Rhino (JavaScript engine)

Rhino

Developer(s)	Mozilla Foundation / Mozilla Corporation
Stable release	1.7R2 / March 22, 2009
Written in	Java
Operating system	Cross-platform
Platform	Java Virtual Machine
Development status	Active
Type	JavaScript engine
License	MPL 1.1/GPL 2.0
Website	http://www.mozilla.org/rhino/

Rhino is an open source JavaScript engine. It is developed entirely in Java and managed by the Mozilla Foundation. The Foundation also provides another implementation of JavaScript engine written in C known as SpiderMonkey.

Rhino converts JavaScript scripts into Java classes. Rhino works in both compiled as well as interpreted mode. It is intended to be used in server-side applications, hence there is no built-in support for the browser objects that are commonly associated with JavaScript.

Rhino can be used as a debugger by making use of the Rhino shell. It can be used in applications by embedding Rhino.

A slightly modified version of Rhino 1.6r2 comes bundled with the Sun Microsystems release of Java SE version 6, which was released in December 2006. This makes it easier to integrate JavaScript as part of Java programs and to access Java resources from JavaScript. Other implementations of Java 6 may differ.

History

The Rhino project was started at Netscape in 1997. At the time, Netscape was planning to produce a version of Navigator written entirely in Java and so it needed an implementation of JavaScript written in Java. When Netscape stopped work on "Javagator", as it was called, the Rhino project was finished as JavaScript engine. Since then, a couple of major companies (including Sun Microsystems) have licensed Rhino for use in their products and paid Netscape to do so, allowing work to continue on it.

Originally, Rhino compiled all JavaScript code to Java bytecodes in generated classfiles. This produced the best performance (often beating the C implementation of JavaScript when run on a JIT), but suffered from two faults. First, compilation time was long since generating Java bytecodes and loading the generated classes was a heavyweight process. Also, the implementation effectively leaked memory since most JVMs don't collect unused classes or the strings that are interned as a result of loading a class file.

So in Fall of 1998, Rhino added an interpretive mode. The classfile generation code was moved to an optional, dynamically-loaded package. Compilation is faster and when scripts are no longer in use they can be collected like any other Java object.

Rhino was released to Mozilla Foundation in April of 1998. Originally Rhino classfile generation had been held back from release. However the licensees of Rhino have now agreed to release all of Rhino to open source, including class file generation. Since its release to open source, Rhino has found a variety of uses and an increasing number of people have contributed to the code . The project gets its name from the animal on the cover of the JavaScript book from O'Reilly Media . Starting with version 1.7R1, Rhino relies on the Java 5 platform, and supports version 1.7 of JavaScript.

Example

Below is an example of java code running JavaScript print('Hello, world!')

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

public class RhinoEngine {
    public static void main(String[] args) {
        ScriptEngineManager mgr = new ScriptEngineManager();
        // Now we can go and get a script engine we want. 
        // This can be done either by finding a factory that supports 
        // our required scripting language 
        // (engine = factory.getScriptEngine();)
        // or by requesting a script engine that supports a 
        // given language by name from the script engine manager.
        ScriptEngine engine = mgr.getEngineByName("JavaScript");
        
        // Now we have a script engine instance that 
        // can execute some JavaScript
        try {
            engine.eval("print('Hello, world!')");
        } catch (ScriptException ex) {
            ex.printStackTrace();
        }    
    }
}

Here is a simple example showing a Rhino Script that outputs each line in the stdin converted to uppercase.

// The same as: import java.io.*;
importPackage(java.io);
importPackage(java.lang);

// "in" is a keyword in Javascript. 
// In Rhino you could query for an attribute using [] syntax: 
// Ex: System['out']
S = new BufferedReader( new InputStreamReader(System['in']) );
s = true;

while (s){
    s = S.readLine().toUpperCase();
    if (s) System.out.println(s);
}

Rhino Shell

The JavaScript shell provides a simple way to run scripts in batch mode or an interactive environment for exploratory programming. Invoking the Rhino Shell with the command below:

java org.mozilla.javascript.tools.shell.Main

The Rhino Shell can also be invoked with this command:

java -jar js.jar

The advantage is that you don't have to configure the classpath to use this form.

See also

• JavaScript engine
• List of JavaScript engines
• Mozilla Grendel

External links

• Rhino - JavaScript for Java
• Download Rhino
• Download Archive (Main download page above doesn't work currently)