How can I invoke a Java program from Perl?

Question

I'm new with Perl and I'm trying to do something and can't find the answer.

I created a Java project that contains a main class that gets several input parameters.

I want to wrap my Java with Perl: I want to create a Perl script that gets the input parameters, and then passes them to the Java program, and runs it.

For example:

If my main is called mymain, and I call it like this: mymain 3 4 hi (3, 4 and hi are the input parameters), I want to create a Perl program called myperl which when it is invoked as myperl 3 4 hi will pass the arguments to the Java program and run it.

How can I do that?

Sinan Ünür · Accepted Answer · 2017-08-09 18:03:20Z

6

Running a Java program is just like running any other external program.

Your question has two parts :

How do I get the arguments from Perl to the Java program?
How do I run the program in Perl?

For (1) you can do something like

my $javaArgs = " -cp /path/to/classpath -Xmx256";
my $className = myJavaMainClass;
my $javaCmd = "java ". $javaArgs ." " . $className . " " . join(' ', @ARGV);

Notice the join() function - it will put all your arguments to the Perl program and separate them with space.

For (2) you can follow @AurA 's answer.

Using the system() function
```
my $ret = system("$javaCmd");
```

This will not capture (i.e. put in the variable $ret) the output of your command, just the return code, like 0 for success.

Using backticks
```
my $out = `$javaCmd`;
```

This will populate $out with the whole output of the Java program ( you may not want this ).

Using pipes

open(FILE, "-|", "$javaCmd");
my @out = <FILE>

This is more complicated but allows more operations on the output.

For more information on this see perldoc -f open.

edited Aug 9, 2017 at 18:03

Sinan Ünür

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answered May 17, 2012 at 7:27

Chip

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1 Comment

iltaf khalid Over a year ago

Running java calling perl script on a windows machine: process = r.exec("cmd /c perl D:\\perlexamples\\hello.pl");\

AurA · Accepted Answer · 2012-05-17 07:22:34Z

2

$javaoutput = `java javaprogram`;
or
system "java javaprogram";

For a jar file

$javaoutput = `java -jar filename.jar`;
or
system "java -jar filename.jar";

edited May 17, 2012 at 7:22

answered May 17, 2012 at 7:11

AurA

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3 Comments

Ben Hoffman Over a year ago

Thank you for the fast reply;

Ben Hoffman Over a year ago

Thank you for the fast reply, now i/m getting: Error: Could not find or load main class dbtools.jar

Chip Over a year ago

You probably need to set the classpath. Try to run the java program outside first and then use the same syntax inside.

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