Developing Web Services

Developing Web Services

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Agenda

Quick Review Web Service Architecture Web Services Interoperability Java APIs .NET APIs

The World, Late 80’s-Early 90’s

Database

Organization

Web Apps

DatabaseOrganization

Internet

Web AppServer

Web Services


Internet

Web AppServer

Database

Organization

Web AppServer

Database

Organization

Web AppServer


Web AppServer

Web Service Architecture

Provider Agent Architecture Requestor Agent Architecture Provider and Requestor Combined Asynchronous web services Web Services And The Rest Of Your

Application

Web Services Architecture

HTTP (or otherbinding) Listener

HTTP (or otherbinding) Sender

ProviderApplication Logic

RequestorApplication Logic

SOAPMessageRequest

Object(s) tosend

ObjectsXML-ified

SOAPMessageResponse

ExtractedXML

Object(s) tosend

Object(s) tosend Object(s) to

send

Object(s) tosend

ResponseObject(s) Object(s) to

send

Object(s) tosend

Object(s)response Object(s) to

send

Object(s) tosend

Object(s)received

SOAPMessageRequest

ObjectsXML-ified

SOAPMessageResponse

ExtractedXML

Requestor & Provider combined

HTTP (or otherbinding) Listener

HTTP (or otherbinding) Sender

ProviderApplication Logic

RequestorApplication Logic

SOAPMessageRequest

Object(s) tosend

ObjectsXML-ified

SOAPMessageResponse

ExtractedXML

Object(s) tosend

Object(s) tosend Object(s) to

send

Object(s) tosend

ResponseObject(s) Object(s) to

send

Object(s) tosend

Object(s)response Object(s) to

send

Object(s) tosend

Object(s)received

SOAPMessageRequest

ObjectsXML-ified

SOAPMessageResponse

ExtractedXML

From Monday: Faults With XML-RPCHTTP/1.1 200 OKConnection: closeContent-Length: 426Content-Type: text/xmlDate: Fri, 17 Jul 1998 19:55:02 GMTServer: UserLand Frontier/5.1.2-WinNT

<?xml version="1.0"?><methodResponse> <fault> <value> <struct> <member> <name>faultCode</name> <value><int>4</int></value> </member> <member> <name>faultString</name> <value><string>Too many parameters.</string></value> </member> </struct> </value> </fault> </methodResponse>

From Monday:UDDI, Metatags & the Yahoo/Google Metaphor

Metaphor: “UDDI is to web services like Yahoo or Google is to the traditional web”

Q: “Do you use meta tags for web services like you do with Google and Yahoo?”

A: “No. UDDI is structured data. They aren’t needed. Search engines need them because web pages aren’t structured.”

Better Metaphor: “UDDI is like a phone book. UDDI is somewhat like Yahoo.”

Web Services Interoperability

Web Services is interoperable because it is rooted in text (XML) and is independent of a particular transport (http, smtp, etc.)

However… the different components of web services may have interoperability problems

Similar to the Browser Wars of the mid ’90’s – standards exist, but product-specific implementations and additional features vary

Web Services Interoperability Web Services World is much more complex than the

web The main point of fragmentation for the Browser

Wars was the browser For Web Services, there are (and will be) many

tools – people won’t parse SOAP messages directly More tools, more points of fragmentation, more

interoperability problems No one makes money selling commodity software Innovative open source developers will move faster

than standards

WS-I

Web Services Interoperability (WS-I) Organization: Industry group that promotes interoperability

WS-I Basic Profile 1.0: SOAP 1.1 WSDL 1.1 Must use HTTP binding, should use HTTP 1.1 XML Schema Part 1, Part 2 May use HTTPS

Similar to the J2EE certification program

Interoperability – bottom line

Over time, software will be talking to software more and more over the Internet

Software will have to be more and more interoperable

It’s doubtful that a single web app development platform (i.e., J2EE vs. NET vs. LAMP) will monopolize

The big bosses don’t want to hear about the J2EE vs. .NET vs. LAMP

Over time, web services is best positioned to solve interoperability problems

Developers’ Burden…

It’s the software developers’ burden…. to ensure interoperability by the tools, patterns

and strategies they Scrutinize tools & middleware from an

interoperability perspective

Examples

JAXP DOM SAAJ JAXB JAX-RPC

Building DOM Documentpublic static Document buildDom() { DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); try { DocumentBuilder builder = factory.newDocumentBuilder(); return builder.newDocument(); } catch (ParserConfigurationException pce) { // Parser with specified options can't be built pce.printStackTrace(); } catch (IOException ioe) { ... } }

Adding Elements

document = builder.newDocument();

// Create from whole cloth

Element root = (Element)

document.createElement("rootElement");

document.appendChild(root);

root.appendChild(document.createTextNode(“Text") );

root.setAttribute(“name”,”value”);

Loading DOM Documents

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

try {

DocumentBuilder builder = factory.newDocumentBuilder();

document = builder.parse( new File(“doc.xml”) );

} catch (SAXParseException spe) {

…

}

Reading DOM Documents

Example: jwsdp/jaxp/samples/DOMEcho/DOMEcho.java

Reading SAX Documents

Example: jwsdp/jaxp/sax/samples/Echo4.java

SAAJ

SOAP with Attachments API for Java (SAAJ) Simple overlay for creating and consuming

SOAP messages On the requestor side, it abstracts the

transport interface Higher level standards (JAX-RPC, JAXM)

use it

Web Services ProviderMessageFactory messageFactory = MessageFactory.newInstance();

// Create a messageSOAPMessage message = messageFactory.createMessage();

// Get the SOAP header from the message and remove it SOAPHeader header = message.getSOAPHeader();header.detachNode();

// Get the SOAP body from the messageSOAPBody body = message.getSOAPBody();

// Add the DOM document to the message bodySOAPBodyElement docElement = body.addDocument(doc);

message.saveChanges();

message.writeTo(out);

WebServicesRequestor

SOAPMessage message = getSOAPMessage();// The requestor constructs the message

SOAPConnectionFactory sCFactory = SOAPConnectionFactory.newInstance();

SOAPConnection conn = sCFactory.createConnection();

SOAPMessage response = conn.call(message,new URL("http://localhost:8080/servlets-examples/servlet/servlets.WebServicesProvider"));

response.writeTo(System.out);

Marshalling And Unmarshalling Objects

Often, a requestor serializes an object to XML

The provider generates an object of the same type from the XML

The marshalling & unmarshalling code is pretty mechanical

JAXB provides a mechanism to bind Java objects to XML schemas

Marshalling & unmarshalling is transparent

JAXB Binding Process

Unmarshalling An Object

JAXBContext jc = JAXBContext.newInstance(

"com.acme.foo:com.acme.bar" );

Unmarshaller u = jc.createUnmarshaller();

FooObject fooObj = (FooObject)u.unmarshal( new URL(“http://mdthomas.org/fooObject.xml“) );

Unmarshalling From SOAPPayrollObject getPayroll(SOAPBody soapBody) {

PayrollObject payroll = null;

try { JAXBContext jc = JAXBContext.newInstance( "com.acme.foo" ); Unmarshaller u = jc.createUnmarshaller();

Iterator children = soapBody.getChildElements(“Payroll”); payrollNode = (Node) children.next(); PayrollObject payroll = u.unmarshal( payrollNode ); } catch (Exception e) { //handle } return payroll;}

ValidationPayrollObject getPayroll(SOAPBody soapBody) {

PayrollObject payroll = null;

try { JAXBContext jc = JAXBContext.newInstance( "com.acme.foo" ); Unmarshaller u = jc.createUnmarshaller(); u.setValidating(true);

Iterator children = soapBody.getChildElements(“Payroll”); payrollNode = (Node) children.next(); PayrollObject payroll = u.unmarshal( payrollNode ); } catch (Exception e) { //handle } return payroll;}

Marshallerpublic class WebServicesProvider extends HttpServlet {

public void service (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { OutputStream out = response.getOutputStream(); JAXBContext jc = JAXBContext.newInstance( "com.acme.foo" ); PayrollObject payroll = goGetThePayrollObject();

Marshaller m = jc.createMarshaller(); m.marshal( payroll, out); out.close(); } }

JAX-RPC

JAX-RPC gives you end-to-end remote procedure calls

Hides the details we’ve been discussing thus far

Writing An Interface

package helloservice;

import java.rmi.Remote;import java.rmi.RemoteException;

public interface HelloIF extends Remote {

public String sayHello(String s) throws RemoteException;

}

Writing The Implementation

package helloservice;

public class HelloImpl implements HelloIF {

public String message ="Hello";

public String sayHello(String s) { return message + s; }}

jaxrpc-ri.xml file<?xml version="1.0" encoding="UTF-8"?><webServices xmlns="http://java.sun.com/xml/ns/jax-rpc/ri/dd" version="1.0" targetNamespaceBase="urn:Foo" typeNamespaceBase="urn:Foo" urlPatternBase="/ws">

<endpoint name="MyHello" displayName="HelloWorld Service" description="A simple web service" interface="helloservice.HelloIF" model="/WEB-INF/model.gz" implementation="hello.HelloImpl"/> <endpointMapping endpointName="MyHello" urlPattern="/hello"/>

</webServices>

Jaxrpc-ri.xml

Auto-generated Not part of spec

Generated WSDL

(View online)

A Simple Static Client

The JAX-RPC client invokes the JAX-RPC service from the command line

jwstutorial13/examples/jaxrpc/staticstub/src/

Dynamic Clients

Dynamic Proxy Client – underlying stub class is generated at runtime

/jwstutorial13/examples/jaxrpc/dynamicproxy/ Dynamic Interface Invocation – signature of

remote method isn’t known until runtime jwstutorial13/examples/jaxrpc/dii/src/

JAX-RPC

Document-style vs. RPC-style generally refers to how a message is encoded

JAX-RPC allows you to do complex types which are based on XML Schema

If an XML element isn’t bound to an object, it shows up as a SOAPElement

JAXM

Like JAX-RPC, JAXM is an API that abstracts away underlying mechanisms of web services

JAXM is more of an API around SOAP (and SAAJ) that

With JAX-RPC, you never have to deal with SOAP if you don’t want to

JAX-RPC is part of J2EE 1.4, JAXM isn’t

Web Service C#<%@ WebService Language="C#" Class="Hello" %>

using System.Web.Services;

[WebService(Namespace="urn:Hello")]

public class Hello {

[ WebMethod ]

public string sayHello(string name) {

return "Hello " + name;

}

}

Security & Web Services

HTTPS solves wireline security Authentication is another part of security If you are bound to HTTP, you can use HTTP

security and authentication… HTTP is only point-to-point, not end-to-end WS-Security is end-to-end, SOAP based and

transport independent Difficult use cases: federated web services

Transactions & Orchestration

We’ve focused on the idea of one provider, one requestor

How about many requestors and many providers? The orchestration and transaction efforts are about

interoperability between different loosely coupled web services systems

E.g., Doing two-phase commit across loosely coupled web services (WS-Transaction)

Orchestrating true business processes out of loosely coupled web services (BPEL)

Final Thoughts

Focus on interoperability Remember the Browser Wars: test your code

in foreign environments (.NET vs. J2EE) Be wary of the RPC metaphor

Remote Procedure Calls are slow and are not the same as local calls

RPC for Web Services has been observed to be an order of magnitude slower (SOAP vs. RMI)