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Re: 9i database: Java?

From: Hans Forbrich <forbrich_at_telusplanet.net>
Date: Tue, 20 May 2003 01:39:13 GMT
Message-ID: <3EC985FA.A4E6EAC8@telusplanet.net>


Answered in 3 parts: JVM, J2EE in Oracle, J2xE & JSP. This is a very high level summary - others will find holes, but this (hopefully) will provide the concepts.

Stephan wrote:

> Hi,
>
> Can someone explain me what JVM really means?

  1. JVM = Java Virtual Machine.

Java's claim to fame is programmer independance from the underlying CPU architecture (SUN Sparc, Intel X86, HP Risc, ARM, etc.) The way they do this is providing a virtual computer to execute the Java code and then having that virtual computer (or virtual machine) responsible for translating the results into the native computer op codes. Side note - since this translation is not perfect, Java is occasionaly known as write once, debug everywhere.

> Can I run JSP's directly in the database or do I need 9iAS?

2) J2EE in Oracle

You need a JVM with the J2EE and appropriate JSP tag libraries. Oracle8i provided the JVM in the database, AFAIK it's been removed from the database but is still available with automatically installed Apache server in 9i. (see below for J2EE & JSP def's)

You don't mention your operating system - if Windows, check the program group to see whether you have a 'start/stop apache icons. If so, start & see whether you can get a page from
"http://{substitute-your-machines-name}:7878

You don't need to use Oracle's 9iAS or the Oracle supplied Apache server (unless the tag library you are running includes Oracle specific tags). But you may want to consider using one or the other instead of going to the alternatives JVM/J2EE engines (WebSphere, BEA, Orion, JBoss, etc.). I believe I get better support having a single vendor (read 'single neck to choke') than having the vendors passing the buck.

> Additional (global) info concerning Oracle 9i database and Java is
> welcome...
>
> thanks
> Stephan

3) J2xE & JSP

Java is a very small and simple language. So small, in fact, that it doesn't really have a lot of intrinsic functionality. As a result, people have written a lot of libraries to provide the functionality they want.

There are 3 'standard' libraries that are very interesting - J2ME, J2SE and J2EE.

J2 originally stood for Java version 1.2 (the 2 part) as there were a lot of very important enhancements to the core Java engine between verions 1.1 and version 1.2

J2EE is a specification - current version is 1.3 (final draft for 1.4 is available). This spec includes a lot of interesting stuff like JNDI (directory interface,) JDBC, transactions, etc. Version numbers get real confusing here because the J2EE spec makes reference to specific versions of JNDI, JDBC, JTS, etc.

All sorts of detail is available at http://www.javasoft.com

Java Server Pages run in the J2EE environment. Easiest way to think about them - start with a web page template, add "tags" that are part of the JSP tag library. Each tag refers to some specific functionality such as 'select x from table y', or other function that can be done in Java. (tags look at lot like the paragraph tags in HTML pages)

When the user requests a Java Server Page, the J2EE engine passes the request to the JSP engine [portion of J2EE] which expands the tags and then executes the resulting file. The results are then returned, usually as a pure HTML page, back to the requesting system - user's browser.

HTH
/Hans Received on Mon May 19 2003 - 20:39:13 CDT

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