How to use Nashorn in Java 15 and later?

I have an existing Spring Boot application that is non-modular and uses Nashorn. The application works well on Java 14.

After adding the Maven coordinates of the new Nashorn available for Java 15, the application fails while starting the script engine.

public static void main(String[] args) throws ScriptException {
    ScriptEngineManager factory = new ScriptEngineManager();
    ScriptEngine engine = factory.getEngineByName("nashorn"); 
    engine.eval("print('Hello, World!');");
}

Error message:

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "javax.script.ScriptEngine.eval(String)" because "engine" is null
    at xxxxx.yyyy.service.JavaScriptServiceImpl.main(JavaScriptServiceImpl.java:52)

Is it required to modularize the whole project to make use of Nashorn?

Solution

According to JEP 372, Nashorn had been removed from JDK 15 but you can get latest nashorn from https://search.maven.org/artifact/org.openjdk.nashorn/nashorn-core/15.0/jar

For Maven, include the below dependency into your pom.xml

<dependency>
  <groupId>org.openjdk.nashorn</groupId>
  <artifactId>nashorn-core</artifactId>
  <version>15.0</version>
</dependency>

For Gradle, include dependency below into your build.gradle

implementation 'org.openjdk.nashorn:nashorn-core:15.0'

Unfortunately, Standalone Nashorn is only usable as a JPMS module. So you might need to follow the solution stated in https://stackoverflow.com/a/46289257 to make it work with a non-modular application.

From the given class xxxxx.yyyy.service.JavaScriptServiceImpl and based on feedback from @JornVernee and @AttilaSzegedi, the command line should look like

jdk-15.0.1/bin/java -classpath /home/nashorn-helloworld/target/classes --module-path /home/org/openjdk/nashorn/nashorn-core/15.0:/home/org/ow2/asm/asm/7.3.1:/home/org/ow2/asm/asm-analysis/7.3.1:/home/org/ow2/asm/asm-commons/7.3.1:/home/org/ow2/asm/asm-tree/7.3.1/home/org/ow2/asm/asm-util/7.3.1 --add-modules org.openjdk.nashorn xxxxx.yyyy.service.JavaScriptServiceImpl