XML and Java for E-Business (3/4) - exploring XML
XML and Java for E-Business
Java 2 Enterprise Edition
The Java 2 Enterprise Edition forms the basis for Java Application Servers. It defines the necessary APIs that servers must implement. This way application servers provide a standardized runtime environment for Java server programs. A central element of J2EE is the Enterprise Java Bean (EJB) component model. A server provides containers that host and execute EJBs. A set of interacting EJBs make up the business logic of a server application. The communication with a Web browser client is accomplished using Java Server Pages (JSP) and Java servlets. Servlets are Java programs that run in a servlet engine of a Web server and work similar to CGI programs. They are triggered by Web browser requests and return dynamic HTML pages. JSPs are HTML pages with specially marked sections of Java code. On request of such a page the code sections are executed and the results inserted into the HTML before sending the page back to the client. Databases are accessed using JDBC (Java Database Connectivity), the equivalent of Microsoft's ODBC. EJB, JSP, servlets and JDBC is the minimal set of APIs for a server application.
When developing a Java server application other enterprise applications usually already exist. Very often these applications need to collaborate with the Java program and exchange information. Important services for this communication are the Java Messaging Service (JMS), the Java Transaction API (JTA), Java Transaction Services (JTS) and J2EE Connectors. JMS is an interface for communicating with message-based systems such as IBM's MQSeries, a common solution for integrating disparate information systems. JTA enables transactions that can span multiple databases, provided they implement the JTS service interface. J2EE Connectors provide a uniform interface to various Enterprise Information Systems. Larger applications should be distributed across multiple servers. Java uses Remote Method Invocation (RMI) for calling remote objects. The current implementation of RMI sits on top of CORBA and its comunications protocol IIOP, allowing for direct access to other CORBA, possibly non-Java applications. Last, but not least the Java Naming And Directory Interface (JNDI) offers access to Naming and Directory Servers for locating services and authenticating users, using LDAP (Lightweight Directory Access Protocol) functions and events.
For a list and description of Java Application Servers see AppServerCentral.com.
We conclude with XML for E-Business.
Created: Jan 03, 2000
Revised: Jan 03, 2000