Converting Java Object To SOAP Request And Response XML

To give you the basic idea about SOAP, the transport of messages in the SOAP and to point out the advantage and disadvantages of SOAP, I have brought the following text from Wikipedia. Following the text is my tutorial on how simply you can transfer a Java object to a SOAP XML and how to understand the SOAP response.

SOAP, originally defined as Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks. It relies on Extensible Markup Language (XML) as its message format, and usually relies on other Application Layer protocols (most notably Remote Procedure Call (RPC) and HTTP) for message negotiation and transmission. SOAP can form the foundation layer of a web services protocol stack, providing a basic messaging framework upon which web services can be built.

As a layman’s example of how SOAP procedures can be used, a SOAP message could be sent to a web service enabled web site (for example, a house price database) with the parameters needed for a search. The site would then return an XML-formatted document with the resulting data (prices, location, features, etc). Because the data is returned in a standardized machine-parseable format, it could then be integrated directly into a third-party site.

The SOAP architecture consists of several layers of specifications for message format, message exchange patterns (MEP), underlying transport protocol bindings, message processing models, and protocol extensibility. SOAP is the successor of XML-RPC, though it borrows its transport and interaction neutrality and the envelope/header/body from elsewhere (probably from WDDX).

SOAP makes use of an Internet application layer protocol as a transport protocol. Critics have argued that this is an abuse of such protocols, as it is not their intended purpose and therefore not a role they fulfill well. Proponents of SOAP have drawn analogies to successful uses of protocols at various levels for tunneling other protocols.

Both SMTP and HTTP are valid application layer protocols used as Transport for SOAP, but HTTP has gained wider acceptance as it works well with today’s Internet infrastructure; specifically, HTTP works well with network firewalls. SOAP may also be used over HTTPS (which is the same protocol as HTTP at the application level, but uses an encrypted transport protocol underneath) with either simple or mutual authentication; this is the advocated WS-I method to provide web service security as stated in the WS-I Basic Profile 1.1. This is a major advantage over other distributed protocols like GIOP/IIOP or DCOM which are normally filtered by firewalls. SOAP over AMQP is yet another possibility, that some implementations support.

XML was chosen as the standard message format because of its widespread use by major corporations and open source development efforts. Additionally, a wide variety of freely available tools significantly eases the transition to a SOAP-based implementation. The somewhat lengthy syntax of XML can be both a benefit and a drawback. While it promotes readability for humans, facilitates error detection, and avoids interoperability problems such as byte-order (Endianness), it can retard processing speed and be cumbersome. For example, CORBA, GIOP, ICE, and DCOM use much shorter, binary message formats. On the other hand, hardware appliances are available to accelerate processing of XML messages.Binary XML is also being explored as a means for streamlining the throughput requirements of XML.

Advantages of SOAP:

  • Using SOAP over HTTP allows for easier communication through proxies and firewalls than previous remote execution technology.
  • SOAP is versatile enough to allow for the use of different transport protocols. The standard stacks use HTTP as a transport protocol, but other protocols are also usable (e.g., SMTP).
  • SOAP is platform independent.
  • SOAP is language independent.

Disadvantages

  • Because of the verbose XML format, SOAP can be considerably slower than competing middleware technologies such as CORBA. This may not be an issue when only small messages are sent. To improve performance for the special case of XML with embedded binary objects, the Message Transmission Optimization Mechanism was introduced.
  • When relying on HTTP as a transport protocol and not using WS-Addressing or an ESB, the roles of the interacting parties are fixed. Only one party (the client) can use the services of the other. Developers must use polling instead of notification in these common cases.
  • Most uses of HTTP as a transport protocol are done in ignorance of how the operation would be modeled in HTTP.[citation needed] This is by design—similar to how different protocols sit on top of each other in the IP stack. But this analogy is imperfect; the application protocols used as transport protocols aren’t really transport protocols. As a result, there is no way to know if the method used is appropriate to the operation. This makes good analysis at the application-protocol level problematic with sub-optimal results—for example, a POST operation is used when it would more naturally be modeled as a GET. The REST architecture has become a web service alternative that makes appropriate use of HTTP’s defined methods.
  • When relying on HTTP as a transport protocol, a firewall designed to only allow web browsing is forced to perform more detailed (and thus less efficient) analysis of the HTTP packages.[clarification needed]
  • Although SOAP is an open standard, not all languages offer appropriate support. Java, .NET and Flex offer excellent SOAP integration and/or IDE support. Python and PHP support is much weaker.

— Source:  Wikipedia /Creative Commons Attribution-ShareAlike License

SOAP uses XML as the data-encoding format. XML-RPC and ebXML use XML as well.

Consider the following Java interface:

public interface SumMyNumbers
{
public int sum(int num1, int num2);
}

A client calling the sum() method with two integer parameters would expect to receive a sum of integers from the server. The request format to send to the server would be some XML data.

<?xml version="1.0"?>;
<SumMyNumbers>;
 <sum>
   <num1>2</num1>
   <num2>13</num2>
 </sum>
</SumMyNumbers>

If you notice the XML above, the interface name has been made the root node. There are also nodes for method and parameter names. Now we must deliver this request to the server. Instead of creating our own TCP/IP protocol, we’ll defer to HTTP. So, the next step is to package the request into the form of an HTTP POST request and send it to the server. The server receives the request, decodes the XML, and sends the client a response, again in the form of XML. For instance, the response might look like below

<?xml version="1.0"?>
 <SumMyNumbers>
  <sumResponse>
  <sumValue>15</sumValue>
 </sumResponse>
</SumMyNumbers>

The root node is still the interface name SumMyNumbers. But this time, instead of just the method name, the node name, sum, is the method name plus the string Response, making the node as sumResponse. Using the method name plus Response word, the client can easily identify which method was called and the response is to what method.

The following show how the same request above is encoded in SOAP:

<SOAP-ENV:Envelope
xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance"
xmlns:xsd="http://www.w3.org/1999/XMLSchema">
<SOAP-ENV:Header></SOAP-ENV:Header>
<SOAP-ENV:Body>
<ns1:sum xmlns:ns1="SumMyNumbers" SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
<num1 xsi:type="xsd:int">2</num1>
<num2 xis:type="xsd:int">13</num2>
</ns1:sum>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>

The following diagram shows the basic functioning of SOAP architecture.

Read my another article Complete Tutorial On Using SOAP-UI to Mock Web Service Request / Response

Webservice Interview Questions

The followings are some commonly asked interview questions related to Web Services. These questions are alphabetically sorted. For other interview questions on other technical topics, go to my page here.

  1. Define SOAP?
  2. Explain the web service architecture?
  3. How do you generate web service client from WSDL files?
  4. How do you test a web service?
  5. Name few standards used in web services.
  6. What are some WSDL operations?
  7. What are the common components of web service?
  8. What is a bottom up approach?
  9. What is a provider and a consumer?
  10. What is a response caching?
  11. What is a top down approach?
  12. What is a web service protocol stack?
  13. What is a web service?
  14. What is an end point?
  15. What is REST protocol?
  16. What is SOAP-UI?
  17. What is UDDI?
  18. What is WSDL?
  19. What is XML RPC?
  20. What kinds of tools can you use for creating RESTful Web Services?
  21. Why would you choose REST instead of SOAP?

Twenty Differences Between SOAP and REST Webservices

Even though comparing SOAP and REST Webservices will be like comparing apples and oranges because one is a protocol the other is an Architecture, I have made an attempt to expose twenty differences aimed at helping people make a decision on using one vs another. Also if you are new to SOAP Webservices, read my article here on using SOAP UI tool to demonstrate the use of SOAP Request Response.

Topic SOAP REST
Acronym Simple Object Access Protocol Representational State Transfer
Efficiency SOAP Uses XML which is not very efficient and may not be a good fit for some languages. SOAP can be slow and is definitely a heavyweight choice. REST is a lightweight protocol and is fast.
Format SOAP has one common and expressive format REST response can be of multiple types.
Security Security can be implemented using WS-Security, WS-Trust and WS-SecureConversation Security is implemented in terms of HTTP andSSL
Protocols SOAP can be used over other protocols not just HTTP such as HTTPS, SMTP, TCP, UDP, JMS. SOAP itself is a protocol. REST is completely based on HTTP and URI’s. REST is not a protocol in itself
Reliability End to end communication is reliable via WS-ReliableMessaging which does retries. The client does not need to retry. REST expects the client implementation to handle communication failures by retrying
Simplicity More complex due to client creation requirements. SOAP also has several parts to it such as envelope, Header, Body, Attachments and Fault. Raw HTTP calls via GET, POST, PUT, DELETE and is simpler invoke
Data The request and response are in XML format. The response object can be on several formats such as XML, JSON, RDF etc.
Capabilities Exposes  Operation and types of data. Exposes Resources
Describing interface WSDL No particular standard
Transactions Support ACID transactions via WS-AtomicTransaction No particular standard
Caching SOAP Reads cannot be cached REST reads can be cached.
Dependency SOAP cannot use REST RESTful architecture may use HTTP or SOAP as the underlying communication protocol.
Scalability Less scalable than REST More Scalable than SOAP
Network Works pretty well in distributed enterprise environments REST assumes direct point to point communication
Extensibility SOAP is extensible in the forms of WS* standards. There are no particular standards in extending REST.
Learning Curve SOAP has a steep learning curve REST has a smaller learning curve.
Interface SOAP  interfaces are not uniform REST provides a uniform interface.
Formal Contract SOAP provides a format contract between the provider and consumer There is no formal contract between the provider and consumer in a RESTful webservice.
State SOAP provides mechanism for stateful communication REST is a totally stateless operation.