Daffodil DB has in–built support for invoking External methods
belonging to Java classes. It facilitates its users to write
procedures in Java, and execute them with the help of database
triggers.

External Java methods can simplify the process of writing complex
business logics, as the developers have a relative freedom that they
no longer have to restrain themselves in the boundaries of procedural
languages since they can be benefited by using the extensive
capabilities of Java.

Used Parameter Types in External Java Methods

While using the External Java methods, we can pass certain information
by the means of parameters to and from the procedures. When you define
the parameter, you also specify the way in which the parameter can be
used. There are three different types of parameters IN, OUT and INOUT.
The type determines how the parameter will be used.

IN parameter

The IN parameter allows you to pass values in to the calling
procedure, but will not be accessible outside the procedure. IN
parameters act like constants, as the value of IN parameters cannot be
changed within the procedure.

OUT parameter

An OUT parameter is like the return value for a procedure, but it
appears in the parameter list. Inside the program, an OUT parameter
acts like an initialized variable. In fact, the OUT parameter has no
value at all until the program terminates successfully. If you are
specifying an OUT type, parameter in the case of external Java
procedure the parameter datatype should be javaparameter (in Java
method signature).

INOUT parameter

With an INOUT parameter, you can pass values into the procedure and
return a value back to the calling procedure.
We have included some elaborative examples to describe the process of
creating external Java methods.

Example-1

CREATE PROCEDURE p1 (OUT b int, IN c Boolean, INOUT d int) specific
spname EXTERNAL NAME
examplejar:examples.testingForProcedure::SQLConnec t(javaparameter,
Boolean, javaparameter)

Where,
spname is the specific name of procedure for unique identification.
examplejar is name of jar where java class is supposed to be found.
examples.testingForProcedure is the name of the class with its package
name (package name is mandatory if class resides in a package).
SQLConnect is the name of the method.

Example-2

CREATE PROCEDURE SELF() specific SSELF EXTERNAL NAME
testingForProcedurerocessData()

Where,
SSELF is name the procedure for unique identification.
testingForProcedure is the name of the class.
processData() is the name of the method.

Example-3

CREATE PROCEDURE p1(IN a int, IN b Boolean) specific specefic2
EXTERNAL NAME examplesjar:testingForProcedure::
verify(Integer,Boolean)

Where,
Specefic2 is the specific name of procedure for unique identification.
examplesjar is name of jar where java class will be found..
testingForProcedure is the name of the class.
verify(Integer,Boolean) is the name of the method along with parameter
list.

Example-4

CREATE PROCEDURE p2() specific specefic3 EXTERNAL NAME
examples.testingForProcedure:check().

Where,
Specefic2 is the specific name of procedure for unique identification.
examples.testingForProcedure is the name of the class with package
name.
check()is the name of the method.


Few things that a user must know


1. The jar name is optional, but the jar, which is specified in the
class path, can be provided.


2. Package name is mandatory if the java class has a package. If you
do not specify package name then java class will not be loaded and
class not found error would be thrown.


3. The Specified Class Name must have a constructor with
java.sql.Connnection as parameter; otherwise, an Exception will be
thrown.


4. The java data type in the specified method must be a javaparameter
for each Out or InOut parameter mentioned in the Procedure Definition.


5. The java data type in the specified method must contain same count
of parameters as defined in the Procedure Definition.


6. The specified Class must contain specified functions having
parameters of same count and same data type as defined in the
Procedure Definition.


7. Jar/ Java class must be available in Daffodil DB classpath.