On the fly JavaScript evaluator

EvaluateJavaScriptController.java

package org.hidetake.lab.controller.admin;

import java.io.PrintWriter;
import java.io.StringWriter;

import org.mozilla.javascript.Context;
import org.mozilla.javascript.Scriptable;
import org.slim3.controller.Controller;
import org.slim3.controller.Navigation;
import org.slim3.controller.validator.Validators;

public class EvaluateJavaScriptController extends Controller
{

	@Override
	public Navigation run() throws Exception
	{
		if(!validate()) {
			throw new IllegalArgumentException(errors.toString());
		}
		
		String js = param("js");
		
		Context context = Context.enter();
		Scriptable scope = context.initStandardObjects();
		String result = Context.toString(context.evaluateString(scope, js, null, 1, null));
		Context.exit();
        
		response.setContentType("text/plain");
		response.setCharacterEncoding("UTF-8");
		response.getWriter().append(result);
		return null;
	}

	@Override
	protected Navigation handleError(Throwable error) throws Throwable
	{
		StringWriter writer = new StringWriter();
		error.printStackTrace(new PrintWriter(writer));
		String message = writer.getBuffer().toString().replaceAll("\t.*\r?\n", "");
		
		response.setContentType("text/plain");
		response.setCharacterEncoding("UTF-8");
		response.getWriter().append(message);
		return null;
	}

	private boolean validate()
	{
		Validators v = new Validators(request);
		v.add("js", v.required());
		return v.validate();
	}

}