Rhino – JavaScript for Java

Speaker: Brent Wilkins

• Hertz – Applications Consultant– Cobol developer – 20+ years– PowerBuilder developer – 6 years– Java developer – 10+ years– Email: bwilkins@hertz.com

Rhino – JavaScript for Java

What is it?

Rhino is an open-source implementation of JavaScript written entirely in Java. It is typically embedded into Java applications to provide scripting to end users.

Rhino – JavaScript for Java

Most people who have used JavaScript before have done so by adding scripts to their HTML web pages. However, Rhino is an implementation of the core language only and doesn't contain objects or methods for manipulating HTML documents.

Rhino contains:

• All the features of JavaScript 1.7• Allows direct scripting of Java• 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

Rhino – JavaScript for Java

Outline:

• JavaScript context• Optimization levels• Initializing and scripting the basic Java

objects• Scripting custom objects• Evaluating JavaScript expressions

Rhino – JavaScript for Java

JavaScript Context

The Rhino JavaScript Context object is used to store thread-specific information about the execution environment. There should be one and only one Context associated with each thread that will be executing JavaScript.

Import org.mozilla.javascript.Context;

To associate the current thread with a Context, simply call the enter method of Context:

Context jsContext = Context.enter();

Context.exit();

Once you are done with execution, simply exit the Context:

Rhino – JavaScript for Java

Optimization Levels

-1 Interpretive mode is used. No objects are compiled.

0 No optimization is performed. Objects are compiled to bytecode.

1 – 9 All optimizations are performed.

Rhino – JavaScript for Java

Initializing and scripting the basic Java objects

The basic Java objects (String, Boolean, Integer, etc.) must be initialized within the JavaScript Context. This allows for access to custom Java objects from with the Context.

org.mozilla.javascript.Scriptable

Scriptable script = jsContext.initStandardObjects();

Rhino – JavaScript for Java

Demo time

Rhino – JavaScript for Java

Scripting custom objects

Convert the object from Java to a JavaScript scriptable object

Scriptable jsArgs = Context.toObject( obj, script );

Add the JavaScript object to the other Scriptable objects in the context

script.put( objectName, script, jsArgs );

Rhino – JavaScript for Java

Rhino – JavaScript for Java

Evaluating JavaScript expressions

Object result = jsContext.evaluateString( script, expression, expression, 1, null );

Determine the result type of the return object:• String String stringResult = Context.toString( result );• Boolean boolean boolResult = Context.toBoolean( result );

Demo time

Rhino – JavaScript for Java

Thermal Printing at Hertz

• Must be able to access data from the Rental Agreement• Must be able to evaluate psuedocode that contains:

– AND, OR– () order of operations– =, <>, <, >, <=, >=– IN and NIN – Evaluates if a variable is in a group of values

Rhino – JavaScript for Java

Thermal Printing at Hertz

• Must be able to access data from the Rental Agreement• Must be able to evaluate psuedocode that contains:

– AND, OR &&, ||– () order of operations– =, <>, <, >, <=, >= ==, !=– IN and NIN – Evaluates if a variable is in a group of values

• IN Java method isInGroup( “|” + var + “|”, “|value|value|value|” )• NIN !isInGroup()

Rhino – JavaScript for Java

Demo time

Rhino – JavaScript for Java

Rhino – JavaScript for Java

Resources

http://www.mozilla.org/rhino/http://www.rhino-tutorial.buss.hk/