Writing Java Applications on Oracle8i

Overview

As discussed in Chapter 1, the Oracle8i JServer platform is a standard, compatible Java environment, which will execute any 100% pure Java application. It has been implemented by Oracle to be compatible with the Java Language Specification and the Java virtual machine specification. It supports the standard Java binary format and the standard Java APIs. In addition, Oracle8i adheres to standard Java language semantics, including dynamic class loading at runtime. However, unlike other Java environments, the JServer is embedded within the Oracle8i RDBMS and, therefore, introduces a number of new concepts. This section gives an overview of the differences between Sun Microsystems's JDK environment and the environment that occurs when you combine Java within the Oracle8i database.

Terminology

Term Definition

JServer

Java-enabled Oracle8i database server.

Aurora

Oracle8i JVM.

Session

As a user who executes Java code, you must establish a session in the server. The word session as we employ it here is identical to the standard Oracle (or any other database server) usage. A session is typically, although not necessarily, bounded by the time a single user connects to the server.

Call

When a user causes Java code to execute within a session, we refer to it as a call. You can initiate a call in different ways.

A SQL client program executes a Java stored procedure.

A trigger can execute a Java stored procedure.

A PL/SQL program calls some Java code.

A CORBA client invokes a method on a CORBA object.

An EJB client invokes a method on an EJB object.

In all cases, a call begins, some combination of Java, SQL, or PL/SQL code is executed to completion, and the call ends.

Term	Definition
JServer	Java-enabled Oracle8i database server.
Aurora	Oracle8i JVM.
Session	As a user who executes Java code, you must establish a session in the server. The word session as we employ it here is identical to the standard Oracle (or any other database server) usage. A session is typically, although not necessarily, bounded by the time a single user connects to the server.
Call	When a user causes Java code to execute within a session, we refer to it as a call. You can initiate a call in different ways. A SQL client program executes a Java stored procedure. A trigger can execute a Java stored procedure. A PL/SQL program calls some Java code. A CORBA client invokes a method on a CORBA object. An EJB client invokes a method on an EJB object. In all cases, a call begins, some combination of Java, SQL, or PL/SQL code is executed to completion, and the call ends.

In your standard Java environment, you run a Java application through the interpreter by executing java <classname>. This causes the application to execute within a process on your operating system.

With the Aurora JVM, you must load the application into the database, publish the interface, and then run the application within a database session. This book discusses how to run your Java applications within the database. Specifically, see the following sections on instructions for Java in the database:

Load and publish your Java applications before execution--See "Java Code, Binaries, and Resources Storage" and "Preparing Java Class Methods for Execution" starting.
Running within a database session--See "Database Sessions Imposed on Java Applications".

In addition, certain features, included within standard Java, change when you run your application within a database session. These are covered in the following sections:

Once you are familiar with this chapter, see Chapter 3, "Invoking Java in the Database" for directions on how to set up your client, and examples for invoking different types of Java applications.