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Developing Web
Services
[email protected]
Agenda
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Quick Review
Web Service Architecture
Web Services Interoperability
Java APIs
.NET APIs
The World, Late 80’s-Early 90’s
Database
Organization
Web Apps
Internet
Web App
Server
Organization
Database
Organization
Web Services
Organization
Database
Web App
Server
Database
Web App
Server
Internet
Web App
Server
Database
Organization
Web App
Server
Organization
Database
Web Service Architecture
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Provider Agent Architecture
Requestor Agent Architecture
Provider and Requestor Combined
Asynchronous web services
Web Services And The Rest Of Your
Application
Web Services Architecture
Requestor
Application Logic
Object(s) to
Object(s) to
Object(s)
to
send
send
send
Response
Object(s) to
Object(s)
to
Object(s)
send
send
Provider
Application Logic
Object(s)
Object(s) to
Object(s)
to
response
send
send
Object(s)
Object(s) to
Object(s)
to
received
send
send
Objects
XML-ified
Extracted
XML
Extracted
XML
Objects
XML-ified
SOAP
Message
Request
SOAP
Message
Response
SOAP
Message
Response
SOAP
Message
Request
HTTP (or other
binding) Sender
HTTP (or other
binding) Listener
Requestor & Provider
combined
Requestor
Application Logic
Object(s) to
Object(s) to
Object(s)
to
send
send
send
Response
Object(s) to
Object(s)
to
Object(s)
send
send
Provider
Application Logic
Object(s)
Object(s) to
Object(s)
to
response
send
send
Object(s)
Object(s) to
Object(s)
to
received
send
send
Objects
XML-ified
Extracted
XML
Extracted
XML
Objects
XML-ified
SOAP
Message
Request
SOAP
Message
Response
SOAP
Message
Response
SOAP
Message
Request
HTTP (or other
binding) Sender
HTTP (or other
binding) Listener
From Monday: Faults With
XML-RPC
HTTP/1.1 200 OK
Connection: close
Content-Length: 426
Content-Type: text/xml
Date: Fri, 17 Jul 1998 19:55:02 GMT
Server: 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
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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
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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
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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
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Web Services Interoperability (WS-I) Organization:
Industry group that promotes interoperability
WS-I Basic Profile 1.0:
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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
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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…
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It’s the software developers’ burden….
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to ensure interoperability by the tools, patterns
and strategies they
Scrutinize tools & middleware from an
interoperability perspective
Examples
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JAXP
DOM
SAAJ
JAXB
JAX-RPC
Building DOM Document
public 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
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Example: jwsdp/jaxp/samples/DOMEcho/DOMEcho.java
Reading SAX Documents
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Example: jwsdp/jaxp/sax/samples/Echo4.java
SAAJ
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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 Provider
MessageFactory messageFactory = MessageFactory.newInstance();
// Create a message
SOAPMessage 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 message
SOAPBody body = message.getSOAPBody();
// Add the DOM document to the message body
SOAPBodyElement 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/servletsexamples/servlet/servlets.WebServicesProvider"));
response.writeTo(System.out);
Marshalling And
Unmarshalling Objects
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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 SOAP
PayrollObject 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;
}
Validation
PayrollObject 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;
}
Marshaller
public 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
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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
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Auto-generated
Not part of spec
Generated WSDL
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(View online)
A Simple Static Client
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The JAX-RPC client invokes the JAX-RPC
service from the command line
jwstutorial13/examples/jaxrpc/staticstub/src/
Dynamic Clients
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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
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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
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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
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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
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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
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Focus on interoperability
Remember the Browser Wars: test your code
in foreign environments (.NET vs. J2EE)
Be wary of the RPC metaphor
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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)