Nashorn parser API provides interfaces to represent ECMAScript source code as abstract syntax trees (AST) and Parser to parse ECMAScript source scripts.

Using parser API user can write Java code to access parse tree representation of ECMAScript source. Script source may be a file, a URL or a String. Unless stated otherwise null argument in methods of this package result in NullPointerException being thrown.

 
 import jdk.nashorn.api.tree.*;
 import java.io.File;

 // Simple example that prints warning on 'with' statements
 public class Main {
     public static void main(String[] args) throws Exception {
         // Create a new parser instance
         Parser parser = Parser.create();
         File sourceFile = new File(args[0]);

         // Parse given source File using parse method.
         // Pass a diagnostic listener to print error messages.
         CompilationUnitTree cut = parser.parse(sourceFile,
             (d) -> { System.out.println(d); });

         if (cut != null) {
             // call Tree.accept method passing a SimpleTreeVisitor
             cut.accept(new SimpleTreeVisitor<Void, Void>() {
                 // visit method for 'with' statement
                 public Void visitWith(WithTree wt, Void v) {
                     // print warning on 'with' statement
                     System.out.println("Warning: using 'with' statement!");
                     return null;
                 }
             }, null);
         }
     }
 }