nashorn-java-attr-access.java

import java.util.HashMap;
import java.util.Map;
import javax.script.Bindings;
import javax.script.Invocable;
import javax.script.ScriptContext;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import javax.script.SimpleBindings;
import jdk.nashorn.api.scripting.NashornScriptEngineFactory;

public class Jx
{
    public static void main(String[] args) throws Exception
    {
        NashornScriptEngineFactory jsEngineFactory = new NashornScriptEngineFactory();
        ScriptEngine jsEngine = jsEngineFactory.getScriptEngine(new String[] {
            //"--language=es6",
            "--no-java",
            "--no-syntax-extensions",
            "-timezone=UTC",
        });

        Map<String, String> params = new HashMap<>();
        params.put("a", "vA");
        params.put("b", "vB");

        Bindings bindings = new SimpleBindings();
        bindings.put("params", new JavaParamsProvider(params));
        jsEngine.setBindings(bindings, ScriptContext.GLOBAL_SCOPE);

        StringBuilder contextCode = new StringBuilder();
        contextCode.append("({\n");
        for (String key : params.keySet()) {
            contextCode
                .append("get ").append(key).append(" () {")
                .append(" return params.getJavaParam('").append(key).append("') ")
                .append("},");
        }
        contextCode.append("})");

        jsEngine.eval("function invoke(contextCode, source) { return (new Function(\"with(this){\\nreturn (\" + source + \")}\\n\")).call(eval(contextCode)) }");

        Invocable inv = (Invocable) jsEngine;
        String ret = (String) inv.invokeFunction("invoke", contextCode.toString(), "a + b");

        System.out.println("a + b = " + ret);  //=> vAvB
    }

    public static class JavaParamsProvider
    {
        private final Map<String, String> params;

        public JavaParamsProvider(Map<String, String> params)
        {
            this.params = params;
        }

        public String getJavaParam(String name)
        {
            return params.get(name);
        }
    }
}