If you publish Java methods as functions, then you can call them from SQL SELECT, INSERT, UPDATE, DELETE, CALL, EXPLAIN PLAN, LOCK TABLE, and MERGE statements. For example, assume that the executable for the following Java class is stored in Oracle Database:

public class Formatter
{
  public static String formatEmp (String empName, String jobTitle)
  {
    empName = empName.substring(0,1).toUpperCase() +
                                     empName.substring(1).toLowerCase();
    jobTitle = jobTitle.toLowerCase();
    if (jobTitle.equals("analyst"))
      return (new String(empName + " is an exempt analyst"));
    else
      return (new String(empName + " is a non-exempt " + jobTitle));
  }
}

The Formatter class has the formatEmp() method, which returns a formatted string containing a staffer's name and job status. Write the call specification for this method, as follows:

CREATE OR REPLACE FUNCTION format_emp (ename VARCHAR2, job VARCHAR2)
RETURN VARCHAR2
AS LANGUAGE JAVA
NAME 'Formatter.formatEmp (java.lang.String, java.lang.String)
return java.lang.String';

Now, call the format_emp function to format a list of employees:

SQL> SELECT format_emp(first_name, job_id) AS "Employees" FROM employees
  2   WHERE job_id NOT IN ('AC_MGR', 'AD_PRES') ORDER BY first_name;

Employees
--------------------------------------------
Adams is a non-exempt clerk
Allen is a non-exempt salesman
Ford is an exempt analyst
James is a non-exempt clerk
Martin is a non-exempt salesman
Miller is a non-exempt clerk
Scott is an exempt analyst
Smith is a non-exempt clerk
Turner is a non-exempt salesman
Ward is a non-exempt salesman

Restrictions

A Java method must adhere to the following rules, which are meant to control side effects:

• When you call a method from a SELECT statement or parallel INSERT, UPDATE, or DELETE statements, the method cannot modify any database tables.

• When you call a method from an INSERT, UPDATE, or DELETE statement, the method cannot query or modify any database tables modified by that statement.

• When you call a method from a SELECT, INSERT, UPDATE, or DELETE statement, the method cannot run SQL transaction control statements, such as COMMIT, session control statements, such as SET ROLE, or system control statements, such as ALTER SYSTEM. In addition, the method cannot run data definition language (DDL) statements, such as CREATE, because they are followed by an automatic commit.

If any SQL statement inside the method violates any of the preceding rules, then you get an error at run time.