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Java WebSocket session resulting to null after onOpen

I am using websockets for the first time on a javafx project, when I start the program the session is set to the local variable session, but after when I call the sendMessage function the session is back to null. Below please find my client class
package myclient;
import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.util.logging.Level;
import java.util.logging.Logger;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;
import javax.websocket.ClientEndpoint;
import javax.websocket.ContainerProvider;
import javax.websocket.DeploymentException;
import javax.websocket.OnClose;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.WebSocketContainer;
#ClientEndpoint
public class Client extends Application {
private static final Logger LOGGER = Logger.getLogger(Client.class.getName());
private Session session;
#OnOpen
public void onOpen(Session session){
this.session = session;
System.out.println("Opened Session " + this.session);
}
#OnClose
public void onClose(){
System.out.println("Closed Session " + this.session);
}
#OnMessage
public void onMessage(String msg){
System.out.println("Websocket message received! " + msg);
}
#Override
public void start(Stage stage) throws Exception {
Parent root = FXMLLoader.load(getClass().getResource("FXMLClient.fxml"));
Scene scene = new Scene(root);
connectToWebSocket();
stage.setScene(scene);
stage.show();
}
private void connectToWebSocket() {
System.out.println("Client WebSocket initialized>> " + this.session);
WebSocketContainer container = ContainerProvider.getWebSocketContainer();
try {
URI uri = URI.create("ws://localhost:8080/Server/endpoint");
container.connectToServer(this, uri);
}
catch (DeploymentException | IOException ex) {
LOGGER.log(Level.SEVERE, null, ex);
System.exit(-1);
}
}
public void sendMessage(String message) throws IOException{
if(this.session != null){
System.out.println(message + ", " + this.session);
this.session.getBasicRemote().sendText(message);
}
else {
System.out.println("Session is null");
}
}
public static void main(String[] args) {
launch(args);
}
}
Any suggestions?
Thanks in advance

I think I now do know the answer to this.
You are probably using tomcat or some other server for this. When you see "tomcat" in this answer, please insert the name of your actually used server.
When a connection to your websocket is opened, tomcat will create an instance of the websocket (your Client) class by itself. This means, the onOpen-Method will be called and it will look as if it was you who created the instance, who opened the connection, when really you did not. Tomcat did.
This in turn means, that when you call sendMessage on your Client instance, the session will be null, because this object never connected anywhere.
Oh, and you don't have access to the connected instance that was created by tomcat.
One way of fixing this would be to do all the work inside the onOpen-Method, however that is not practical. You may want to put the work in another method and call it from onOpen. That way, the instance created by tomcat will do the necessary work.
In my project I needed to poll on an MQTT-Topic and render the data on a website (university assignment). I did the polling in a separate class, resulting in hard to debug errors whenever trying to send received data with my sendMessage-method.
I hope this answer does clear this up a little, if not for you, maybe at least for future generations having the same university assignment...

RemoteApi calls from servlet not loading in local app engine app

I'am trying this example https://cloud.google.com/appengine/docs/java/tools/remoteapi
Everything works fine if I run script as java application, but when I do it as servlet it always loads forever and doesn't throw any errors. Also works fine on localhost. Also I noticed it happens when query is made, when I comment it out (datastore.put), servlet loads instantly.
import java.io.IOException;
import javax.servlet.http.*;
import com.google.appengine.api.datastore.DatastoreService;
import com.google.appengine.api.datastore.DatastoreServiceFactory;
import com.google.appengine.api.datastore.Entity;
import com.google.appengine.tools.remoteapi.RemoteApiInstaller;
import com.google.appengine.tools.remoteapi.RemoteApiOptions;
#SuppressWarnings("serial")
public class Gae_java_Servlet extends HttpServlet {
public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
RemoteApiOptions options = new RemoteApiOptions()
.server("java-dot-project.appspot.com", 443)
.useApplicationDefaultCredential();
RemoteApiInstaller installer = new RemoteApiInstaller();
installer.install(options);
try {
DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
System.out.println("Key of new entity is " +
datastore.put(new Entity("Hello Remote API!")));
} finally {
installer.uninstall();
}
}
}

I figured it out, needed to use RemoteApiOptions().useServiceAccountCredential("service email", "p12key") instead of useApplicationDefaultCredential()

Accessing an Instance of an Object from a Serlvet in Java Web Application

Please could you have a look at this. I have made SO much progress but am stuck on this bit now.
I have a service AnnJAXB.java that performs a GET request and puts the response in an Ann class (which contains Anime and Info classes as attributes). I modified the service to return Ann so I can potentially use the return value. I annotated the Ann, Anime and Info classes to say #Stateless.
I have a servlet ControllerServlet that I want to use to (initially) print attributes of Ann to a JSP webpage frontend. I took code that was initially in the AnnJAXB service class and put it in the servlet. This code is basically the for loop:
for (Anime anime : ann.getAnn()) {
It seems that none of the contents of the for loop are displayed (neither the html nor the Ann/Anime attributes).
My service/method class AnnJAXB:
package main;
import entities.*;
import javax.xml.bind.*;
import java.io.*;
import java.net.URL;
import java.net.MalformedURLException;
import javax.ejb.Stateless;
#Stateless
public class AnnJAXB {
public Ann Unmarshalling(String searchString) throws JAXBException, MalformedURLException {
JAXBContext jc = JAXBContext.newInstance(Ann.class);
Unmarshaller ums = jc.createUnmarshaller();
URL url = new URL( "http://cdn.animenewsnetwork.com/encyclopedia/api.xml?title=~"+searchString );
Ann ann = (Ann) ums.unmarshal(url);
return ann;
}
}
My serlvet class ControllerServlet. Note I have not added anything to config files or anything like that. I just right-clicked and made a servlet class and started modifying it.
package main;
import entities.Anime;
import entities.Ann;
import entities.Info;
import java.io.IOException;
import java.io.PrintWriter;
import javax.ejb.EJB;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
*
* #author J
*/
#WebServlet(name = "ControllerServlet", urlPatterns = {"/ControllerServlet"})
public class ControllerServlet extends HttpServlet {
// #EJB
// private AnnJAXB annJAXB = new AnnJAXB();
#EJB
private Ann ann;
/**
* Processes requests for both HTTP <code>GET</code> and <code>POST</code>
* methods.
*
* #param request servlet request
* #param response servlet response
* #throws ServletException if a servlet-specific error occurs
* #throws IOException if an I/O error occurs
*/
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
try (PrintWriter out = response.getWriter()) {
/* TODO output your page here. You may use following sample code. */
out.println("<!DOCTYPE html>");
out.println("<html>");
out.println("<head>");
out.println("<title>Servlet ControllerServlet</title>");
out.println("</head>");
out.println("<body>");
out.println("<h1>Servlet ControllerServlet at " + request.getContextPath() + "</h1>");
AnnJAXB an = new AnnJAXB();
try{
an.Unmarshalling("evangelion");
}catch(Exception e){}
for (Anime anime : ann.getAnn()) {
out.println("<h1>Loop1</h1>");
out.println("<h1>ID: " + anime.getId() + "</h1>");
out.println("<h1>Name: " + anime.getName() + "</h1>");
for (Info temp : anime.getAnime()) {
if (temp.getSrc() != null) {
out.println("<h1>Info: " + temp.getSrc() + "</h1>");
}
}
}
out.println("<h1>End</h1>");
out.println("</body>");
out.println("</html>");
}
}
(other default methods here)
What happens when it runs:
The IDE asks me for a execution url and I leave it as /ControllerServlet?. A webpage opens and prints the words:
Servlet ControllerServlet at /prototype9
End
It should show Ann attributes inbetween those words.
Here is the Ann class for reference:
package entities;
import javax.xml.bind.annotation.*;
import java.util.*;
import javax.ejb.Stateless;
#Stateless
#XmlRootElement(name = "ann")
public class Ann {
private List<Anime> Ann = new ArrayList<Anime>();
#XmlElement(name="anime")
public List<Anime> getAnn() {
return Ann;
}
public void setAnn(List<Anime> Ann) {
this.Ann = Ann;
}
public Ann() {
super();
}
}
Thankyou so much for reading.

user3474126 solved it as follows:
I changed the loop to say:
for (Anime anime : annj.Unmarshalling("evangelion").getAnn()) {
and removed
annj.Unmarshalling("evangelion");

science web page doesn't print the
out.println("<h1>Loop1</h1>");
it will be right to assume that it had never entered the loop, thus : condition from
(i=0, i< List.size(), i++)
are not met. For debadging purpose, in the code it self, check that
#EJB
private Ann ann; //not null
and
ann.getAnn().size > 0
http://docs.oracle.com/javaee/5/api/javax/xml/bind/annotation/XmlElements.html

Servlet data members keep session?

I'm building a web application from an existing project. In the existing project I have a class that contains all my objects and the things I can do with them.
I was wondering what will happen if I had an instance of this class to a servlet as a data member:
When the same user with same session is directed to the servlet that contains this class will it keep it's data or will it regenerate every time?
Will every user/session have a different copy of this member or is it shared?
If data members in servlets don't keep thir state for the same session, then what do you recommend? Maybe activly adding it to the session?
Thanks for your help

Servlets - thus their data members - are shared between all sessions on the server. Thus
When the same user with same session is directed to the servlet that contains this class will it keep it's data or will it regenerate every time?
The data will be kept around (for all users) until you restart the web application.
Will every user/session have a different copy of this member or is it shared?
It is shared.
If data members in servlets don't keep thir state for the same session, then what do you recommend? Maybe activly adding it to the session?
Session specific data should be stored in an HttpSession.

To be sure of this behavior, I wrote a little TestingServlet - I will show you the lifecycle of a servlet and its members. Also supplied; How to work with session variables
import java.io.IOException;
import java.io.PrintWriter;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Basic servlet for lifecycle testing
*
* #author powermicha
*
*/
public class TestingServlet extends HttpServlet {
/**
*
*/
private static final long serialVersionUID = 4020575563844924588L;
private Logger logger;
private int requestCounter;
#Override
public void init() throws ServletException {
logger = Logger.getLogger("TestingServlet_" + System.currentTimeMillis());
logger.log(Level.INFO, "TestingServlet initialized");
requestCounter = 0;
}
#Override
public void destroy() {
logger.log(Level.INFO, "TestingServlet destroyed");
}
#Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
int requestsPerSession = incrementRequestsPerSession(req);
String logMessage = "TestingServlet was called " + (++requestCounter) + " times. "
+ requestsPerSession + " times from the same session (ID:"
+ req.getSession().getId() + ")";
logger.log(Level.INFO, logMessage);
// send it to the browser
PrintWriter writer = resp.getWriter();
writer.write(logMessage);
writer.close();
}
private int incrementRequestsPerSession(HttpServletRequest req) {
Integer counter = (Integer) req.getSession().getAttribute("requestsPerSession");
if (counter == null) {
counter = 1;
} else {
counter++;
}
req.getSession().setAttribute("requestsPerSession", counter);
return counter;
}
}

how to profile a page request for a spring mvc app

what options do I have to profile a page request in a spring mvc app?
I want to get a breakdown of how long the page request takes, along with the various stages like how long it takes to render the freemarker template, hibernate db calls, etc.

We just accomplished something similar with an interceptor and a custom tag. This solution is "light" enough to be used in production, presents its data as HTML comments at the bottom of the response, and allows you to opt into the more verbose logging with a request parameter. You apply the interceptor below to all request paths you want to profile, and you add the custom tag to the bottom of the desired pages. The placement of the custom tag is important; it should be invoked as close to the end of request processing as possible, as it's only aware of time spent (and objects loaded) prior to its invocation.
package com.foo.web.interceptor;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;
public class PageGenerationTimeInterceptor extends HandlerInterceptorAdapter {
public static final String PAGE_START_TIME = "page_start_time";
public static final String PAGE_GENERATION_TIME = "page_generation_time";
public boolean preHandle(HttpServletRequest request, HttpServletResponse response,
Object handler) throws Exception {
request.setAttribute(PAGE_START_TIME, new Long(System.currentTimeMillis()));
return true;
}
public void postHandle(HttpServletRequest request, HttpServletResponse response,
Object handler, ModelAndView modelAndView) throws Exception {
Long startTime = (Long) request.getAttribute(PAGE_START_TIME);
if (startTime != null) {
request.setAttribute(PAGE_GENERATION_TIME, new Long(System.currentTimeMillis() - startTime.longValue()));
}
}
}
The custom tag looks for the request attributes, and uses them to compute the handler time, the view time, and the total time. It can also query the current Hibernate session for first-level cache statistics, which can shed some light on how many objects were loaded by the handler and view. If you don't need the Hibernate information, you can delete the big if block.
package com.foo.web.taglib;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.SortedSet;
import java.util.TreeSet;
import javax.servlet.ServletContext;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.Tag;
import javax.servlet.jsp.tagext.TryCatchFinally;
import org.apache.log4j.LogManager;
import org.apache.log4j.Logger;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.engine.CollectionKey;
import org.hibernate.engine.EntityKey;
import org.hibernate.stat.SessionStatistics;
import org.springframework.beans.factory.BeanFactoryUtils;
import org.springframework.context.ApplicationContext;
import org.springframework.web.bind.ServletRequestUtils;
import org.springframework.web.context.support.WebApplicationContextUtils;
import org.springframework.web.servlet.tags.RequestContextAwareTag;
import com.foo.web.interceptor.PageGenerationTimeInterceptor;
public class PageInfoTag extends RequestContextAwareTag implements TryCatchFinally {
private static final long serialVersionUID = -8448960221093136401L;
private static final Logger LOGGER = LogManager.getLogger(PageInfoTag.class);
public static final String SESSION_STATS_PARAM_NAME = "PageInfoTag.SessionStats";
#Override
public int doStartTagInternal() throws JspException {
try {
JspWriter out = pageContext.getOut();
Long startTime = (Long)pageContext.getRequest().getAttribute(PageGenerationTimeInterceptor.PAGE_START_TIME);
Long handlerTime = (Long)pageContext.getRequest().getAttribute(PageGenerationTimeInterceptor.PAGE_GENERATION_TIME);
if (startTime != null && handlerTime != null) {
long responseTime = System.currentTimeMillis() - startTime.longValue();
long viewTime = responseTime - handlerTime;
out.append(String.format("<!-- total: %dms, handler: %dms, view: %dms -->", responseTime, handlerTime, viewTime));
}
if (ServletRequestUtils.getBooleanParameter(pageContext.getRequest(), SESSION_STATS_PARAM_NAME, false)) {
//write another long HTML comment with information about contents of Hibernate first-level cache
ServletContext servletContext = pageContext.getServletContext();
ApplicationContext context = WebApplicationContextUtils.getRequiredWebApplicationContext(servletContext);
String[] beans = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(context,
SessionFactory.class, false, false);
if (beans.length > 0) {
SessionFactory sessionFactory = (SessionFactory) context.getBean(beans[0]);
Session session = sessionFactory.getCurrentSession();
SessionStatistics stats = session.getStatistics();
Map<String, NamedCount> entityHistogram = new HashMap<String, NamedCount>();
out.append("\n<!-- session statistics:\n");
out.append("\tObject keys (").append(String.valueOf(stats.getEntityCount())).append("):\n");
for (Object obj: stats.getEntityKeys()) {
EntityKey key = (EntityKey)obj;
out.append("\t\t").append(key.getEntityName()).append("#").append(key.getIdentifier().toString()).append("\n");
increment(entityHistogram, key.getEntityName());
}
out.append("\tObject key histogram:\n");
SortedSet<NamedCount> orderedEntityHistogram = new TreeSet<NamedCount>(entityHistogram.values());
for (NamedCount entry: orderedEntityHistogram) {
out.append("\t\t").append(entry.name).append(": ").append(String.valueOf(entry.count)).append("\n");
}
Map<String, NamedCount> collectionHistogram = new HashMap<String, NamedCount>();
out.append("\tCollection keys (").append(String.valueOf(stats.getCollectionCount())).append("):\n");
for (Object obj: stats.getCollectionKeys()) {
CollectionKey key = (CollectionKey)obj;
out.append("\t\t").append(key.getRole()).append("#").append(key.getKey().toString()).append("\n");
increment(collectionHistogram, key.getRole());
}
out.append("\tCollection key histogram:\n");
SortedSet<NamedCount> orderedCollectionHistogram = new TreeSet<NamedCount>(collectionHistogram.values());
for (NamedCount entry: orderedCollectionHistogram) {
out.append("\t\t").append(entry.name).append(": ").append(String.valueOf(entry.count)).append("\n");
}
out.append("-->");
}
}
} catch (IOException e) {
LOGGER.error("Unable to write page info tag");
throw new RuntimeException(e);
}
return Tag.EVAL_BODY_INCLUDE;
}
protected void increment(Map<String, NamedCount> histogram, String key) {
NamedCount count = histogram.get(key);
if (count == null) {
count = new NamedCount(key);
histogram.put(key, count);
}
count.count++;
}
class NamedCount implements Comparable<NamedCount> {
public String name;
public int count;
public NamedCount(String name) {
this.name = name;
count = 0;
}
#Override
public int compareTo(NamedCount other) {
//descending count, ascending name
int compared = other.count - this.count;
if (compared == 0) {
compared = this.name.compareTo(other.name);
}
return compared;
}
}
}

Take a look here:
Profiling with Eclipse and remote profile agents on Linux
Tutorial: Profiling with TPTP and Tomcat
An introduction to profiling Java applications using TPTP
TPTP = Eclipse Test and Performance Tools Platform
More links to the stack:
Open Source Profilers in Java