SOAP

1
SOAP

• By
• Faraz Kadri
• Sazzad Kamal
• Tabinda Siddiqi
• Sajid Ali

2
What is SOAP

• Communication protocol
• SOAP stands for Simple Object Access Protocol
• communication between applications
• designed to communicate via Internet
• It is a format for sending messages
• based on XML

3
Advantages Distadvantages

• Advantages
• is simple and extensible
• Platform independent
• language independent
• allows you to get around firewalls
• SOAP is developed as a W3C standard
• Disadvantages
• No security facility

4
Why SOAP?

• It allows internet communication between
  programs.
• Todays application communicate using remote
  procedure calls between objects, however http is
  not designed to work with this.
• Communication between application can be improved
  if http was used.
• SOAP was created.
• Independent of operating systems, different
  technologies and programming languages.
• Key element to Microsoft .NET architecture for
  future internet applications.

5
Versions of SOAP

• Some major software and hardware companies
  proposed SOAP 1.1 to W3C the SOAP Internet
  protocol that they hope will revolutionize
  application development by connecting graphic
  user interface desktop applications to powerful
  Internet servers using the standards of the
  Internet HTTP and XML.
• The first public Working Draft on SOAP was
  published by W3C in December 2001. To read more
  about the SOAP activities at W3C please visit our
  W3C tutorial.

6
HTTP Protocol

• Communicates over TCP/IP
• Process
• HTTP client sends a request message to the
  server.
• POST /item HTTP/1.1
• Host 189.123.345.239
• Content-Type text/plain
• Content-Length 200
• Server responds back to client.

7
SOAP HTTP Binding

• A SOAP method is an HTTP request/response that
  complies with the SOAP encoding rules.
• HTTP XML SOAP
• A SOAP request could be an HTTP POST or an HTTP
  GET request.
• The HTTP POST request specifies at least two HTTP
  headers Content-Type and Content-Length.

8
Content-Type Content-Length

• Content-Type header defines the MIME type for the
  message and the character encoding
• POST /item HTTP/1.1
• Content-Type application/soapxml
• charsetutf-8
• Content-Length header specifies number of bytes
  in the body of the request/response.
• POST /item HTTP/1.1
• Content-Type application/soapxml
  charsetutf-8
• Content-Length 250

9
SOAP General Rules

• A SOAP message MUST be encoded using XML
• A SOAP message MUST use the SOAP Envelope
  namespace
• A SOAP message MUST use the SOAP Encoding
  namespace
• A SOAP message must NOT contain a DTD reference
• A SOAP message must NOT contain XML Processing
  Instructions

10
SOAP DTD

• lt?xml version"1.0" encoding"UTF-8"?gt
• lt!ELEMENT Envelope (Header?, Body)gtlt!ELEMENT
  Header (Transaction)gtlt!ELEMENT Body
  (Symbol)gtlt!ELEMENT Transaction
  (PCDATA)gtlt!ELEMENT Symbol (PCDATA)gt
• lt!ATTLIST Envelope name-space CDATA
  REQUIRED encoding-style CDATA REQUIREDgt
• lt!ATTLIST Body method CDATA REQUIREDgt
• lt!ATTLIST Transaction must-understand (0 1)
  REQUIREDgt

11
Basics

• A SOAP message is an ordinary XML document
  containing the following
• A required Envelope element that identifies the
  XML document as a SOAP message.
• An optional Header element that contains header
  information.
• A required Body element that contains call and
  response information.
• An optional Fault element that provides
  information about errors that occurred while
  processing the message.

12
Skelton SOAP Message

• lt?xml version"1.0"?gt
• ltsoapEnvelope xmlnssoap"http//www.w3.org/2001/
  12/soap
• envelope" soapencodingStyle"http//www.w3.org/20
  01/12/soap-
• encoding"gt
• ltsoapHeadergt
• ... ...
• lt/soapHeadergt
• ltsoapBodygt
• ... ...
• ltsoapFaultgt
• ... ...
• lt/soapFaultgt
• lt/soapBodygt
• lt/soapEnvelopegt

13
Envelope Element

• ltsoapEnvelope xmlnssoap"http//www.w3.org/2001/
  12/soap-envelop soapencodingStyle"http//www.w
  3.org/2001/12/soap-encoding"gt
• ...
• lt/soapEnvelopegt
• nameSpace (xmlnssoap) defines the Envelope as a
  SOAP Envelope .
• encodingStyle attribute is used to define the
  data types used in the document.
• will apply to that element's contents and all
  child elements.
• SOAP message have no default encodings.

14
Header element

• An optional Header element that contains header
  information.
• ltsoapHeadergt
• ... ...
• lt/soapHeadergt
• Contains application specific information (such
  as authentication, payment, etc.) about SOAP
  message.
• ltsoapHeadergt
• ltmTrans xmlnsm "http//www.w3school
  s.com/transaction/" soapmustUnderstand"1"gt
• 234
• lt/mTransgt
• lt/soapHeadergt
• Header element has to be first child element of
  Envelope.

15
Header Cont. (actor)

• A SOAP message may travel from a sender to a
  receiver by passing different endpoints along the
  message path. Not all parts of the SOAP message
  may be intended for the ultimate endpoint of the
  SOAP message but, instead, may be intended for
  one or more of the endpoints on the message path.
• The SOAP actor attribute may be used to address
  the Header element to a particular endpoint.
• Syntax soapactor"URI"
• ltsoapHeadergt
• ltmTrans xmlnsm"http//www.w3schools.com/trans
  action/" soapactor"http//www.w3schools.com/app
  ml/"gt
• 234
• lt/mTransgt
• lt/soapHeadergt

16
Header Cont. (mustUnderstand)

• mustUnderstand attribute can be used to indicate
  whether a header entry is mandatory or optional
  for the recipient to process.
• If you add mustUnderstand"1" to a child element
  of the Header element it indicates that the
  receiver processing the Header must recognize the
  element. If the receiver does not recognize the
  element it must fail when processing the Header.
• Syntax soapmustUnderstand"01
• ltmTrans xmlnsm"http//www.w3schools.com/t
  ransaction/" soapmustUnderstand"1"gt
• 234
• lt/mTransgt

17
Body Element

• A required Body element that contains call and
  response information.
• ltsoapBodygt
• ... ...
• lt/soapBodygt
• Contains the actual message for ultimate endpoint
  of the message.

18
Body Element Example

• A client requests price for a fruit.
• Request
• ltsoapBodygt
• ltmGetPrice xmlnsm "http//www.w3sch
  ools.com/prices"gt ltmItemgt
• Apples
• lt/mItemgt
• lt/mGetPricegt
• lt/soapBodygt
• Response
• ltsoapBodygt
• ltmGetPriceResponse xmlnsm
  "http//www.w3schools.com/prices"gt
  ltmPricegt
• 1.90
• lt/mPricegt
• lt/mGetPriceResponsegt
• lt/soapBodygt

19
Fault element

• An optional Fault element that provides
  information about errors that occurred while
  processing the message.
• An error message from a SOAP message is carried
  inside a Fault element.
• If a Fault element is present, it must appear as
  a child element of the Body element. A Fault
  element can only appear once in a SOAP message.

20
Fault Element (cont.)

• SOAP Fault Element
• The SOAP Fault element has the following sub
  elements
• Sub Element Description
• ltfaultcodegt A code for identifying the fault
• ltfaultstringgt A human readable explanation of
  the fault
• ltfaultactorgt Information about who caused the
  fault to happen
• ltdetailgt Holds application specific
  error information related to
• the Body element
• SOAP Fault Codes
• The faultcode values defined below must be used
  in the faultcode element when describing faults
• Error Description
• VersionMismatch Found an invalid
  namespace for the SOAP Envelope
  element
• MustUnderstand An immediate child
  element of the Header element, with the
  mustUnderstand attribute set to "1", was
  not understood
• Client The message was
  incorrectly formed or contained incorrect
  information
• Server There was a problem with
  the server so the message could not proceed

21
Fault Example

• ltSOAP-ENVFaultgt ltfaultcodegt
• SOAP-ENVClient
• lt/faultcodegt    ltfaultstringgt
• Can't find symbol Apples
• because it is not in the database.
• lt/faultstringgt
• lt/SOAP-ENVFaultgt

22
HTTP Protocol

• Communicates over TCP/IP
• Process
• HTTP client sends a request message to the
  server.
• POST /item HTTP/1.1
• Host 189.123.345.239
• Content-Type text/plain
• Content-Length 200
• Server responds back to client.

23
SOAP HTTP Binding

• A SOAP method is an HTTP request/response that
  complies with the SOAP encoding rules.
• HTTP XML SOAP
• A SOAP request could be an HTTP POST or an HTTP
  GET request.
• The HTTP POST request specifies at least two HTTP
  headers Content-Type and Content-Length.

24
Content-Type Content-Length

• Content-Type header defines the MIME type for the
  message and the character encoding
• POST /item HTTP/1.1
• Content-Type application/soapxml
• charsetutf-8
• Content-Length header specifies number of bytes
  in the body of the request/response.
• POST /item HTTP/1.1
• Content-Type application/soapxml
  charsetutf-8
• Content-Length 250

25
SOAP Example

• Server has a method sayGreeting() that a client
  wants to call with a String argument and the
  result is returned.
• public class SoapService
• public SoapService()
• / Method to be called by client /
• public String sayGreeting(String name)
  return "Hello "name

26
Before we move further

• The server needs to know how to handle the SOAP
  requests coming in from clients.
• This is achieved with the help of Deployment
  Descriptors.
• Deployments Descriptors contains all the
  information needed to identify and process a
  client SOAP request.

27
Deployment Descriptor

• The Deployment Descriptor basically contains the
  following things
• The id of the service.
• The provider type.
• The scope of the service (Request/Session/Applica
  tion).
• The provider class or script name.
• The method(s) that the client wants to access.
• The fault listener (optional)

28
Back to SOAP Example

• In our example, servlet is given the following
  XML document to let it know how to handle the
  request.
• ltisdservice xmlnsisd"http//xml.apache.org/xml-
  soap/deployment" id"urngreetingService"gt
• ltisdprovider type"java" scope"Request
  methods"sayGreeting"gt
• ltisdjava class
• "sam.soap.service.SoapService"
  static"false"/gt
• lt/isdprovidergt
• lt/isdservicegt

29
The Client

• In order to make a method call to server, the
  client side
• builds up a Call object which represents the RPC
  in Java
• SOAP.
• Call call new Call()
• Essential ingredients in Call.
• The name of the service at the server.
  SoapService object in the example.
• call.setTargetObjectURI(
• "urngreetingService")

30

• Essential ingredients in Call continued
• The name of the RPC method in server.
  sayGreeting() in the example.
• call.setMethodName("sayGreeting")
• Information about encoding style.
• call.setEncodingStyleURI(
• Constants.NS_URI_SOAP_ENC)
• Data (argument) to be passed to the RPC method.
• Vector params new Vector()
  params.addElement(new Parameter("name",
  String.class, name, null))
• call.setParams(params)

31
The Client (continued)

• Invoking Call method
• Now that we have build the Call object, we can
  invoke it to get a response from the server
• Response res call.invoke(
• new URL(urlString), "")

32

• Parsing the Response
• The Response object contains the result of the
  RPC call made by the Call object.
• if( res.generatedFault() false)
• Parameter retValue res.getReturnValue
  ()
• Object value retValue.getValue()
  System.out.println(value)
• else
• System.out.println("The fault is
  res.getFault().getFaultString())

33
High level implementation

• How are the soap xml messages generated and dealt
  with

34
Underlying mechanism

• Apache soap API
• The Call object in the client
• The soap handler servlet in the server

35
How did it all work together

• Flow of messages

36
SOAP-Java Data Types

• Definitions
• In SOAPs context we need to undertand
• Serializer
• Java class that converts a specific Java
  object to XML.
• Deserializer
• Java class that converts specific XML to a
• Java object.

37
Simple data-types in SOAP

• There are several data types already defined by
  Java for serialization/deserialization in SOAP.

38
Simple data-types in SOAP

• QName
• - a special data type (class) that can be
  user-defined.
• - provided a serialization/deserialization
• class (QNameSerializer).
• - limitations of how the class can be defined.
  Must follow Java Bean model for classes i.e.
  empty constructor, getters/setters for all the
  variables.

39
Custom data-types in SOAP

• The real power and flexibility of SOAP compared
  to other RPC models can only be revealed if we
  had the complete freedom to define and pass our
  own data types. To do this
• We need to write our own Serializers/Deserializers
  .
• Writing our own (De)serializers will have
  flexibility of defining data-type in our own way
  without conforming to Java Bean specifications.
• Need to make sure there is a copy of the
  (De)serializers at both client and the server end.