Servlets :: Static Variables In Thread-safe?
Jan 22, 2015Are the static variables in servlet thread-safe?
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Servlets :: Thread Safety Should Not Use Any Variables Or Objects At Instance / Class Level
Jun 3, 2014As web server has multiple threads to serve client requests in Thread Pool & to ensure Thread Safety we should not use any variables or Objects at Instance/Class level.But in case of Session Variable which one is the Best Practice as the Session object is used by all the requests to have the same Session ID.
My Code :
public class MyServlet extends HttpServlet {
private static Logger log = Logger.getLogger(ClientRegistrationServlet.class);
private HttpSession session; /* This is used at Instance Level*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
[code]....
Implementing A Thread-safe Queue
Jul 10, 2014I have situation where a user can request java server to send a value to an embedded device, and if the device is asleep, that value needs to be stored in a queue until the device wakes up and sends a position to java server, at which point the server checks if there is a value in the queue and if there is, it then sends that value to the device. The maximum size of the queue is 1 for now. And if the user makes continuous requests to java server, the old value is removed and the new value is added.
Initially I was looking into BlockingQueue, but the problem with that is, well, it blocks. queue.put(value) will block if queue is full, and queue.take() will block if queue is empty. I can't have something that blocks. When the device responds to server, server checks if value is in queue, if it is not then the server carries on the rest of its responsibility. Thus, I then entertained ConcurrentLinkedQueue. While queue.offer(value) and queue.poll(); allow you to add and remove values respectively from the queue without blocking, it does not allow you to set a maximum size limit of the queue. My queue must have a maximum size limit and it has to always be the newest value the user submits to the queue (where old values are removed).So this is what I came up with:
Java Code: class Unit {
private List<Integer> cmdQueue;
public Unit(){
cmdQueue = Collections.synchronizedList(new LinkedList<Integer>());
[code]....
I use Collections.synchronizedList, as I do here, do I still need to use synchronize as I did above?
Instance Variable Are Not Thread Safe
Jul 10, 2014Implementation that proves that instance variables are not thread safe ....
View Replies View RelatedRMI :: Using RMI To Wrap A Process That Is Not Thread Safe
Apr 3, 2013I have a multi-threaded application but one function (A) I need to call, that is provided by a third party, is not thread safe. I need to make parallel calls to function (A) so my only option is to start multiple process that I can call from each of my main applications threads.
To do this I created a RMI interface between a the client and the remote process. On the server side I start multiple processes each assigned a different port. On the client side I have a queue manager that connects to the processes I started and builds a queue of them. It passes the client to the threads as needed so they can function in parallel.
I am new to Java development and have the following questions:
1. Each of the server processes require an init function to be run before providing the service. How do I setup the server processes to continue to run in memory listening for a a service request after running the init processes.
2. Is there a better implementation of what I am trying to do?
Servlets :: Using Static Variables Or Object Set?
Aug 6, 2014Can we use static variables or static objects in servlets ?? I want to restrict same user to enter into the application from different system when the user is already working, he needs to get a message saying "User is already in use ".
I have created static SET object in LoginServlet and inside doget() I checked if SET contains user ,if yes display him above message otherwise add the user in SET object and forward it to next page . Later while logging out user is removed from SET .
Can I follow any other approach other than using static object SET in servlets??
Enterprise JavaBeans :: Does Container Managed Entity Manager Is Thread-safe In Stateless Session Bean?
May 8, 2014I read JEE6 doc and confused with : Does container managed entity manager (injected by PersistenceContext annotation) is thread-safe in stateless session bean in multiple-thread env?
See code below, if there are 2 requests to stateless sesion bean in 2 concurrent threads , is it using same Entity Manager Instance or not?
@Stateless(name = "HRFacade", mappedName = "HR_FACES_EJB_JPA-HRFacade-HRFacade")
public class HRFacadeBean implements HRFacade, HRFacadeLocal {
@Resource
SessionContext sessionContext;
@PersistenceContext(unitName = "HRFacade")
private EntityManager em;
[Code] .....
Instantiating Class With Non Static Variables From Within Static Method
Oct 28, 2014Why I can create an Instance of a class that contains non static variables within the static main method ?
This program runs fine
import java.util.*;
public class Test{
public int j;
public static void main(String[] args) {
Test test1=new Test();
System.out.println(test1.j);
[Code] .....
Servlets :: Cannot Make Static Reference To Non-static Method GetQuery From Type Resource
Mar 26, 2015This is my code inside the method:
@Post
public static String getDetails(Representation entity) throws Exception {
String customerId = getQuery().getValues("cus_id");
}
I use this code in Restlet Representation. I try to get the value from the Request API. But I am facing the problem as "Cannot make a static reference to the non-static method getQuery() from the type Resource".
Netbeans And Non-static Variables
Feb 11, 2014I'm doing in this small piece of code -
JavaApplication3.java
package javaapplication3;
public class JavaApplication3 {
public class robot {
int xlocation;
int ylocation;
String name;
static int ccount = 0;
[Code] .....
When I'm trying to compile it with netbeans i get these errors and i just can't figure why is that!
C:UsersuserDocumentsNetBeansProjectsJavaApplication3srcjavaapplication3JavaApplication3.java:16: error: Illegal static declaration in inner class JavaApplication3.robot
static int ccount = 0;
modifier 'static' is only allowed in constant variable declarations
C:UsersuserDocumentsNetBeansProjectsJavaApplication3srcjavaapplication3JavaApplication3.java:30: error: non-static variable this cannot be referenced from a static context
robot firstrobot = new robot(34,51,"yossi");
Final Static Variables In GregorianCalendar
Oct 27, 2014why using the get method(c.get(c.HOUR_OF_DAY)); gives me the correct hour(currently 19) but directly accesing c.HOUR_OF_DAY returns 11 ? It shows In the documentation that HOUR_OF_DAY is public.
import java.util.*;
public class calendar2 {
public static void main(String[] args) {
new calendar2().timer();
}
private void timer() {
Calendar c=Calendar.getInstance();
//c.clear();
System.out.println(c.get(c.HOUR_OF_DAY));
System.out.println(c.HOUR_OF_DAY);
}
}
Subclasses With Unique Static Variables
Oct 22, 2014Say I have a class called ClassA which I want to hold my data. Now inside ClassA want to hold instances of a class lets call ClassB. So far we are here.
import blah.B
public class A {
private B myB;
(Getters setters etc)
public String getBString() {
B.getString();
}
}
However I want to have multiple extensions of ClassB which have UNIQUE static variables.
public class B-1 extends B {
private static String mString;
private static int mInt;
}
The problem I have run into is I can't have subclasses with their own static variables. I need the A class to hold any type of B class. How can I manage this?meant
public String getBString{
return B.getString();
}
Spanning Tree - Dealing With Static Variables
Feb 20, 2014I'm new to Java and I'm trying to create a spanning tree in the desired order with 4 nodes (0,1,2,3). I've got the following code:
import java.util.ArrayList;
public class A {
public static boolean any(ArrayList<Integer> input) //To check for if any element in the ArrayList == 1
{
boolean answer = false;
for(int i=0;i<input.size();i++) {
if(input.get(i)==1)
[Code] ....
What happens is that the input parameter adj and hence the original adjmat inside main gets changed everytime I enter the method "connected", and I don't want this to happen. I understand that this is due to the main method being static and hence adjmat becomes static as well, but how do I change the code such that adjmat only gets modified after coming out of the connected function, and not while inside it?
Instance Variables Passed In As Arguments To Static Methods?
Feb 19, 2011I thought static methods could never use instance variables, because they wouldn't know which instance to look at.
From Head First Java, p. 284: "A static method is not associated with a particular instance - only the class - so it cannot access any instance variable values of its class. It wouldn't know which instance's values to use."
Now I was answering some mock exam questions from Cameron McKenzie's SCJA book, and I don't understand one of the options. On page 205, the last question has an option that says: "Instance variables ... are not visible in static methods, unless passed in as arguments." This option is supposed to be correct. Now... how does that work?
Code To Search For Static Variables That Look Like Username Or Password
Sep 24, 2014a code to search for static variables that look like username or password.i want to be able to search through a source code for such variables.
View Replies View RelatedServlets :: ROOT Mapping Causes Static Files To Not Be Served
Mar 16, 2015When I map my servlet to the ROOT of the site, the javascript, CSS and image files are not served. The conversation between the server and browser shows the files are being sent, but they are not rendered in the browser. This happens in both Firefox and Chrome.
If I change the mapping to anything other than the root, such as /x/, everything works as it should.
Here's my web.xml file:
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
version="2.5">
[Code] .....
Servlets :: How Does Web Server Differentiates Between Request For Static And Dynamic Web Page
Mar 4, 2014How does web server differentiates between request for static web page and request for dynamic web page? i think if web server receives request for static page directly renders that to server or else if request is for dynamic web page passes that to web app which processes the request and renders that to client. bUT how does web server differentiates between both the request.
View Replies View RelatedSwing/AWT/SWT :: What Is Event-dispatching Thread For GUIs And Why Use It Over Main Thread
Sep 20, 2014I'm currently learning about Swing but I can't get my head round this piece of the code. Here is a simplified gui (not interested in the gui part but the execution)
public class SwingDemo implements ActionListener {
SwingDemo(){
JFrame jfrm = new JFrame("Simple gui pro");
//rest of code
public static void main(String[] args) {
new SwingDemo();
}
I get the above, create a new instance of SwingDemo in the main thread which starts up the gui through the constructor. However, then the tutorial says that I should avoid doing the above but do this instead:
public class SwingDemo implements ActionListener {
SwingDemo(){
JFrame jfrm = new JFrame("Simple gui pro");
//rest of code
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() { //why do this instead?
public void run(){
new SwingDemo();
}
});
}
}
Reading, it talks about an event-dispatching thread which has completely lost me... Why not just instantiate the object directly instead of creating another thread?
Passing 2 Sub Arrays Into Sorting Thread Then To A 3rd Thread Merge
Oct 17, 2014im having an issue with the 3rd thread that are supposed to merge the two sorted sub arrays , i pass the 2 subarrays to my runnable function sortlist and they are renamed IntSortList 1 and 2 and th1.start() and th1.join() are called and it works fine, but then i have another runnable constructor that takes IntSortList 1 and 2 but it does take a runnable. below is the code in my main,
Runnable InSortlist1 = new sortList(data2p1);
Runnable InSortlist1 = new sortList(data2p1);
Thread th1 = new Thread (IntSortlist1);
Thread th2 = new Thread (IntSortlist2);
try
{
th1.start();
th1.join();
[code]....
Is It Safe To Set Font With Absolute Parameters
Feb 14, 2015I was wondering, if, for example I set font for my textarea like this:
area.setFont(new Font("Serif", Font.ITALIC, 18));
Is that last parameter, in this case 18, will be actually the same size for all users? Maybe I should avoid these absolute numbers?
Accessing A Variable Of A Thread From Another Thread
Jul 16, 2014class A extends Thread
{
String str;
public void run( )
{
//random stuff
}
}
[Code]....
Servlets :: How To Create A Room That Should Be Like Static On The Server Until Server Is Down
Apr 1, 2014I am working on a chess game. I need to construct a game room where all the player are present and room chat is up. Also some tables where games are being played. Now my question is how to create this game room?
To me this room must need to be like static or global (if I am not mistaken) that is up when server starts and players can join this room and should be down when server is done. How can I implement such room that would stay up for infinite time.
Can Static Method Return Instances Of Same Class In Special Case Where Everything Is Static?
Jun 27, 2014From what i understand static methods should be called without creating an instance of the same class . If so why would they return an instance of the same class like in the following : public static Location locateLargest(double[][] a) , the Location class being the same class where the method is defined . I don't understand this , does it mean that every field and every method in the class must be static ? Meaning that you cannot have instances of the class because everything is static . Or it's just a mistake and the class Location cannot have a static method: public static Location locateLargest(double[][] a) ?
View Replies View RelatedHow To Access One Thread From Another Thread
Oct 8, 2014How to access one thread from another thread?
View Replies View RelatedUpdate User - Cannot Make Static Reference To Non-Static Method
Apr 26, 2015I can't figure out what this error message "Cannot make a static reference to the non-static method getEndUserCharge(long, long, long, long) from the type UpdateUserWS" actually means.
The error is coming from:
public void updateDetailsPackage() {
some unrelated code
long zero=0;
double endUserCharge=0;
endUserCharge = UpdateUserWS.getEndUserCharge(long zero, long zero, long zero, long zero); <-------- error is here
[Code] ....
Player Class - Cannot Make Static Reference To Non-static Method
May 26, 2015Alright, I have two classes, this one
public class Player {
private String player;
public String getPlayer() {
return player;
}
private int strength;
private int defense;
[Code] .....
However, it says that under Player.getPlayer() that it 'Cannot make a static reference to the non-static method'.