EMBEDDING GROOVY IN A
JAVA APPLICATION
paolo.predonzani@manydesigns.com

Java-Groovy integration
Compiling Embedding
(loading at run-time)
BSF and JSR 223 Native embedding
GroovyShell GroovyClassLoader GroovyScriptEngine

COMPILING
MyClass.groovy MyClass.class
Maven Ant
Joint compilation: Java references Groovy and vice versa

BEAN SCRIPTING
FRAMEWORK AND JSR 223
http://commons.apache.org/bsf/
http://groovy.codehaus.org/Bean+Scripting+Framework
http://groovy.codehaus.org/JSR+223+Scripting+with+Groovy

NATIVE EMBEDDING
GroovyScript
Engine
Scripts +
GroovyClass
classpath +
Loader
reload +
Introduces the dependency
GroovyShell concept of management
classpath
Simple isolated
scripts

BEHIND THE SCENES...
GroovyShell GroovyScriptEngine
ScriptClassLoader
dependency
mgmt.
GroovyClassLoader

GROOVYSHELL
GroovyShell
.evaluate(String) Object
.run(File, String[]) Object
Script
.parse(File)
.run()
.invokeMethod() Object

BINDING

GROOVYCLASSLOADER
GroovyClass
Loader .addClassPath(“/home/groovy”)
.loadClass(“com.manydesigns.Foo”) Class
.parseClass(“/home/groovy/com/manydesigns/Foo.groovy”)
Class

GROOVYSCRIPTENGINE
GroovyScript
Engine GroovyScriptEngine(String[] roots)
.loadScriptByName(String) Class
.run(String, Binding) Object
Script
.createScript(String) .run()

SCRIPT == CLASS
Script
run()
def f() {} main()
println “Hello world!” f()

IT MAKES SENSE TO DEAL WITH
SCRIPTS AND CLASSES SEPARATELY
} Classpath, packages, classes,
reuse, engineering
} Scripts, files, “spot” usage,
hacking
Groovy is groovy because it supports both perspectives!

GROOVY IN PORTOFINO 4
Classpath for
common groovy
classes
Groovy actions

Groovy actions:
URL structure same as directory
structure
One action.groovy per directory
Packages are not required
URL’s can be moved/renamed
by moving/renaming the
directories
Nobody can depend on an
action
No refactoring is required
Editable from browser or IDE
Each action.groovy is self-
contained. We treat it as a script.

Groovy classpath:
A real classpath with packages
and classes
Contains beans, base classes for
actions, utility classes invokable
by actions
Typically edited from an IDE
Refactoring
Groovy classpath: similar to a
Java classpath but dynamically
reloadable

CLASS LOADING
ClassLoader Loads Java classes only
parent
classloader
GroovyClassLoader Loads Java & Groovy classes

This is the main problem of embedding.
If Groovy was compiled, Java and Groovy
would live in the same class loader

CLASS LOADING: OGNL
OGNL: %{@org.example.MyGroovyClass@myMethod()}
... does not work because OGNL uses the Java classloader
and cannot resolve Groovy classes

CLASS LOADING: HIBERNATE
In Groovy this works:
From Java it works only if we retrieve Book from the
GroovyClassLoader

PERFORMANCE:
CACHING & RELOADING
Test strategy:
1. “engine warm up”
2. measure the first run
3. measure the second run
4. “touch” the script
5. measure the third run

PERFORMANCE:
CONCLUSIONS
Caching Reloading
GroovyShell.evaluate(String) No --
GroovyShell.run(File) Yes No
GroovyClassLoader Yes No
GroovyScriptEngine Yes Yes

DEPENDENCY RELOADING
A
A depends on B
B is modified
B is reloaded
B
Also A should be reloaded
In theory, but until Groovy 1.8.8/2.0.4 there was a bug:
http://jira.codehaus.org/browse/GROOVY-4975

REFERENCES
http://groovy.codehaus.org/Embedding+Groovy
http://groovy.codehaus.org/The+groovyc+Ant+Task
http://docs.codehaus.org/display/GMAVEN/Home
http://groovy.codehaus.org/api/groovy/lang/GroovyShell.html
http://groovy.codehaus.org/api/groovy/lang/
GroovyClassLoader.html
http://groovy.codehaus.org/api/groovy/util/
GroovyScriptEngine.html

THANK YOU!
paolo.predonzani@manydesigns.com
http://www.manydesigns.com/