Scripting Languages and COBOL

spgennard — Tue, 19 Jan 2010 10:39:04 +0000

The use of scripting languages with other languages has increased over the last couple of years, from a simple case of interoperability, reuse of scripting code to allowing your code to customised via the user of external scripts. All of which are real world examples I have seen customers use.

Interoperability between languages is very important to COBOL environments just as much as other languages. Some platforms such as Microsoft’s .Net with their CLR makes life much easier by allowing all languages to share a common infrastructure ie: the instruction set and the VM (MSIL and CLR) along with a base class library to get you started.

Environments such as Sun’s VM (JVM) provide two different approaches to interoperability with Java, the first is via JNI/JNA and the second is producing bytecode that runs as is on the VM.

Although the Micro Focus COBOL compiler does not support JVM bytecode or Java source generation it does have support for invoking classes/methods via the OO invoke verb.

This mechanism is very simple to use, you just need to let our object COBOL runtime know the class is a Java class, which can be done by placing $JAVA$ before the name of the class and ensuring the class itself can be found by the JVM itself usually by adding an extra directories or .jar files to the CLASSPATH environment variable.

With Java 6.0 and JSR 223 support for Java based scripting languages were provided via the package javax.script.

Java has a wealth of scripting languages from awk to xlst. My favourites being jpython, jruby and javascript.

The java.net website has a comprehensive list of scripting languages -
https://scripting.dev.java.net/.

To use the scripting packages, you first need to create a ScriptEngineManager, then use this to create a specific ScriptEngine object for your chosen scripting language and use it.

For example:

Create a ScriptEngineManager object.

Retrieve a ScriptEngine object from the manager.

Evaluate a script using the ScriptEngine object.

In COBOL this is quite simply:

The actual Javascript being execute is contained in the invoke statement, which is simply:

print('Hello, world!')

To use the above example, we first need to compile the code and run it.. which is done as follows:

C:\jscripting\HelloWorld>cobol cbljscript.cbl int();
Micro Focus Net Express V5
Version 6.0.00059 Copyright (C) 1984-2009 Micro Focus (IP) Limited.
URN AXCGG/AA0/00000
* Checking complete with no errors - starting code generation
* Generating cbljscript
* Data: 848 Code: 1992 Literals: 904

C:\jscripting\HelloWorld>runm cbljscript
Micro Focus Net Express V6.0.00059
RUN TIME ENVIRONMENT Copyright (C) 1984-2009 Micro Focus (IP) Limited.
URN AXCGG/AA0/00000
Hello, world!

This is just the start, the next thing piece that is required with interoperability to another language is the ability to pass parameters to in and out of the script. Luckily for us the clever chaps on the jsr group have provided ‘put’ and ‘get’ methods that allows us to simply put a name parameter and get the resulting updated or new parameter.

So consider the example, where we need to setup a parameter called ‘message’ for the script and then read a parameter called ‘replyMessage’ after the script has been executed. The javascript to do this is:

/* Do some insanity checking! */
if (typeof(message) == 'undefined')
{
message = "ERROR - 'message' has not been setup"
}

println(message)

replyMessage = "Hello from javascript"

To setup the message parameter, we just need todo.

*> Put a variable in engine, so the javascript
*> can use it.
invoke ws-javascript "put" using
z"message"
z"Hello World from COBOL!"
end-invoke

The after the script has executed, we just need to use the ‘get’ method..

*> get a variable in engine
invoke ws-javascript "get" using
z"replyMessage"
returning ws-message
end-invoke

*> now display the replyMessage if it is available
if ws-message not equal null
invoke ws-pout "println" using ws-message
else
display "Javascript did not set a replyMessage var"

The completed COBOL example below, uses a side file for the javascript too, the code is as follows:

*> ooctrl(+p) required for COM and Java classes
*> ooctrl(-f) used to preserve case of method names for Java
$set ooctrl(+p) ooctrl(-f)

class-control.
cls-Script-EngineManager is
class "$JAVA$javax.script.ScriptEngineManager"
cls-Script-Engine is
class "$JAVA$javax.script.ScriptEngine"
cls-object is
class "$JAVA$java.lang.Object"
cls-System is
class "$JAVA$java.lang.System"
cls-PrintStream is
class "$JAVA$java.io.PrintStream"
cls-FileReader is
class "$JAVA$java.io.FileReader"
.

working-storage section.
01 ws-file object reference cls-FileReader.
01 ws-obj-sem object reference cls-Script-EngineManager.
01 ws-javascript object reference cls-Script-Engine.
01 ws-obj object reference cls-object.
01 ws-message object reference cls-object.

01 ws-pout object reference cls-PrintStream.
procedure division.
*> setup ws-pout to be System.out object
invoke cls-System "getout" returning ws-pout

*> Setup a FileReader object for the external helloworld.js file
invoke cls-FileReader "new" using
z"helloworld.js"
returning ws-file
end-invoke

*> Create a new script manager
invoke cls-Script-EngineManager "new"
returning ws-obj-sem
end-invoke

*> Find the javascript engine
invoke ws-obj-sem "getEngineByName" using
"JavaScript" returning ws-javascript
end-invoke

*> Put a variable in engine, so the javascript
*> can use it.
invoke ws-javascript "put" using
z"message"
z"Hello World from COBOL!"
end-invoke

*> do some javascript stuff!
invoke ws-javascript "eval" using
ws-file
returning ws-obj-sem
end-invoke

*> get a variable in engine
invoke ws-javascript "get" using
z"replyMessage"
returning ws-message
end-invoke

*> now display the replyMessage if it is available
if ws-message not equal null
invoke ws-pout "println" using ws-message
else
display "Javascript did not set a replyMessage var"
end-if

*> cleanup code, not strickly needed for the example but
*> its good practice, to do it.
$if NO-FINALIZE not defined
if ws-message not equal null
invoke ws-message "finalize" returning ws-message
end-if
if ws-pout not equal null
invoke ws-pout "finalize" returning ws-pout
end-if
invoke ws-obj-sem "finalize" returning ws-obj-sem
invoke ws-javascript "finalize" returning ws-javascript
$end

stop run.

C:\jscripting\HelloWorld3>cobol cbljscript.cbl int();
Micro Focus Net Express V5
Version 6.0.00059 Copyright (C) 1984-2009 Micro Focus (IP) Limited.
URN AXCGG/AA0/00000
* Checking complete with no errors - starting code generation
* Generating cbljscript
* Data: 888 Code: 2528 Literals: 1296

C:\jscripting\HelloWorld3>runm cbljscript
Micro Focus Net Express V6.0.00059
RUN TIME ENVIRONMENT Copyright (C) 1984-2009 Micro Focus (IP) Limited.
URN AXCGG/AA0/00000
Hello World from COBOL!
Hello from javascript

As you can see from the code above, setting up parameter is pretty easy todo but sometimes we just want to execute a function in the scripting language such as:

function testMessage(msg)
{
print("testMessage : " + msg);
}

The ScriptEngine object that we have created to use the scripting engine may implement an optional interface called javax.script.Invocable, if the scripting engine we are using does provide this interface then a method called invokeFunction(..) can be used.

In order to reduce the size of the COBOL code, I have coded a simple utils class in java as a simple proxy layer, the code is pretty simple but does make it easier for the COBOL to use the invokeFunction() method.

Then from the COBOL side, we can just use the invokeFunction above.p>

<p>For example:p>
<code lang="cobol" width="800" lines="-1" nowrap="0">
*> invoke a function with one parameter
invoke cls-utils "invokeFunction" using
ws-javascript
z"testMessage"
z"Hello to function testMessage from COBOL"

Which gives us the following output when executed.

C:\jscripting\InvokeFunction>runm cbljscript
Micro Focus Net Express V6.0.00059
RUN TIME ENVIRONMENT Copyright (C) 1984-2009 Micro Focus (IP) Limited.
URN AXCGG/AA0/00000

testMessage : Hello to function testMessage from COBOL

The completed example is as follows:

*> ooctrl(+p) required for COM and Java classes
*> ooctrl(-f) used to preserve case of method names for Java
$set ooctrl(+p) ooctrl(-f)

class-control.
cls-Script-EngineManager is
class "$JAVA$javax.script.ScriptEngineManager"
cls-Script-Engine is
class "$JAVA$javax.script.ScriptEngine"
cls-object is
class "$JAVA$java.lang.Object"
cls-System is
class "$JAVA$java.lang.System"
cls-PrintStream is
class "$JAVA$java.io.PrintStream"
cls-FileReader is
class "$JAVA$java.io.FileReader"
cls-Utils is
class "$JAVA$utils"
.

working-storage section.
01 ws-file object reference cls-FileReader.
01 ws-obj-sem object reference cls-Script-EngineManager.
01 ws-javascript object reference cls-Script-Engine.
01 ws-message object reference cls-object.

01 ws-pout object reference cls-PrintStream.
procedure division.
*> setup ws-pout to be System.out object
invoke cls-System "getout" returning ws-pout

*> Setup a FileReader object for the external helloworld.js file
invoke cls-FileReader "new" using
z"helloworld.js"
returning ws-file
end-invoke

*> Create a new script manager
invoke cls-Script-EngineManager "new"
returning ws-obj-sem
end-invoke

*> Find the javascript engine
invoke ws-obj-sem "getEngineByName" using
"JavaScript" returning ws-javascript
end-invoke

*> do some javascript function
invoke ws-javascript "eval" using
ws-file
returning ws-obj-sem
end-invoke

*> invoke a function with one parameter
invoke cls-utils "invokeFunction" using
ws-javascript
z"testMessage"
z"Hello to function testMessage from COBOL"
returning ws-message
end-invoke

*> cleanup code, not strickly needed for the example but
*> its good practice, to do it.
$if NO-FINALIZE not defined
if ws-file not equal null
invoke ws-file "finalize" returning ws-file
end-if
if ws-message not equal null
invoke ws-message "finalize" returning ws-message
end-if
if ws-pout not equal null
invoke ws-pout "finalize" returning ws-pout
end-if
if ws-obj-sem not equal null
invoke ws-obj-sem "finalize" returning ws-obj-sem
end-if
if ws-javascript not equal null
invoke ws-javascript "finalize" returning ws-javascript
end-if
$end

stop run.

Conclusions: Using a Java based scripting language from COBOL is quite easy, so feel free to use it. Now which scripting language should I use…?

The ramblings of a yorkshire tyke » javascript

Scripting Languages and COBOL