Oracle PL/SQL Programming, 5th Edition

Publishing and Using Java in PL/SQL

Once you have written your Java classes and loaded them into the Oracle database, you can call their methods from within PL/SQL (and SQL)—but only after you “publish” those methods via a PL/SQL wrapper.

Call Specs

You need to build wrappers in PL/SQL only for those Java methods you want to make available through a PL/SQL interface. Java methods can access other Java methods in the Java Virtual Machine directly, without any need for a wrapper. To publish a Java method, you write a call spec—a PL/SQL program header (function or procedure) whose body is actually a call to a Java method via the LANGUAGE JAVA clause. This clause contains the following information about the Java method: its full name, its parameter types, and its return type. You can define these call specs as standalone functions or procedures, as programs within a package, or as methods in an object type:

CREATE [OR REPLACE] --If standalone (not in a package)
Standard PL/SQL procedure/function header
{IS | AS} LANGUAGE JAVA
NAME 'method_fullname (java_type[, java_type]...)
  [return java_type]';

where java_type is either the full name of a Java type, such as java.lang.String, or a primitive type, such as int. Note that you do not include the parameter names, only their types.

The NAME clause string uniquely identifies the Java method being wrapped. The full Java name and the call spec parameters, which are mapped by position, must correspond, one to one, with the parameters in the program. ...