Java 8 - Nashorn JavaScript

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

jjs

For Nashorn engine, JAVA 8 introduces a new command line tool, jjs, to execute javascript codes at console.

Interpreting js File

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

sample.js

print('Hello World!');

Open console and use the following command.

C:\JAVA>jjs sample.js

It will produce the following output:

Hello World!

jjs in Interactive Mode

Open the console and use the following command.

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

Pass Arguments

Open the console and use the following command.

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

Calling JavaScript from Java

Using ScriptEngineManager, JavaScript code can be called and interpreted 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 as follows −

C:\JAVA>java Java8Tester

It should produce the following result −

Mahesh
12

Calling Java from JavaScript

The following example explains 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 the console and use the following command.

C:\JAVA>jjs sample.js

It should produce the following output −

78952000000000000003.20