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IBM Software Group
© 2006 IBM Corporation
EGL Calling Java
This Learning Module shows how to use EGL to call Java classes, methods and
access class variables.
2
EGL externalType Part
 An externalType part provides the EGL mapping to a Java Class. This is similar to the mapping that an EGL Interface provides for Web Service functions, but extends to map Java class
variables and constructors.
 Invoking ExternalType functions

If the class or function is marked static,

Simply invoke it using the name of its
externalType
externalType part and use dot syntax to reference the methods
typeName
typeName
.
.
methodName();
methodName();
 If the class or function is non-static (more typical)

Create a variable based on its
externalType
externalType part – initialize it with a
new
new keyword


Initialize class variable valuesCall calculateTax routine
Call calculateTax routine
3
EGL Calling Java Calling EGL – 1 of 2

The following types of transfer of control are possible in EGL:
1. EGL-generated Java™ program to EGL-generated Java program
2. Non-EGL (native or hand-coded) Java program to EGL program
3. EGL-generated Java program to non-EGL Java program
4. EGL-generated Java program to DLL
5. EGL-generated Java program to .EXE or .BAT file
1. EGL-generated Java
program
program to EGL-generated Java program

Calling one EGL-generated program from another is as simple as invoking the Java class for the target
program using a call statement. Be aware, however, of package dependencies. You must invoke a class
that is one of the following:

Within the same package as the calling program.

Qualified with a package name using dot syntax.

Identified with a linkage option part.
2. Non-EGL Java program to EGL program

To invoke an EGL-generated program from a non-EGL Java program, you must do one of the following:

Access the functions by using dot syntax (library.function()) or by creating a use
declaration for the library to make its functions global to your program.

EGL-generated Java program to .EXE or .BAT file

EGL provides two functions that allow you to call a system command (such as a .bat or a
.exe executable file). These were covered as optional exercises in a previous section:

sysLib.callCmd();
–
This function transfers control to a specified executable; when the executable terminates, control returns to the
calling EGL program.

sysLib.startCmd();
–
This function transfers control to a specified executable, then keeps running; both the EGL program and the
executable run at the same time.

Related concepts – See product help

Transfer of control across programs

Linkage options part

Related tasks – See product help

Generating EGL and Web services

Generating Java wrappers
5


After finishing that, we’ll do two additional things:

Learn how to call Java API’s through the EGL JavaLib (built-in system) functions

Pass string arrays back and forth between EGL and Java

Important Note:
Important Note: Java is a case-sensitive language (okay we said that already). As such, be careful naming your classes and all the other files you
create in this workshop, as the copy/paste code will pre-determine your part names.
7
Create a new Java Package and Class

From Project Explorer:
From Project Explorer:

Right-click over \Java Resources: src\ and
create a
package
package named:
egljava
egljava

Right-click over
Right-click over
egljava
egljava and create a new
Java class named:
HelloEGLworld
HelloEGLworld


Ctrl/S
Ctrl/S (why)?
•

Ctrl/G
Ctrl/G (why)?
9

 Workshop continued – Debug the EGL Program and Java Calls

Add a Breakpoint to the
callJava.egl
callJava.egl

program

From Project Explorer, right-click over the \EGLSource\programs\callJava.egl select
Debug EGL Program…
Debug EGL Program…
Step through the code
 Note the variable
values before and
after the calls
to the Java Class!
10
Additional Info on External Types

When creating external types, you may
run into a Java

Java (terms and concepts)

Calling Java using the externalType Part


Calling Java using
Calling Java using
JavaLib
JavaLib

Calling COBOL Programs

Calling RPG Programs
Sub-Topics:
EGL and Remote Programs
EGL and Remote Programs
12
EGL’s JavaLib Built-in System Function

If you are not calling a custom Java Class, but only calling a
static Java API
static Java API (think of these as
Java library “built-in-functions”) – you can dispense with having to define a new externalType,
and call the API using the
JavaLib
JavaLib Built-in Function.
Here are the JavaLib
function calls
We are interested in:


You specify which package.sub-package.class, etc.

And the method that returns the Java object into the temporary variable
14

 Workshop - EGL’s JavaLib invoke() and store() Functions
 From Project Explorer, edit the \EGLSource\programs\callJava.egl

Towards the end of the program (as shown here in the screen capture) insert the following two functions (found in the Notes
section of this slide)
 Un-comment the calls to these functions in the
main()
main() function
With your mouse cursor
inside the source,
press:
•

Ctrl/S
Ctrl/S
•

Ctrl/G
Ctrl/G
15

 Workshop continued – Debug the EGL Program and Java Calls

From Project Explorer, right-click over the \EGLSource\programs\callJava.egl
select Debug EGL Program and once again, step through the code

Ctrl/S
Ctrl/S

Ctrl/G
Ctrl/G
18

 OPTIONAL Workshop – Passing a String Array – Create a new JSP Page

From
\WebContent\
\WebContent\ – As you’ve done before, create a new JSP page, named:
callJavaPage
callJavaPage
 For the page’s JSFHandler, add the following code (which you can copy from the Notes section below)
Notes:
Notes:

Import
Import statement
– provides reference-ability to the externalType definition
– provides reference-ability to the externalType definition

Two fixed-length string arrays
Two fixed-length string arrays
– one initialized with values (to be passed into the Java Class), one empty that will contain data returned from the Java Class call
– one initialized with values (to be passed into the Java Class), one empty that will contain data returned from the Java Class call

Variable for the externalType
Variable for the externalType