Datasheet

Apache and Jakarta Tomcat

In these situations, where a single server simply cannot meet the needs of a software system, a

distributed system is ideal. Multiple servers can work together to meet demands that a single server

could not.

But, why bother creating a distributed system? Why not just copy the same application and deploy it on

multiple servers? Surely load balancing – splitting up the requests amongst the different servers – can

then handle the load?

It turns out that by separating the different logical components of an application, system administrators

are free to tune the various components of the distributed system according to their unique needs. For

example, the servers that read and write to the database will require different optimizations than those

servers which are communicating with web clients via HTTP over TCP.

The J2EE APIs

Creating the distributed systems that we've described in the preceding paragraphs is not an easy task.

We mentioned a few paragraphs ago that J2EE is a collection of code libraries called APIs. The J2EE

APIs are designed to work together to simplify the creation of robust and efficient distributed systems.

Here is a list of some of the key J2EE technologies and a brief description of each:

J2EE API Description

Enterprise JavaBeans (EJB)

EJB technology provides a simple mechanism for

creating distributed business logic components. EJB

authors follow a simple pattern to write business

logic and the rest of the low-level details relating to

lifecycle, distribution, persistence, and so on are

handled automatically.

Java Message Service (JMS) JMS provides asynchronous messaging capability to

J2EE applications.

Java Naming and Directory Service (JNDI) JNDI enables J2EE applications to communicate

with registries and directories. A

registry/directory is a centralized location for

storing business information. JNDI supports the

industry standard LDAP protocol and interfaces

with many other popular registry standards. JNDI

makes it possible to centralize the configuration

of a distributed system.

Servlets As explained earlier in this chapter, servlets work

with special servers called servlet containers to

process HTTP requests and send HTTP responses.

Servlets often work directly with EJBs.

JavaServer Pages (JSP) JSP technology is an alternative, HTML-like

interface for creating servlets. At runtime, the servlet

container converts a JSP into a servlet.

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