and output messages

encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" namespace="urn:examples:helloservice" use="encoded"/> </input> <output> <soap:body encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" namespace="urn:examples:helloservice" use="encoded"/> </output> </operation> </binding>

WSDL port

<service name="Hello_Service"> <documentation>WSDL File for HelloService</documentation> <port binding="tns:Hello_Binding" name="Hello_Port"> <soap:address location="http://www.examples.com/SayHello/"> </port> </service>

• <port> element defines individual endpoint. Specifies single address

for binding

• name attribute: unique name among all ports defined
• binding attribute: refers to binding element

</service>

WSDL service

<service name="Hello_Service"> <documentation>WSDL File for HelloService</documentation> <port binding="tns:Hello_Binding" name="Hello_Port"> <soap:address location="http://www.examples.com/SayHello/"> </port> </service>

• Defines ports supported by Web service
• Service element: a collection of ports
• For each supported protocol, there is one port element
• clients learn from service element

–where to access the service –through which port to access the Web service

• Human-readable documentation
• Binding attribute associates service with binding element

Apache Tomcat

• Open source servlet container
• HTTP web server environment for serving Java

Implements

• Java Servlet: class for responding to HTTP requests

–Create object that receives a request –Generates responses based on requests

• JavaServer Pages (JSP): serve dynamically generated

web pages

–Java code interleaved with static web content –Compiled and executed on server –Resulting HTML or XML document served

Apache AXIS2

• Web service framework
• Will run over Tomcat
• SOAP / WSDL engine
• Also supports RESTful web services
• Web service creation example

– http://netbeans.org/kb/docs/websvc/gs- axis.html#deploy_axis – http://today.java.net/pub/a/today/2006/12/13/in voking-web-services-using-apache-axis2.html

Apache AXIS2

• Send SOAP messages
• Receive and process SOAP messages
• Create a Web service out of a plain Java class
• Create implementation classes for both the
• Create implementation classes for both the

server and client using WSDL

• Easily retrieve the WSDL for a service
• Send and receive SOAP messages with

attachments

• Create or utilize a REST-based Web service

Netbeans IDE

• Creating an Axis2 “Hello World” Web Service
• First setup Axis2 and Tomcat

–http://netbeans.org/kb/docs/websvc/gs- axis.html#setup –http://netbeans.org/kb/docs/websvc/gs- axis.html#axis_options_tomcat

Netbeans IDE example

File -> New Project Name it AxisHello, click Finish Right-click project node , context menu opens choose New -> Other, Wizard opens

Netbeans IDE example

• Click Next, Name the Java class HelloAxisWorld.
• Name the package axishello. Click Finish.
• Application created.

Netbeans IDE example

Netbeans IDE example

• Time to deploy Axis2 web service to the server
• Right-click the web service's node -> Deploy to

Server

• Axis2 AAR file created, copied to .war file used by

server server

• To test service, expand web service node
• Right-click “hello: String” node. -> Test in Browser

Netbeans IDE example

• Browser opens, with test value for variables

Netbeans IDE example

• Change value and press Enter. Results change.

Netbeans IDE example

• Change Web Service Operation.
• Edit Java file in Editor.
• Save the Java file, Redeploy Web Service and

test!!!

Apache JUDDI

• XML-based registry for registering and locating

web service applications

• Interact through SOAP, access WSDL documents

Link1, link2, link3