How Java becomes agile riding Rhino

Xavier CasellatoVP of engineering, Liligo.com

Let the ride begin !

Change request : Simon says

We need a white rectangle

We need a white rectangle The rectangle

should be blue

The rectangle should be blue

The rectangle should be blue when it’s sunny

and white when it rains

The rectangle should be blue when it’s sunny

and white when it rains

The rectangle must be yellow if temperature is less than 23°

The rectangle must be yellow if temperature is less than 23°

Who decided it must be a rectangle ?

Who decided it must be a rectangle ?

Didn’t we say it should be orange

?

Didn’t we say it should be orange

?

The border should be

yellow except if it’s sunny

The border should be

yellow except if it’s sunny

The rectangle is circle if

temperature is less than 0° and it’s

sunny

The rectangle is circle if

temperature is less than 0° and it’s

sunny

The circle must be green

The circle must be green

The rectangle is blue and green every

Monday

The rectangle is blue and green every

Monday

Tuesday we want a circle but only if it

rains

Tuesday we want a circle but only if it

rains

Why don’t we do a triangle ?

Why don’t we do a triangle ?

Flexibility is required

Many inputs affect the final result Many rules can be applied Rules change often

Modeling flexibility

Database needs a modelXML needs a DTDHome made data storage ! Are you sure it’s a

solution ?

None of these solutions are really flexible.

Stuck !?

Constraints

Application behavior must be modified quickly Deploying compiled code is time consuming Compiled code required IT resources

Needs

Empower business decision Reduce change requests delay Introduce customizable business logic in

application

Rhino, inside the beast

Rhino History

Netscape project started in 1997 First Release in 1998 Embedded in JVM since Java Standard Edition 1.6

What is Rhino ?

Full-java API Rhino contains

All the features of JavaScript 1.6 A JavaScript shell for executing JavaScript

scripts A JavaScript compiler to transform JavaScript

source files into Java class files A JavaScript debugger for scripts executed with

Rhino

Embed and execute JavaScript codesinside a Java application

General concepts

Context stores information about the execution

environment of a script. Scope

set of JavaScript objects Host

Host objects implement special JavaScript features like dynamic properties.

How it works

Basic Rhino Execution sequence

// Create ContextContext cx = Context.enter();// Initialize standard objectsScriptableObject scope = cx.initStandardObjects();// Build scopescope.put(“input”,input1);// use Script…// Exit Contextcx.exit();

// Create ContextContext cx = Context.enter();// Initialize standard objectsScriptableObject scope = cx.initStandardObjects();// Build scopescope.put(“input”,input1);// use Script…// Exit Contextcx.exit();

Access javascript variables with java

Object x = scope.get("x", scope); if (x == Scriptable.NOT_FOUND) {

System.out.println("x is not defined."); } else {

System.out.println("x = " + Context.toString(x));}

Object x = scope.get("x", scope); if (x == Scriptable.NOT_FOUND) {

System.out.println("x is not defined."); } else {

System.out.println("x = " + Context.toString(x));}

“X” variable is read from script

Using javascript function in Java

Object fObj = scope.get("f", scope); if (!(fObj instanceof Function)) { System.out.println("f is undefined or not a function."); } else { Object functionArgs[] = { "my arg" }; Function f = (Function)fObj; Object result = f.call(cx, scope, scope, functionArgs); String report = "f('my args') = " + Context.toString(result); System.out.println(report); }

Object fObj = scope.get("f", scope); if (!(fObj instanceof Function)) { System.out.println("f is undefined or not a function."); } else { Object functionArgs[] = { "my arg" }; Function f = (Function)fObj; Object result = f.call(cx, scope, scope, functionArgs); String report = "f('my args') = " + Context.toString(result); System.out.println(report); }

Call expects two scriptable objects :

scope to execute the function relative to

JavaScript this object

Create java object in Javascript

String script = "var x =5; System.out.println(x);";

result = cx.evaluateString(scope, script, “<cmd>", 1, null);

String script = "var x =5; System.out.println(x);";

result = cx.evaluateString(scope, script, “<cmd>", 1, null);

“X” variable is declared in the JavaScript and console output is called from JavaScript.

You can access to native java classes from JavaScript.

Sharing java object with javascript

Object wrappedOut = Context.javaToJS(System.out, scope); ScriptableObject.putProperty(scope, "out", wrappedOut); Object wrappedOut = Context.javaToJS(System.out, scope); ScriptableObject.putProperty(scope, "out", wrappedOut);

Object is wrapped as a scope element.

Method calls uses reflection.

Host object

Host is a java class that can be manipulated as a JavaScript prototype.

Naming pattern should be applied to the methods Constructor Getter and Setter Functions

Declare a constructor for Host object

Host class signature

public class Counter extends ScriptableObject { public void jsConstructor(int a) {

…

}

Javascript

…

var counter = new Counter(7);

…

Getter and setter syntax

Host class signature

public int jsGet_field()

{

return field;

}

public void jsSet_field(int value)

{

field = value;

}

Javascript

…

var x =counter.field;

counter.field = x;

…

Host object : functions

Host class signature

public int jsFunction_increment()

{

field++;

}

Javascript

…

counter.increment();

…

Declare host object

ScriptableObject.defineClass(scope, Counter.class);

Host object definition must be declared in the scope.

The line above declares the counter class a JavaScript prototype.

Java class becomes a JavaScript prototype.

You can refer it using as a JavaScript object.

Scope types

Shared scopeUse it to share object defined in a scope without modifying their values between to concurrent scope execution.

Sealed shared scopeObject sealed properties can not be added/deleted to the object and the existing object properties can not be changed

Dynamic scopeAllow to enclose common functions and shared objects in a multi-threaded environment.

Rhino performances

Execution time almost 3 times faster with compiled code

Even compiled code is almost 10 times slower than java compiled code.

Performances concerns

There is a huge difference between evaluated script and compiled ones.

To keep good performances you must compile your script before execution and focus the Rhino usage to the relevant code part.

Rhino in action

Identify use cases

Identify logical components which requires adaptive behavior.

Need to have a flexible behavior

Identify complex rules Various input data and outputs

Estimate execution frequency JavaScript is slower than compiled Java

Embedding strategy

JAVA JAVA

Script Script

Java Native classes

Function Host objects

Out-of-box integration

Deep integration

Storing the script

Flexibility works with a correct storage support !

Don’t miss your target !

SCRIPT MUST BE EASILY MANAGEABLE

Customizable function

JAVA BEANJAVA BEAN

Javascript function

Script Source is an attribute of the object.

Script execution is a bean method.

Customizable process

Java bean initial state

(Host)

Java bean initial state

(Host)

Bean Manager(Context)

Bean Manager(Context)

JavaScript function

JavaScript function

Java beannew state

Host object

Java beannew state

Host object

State change

Rhino Use case : Workflow

Workflow Manager ( Context manager )

Workflow Manager ( Context manager )

Workflow taskHost object

Workflow taskHost object

Workflow definition

Workflow definition

Workflow taskHost object

Workflow taskHost object

Liligo use case 1 : Categorization

Storage processStorage processScript

Storage rules

ScriptStorage

rules

SkiSki Week-endsWeek-ends CruisesCruises

Package offersPackage offers

Liligo use case 2 : Flexible processing

Data processingScript

Data processingScript

Data Host object

Data Host object

HTMLHTMLXMLXML CSVCSV Text fileText file

A few more words

J2SE integrates a higher level of integration which allows you to decide the scripting engine you want to use.

JRuby, Jython are alternative to JavaScript and Rhino.

Helma framework embeds Rhino to provide a full JavaScript server-side framework.

To learn more

www.mozilla.org/rhino/ https://scripting.dev.java.net/ http://java.sun.com/developer/technicalArticles/

J2SE/Desktop/scripting/

Conclusion

Rhino is a really powerful tool.

Rhino is easy to integrate especially since the J2SE1.6.

Performance concerns imply to clearly identify the right embedding strategy.

Properly used in your application it will convert a monolithic java application

into a customizable user-oriented one !!!

Any questions ?

“ and don’t hesitate to contact me with questions or if you were interested in working in our

team: xavier.casellato@liligo.com ”