SENGER 060504 Web Services

8/14/2019 SENGER 060504 Web Services

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Web ServicesWeb Services

Martin SengerMartin Senger

[email protected]@ebi.ac.uk


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AbstractAbstract

Web Services is a technologyWeb Services is a technology

applicable for computationallyapplicable for computationally

distributed problems, includingdistributed problems, including

access to large databasesaccess to large databases

What other technologies were/areWhat other technologies were/are

available and how they compare withavailable and how they compare with

Web Services?Web Services?The main buzzwords:The main buzzwords:

Integration & Standardization & AccessIntegration & Standardization & Access

by programsby programs


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Why to use more than oneWhy to use more than one

computer?computer? Distributed resourcesDistributed resources

access to shared dataaccess to shared data

access to shared programsaccess to shared programs

access to CPU (e.g. many desktop PCsaccess to CPU (e.g. many desktop PCs

together), to memory, to special devicestogether), to memory, to special devices

(e.g. printer)(e.g. printer) Complete independence on theComplete independence on the

internal implementationinternal implementation


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DistributedDistributed

architecturearchitecture gives

gives

access to distributed resourcesaccess to distributed resources

development encapsulationdevelopment encapsulation

maintainability, re-usability, legacy-maintainability, re-usability, legacy-

awarenessawareness

implementation independenceimplementation independence

requires

requires adding a communication layeradding a communication layer

between partsbetween parts

synchronization of effortssynchronization of efforts includin such nast thin s as distributedincludin such nast thin s as distributed


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Sending

requests,

getting

results

Waiting for

requests(known location,

known port)

Communication protocol, Data format

Distributed architecture

Basic questions are:

What kind of protocol to use, and whatdata to transmit

What to do with requests on the serverside


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Sending

requests,

getting

results

Waiting for


known port)

Data as name/value pairs

Traditional CGI-based approach

cgi-bin scripts:

Data transmitted as name-value pairs(HTML forms)

Transport over (state-less) HTTP protocol

no standards for keeping user sessions(state-fullness)


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Sending

requests,

getting

results

Waiting for


known port)

Data in binary format

CORBA-based approach

CORBA:

Data transmitted as objects (at least itlooks like that)

Transport (usually) over well standardisedIIOP protocol

user sessions (state-fullness) very inter-


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Sending

requests,

getting

results

Waiting for


known port)

Data in XML format

SOAP-based communication

SOAP:

Data in a well-defined XML formatTransport over various protocols

HTTP, SMTP are the most used, perhapsbecause they are firewall-friendly

server side: either an RPC call or a


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Web servicesWeb services

A collection of XML-basedA collection of XML-basedtechnologies developed by the e-technologies developed by the e-

business community to address issuesbusiness community to address issues

of:of: service discoveryservice discovery

interoperable data exchange and/orinteroperable data exchange and/or

application invocationapplication invocation service compositions (workflow, businessservice compositions (workflow, business

processes)processes)

Major developers include:Major developers include:


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W3C (working group)W3C (working group)

definitiondefinition

"A Web service is a software"A Web service is a software

applicationapplication identified by a URIidentifiedby a URI, whose, whose

interfaces and bindings are capableinterfaces and bindings are capableof being defined,of being defined, described anddescribed and

discovereddiscoveredas XML artefacts. A Webas XML artefacts. A Web

service supports direct interactionsservice supports direct interactions

with other software agents usingwith other software agents usingXMLXML

based messagesbased messages exchanged viaexchanged via

internet-based protocolsinternet-based protocols."."

- - -htt : www.w3c.or TR 2002 WD-wsa-re s-


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Web Services ArchitectureWeb Services Architecture

Let a program click on a web page


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Web Services StackWeb Services Stack


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SOAPSOAP

SSimpleimple OObjectbject AAccessccess PProtocolrotocol

http://www.w3c.org/TR/SOAP/http://www.w3c.org/TR/SOAP/

A lightweight protocol for exchangeA lightweight protocol for exchangeof information in a decentralised,of information in a decentralised,

distributed environmentdistributed environment

Two different styles to use:Two different styles to use:

to encapsulate RPC calls using theto encapsulate RPC calls using the

extensibility and flexibility of XMLextensibility and flexibility of XML

or to deliver a whole documentor to deliver a whole document

without any method calls encapsulatedwithout any method calls encapsulated


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Request:Request:setHelloMessasetHelloMessa

gege

Request:getHelloMessag

e


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XML Messaging UsingXML Messaging Using

SOAPSOAP


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WSDLWSDL

WWebeb SServiceservices DDefinitionefinition LLanguageanguage

http://www.w3.org/TR/wsdl/http://www.w3.org/TR/wsdl/

An XML-based language forAn XML-based language fordescribing Web Servicesdescribing Web Services

what the service does (description)what the service does (description)

how to use it (method signatures)how to use it (method signatures)

where to find the servicewhere to find the service

ItIt does notdoes notdepend on the underlyingdepend on the underlying

protocolprotocol

-But: It is not much human-readable


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Hello.wsdlHello.wsdl

message="intf:setHelloMessageResponse"/>


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UDDI (and alternatives)UDDI (and alternatives)

UUniversalniversal DDescription,escription, DDiscovery andiscovery andIIntegrationntegration

http://www.uddi.orghttp://www.uddi.org

UDDI creates a platform-independent,UDDI creates a platform-independent,open framework & registry for:open framework & registry for:

Describing servicesDescribing services

Discovering businessesDiscovering businesses

Integrating business servicesIntegrating business services

The UDDI may be less used thanThe UDDI may be less used than

predicted, especially on the Internetpredicted, especially on the Internetlevel


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BioMobyBioMobyhttp://biomoby.orghttp://biomoby.org


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A Web Service exampleA Web Service example

in Javain Java

SOAP-awareSOAP-aware

ServletServlet(e.g. Apache Axis)(e.g. Apache Axis)

Any classprocessing

the incomingrequests

(business logic

Any classprocessing

the incomingrequests

(business logic

Any classprocessing

the incoming

requests(business logic

Any classAny class

processingprocessing

the incomingthe incomingrequestsrequests

(business logic(business logic

HTTP ServerHTTP Server

Servlet engine (e.g. Apache Tomcat)Servlet engine (e.g. Apache Tomcat)

Sending

requests,

getting

results


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Usual principles of JavaUsual principles of Java

toolkitstoolkits Writing server is easier than writing clientsWriting server is easier than writing clients

(but only regarding the toolkit, not the(but only regarding the toolkit, not thebusiness logic)business logic)

ServersServers maymay be written independently onbe written independently on

the used toolkitthe used toolkit Always test interoperability with a non-Always test interoperability with a non-

Java client (because of data serializationJava client (because of data serializationand de-serialization)and de-serialization)

Steps:Steps: write your service implementationwrite your service implementation make all your classes available to the toolkitmake all your classes available to the toolkit deploy your servicedeploy your service (usually done just once)(usually done just once)

restart the whole servlet enginerestart the whole servlet engine

test it with a client requesttest it with a client request


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Java SOAP ToolkitsJava SOAP Toolkits

Apache SOAP (was IBMs SOAP4J)Apache SOAP (was IBMs SOAP4J)

Apache Axis (a follow-on to theApache Axis (a follow-on to the

Apache SOAP)Apache SOAP)

and many othersand many others

but lets stay with Apache Axis:but lets stay with Apache Axis:

http://http://ws.apache.orgws.apache.org/axis//axis/
http://ws.apache.org/axis/http://ws.apache.org/axis/http://ws.apache.org/axis/http://ws.apache.org/axis/http://ws.apache.org/axis/http://ws.apache.org/axis/http://ws.apache.org/axis/http://ws.apache.org/axis/http://ws.apache.org/axis/


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package hello;public interface HelloWorld {

String getHelloMessage();void setHelloMessage (String newHello);

}

package hello;public class HelloWorldService

implements HelloWorld {String message = "Hello, world!";

public String getHelloMessage() {return message;

}public void setHelloMessage (String newMessage) {

message = newMessage;}

}

hello/HelloWorld.java

hello/HelloWorldService.java

H ll W ldCli t j


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import org.apache.axis.client.*;public class HelloWorldClient {

public static void main (String [] args) {try {// prepare the call (the same for all called methods)

Call call = (Call) new Service().createCall();call.setTargetEndpointAddress(new java.net.URL("http://localhost:8080/axis/services/Hello"));

// call "get message"if (args.length == 0) {call.setOperationName ("getHelloMessage");String result = (String) call.invoke ( new Object [] {} );

System.out.println (result);System.exit (0);

}

// call "set message" and afterwards "get message"call.setMaintainSession (true); // TRY also without this line...call.setOperationName ("setHelloMessage");

call.invoke ( new Object [] { args[0] } );call.setOperationName ("getHelloMessage");System.out.println (call.invoke ( new Object [] {} ));

} catch (Exception e) {System.err.println ("ERROR:\n" + e.toString());

}}

}

HelloWorldClient.java

Generated forGenerated for


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Generated forGenerated for

HelloWorldHelloWorld

HelloWorldServiceLocator

implements

HelloWorldService

HelloSoapBindingStub

implements

HelloWorld

getHello()

1. Make an instance of this

Call methods on this proxy object

2. Use it to make an instance of t

e o or en rom u s


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public class HelloWorldClientFromStubs {public static void main (String [] args) {

try {// prepare the calls (the same for all called methods)hello.generated.HelloWorldService service =new hello.generated.HelloWorldServiceLocator();

hello.generated.HelloWorld myHelloProxy = service.getHello();

// call "get message"if (args.length == 0) {

String result = myHelloProxy.getHelloMessage()System.out.println (result);System.exit (0);

}

// call "set message" and afterwards "get messagemyHelloProxy.setHelloMessage (args[0]);System.out.println (myHelloProxy.getHelloMessage());

} catch (Exception e) {System.err.println ("ERROR:\n" + e.toString());

}}

}

e o or en rom u s.java


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Java XML DataJava XML Data

MappingMapping How Java objects are convertedHow Java objects are converted

to/from XML data (in order to be ableto/from XML data (in order to be able

to be put into SOAP messages)to be put into SOAP messages)

Important especially for the non-Important especially for the non-

basic data typesbasic data types

Its easier if your non-basic dataIts easier if your non-basic data

types are Java Beans (havingtypes are Java Beans (having setset//getgetmethods for members)methods for members)

A We erv ce examp ee erv ce examp e


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A We erv ce examp ee erv ce examp ein Perlin Perl

This is a module implementingthe business logic

package HelloPerl;use strict;use vars qw( $Message );

$Message = 'Hello, here is Perl.';sub getHelloMessage { $Message; }sub setHelloMessage { $Message = shift; }1;

This is a cgi-bin

script

#!/usr/bin/perl -w -- Perl

use SOAP::Transport::HTTP;SOAP::Transport::HTTP::CGI

-> dispatch_to('HelloPerl')-> handle;

#!/usr/bin/perl wuse SOAP::Lite

on_fault => sub {};print SOAP::Lite

-> uri ('HelloPerl')-> proxy ('http://localhost/cgi-bin/helloserver.cgi')-> getHelloMessage

-> result;

This is a client


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SOAP::LiteSOAP::Lite

a collection of (many) modulesa collection of (many) modules but they are loaded automatically when neededbut they are loaded automatically when needed

supports SOAP 1.1 specificationsupports SOAP 1.1 specification

all methods can be used for both settingall methods can be used for both setting

and retrieving values:and retrieving values: if you provide no parameters, you will get current value,if you provide no parameters, you will get current value,

and if parameters are provided, a new value will beand if parameters are provided, a new value will be

assigned to the objectassigned to the object

and the method in question will return the current objectand the method in question will return the current object

(if not stated otherwise) which is is suitable for stacking(if not stated otherwise) which is is suitable for stackingthese calls like:these calls like:

$lite = SOAP::Lite$lite = SOAP::Lite

-> uri(openBQS')-> uri(openBQS')

-> proxy('http://industry.ebi.ac.uk/soap/openBQS')-> proxy('http://industry.ebi.ac.uk/soap/openBQS')

;;


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Using wsdl - directlyUsing wsdl - directly

#!/usr/bin/perl -w

use SOAP::Lite on_fault => sub {};print SOAP::Lite

-> service ('file:/home/senger/ws-ws/perl/Hello.wsdl')-> setHelloMessage (123);

getting .wsdl file by using its URL then, you do not need to worry about

autotyping

#!/usr/bin/perl -w

use SOAP::Lite on_fault => sub {};my $service = SOAP::Lite -> service ('file:./Hello.wsdl');$service->setHelloMessage ($ARGV[0] or "Hello!!!");print $service->getHelloMessage, "\n";

W y to use Wey to use e


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W y to use Wey to use eServicesServices

(comparing to CORBA)(comparing to CORBA) WS are easier to deploy because ofWS are easier to deploy because of

their firewall-friendlinesstheir firewall-friendliness

WS are quite well marketed (bothWS are quite well marketed (both

from IT companies and Open Sourcefrom IT companies and Open Sourceprojects)projects)

However:However:

user sessions are less standardiseduser sessions are less standardised many parts yet-to-be-done (notification,many parts yet-to-be-done (notification,

transactions, security, etc.)transactions, security, etc.)

The programming effort andThe programming effort and


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1. What is similar1. What is similar

The programming effort andThe programming effort andmaintainability is roughly the samemaintainability is roughly the sameboth for Web Services and CORBAboth for Web Services and CORBA

For CORBA I need an ORBFor CORBA I need an ORB but do you know anybody doing WS withoutbut do you know anybody doing WS without

a SOAP toolkit?a SOAP toolkit?

For CORBA I need an IDL compilerFor CORBA I need an IDL compiler

not always (ask Perl folks)not always (ask Perl folks) for WS you use frequently stubs generatedfor WS you use frequently stubs generated

from WSDLfrom WSDL

similar answers for valuetype/customsimilar answers for valuetype/custom

encoding, etc.encoding, etc.


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2. What is2. What is (IMHO)(IMHO) betterbetter

WS are easier to deploy because ofWS are easier to deploy because of

their firewall-friendlinesstheir firewall-friendliness

WS are quite well marketed (bothWS are quite well marketed (both

from IT companies and Open Sourcefrom IT companies and Open Source

projects)projects)

Integration of WS into workflowsIntegration of WS into workflows

seems to be very dynamic and veryseems to be very dynamic and very

real topicreal topic

comparing with CORBA Componentscomparing with CORBA Components


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3. What is3. What is (IMHO)(IMHO) worseworse

Peer-to-peer access is problematicPeer-to-peer access is problematic

notification by server-push is harder tonotification by server-push is harder to

achieveachieve

User sessions (servers state-User sessions (servers state-

fullness) are less standardisedfullness) are less standardised

and therefore less inter-operableand therefore less inter-operable

Many parts yet-to-be-done, or theyMany parts yet-to-be-done, or they

are quite complex (notification,are quite complex (notification,

transactions, security, etc.)transactions, security, etc.)


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So what?So what?

Don't throw the baby out with theDon't throw the baby out with the

bathwaterbathwater

combine the existing projects with acombine the existing projects with a

new Web Services layer; in most cases itnew Web Services layer; in most cases itis not so difficultis not so difficult

Apply existing standards to new WebApply existing standards to new Web

Services projectsServices projects think MDA it may help, even withoutthink MDA it may help, even without

the whole OMG adoption processthe whole OMG adoption process


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ConclusionsConclusions

Distributed computing is inevitableDistributed computing is inevitable

More accesses by programs than byMore accesses by programs than byclicking on hyperlinksclicking on hyperlinks

More technologies of distributedMore technologies of distributedarchitecture will collaboratearchitecture will collaborate

The better standards we have theThe better standards we have the

better results well getbetter results well get Web Services is not a new hype but aWeb Services is not a new hype but a

trend to followtrend to follow

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SENGER 060504 Web Services