Using Oracle DropJava Oracle Tips by Burleson Consulting

The DropJava utility drops individual Java sources and binaries and entire JAR files. It also maintains the hash table that LoadJava uses to track the loading of Java library units. You can enter .java, .class, and .jar files on the command line in any order. Here is the syntax:

dropjava
[{-v | -verbose}]
[{-t | -thin} | {-o | -oci81}]
[{-u | -user} username/password@host_name:port_number:database_sid]
{filename.java | filename.class | filename.jar} ...

The following list presents the DropJava command-line options:

DropJava Examples  

In the first example, DropJava drops various Java binaries and resources. The utility reads the JAR files, then drops each Java class or resource from your schema.

> dropjava -u scott/tiger@myComputer:1521:orcl manager.jar
managerText.jar

In the next example, operating in verbose mode, DropJava drops a Java class:

> dropjava -v -u scott/tiger@myComputer:1521:orcl Calculator.class
...
files:
    Calculator.class
dropping Calculator

Using CREATE Java

In Oracle8i and Oracle9i, Java, an object-oriented development language, was added to the Oracle kernel. In previous versions, Java, JDBC (Java Database Connectivity), and SQLJ, Oracle’s PRO*Java product, provided connectivity to the database, but Java was relegated to the outside, along with the other languages, such as C, C++, FORTRAN, and COBOL. Now Java is allowed inside the database. Java can be used for procedures, functions, and methods and will be stored inside the database just like PL/SQL.

However, in order to move Java into the database, a way had to be provided to bridge the gap between the normal database lingua franca, PL/SQL, and the new Java classes. This bridge between Java and PL/SQL is the Java object.

Creation of a Java Object

The Java object is created using the CREATE JAVA command, which is documented in the SQL Reference Manual on the documentation website. Java is stored in much the same way as PL/SQL in database tables. Once called into memory (by standard function, procedure, and method calls), it is placed in its own area. The area where Java resides is appropriately called the Java Pool and is configured at 20 MB by default but can be increased by use of the JAVA_POOL_SIZE initialization parameter if required.  Let’s look at an example of the CREATE JAVA command.

Note: Java is not available until version 8.1.4.

CREATE OR REPLACE JAVA Source NAMED 'Login' AS
PUBLIC CLASS Login (
Public static String Login() (
Return 'You are logged into ORTEST1'; ) );
/

Use of the Java Object

A function or procedure call is wrapped around the Java object in order to make it callable:

CREATE OR REPLACE FUNCTION login
RETURN VARCHAR2 AS
LANGUAGE JAVA NAME 'Login() return String()';
/

Once the Java object is wrapped, it is called just as the function or procedure would be called; in addition, the object can be included in a package specification. The Login Java object would be called like this:

SQL> VARIABLE t VARCHAR2;

Finally, we are ready to call the function Login. Remember, in a CALL statement, host variables must be prefixed with a colon.

SQL> CALL Login() INTO :t;

Call completed.

SQL> PRINT t

t
—————————————-
You are logged into ORTEST1

For more complex examples, refer to the Java Developer’s Guide.

Altering Java Objects

The ALTER JAVA command is used to alter Java objects. The syntax for the ALTER JAVA command is:

ALTER JAVA Source|CLASS [schema.]object_name
[RESOLVER ((match_string [,] schema_name|- ))
[COMPILE|RESOLVE] [invoker_rights_clause]

The ALTER JAVA command is only used to force resolution of Java objects (compilation). The Java source must be in your own schema, or you must have the ALTER ANY PROCEDURE, or the source must be declared PUBLIC. You must also have EXECUTE privilege on the Java object.

An example use of the ALTER JAVA command is:

ALTER JAVA CLASS "Agent"
RESOLVER (("D:\orant81\java\bin\*.*" , tele_Remote DBA)(* public))
RESOLVE;

Dropping Java Objects

If you don’t use the DropJava utility, you may cause inconsistencies in Oracle internal tables; that is, the command for dropping Java objects is:

DROP JAVA [schema.]java_name;

Memory and Java Objects

Java uses the shared pool and the Java pool. The default in 8.1.3 for the Java pool is almost 10 MB; for the 8.1.4 beta it was upsized to 20 MB, and there it has remained. If you get memory-related errors when dealing with Java objects, increase the size of the Java pool. In Oracle9i the Java pool should be near 60 megabytes.

Error reporting in out-of-memory situations is inconsistent and in some cases may result in a core dump.  If you suspect that memory usage is the cause of a core dump, adjust the JAVA_POOL_SIZE in the init.ora file. JAVA_POOL_SIZE should be set to 60,000,000 or higher for large applications in Oracle9i.  The default value of 20,000,000 in 8.1.4 and 8.1.5 should be adequate for typical Java Stored Procedure usage before release 9i.

See Code Depot for Full Scripts

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This is an excerpt from Mike Ault, bestselling author of "Oracle 10g Grid and Real Application Clusters". You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.

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