1.19.1 Example

Let's write a simple "Hello, World" JSP that will accept an argument:

package oreilly.plsquick.demos;

public class Hello {
   public static String sayIt (String toWhom) {
      return "Hello, " + toWhom + "!";
   }
}

Saved in a file called Hello.java, we can load the source code directly into Oracle. Doing so will automatically compile the code. A simple form of the loadjava command:

loadjava -user scott/tiger -oci8 oreilly/plsquick/
   demos/Hello.java

The Hello.java file follows the Java file placement convention for packages and so exists in a subdirectory named oreilly/plsquick/demos.

Now we can fire up our favorite SQL interpreter, connect as SCOTT/TIGER, and create the call spec for the Hello.sayIt( ) method:

CREATE FUNCTION hello_there (to_whom IN VARCHAR2)
   RETURN VARCHAR2
   AS LANGUAGE JAVA
   NAME 'oreilly.plsquick.demos.Hello.sayIt
     (java.lang.String) return java.lang.String';
/

Now we can call our function very easily:

BEGIN
   DBMS_OUTPUT.PUT_LINE(hello_there('world'));
END;
/

And we get:

Hello, world!

as the expected output.

1.19.2 Publishing Java to PL/SQL

To write a call spec, use the AS LANGUAGE JAVA clause in a CREATE statement. The syntax for this clause is:

{ IS | AS } LANGUAGE JAVA
   NAME 'method_fullname [ (type_fullname,... ] 
      [ return type_fullname ]'

method_fullname is the package-qualified name of the Java class and method. It is case-sensitive and uses dots to separate parts of the package full name. type_fullname is the package-qualified name of the Java datatype.

Notice that a simple string, not an SQL name, follows the NAME keyword.

Type mapping follows most JDBC rules regarding the legal mapping of SQL types to Java types. Oracle extensions exist for Oracle-specific datatypes.

Most datatype mappings are relatively straightforward, but passing Oracle8 objects of a user-defined type is harder than one would think. Oracle provides a JPublisher tool that generates the Java required to encapsulate an Oracle8 object and its corresponding REF. Refer to Oracle's JPublisher documentation for guidelines on usage.

The AS LANGUAGE JAVA clause is the same whether you are using Java as a standalone JSP, the implementation of a packaged program, or the body of an object type method. For example, here is the complete syntax for creating JSPs as PL/SQL-callable functions or procedures:

CREATE [OR REPLACE]
{  PROCEDURE procedure_name [(param[, param]...)]
   | FUNCTION function_name [(param[, param]...)] 
      RETURN sql_type
}
[AUTHID {DEFINER | CURRENT_USER}]
[PARALLEL_ENABLE]
[DETERMINISTIC]
{ IS | AS } LANGUAGE JAVA
   NAME 'method_fullname [ (type_fullname,... ] 
      [ return type_fullname ]'

When using Java as the implementation of a packaged procedure or function, Oracle allows you to place the Java call spec in either the package specification (where the call spec substitutes for the subprogram specification) or in the package body (where the call spec substitutes for the subprogram body).

Similarly, when using JSPs in object type methods, the Java call spec can substitute for either the object type method specification or its body.

Note that Java functions typically map to PL/SQL functions, but Java functions declared void map to PL/SQL procedures. Also, you will quickly learn that mistakes in mapping PL/SQL parameters to Java parameters become evident only at runtime.

1.19.3 Data Dictionary

To learn what Java library units are available in your schema, look in the USER_OBJECTS data dictionary view where the object_type is like `JAVA%'. If you see a Java class with INVALID status, it has not yet been successfully resolved. Note that the names of the Java source library units need not match the names of the classes they produce.

As of press time, there is no apparent way to discover which stored programs are implemented as Java stored procedures. You can look in the USER_SOURCE view for named programs that contain the source text `AS LANGUAGE JAVA', but that may not yield accurate results. The USER_DEPENDENCIES view does not track the relationship between PL/SQL cover programs and their underlying Java class.

Even if you have loaded the Java source code into the database, there is no supported way of retrieving the source from the data dictionary.