Web Services and Application Development Frameworks Supplemental Lecture NOT ASSESSIBLE

ICT337 Week13 Supplemental: Web Services 1

Web Services and Application Development Frameworks

Supplemental Lecture**NOT ASSESSIBLE**


Web Services

•Web Services are used primarily as a means for businesses to communicate with each other and with clients.

• They allow organisations to transfer data without knowing the details of the IT systems behind the firewall.

•Web services do not provide the user with a GUI, rather they share business logic, data and processes through a programmatic interface across a network.


Web Services

•Web services allow different applications from different sources to communicate with each other without custom coding, and because all communication is in XML, Web services are not tied to any one operating system or programming language.

– For example, Java can talk to Perl, Windows applications can talk with UNIX applications.


Web Services

• Web Services is our current generation of technologies to allow application-to-application (program-to-program) communication by using XML.

• It covers how to:• define modular, self-describing applications

• publish the applications so they are available

• locate these available applications from anywhere

• invoke these applications remotely

• All these using open Internet standards like XML, HTTP and SMTP.


Web Services

• Please note the difference between this technical use of the word “Web Services” and the non-technical use of “web services”, which refers to any program available through an HTML form over the web.


Distributed Object Technologies

• There have been past efforts to provide program-level object exchange:

• OMG’s CORBA/IIOP (www.corba.org/)

• Microsoft’s DCOM (www.microsoft.com/com/tech/dcom.asp)

• Java RMI (java.sun.com/rmi)

• But all of these technologies suffer from:• Complex set-up and object invocation.

• Platform and language dependence.

• Lack of universal acceptance.

• Lack of extensibility to different problem areas.


What is missing today?

• What is missing today is a consistent way to allow a service (program, application) communication with another:

• There is no consistent framework for describing how a service can be invoked. eg. how do I use a particular PHP application?

• There is no consistent framework for listing available services, and how clients can discover them. eg. how do I find out what other PHP applications are available?

• Location of services on the web and how to use them have to be manually determined, and then manually invoked - they can’t be done by programs automatically.


Developing Web Services

• Various companies and organisations have taken strong initiatives to gain and maintain the loyalty of software developers as we move towards Web Services.

• The two biggest initiatives:• SUN and the Java approach

• Microsoft’s .NET


Microsoft .NET

• .NET is a model targeted at migrating Microsoft’s focus from desktop-based software towards Internet-based software.

• Uses XML as the basis for data exchange.


Components of .NET

• Different parts of the .NET initiative:• Tools for software developers

» Visual Studio .NET» the .NET Framework (consisting of a runtime engine CLR,

languages ASP.NET and C#, XML classes, etc)

• .NET Enterprise Servers» where all the data will reside and be served from» e.g.. BizTalk 2000, Commerce Server 2000, SQL Server 2000, etc.

• .NET operating systems.

• Building Block Services.» Collections of complete services for integrating into other software. » e.g.. Passport .NET for user authentication


Sun’s ONE

• Sun Microsystems's future vision of web services is based on its Open Net Environment (ONE) initiative.

• Heavy promotion of developments in Java technologies

• Especially in its J2EE (Java 2 Enterprise Edition)


Platform Independence

• These are the two biggest initiatives in the industry today to lock Internet service and application developers into one environment.

• Microsoft claims programming language independence with .NET (ONE uses Java), while Sun claims operating system independence with ONE (.NET requires Microsoft OS and servers to operate).


Advantages claimed by .NET

• Cross-language development.• Power and Integration of Visual Studio.Net as a

development tool.• Simpler programming model - easier to pick up.• Interweaved with the operating system - makes

use of the powerful facilities available.


Advantages claimed by Java

• Proven technology in the enterprise environment.• Systems portable to other operating systems.• More advanced and powerful programming

model.• Standards developed by an industry instead of

one vendor.


Other Frameworks

• Other organisations also push their own versions of development frameworks, although not as extensive or as fanatically, as Java or .NET.

• eg.• IBM’s WebSphere

» http://www-3.ibm.com/software/info1/websphere/index.jsp?tab=highlights

• BEA’s WebLogic» http://www.bea.com/products/weblogic/platform/index.shtml

• Apache XML Project» http://xml.apache.org/


Source: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconwebservicesinfrastructure.asp

Web Service Example


Components of Web Services

• In Web Services, we

• describe a service using the Web Services Description Language (WSDL).

• define a way to publish and discover information about Web services using Universal Description, Discovery and Integration (UDDI), and

• invoke the service using Simple Object Access Protocol (SOAP).

• We will look at WSDL and SOAP.


WSDL

• A WSDL document describes– What the service can do– Where it resides– How to invoke it

• WSDL are like IDL but lot more flexible and extensible

• Defines binding for SOAP1.1, HTTP GET/POST and MIME

• WSDL descriptions can be made available from an UDDI registry

WSDL1.1 DocumentStructure

WSDLDocument

[Types]

{Messages}

{Port Types}

{Bindings}

{Services}


WSDL

• WSDL can be generated dynamically by web service frameworks, or from scratch.

• Creating a WSDL from scratch allows for a great deal of flexibility and makes it easier for consumers of web services to create clients when not using proxy-generated classes.

• WSDL has the ability to specify a specific ordering of element, cardinality and optionality, etc.


SOAP• XML based protocol for

exchange of information– Encoding rules for datatype

instances– Convention for representing

RPC invocations

• Designed for loosely-coupled distributed computing– No remote references

• Used with XML Schema• Transport independent• SOAP with Attachments

allow arbitrary data to be packaged.

SOAP1.1 MessageStructure

SOAPEnvelope

HeaderEntries

[Header Element]

Body Element

[FaultElement]


Methods of Implementing in Java

• Many text books on Web Services tend to present far too much theory and few examples that can help you to create your own Web Services.

• No service, regardless of its percieved benefits can be considered useful unless there are applications, tools, and reference materials that make development easier

• Look for very recent text books. Most of the older ones are heavy on theory and use packages that are out of date. Many of the examples wont work unless you can track down an older version of the tool.


Methods of Implementing in Java

• There are Applications/Tools that can make creating and running your own web services in Java very easy. The most notable include.– Java Web Services Developer Pack– AXIS– Electric Glue


AXIS

• Axis is essentially a SOAP engine -- a framework for constructing SOAP processors such as clients, servers, gateways, etc.

• The current version of Axis is written in Java.• Supports 3 modes of services-

– RPC – default – Object based. AXIS hides all the complicated implementation from you.

– Document/Wrapped – uses plain XML.– Message based – XML contained in java XML objects.

• a simple stand-alone server.• a server which plugs into servlet engines such as Tomcat, • extensive support for the Web Service Description Language (WSDL), • emitter tooling that generates Java classes from WSDL. • some sample programs, and • a tool for monitoring TCP/IP packets.• A tool for monitoring raw SOAP messages.


AXIS - Installation• Make sure that you have

– J2SE SDK 1.3 or 1.4: We will use 1.4– A Servlet Container: We will use Tomcat – Download the AXIS package from

http://xml.apache.org/axis• Unzip it and look at the dir. tree. Note

that Axis runs as a Servlet.• Deploy Axis.

– Copy webapps\axis tree to webapps directory of Tomcat.

– Alternatively, modify server.xml of Tomcat.• Run Tomcat.• Test the installation with the test JSP. Load

http://localhost/axis/happy.jsp. This script will tell you if anything else is required.

Direcotry Structure:

axis

docslibwebapps samples

axis

WEB-INF

lib

classes

web.xml

……


AXIS - Setup

• The above will generally install AXIS for use by Tomcat.• If you compile/run anything from the command line, you will need to

make the AXIS jars (axis/lib directory) visible so the java compiler and interpreter can find them.

• You can do this by: -– creating a simple batch file that adds each of these jars to the classpath.

Then run this each time you run from the command line.– Adding each AXIS jar to the CLASSPATH environment variable in

windows. If you do it this way java can find the jars without having to do anything supplemental.

– Create a new environment variable in windows and then include the environment variable when you compile of run java files.

– If you are using JBuilder or similar, specify the jars as required libraries.


Creating web services in AXIS

• Two mechanisms.

• Java Web Service (JWS) – easiest.

• Custom deployment.


Creating web services in AXIS - JWS

• JWS• Simple way to create basic web services• Step 1: Create a java class with the services you want to

deploy.• Step 2: Save the file with a .jws extension.• Step 3: move to webapps/axis directory on Tomcat.

That’s it.public class echo { public String echoBack(String word) { return "You said "+word; }}


Creating web services in AXIS - JWS

• AXIS takes care of everything for you.• If you want to view the wsdl just append ?wsdl to

the end of the url.• As axis creates a wsdl, the web service can be

invoked by any client on any platform using any language (as long as it has any SOAP API).


AXIS – JWS Clients – Manual Client

• You can create a client in one of two ways in AXIS.– Create a client from scratch.– Dynamically create stubs and skeletons using

wdsl2java.

• Code can be embedded into other applications, servlets, JSPs, etc.

• Clients that use AXIS are generally object based. However AXIS does support pure XML exchange.


AXIS – JWS Clients – Option 1

import org.apache.axis.client.Call;import org.apache.axis.client.Service;

public class echoClient{ public static void main(String [] args) throws Exception { String endpoint = "http://localhost/axis/echo.jws"; Service service = new Service(); Call call = (Call) service.createCall(); call.setTargetEndpointAddress( new java.net.URL(endpoint) ); call.setOperationName("echoBack"); String ret = (String) call.invoke( new Object [] { "Your mother" }); System.out.println("Got result : " + ret); } }





• In the second option we use wsdl2java to generate some skeletons and stubs and the write a small client.

• Issue the command: -java org.apache.axis.wsdl.WSDL2Java http://localhost/axis/echo.jws?wsdl

• This will create a package with some java skeletons in it. In our case it created-– localhost\axis\echo_jws\Echo.java– localhost\axis\echo_jws\EchoService.java– localhost\axis\echo_jws\EchoServiceLocator.java– localhost\axis\echo_jws\EchoSoapBindingStub.java

• EchoSoapBindingStub is the one we are concerned with. It provides an object with a number of constructors and an echoBack method that we can use like a normal java object.



import localhost.axis.echo_jws.*;import java.net.URL;import org.apache.axis.client.Service;

public class echoClient2{ public static void main(String [] args) throws Exception { EchoSoapBindingStub ser=new EchoSoapBindingStub(new

URL("http://localhost/axis/echo.jws"),new Service()); String ret = ser.echoBack("my mother"); System.out.println("Got result : " + ret); } }




Creating web services in AXIS – Custom Deployment using Web Service Deployment Descriptor (WSDD) • JWS is easy and fast but with the following

limitations-– you need to expose the source.– the amount of configuration you can do as to how the

service gets accessed is pretty limited.– you can't specify custom type mappings, or control

which Handlers get invoked when people are using your service.

– Using WSDD we can run configurable services with advanced options.


AXIS - WSDD

• Implementing a web service using WSDD only requires a few additional steps.– Compile the java class, rather than just giving it a .jws

extension.– Create a WSDD file which tells AXIS how to deploy the

class.– Run the adminClient to send the service to the AXIS

server for deployment.


AXIS – WSDD – deploying a service

• To deploy echo.java as a service– Compile echo.java.– Move echo.class to webapps\axis\WEB-INF\classes.– Create a WSDD file

<deployment xmlns="http://xml.apache.org/axis/wsdd/" xmlns:java="http://xml.apache.org/axis/wsdd/providers/java"> <service name="echo" provider="java:RPC"> <parameter name="className" value="echo"/> <parameter name="allowedMethods" value="*"/> </service></deployment>



• Use the adminClient to deploy the service. The –p80 at the end is used to specify the port (needed if not running on port 8080).



• Test the service is up and running by loading in a browser. Note the addition of “services” in the url.



• The clients created earlier will still work after we modify the url.


AXIS – WSDD – undeploying a service

• If we need to remove a web service then we need to undeploy it. – Create an undeploy wsdd file

<undeployment xmlns="http://xml.apache.org/axis/wsdd/"> <service name="echo"/></undeployment>

– Run the adminClient to undeploy the service


AXIS – WSDD

• The process of deploying/undeploying is relatively simple.

• Unless we need to configure the service differently, you can copy the wsdd files and change a couple of values which represent the name of your class/service.


AXIS - SoapMonitor

• Axis provides an applet that monitors raw soap requests/responses.

• Can be used for debugging.• Can also be used to determine the XML needed

to support a particular WSDL. WSDL files that are generated dynamically can be a bit hard to read. If you need the XML, you can use wsdl2java, run the client and then you will have the necessary XML.


AXIS – Conclusion

• AXIS provides an easier mechanism to deploy and consume services.

• Similar tools exist in other packages. AXIS is open source.• AXIS can connect to other web services in other

platforms, and can process requests made from clients on other platforms.

• A good choice when starting off in web services. You can use the object-based implementations while you are learning XML/XSLT, etc.

• If you are not undertaking serious development in web services, you wont have to learn XML at all.


References

• ICT211 Week 9 Lecture Notes.• AXIS installation and user guides.• Web Services and the Semantic Web

• http://www.w3.org/2002/ws/• http://www.w3.org/2001/sw/

• Microsoft’s .NET• http://msdn.microsoft.com/net/default.asp

• Java• http://java.sun.com

Documents

Web Services and Application Development Frameworks Supplemental Lecture **NOT ASSESSIBLE**

Web Services and Application Development Frameworks Supplemental Lecture NOT ASSESSIBLE