Rhino Migration Guide
jdk8 replaces Rhino based jsr-223 script engine with nashorn based jsr-223 script engine. If you are using Rhino based jsr-223 script engine in jdk 6 or jdk 7, you'll have some migration work when moving to jdk 8. This document is a migration guide towards that task.
Nashorn implements ECMAScript 5.1 specification with a number of syntax and API extensions as documented in Nashorn extensions Few of those are Rhino specific extensions as well. You may want to go through that document to check if a Rhino specific extension is already supported by nashorn.
Accessing Java packages and classes from script
Nashorn supports top-level "Packages" object and "java", "javax" etc. as supported by Rhino. You can use Packages object to access Java packages and classes. But, Nashorn's recommended way to access Java classes is to use Java.type.
Java.type is recommended because
1) It avoid multiple step object.property resolution as done by Packages method. Class resolution is done in one step - from String name to class
2) Java.type throws ClassNotFoundException rather than silently treating an unresolved name to be package name!
java.util.vector results in a package object named "java.util.vector" whereas Java.type("java.util.vector") results in ClassNotFoundException.
Creating Java arrays from script
In Rhino, you create a Java array using Java reflection from script. In Nashorn, you can resolve to a Java array class using the same Java.type API. And array creation is done using new operator
Java array elements are accessed/modified using  operator in both rhino as well as nashorn. Also special "length" property is supported both in rhino and nashorn.
Class object and .class property
If a java API accepts a java.lang.Class object, in rhino you can pass script representation of class "as is". In Nashorn, you've to use ".class" property (similar to Java).
In the above example, better way to create Java string array from Nashorn would be to get String type from Nashorn using Java.type. The example is written this way only to demonstrate ".class" property.
__proto__ magic property
JavaImporter and with
Nashorn supports JavaImporter constructor of Rhino. It is possible to locally import multiple java packages and use it within a 'with' statement.
Rhino wraps Java exceptions as a script object. If you want underlying Java exception, you've to use "javaException" property to access it. Nashorn does not wrap Java exceptions. Java exception objects as thrown "as is". So, in catch blocks you can access Java exceptions "as is".
Also, no Java object is wrapped as "script object" in Nashorn (unlike Java).
Implementing Java interface
Both Rhino and Nashorn support java anonymous class-like syntax to implement java interfaces in script.
The example @ https://github.com/mozilla/rhino/blob/master/examples/enum.js works on Nashorn as well.
Extending Java class
To extend a concrete Java class or to implement multiple interfaces, you have to use Java.extend in Nashorn - unlike "JavaAdapter" in Rhino. Java.extend is explained in Nashorn extensions document.
There are few Rhino/Mozilla extensions that are supported only if you load the compatibility script provided by nashorn. The compatibility script is loaded using "load('nashorn:mozilla_compat.js")
The compatibility script implements the following Rhino extensions:
- importClass global function to import a specific Java class. Recommended alternative is to use Java.type and assign the result to global variable
- importPackage global function to import a specific Java package. Recommended alternative is to use JavaImporter and with statement.
- JavaAdapter global function to subclass java class or implement java interfaces (this is a wrapper over Java.extend API of nashorn). Recommended alternative is to use Java.extend API directly.
- toSource method on number of builtins - for example, function object to get source code of the function
- A number of HTML generation String methods like "anchor", "sup" etc.