Build a Polyglot Native Executable (Java and JavaScript)

With GraalVM Polyglot API you can embed and run code from a guest language in a Java-based host application. GraalVM makes it possible to ahead-of-time compile a Java application with embedded JavaScript too and create a polyglot native executable. Embedding Reference on how to interact with a guest language like JavaScript from a Java host application for more information.

This guide will show how to build a polyglot native executable with Java host language and JavaScript as a guest language.

For a demo, you will use this JSON pretty-printer Java application that prints the output in the JSON format:

import java.io.*;
import java.util.stream.*;
import org.graalvm.polyglot.*;

public class PrettyPrintJSON {
  public static void main(String[] args) throws java.io.IOException {
    BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
    String input = reader.lines()
    .collect(Collectors.joining(System.lineSeparator()));
    try (Context context = Context.create("js")) {
      Value parse = context.eval("js", "JSON.parse");
      Value stringify = context.eval("js", "JSON.stringify");
      Value result = stringify.execute(parse.execute(input), null, 2);
      System.out.println(result.asString());
    }
  }
} 
  1. Save it in the PrettyPrintJSON.java file and compile:

     javac PrettyPrintJSON.java
    
  2. Build a native executable by enabling the JavaScript interoperability:

     native-image --language:js --initialize-at-build-time PrettyPrintJSON
    

    The --language:js argument ensures that JavaScript is available in the generated image. It will take several minutes as it does not just build the executable, but also pulls in the JavaScript engine.

    Note: Building a polyglot native executable requires more physical memory because the Truffle framework is included.

  3. Run the resulting executable and perform some pretty-printing:

     ./prettyprintjson <<EOF
     {"GraalVM":{"description":"Language Abstraction Platform","supports":["combining languages","embedding languages","creating native images"],"languages": ["Java","JavaScript","Node.js", "Python", "Ruby","R","LLVM"]}}
     EOF
    

    The expected output is:

     {
     "GraalVM": {
         "description": "Language Abstraction Platform",
         "supports": [
         "combining languages",
         "embedding languages",
         "creating native images"
         ],
         "languages": [
         "Java",
         "JavaScript",
         "Node.js",
         "Python",
         "Ruby",
         "R",
         "LLVM"
         ]
     }
     }
    

The native executable version runs faster than running the same application on the JVM.

Note: JavaScript support by GraalVM Native Image is considered general availability. The remaining languages support is experimental.

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