Embedding Groovy in Java (Binding)

Question

I try to Bind Variables to Groovy and from Groovy back zu Java:

Java code:

Binding binding = new Binding();
binding.setVariable("SRESULT", "foo");
GroovyShell gs = new GroovyShell(binding);
gs.evaluate(script);
String sResult = (String) gs.getContext().getVariable("SRESULT");
System.out.println("FROM GROOVY: " + sResult);

Groovy Code:

class Est {  
  static SRESULT
  public static void main(String[] args) {
    println 'From Java: '+SRESULT
    SRESULT = 'bar'
  }
}

Output:

From Java: foo
FROM GROOVY: foo

My Question: I want to change SRESULT in Groovy and have access to the Value in Java.

Can anybody help me?

score 8 · Answer 1 · answered Feb 26 '13 at 14:42

8

The binding only applies to scripts, not to classes. If your Groovy code were a script, i.e. just the content of the main method without the surrounding class body

println 'From Java: '+SRESULT
SRESULT = 'bar'

then it would produce the result you expect. In particular you must not declare the SRESULT variable in the script, i.e.

def SRESULT = 'bar'

would not work. This is because the declarations (with def or with an explicit type) create local variables within the script, they do not assign to the binding.

answered Feb 26 '13 at 14:42

Ian Roberts

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@user1734715 if the answer worked for you you should consider _accepting_ it by clicking the tick mark to the left. Building a track record of accepting good answers is the best way to encourage people to help you with future questions. – Ian Roberts Mar 06 '13 at 15:27

score 4 · Answer 2 · answered Feb 26 '13 at 13:52

Given Test.java containing:

import groovy.lang.Binding ;
import groovy.lang.GroovyShell ;
import java.io.File ;

public class Test {
    public static void main( String[] args ) throws Exception {
        Binding binding = new Binding() ;
        binding.setVariable( "SRESULT", "foo" ) ;

        GroovyShell gs = new GroovyShell( binding ) ;
        gs.evaluate( new File( "script.groovy" ) ) ;

        String sResult = (String)binding.getVariable( "SRESULT" ) ;
        System.out.printf( "FROM GROOVY: %s\n", sResult ) ;
    }
}

And script.groovy containing:

println "From Java: $SRESULT"
SRESULT = 'bar'

We can compile Test.java by doing:

javac -cp $GROOVY_HOME/embeddable/groovy-all-2.1.1.jar:. Test.java

And then running it with:

java -cp $GROOVY_HOME/embeddable/groovy-all-2.1.1.jar:. Test

Gives the output:

From Java: foo
FROM GROOVY: bar

2023-01-01: There is no `$GROOVY_HOME/embeddable/groovy-all-###.jar` anymore, but `$GROOVY_HOME/lib/groovy-###.jar` can be used instead. — kol, Jan 01 '23 at 09:29

Embedding Groovy in Java (Binding)

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