Java 8 - Nashorn JavaScript Engine

With Java 8, Nashorn, a much improved javascript engine is introduced to replace the existing Rhino java script engine. Nashorn provides 2 to 10 times better performance as it directly compiles the code in memory and passes the bytecode to JVM.Nashorn uses invokedynamics feature, introduced in java 7 to improve performance.

jjs

For Nashorn engine, JAVA 8 introduces a new command line tool, jjs to execute java script code at console.

Interpretting js file.

Create and save sample.js in c: > JAVA folder.

sample.js 
print('Hello World!');

Open console and use the following command.

C:\JAVA>jjs sample.js

See the result.

Hello World!

jjs in interactive mode

Open console and use the following command.

C:\JAVA>jjs 
jjs> print("Hello, World!")
Hello, World!
jjs> quit()
>>

pass arguments

Open console and use the following command.

C:\JAVA> jjs -- a b c
jjs> print('letters: ' +arguments.join(", "))
letters: a, b, c
jjs>

Calling JavaScript in JAVA

Using ScriptEngineManager, JavaScript code can be called and interpretted in java.

Example

Create the following java program using any editor of your choice in say C:/> JAVA

Java8Tester.java 
import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;
import javax.script.ScriptException;

public class Java8Tester {
   public static void main(String args[]) {
      ScriptEngineManager scriptEngineManager = new ScriptEngineManager(); 
      ScriptEngine nashorn = scriptEngineManager.getEngineByName("nashorn"); 
      String name = "Mahesh"; 

      Integer result = null;
      try {
         nashorn.eval("print('" + name + "')");
         result = (Integer) nashorn.eval("10 + 2");   
      } catch(ScriptException e) {
         System.out.println("Error executing script: "+ e.getMessage());
      }
      System.out.println(result.toString());
   } 
}

Verify the result

Compile the class using javac compiler as follows

C:\JAVA>javac Java8Tester.java

Now run the Java8Tester to see the result

C:\JAVA>java Java8Tester

See the result.

Mahesh
12

Calling Java from JavaScript

Following example will show how to import and use java classes in java script.

Create and save sample.js in c: > JAVA folder.

sample.js 
var BigDecimal = Java.type('java.math.BigDecimal'); 

function calculate(amount, percentage) { 
   var result = new BigDecimal(amount).multiply( 
      new BigDecimal(percentage)).divide( 
         new BigDecimal("100"), 2, BigDecimal.ROUND_HALF_EVEN); 
   return result.toPlainString(); 
}
var result = calculate(568000000000000000023,13.9); 
print(result);

Open console and use the following command.

C:\JAVA>jjs sample.js

See the result.

78952000000000000003.20
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