Global Java FAQ repository of java, ejb, j2ee related faq

Java API for XML-Based RPC (JAX-RPC)

Q. What is the Java API for XML-Based RPC (JAX-RPC)?

A. The Java API for XML-Based RPC (JAX-RPC) enables Java technology developers to build Web applications and Web services incorporating XML-based RPC functionality according to the SOAP (Simple Object Access Protocol) 1.1 specification.

Q. How does JAX-RPC use SOAP?

A. Please refer to JSR-101.

Q. What is RPC?

A. RPC stands for remote procedure call, a mechanism that allows a client to execute procedures on other systems. The RPC mechanism is often used in a distributed client/server model. The server defines a service as a collection of procedures that may be called by remote clients.

Q. How is XML related to RPC?

A. The remote procedure call is represented by an XML-based protocol, such as SOAP. In addition to defining envelope structure and encoding rules, the SOAP specification defines a convention for representing remote procedure calls and responses.

Q. What does JAX-RPC have to do with Web services?

A. An XML-based RPC server application can define, describe, and export a Web service as an RPC-based service. WSDL (Web Service Description Language) specifies an XML format for describing a service as a set of endpoints operating on messages. With the JAX-RPC API, developers can implement clients and services described by WSDL.

Q. What are the modes of interaction between clients and JAX-RPC services?

A. There are three different modes:

Synchronous Request-Response: The client invokes a remote procedure and blocks until it receives a return or an exception.

One-Way RPC: The client invokes a remote procedure but it does not block or wait until it receives a return. The runtime system for the JAX-RPC client may throw an exception.

Non-Blocking RPC Invocation: The client invokes a remote procedure and continues processing in the same thread without waiting for a return. Later, the client processes the remote method return by blocking for the receive or polling for the return.

Q. Can a remote method call or response carry service context information?

A. Yes. For example, it may carry a unique transaction identifier or digital signature.

Q. Why doesn't xrpcc generate a WSDL file?

A. The xrpcc tool does in fact generate the WSDL file, but due to a bug it gets deleted along with the source files if the -keep option is not specified. You can use the -keep option which will cause xrpcc to not delete the WSDL or .java source files. If you also use the -s sourcepath option, all of the source files will be placed in the sourcepath directory and then you can easily delete them. The WSDL file will still be placed in the current directory or the directory specified by the -d option.

Q. Does the Java 2 Platform, Enterprise Edition (J2EE) use XML?

A. The Java 2 Platform, Enterprise Edition (J2EE) promotes the use of XML for data messaging between loosely-coupled business systems. The J2EE reference implementation includes the Java API for XML Parsing (JAXP).

JavaServer Pages (JSP) can generate and consume XML between multi-tier servers or between server and client. Java Message Service (JMS) provides an asynchronous transport mechanism for XML data messaging. Enterprise JavaBeans (EJB) offers a robust, synchronous transport mechanism by allowing a business service object to be invoked by XML tags. EJB also uses XML to describe its deployment properties, such as transactions and security.

Q. Can I generate dynamic XML documents using JSP pages?

A. JSP pages enables the authoring of XML pages. XML pages can be generated using JSP pages, which include elements to produce the dynamic portions of the document. The JSP specification includes a powerful tag extension mechanism that can be used to perform XML-based operations, such as applying an XSLT transformation to an XML document.