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Rhino is an open-source implementation of JavaScript written entirely in Java. It is typically embedded into Java applications to provide scripting to end users.

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/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

package org.mozilla.javascript.engine;

import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.Writer;
import javax.script.ScriptContext;
import org.mozilla.javascript.Context;
import org.mozilla.javascript.Function;
import org.mozilla.javascript.ScriptRuntime;
import org.mozilla.javascript.Scriptable;
import org.mozilla.javascript.ScriptableObject;

/**
 * 
 * This class defines the following built-in functions for the RhinoScriptEngine.
 * 
 * 
 * print(arg, arg, ...): Write each argument, concatenated to the ScriptEngine's
 * "standard output" as a string.
 * 
 */
public class Builtins {

  static final Object BUILTIN_KEY = new Object();

  private Writer stdout;

  void register(Context cx, ScriptableObject scope, ScriptContext sc) {
    if (sc.getWriter() == null) {
      stdout = new OutputStreamWriter(System.out);
    } else {
      stdout = sc.getWriter();
    }

    scope.defineFunctionProperties(new String[]{"print"},
        Builtins.class,
        ScriptableObject.PERMANENT | ScriptableObject.DONTENUM);
  }

  public static void print(Context cx, Scriptable thisObj, Object[] args, Function f)
      throws IOException {
    Builtins self = getSelf(thisObj);
    for (Object arg : args) {
      self.stdout.write(ScriptRuntime.toString(arg));
    }
    self.stdout.write('\n');
  }

  private static Builtins getSelf(Scriptable scope) {
    // Since this class is invoked as a set of anonymous functions, "this"
    // in JavaScript does not point to "this" in Java. We set a key on the
    // top-level scope to address this.
    return (Builtins) ScriptableObject.getTopScopeValue(scope, BUILTIN_KEY);
  }
}