The ramblings of a yorkshire tyke » JVM

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…?

Using sun.jvmstat.monitor to see active Java processes

spgennard — Sat, 05 Dec 2009 10:56:38 +0000

Monitor’ing Java processes can be achieved using the jvmstat monitor classes provided in the JVM. The documentation is a bit sketchy but with a little experimenting it can be done.

Below is a little example that shows you how to get a list of active Java processes.. which of course can then be used for other things

Here’s the code…

import java.net.URISyntaxException;
import java.util.Set;

import sun.jvmstat.monitor.*;

public class sjps
{
public static void main(String[] args)
throws MonitorException, URISyntaxException
{
MonitoredHost monitoredHost = MonitoredHost.getMonitoredHost("localhost");
Set<Integer> activeVms = monitoredHost.activeVms();
for (int psId : activeVms)
{
MonitoredVm monitoredVm = monitoredHost.getMonitoredVm
(new VmIdentifier(String.valueOf(psId)));
String mainClass = MonitoredVmUtil.mainClass(monitoredVm, false);
String vmVersion = MonitoredVmUtil.vmVersion(monitoredVm);
String commandLine = MonitoredVmUtil.commandLine(monitoredVm);
System.out.println(mainClass + " [" + psId + "]" +
" using : "+vmVersion);
System.out.println(" -> "+commandLine);
}
}

}

And to see the code running..

$ java sjps
sjps [865] using : 14.1-b02-90
-> sjps
JConsole [863] using : 14.1-b02-90
-> sun.tools.jconsole.JConsole

Java process id via java.lang.management

spgennard — Fri, 04 Dec 2009 23:53:13 +0000

While working on a project recently I need to find out the current process of the active running Java process (for tracing/auditing), however I never found a 100% perfect solution but did come across an acceptable solution to use the management classes to query its name, which happens to have encoding in it, so here is the quick solution:

import java.lang.management.ManagementFactory;

public class getpid
{
public static void main(String args[]) throws Exception
{
System.out.println("Process id : "+getProcessId());
}

public static long getProcessId()
{
String name = ManagementFactory.getRuntimeMXBean().getName();
String[] nameBits = name.split("@");

return nameBits == null ? -1 : Long.valueOf(nameBits[0]);
}
}

$ java getpid
Process id : 377

Type Safety and COBOL

spgennard — Mon, 23 Nov 2009 23:27:34 +0000

Having read a recent bog about COBOL and type-safety, I though I would jot down some comments.

ANS85 COBOL is naturally is type-unsafe due as every data item being part of one memory region (or storage area), because of this it can make is difficult to talk to type-safe language such as Java or the CLR.

However, just like any computer language it does not stay still. Object oriented features were added to COBOL, at this point in time you we were given the verbs to create 100% type safe application.

The key to writing type safe code is the use OBJECT-REFERENCE will a TYPE and using them on in your methods and using the INVOKE verb.

For example:

IDENTIFICATION DIVISION.
PROGRAM-ID. "TypeSafeExample".
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
REPOSITORY.
CLASS SYS-STRING AS "System.String".
DATA DIVISION.
WORKING-STORAGE SECTION.
01 hello-world-string OBJECT REFERENCE SYS-STRING.

PROCEDURE DIVISION.
SET hello-world-string TO "Hello World"
DISPLAY hello-world-string
STOP RUN.

The use of COBOL pictures can still be used, however for easy interop with other type-safe languages you really have to stick to the right types for your target environment when exposing your COBOL program to the other languages, this means if you are creating classes, the method to be consumed by other languages should use standard types, for .Net/CLR applications the use of CLS-COMPLIANT types is the right approach. For JVM applications, keep to the “core” java.lang types.

Keep to these simple rules and COBOL will happy interop with type-safe languages.

Fiddling with the JVM

spgennard — Mon, 09 Nov 2009 20:10:49 +0000

Java is a very safe language if used in a normal way, however just like the CLR it can be used in an unsafe manor.

The main reason for using Java in a unsafe manor is performance, some unsafe operations are optimised by the JVM itself.

The boot class loader grants enough permissions to access a key undocumented class sun.misc.Unsafe. As I will state, this is an undocumented class and as the name implies it’s unsafe.

This class provides methods that allows you to manipulate objects and the memory of the objects directly.

For example, you could use it to access the object itself, lets look at an example to manipulate a String object.. not nice I hear you say…. and boy are you are so right. The purpose of this example is to demonstrate the power of the JVM if used to the extreme but not to demonstrate how to destroy the JVM.

import sun.misc.Unsafe;
import java.lang.reflect.Field;

// To Compile: javac BadBoy.java
// To Run: java -Xbootclasspath/p:. BadBoy

public class BadBoy
{
private final static Unsafe unsafe = Unsafe.getUnsafe();

public static void main(String args[]) throws Exception
{
// Find the field "count" inside java.lang.String
Field field = String.class.getDeclaredField("count");

// Find the memory offset within the field...
long countOffset = unsafe.objectFieldOffset(field);

field = String.class.getDeclaredField("offset");
long offset4Offset = unsafe.objectFieldOffset(field);

// Lets read the memory directory...
Object object = "Hello World from Java, the ultra safe language... or is it..";

int length = unsafe.getInt(object, countOffset);
System.out.println("The original Length is length: " + length);

System.out.println("1- The 'object' contains : ");
System.out.println(" -> "+object);
System.out.println(" hashCode is : " + object.hashCode());

unsafe.putInt(object, offset4Offset, 17);
unsafe.putInt(object, countOffset, 32);
System.out.println("2- The 'object' contains : ");
System.out.println(" -> "+object);
System.out.println(" hashCode is : " + object.hashCode());
}
}

Then, the output of the example on my little macbook is:

stephen-gennards-macbook:blob spg$ java -Xbootclasspath/p:. BadBoy
The original Length is length: 60
1- The 'object' contains :
-> Hello World from Java, the ultra safe language... or is it..
hashCode is : 573430574
2- The 'object' contains :
-> Java, the ultra safe language...
hashCode is : 573430574

As you can see the String object is changed but the hashCode remains the same.

Even if the above example seems weird to the extreme and it is, I offer you one take home from this blog…

Be very careful what you place on your “bootclasspath!”

Object COBOL/Java default exception handler

spgennard — Tue, 03 Nov 2009 22:16:54 +0000

While working on some support recently for our compiler (Micro Focus COBOL compiler that is), I became annoyed with the lack of a reasonable error messages/stack trace output from our Java/COBOL Object support.

I have no idea why our default exception handler for Java exceptions just displays a such a simple message with little or no information.

For those who have not seen it, display something similar to:

Exception 65537 not trapped by the class javaexceptionmanager.
Description: "Java exception"
Test error
Hit T to terminate program. Hit any other key to continue.
instantiated - test

Exception 65537 not trapped by the class javaexceptionmanager.
Description: "Java exception"
Test error
Hit T to terminate program. Hit any other key to continue.

Luckily for me and you, we do expose a mechanism for replacing the default exception handler.

Anyway, with very little effort I created a different “default” system exception handler that display this instead:

instantiated - test 1
java.lang.Exception: Test error
at SimpleClass.TestException(SimpleClass.java:10)

WARNING: JavaException: Test error
instantiated - test 2
java.lang.Exception: Test error
at SimpleClass.TestException(SimpleClass.java:10)
WARNING: JavaException: Test error

The key difference being that a Java stack trace is included, boy did this help me.

The program below is the code that implements the exception handler. I am sure someone else can take this example and make it much nicer and provide more features but for this blog I will keep it simple.

$set ooctrl (+p-f) case
program-id. ExceptionCatcher.

class-control.
EntryCallback is class "entrycll"
JavaExceptionManager is class "javaexpt"
ExceptionManager is class "exptnmgr"
Javasup is class "javasup"
.

working-storage section.
01 wsCallback object reference.
01 wsIterator object reference.
01 theJavaException object reference.
local-storage section.
01 filler pic x. *> dummy storage item to allow recursion
linkage section.
01 lnkException object reference.
01 lnkErrorObject object reference.
01 lnkErrorTextCollection object reference.
01 lnkErrorNumber pic x(4) comp-5.
01 anElement object reference.
procedure division.
*>---Set up system level Exception handler
invoke EntryCallback "new" using
z"JException"
returning wsCallback
end-invoke

invoke ExceptionManager "register" using
javaexceptionmanager
wsCallback
end-invoke

invoke EntryCallback "new" using z"DispError"
returning wsIterator
end-invoke

goback.

entry "Jexception" using
lnkException
lnkErrorNumber
lnkErrorTextcollection
.

invoke javasup "exceptionOccurred"
returning theJavaException
end-invoke

if theJavaException not equal null
invoke theJavaException "printStackTrace"
end-if

invoke lnkErrorTextCollection "do" using wsIterator
goback.
.

entry "DispError" using anElement
display "WARNING: JavaException: " with no advancing
invoke anElement "display"
display " "
goback.
.

To use the above code, you just have to first cut-paste to code into a file called ExceptionCatcher.cbl and include this in your project, and then add the directive INITCALL”ExceptionCatcher”, then away you go.

My test programs for the above example are:

$set ooctrl (+p-f) case
program-id. jtest.

class-control.
SimpleClass is class "$JAVA$SimpleClass"
.

working-storage section.
01 theInstance object reference.
local-storage section.
01 filler pic x. *> dummy storage to allow the local entry
procedure division.
*>---Instantiate the class
invoke SimpleClass "new" returning theInstance

display "instantiated - test 1"
invoke theInstance "TestException"

display "instantiated - test 2"
invoke theInstance "TestException"
stop run.

and the Java class itself:

import java.lang.* ;

public class SimpleClass {
public SimpleClass() { }

public void TestException() throws Exception {
throw new Exception ("Test error" );
}
}

References: Studio Enterprise 6.0 Document for COBOL/Java Interop