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Poking Around Your REST Application with a Scriptable Endpoint

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Poking Around Your REST Application with a Scriptable Endpoint

· Java Zone ·
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Learn how to build stream processing applications in Java-includes reference application. Brought to you in partnership with Hazelcast.

I love the fact that JDK comes with a ScriptEngine. It's so flexible when you want to evaluate and troubleshoot your application that's already deployed in an server environment. Add this REST endpoint into a Java EE app, and it will give you instant access to internal states of the app.

package myrestapp;

import java.io.StringReader;
import java.util.logging.Logger;
import javax.script.Bindings;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;
import javax.ws.rs.POST;
import javax.ws.rs.Path;
import javax.ws.rs.core.Context;

/**
 * Give instant access to your internal application with dynamic scripting.
 * 
 * <p>Example script:
 * <pre>
 * "sc" + servletContext + ", req=" + request;
 * </pre>
 * 
 * <p>Example2
 * <pre>
 * names = servletContext.getAttributeNames();
 * while(names.hasMoreElements()) {
 *  name = names.nextElement();
 *  println(name);
 * }
 * </pre>
 */
@Path("script")
public class ScriptResource {
  private static final Logger logger = Logger.getLogger(ScriptResource.class.getName());
 
  @Context
  private ServletContext servletContext;
 
  @POST
  public String script(@Context HttpServletRequest request, String scriptText) throws Exception {
  String engineName = "JavaScript";
  ScriptEngineManager manager = new ScriptEngineManager();
  ScriptEngine engine = manager.getEngineByName(engineName);
  logger.info("Running script text length=" + scriptText.length() + ", engine=" + engine);
  Object result = null;
  try (StringReader reader = new StringReader(scriptText)) {
  Bindings bindings = engine.createBindings();
  bindings.put("servletContext", servletContext);
  bindings.put("request", request);
  result = engine.eval(reader, bindings);
  }
  logger.info("Result " + result);
  return "" + result;
  }
}

Notice that I gave couple JavaScript examples in the comment area already. You will have access to two binding variables that should give you full access to many internal components of your application. And here is a quick reference on scripting JDK 7.

Need an UI to test out this endpoint? How about give the "Advance Rest Client" Chrome Extension a try? (Thanks to my co-worker Chris Griffith's tips on this cool extension. It's really handy tool to have!).

Learn how to build distributed stream processing applications in Java that elastically scale to meet demand- includes reference application.  Brought to you in partnership with Hazelcast.

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