Java Applications Communication On Different Systems
Nov 1, 2014
I'm new to java and haven't develop any application before that... I need to develop an application through which i can send data from 1 computer to another computer. These communication in between the computers are those are under one router connection. Means they can connect even without internet access
Main concept is as follow
1. Java application on computer A [server side application]
2. Java application on Computer B [Client side application]
3. Java application on computer C [Client side application]
Now computer B and C communicate with computer A. but they don't know about presence of each other
I'm deployed application A and application B in TOMCAT server applications, the U1 user enters into the application A, he authenticates and generates a call to a page of the app B. As I was able to access the session of user U1 en A from B, it could have a single session.
I have two separate java Program that run on the same computer : Program -1 & Program-2 .
Explain Program-1 :
Name of Program -1 is “InputFrame” that is a simple frame that contain a JTextField and a Button and a JTextArea .
Explain Program 2 : Name of Program-2 is “OutputFrame” that is a simple frame that contain a simple JTextArea that this JTextArea is a Instance object from a class with name of “DisplayFrame” .
This instance object from class of “DisplayFrame” added to frame of “OutputFrame”.Now I want run both Program 1 & 2 simultaneously in the same computer and when I enter a text in JTextField in Program-1 and after click on the Button “OK” that Text Entered in this JTextField In addition to JTextArea in Program-1 display In JTextArea in Program-2 .
I do not want use a share file between two Program-1 and -2 Or DataBase .I want if Program-1 run but Program-2 is not running and i enter a text in JTextFeild in Program-1 , after running Program-2 that Entered Text Displaye in JTextArea in Frame of Program-2 .(Offline Message) .Both Source code of Program-1 and Program-2 is Attached .
1. I have a java application which accepts bio potential data every second or two and stores it in the database. This is a socket server which accepts this data from multiple clients and spawns a new thread for processing it to store in the db.
2. I have a jsp page on tomcat server which reads historic client data from database (stored by application 1) and displays it on the page.
The socket server program in 1.) above is not running inside of tomcat server.The new requirement now is : Display all of the human data coming in live on the jsp page.Now the problem: I will now need to pass the live data from socket server (which is stand alone) to the jsp which is running on a tomcat server.
Possible solutions:
APPROACH 1: Run the socket server in the tomcat instead of stand alone and store the frequently incoming data in a java object so the jsp can access this object every second and display it on a graph.
PROBLEM : The stand alone java application does not need to be included in a tomcat server except for the fact that the jsp needs access to the live data. Also, I have read that this is not the best way.
APPROACH 2: Expose the stand alone java application as a web service and communicate with the jsp using REST architecture.
PROBLEM : The complication of using this method is that it will not have the flexibility offered by websockets or server sent events (SSE) of auto updating the latest data. The jsp will have to keep polling for new data every one second which is also not a very good option.
I have an application written in Java on the Linux platform. My application will work the following way:
User A will open application. User B will open application.User A will need to send User B a message but without a socket connection.User B will need to send User A a message but without a socket connection.The user should be able to identify the messages sent to each other.If User A reads user B's message the message will no longer be available in the channel of communication.If one user exits their application their message should be removed.User C should not be able to read user A and user B message (This is only via the application design, no real security here).Applications should be able to work on different machines however they will utilize a shared network mount to access files modified by each other.
I do have to note that the messages being sent is rather small and only 1 message is sent from each user, so in that regard I did not want to setup a client/server model to do this using sockets.
Basically I am looking for a similar concept as a message queue but more relevant to my requirements done in Java. What are some good options to use that will address some of my requirements? I have not touched Java in a long time and only have used it for certain usage so I am trying to get an idea of which current technologies are best for what I need.
I just installed java on my computer because i was getting messages that it was no longer there. And I figured out how to solve my problems on my browsers. but i don't see how to enable java in my applications on the hard drive. in particular, i want to use the database in open office but don't see how to enable it.
I want to make project about java communication with hardware (wiz110sr) via LAN (Rj45). And for example, my hardware have ip address 198.168.0.1 ; port: 1202, connected with my PC(via lan/Rj45). I want show the output (such as numbers and letters) from my hardware in console netbeans.
When I running my code, appear :
" Exception in thread "Thread-0" java.lang.RuntimeException: Uncompilable source code at mypkg.startListenForTCP$1.run(startListenForTCP.ja va:48) at java.lang.Thread.run(Thread.java:745) BUILD SUCCESSFUL (total time: 1 second) "
Firstly, my code is just a demo of my multiplayer game (2 or more players can play simultaneously) to demonstrate my problem without any extra things. I have successfully implemented peer-to-peer (P2P) communication in my game. Later, I decided to add support for client-server communication (ie a central server which is also a player) in my game. It should be much easier than P2P. Now here is the problem:
Suppose, I have 1 server and some clients (may be 1 or more clients). They all should give the following output:
Starting... A B C E F ... ... Done!
They all give the above output without using multi-thread. But using multi-threading, it gives the above output only when there're 1 server and 1 client. I'm using 2 threads (1 for sending, 1 for receiving) for each Socket. That means, each client has only 2 threads for communication but the server has (2 * totalClients) threads.
I've attached my full test project. So, here I'm only showing my 2 thread classes.
ReceiveThread class: class ReceiveThread extends Thread { private ObjectInputStream receiveStream; private BlockingQueue<Character> queue = new ArrayBlockingQueue<Character>(Common.totalClients);
[Code] ....
Since I've attached my full test project, I'm not showing the other 3 classes. They are ServerMain, ClientMain and Common. If I've 2 clients to be connected, then I get the following output:
Server: (Runs first)
Starting... A Client 1 (clientID is 1): (Runs after the server)
Starting... A B B Client 2 (clientID is 2): (Runs after Client 1)
Starting... A
They are stuck at there, even no exception. Actually, the server and the clients are stuck at the line try { ch = queue.take(); } if more than 1 client are connected. It seems that all are trying to receive data. But without using the dedicated threads, they all work as expected even for more than 1 client. Why is this behaviour? How to solve it? Note that I have used the same SendThread and ReceiveThread classes by which I have succcessfully implemented P2P communication.
About my attached test project file:
It has 5 small .java files for the classes as stated above. It is currently faulty when using additional threads. You have to change clientID variable for each client (they are described inside). But it works as expected without additional threads. To test it without the additional threads:
Comment " TODO" linesUncomment the single lines just after " TODO" linesComment the additional thread construction lines (4 lines)
Currently, for a workaround, I'm not using the dedicated threads for sending and receiving data only for client-server communication in my multi-player game. But I'm still using these threads for P2P communication. I don't know why it is and how to solve it.This is the attached test project file as described above.
I am maintaining an existing Java product (which has a HUGE code-base). I discovered that it is setting (and getting) two of its internal passwords as Java system properties, at no less than 4-5 different places (methods). Now, the problem is, the passwords are being stored as plain text in the Java system properties, and so, the same is visible to external entities, as the application is not using any Java Security Manager. For example, if the application (process) is running on port number 1234, we can run the Java command:
jinfo -sysprops 1234
to view both the passwords as values of the corresponding Java system properties. I wish to ask if there is any remedy to this without changing the existing code-base too much? The desired effect would be to "hide" the two Java system properties (denoting the two passwords) from all external entities.
It may be noted that introducing a Java Security Manager into the application may not be a solution, as if we revoke read permissions from the said two Java system properties using the Java Security Manager, the application codes which read those properties would crash. Same is applicable for storing the passwords in encrypted form, as that would crash all codes within the application which are expecting to read the passwords in clear text form.
To give a bit more context, the said two passwords we are storing as Java system properties are actually passwords to access two key-stores, and Tomcat requires that we store the said two passwords in plain-text format. Any workarounds, such that only Tomcat will be able to see the two passwords as-is, while they will be invisible to all other external entities?
Or, is there any way to place the said passwords in other in-memory locations (like static variables) which only Tomcat can (be made to) read instead of placing them as system properties which is exposed to anyone?
I have a problem with several java applications. When I start them Java wants to connect to the certificate authority, to check if the certificate is still valid and not on a blacklist.
The problem is: my whole internet is behind a password protected proxy. If I open my browser i get a windows with username and password. I enter it and internet in the browser works. But for Java it isn't working, because I see no point, where I can enter the password and username for the proxy. I can enter the proxy ip and port in the java settings, but not the password and username. So I get a error screen from java, telling me, that java could not connect. I can disable the check in the java settings, but I don't wont that.
Is there a way to tell java, that java uses my proxy with my password and username? I already googled this problem and found nothing except tutorials for connecting with proxy in the java code. But these applications are not from me, I can't change the code ...
This piece of java software I am responsible for is running throughout numerous locations in my country, there is only 1 location which has trouble with the dates being displayed incorrectly, birthdates of clients are displayed as a day earlier. It seems pretty safe to say it is a problem on their end... But still, they're asking me for an explanation as to why java would treat a date differently in this rare case.
The date (a birthdate) comes from an oracle database, it is a date without a time (trunced date). It enters the application as a member of the client-class, it is NOT being set or changed after that. It goes through several layers in the application, then ends up in a GUI class which unwraps it from the "client"-object and puts a SimpleDateFormat (new SimpleDateFormat("dd-MM-yyyy")) on it. My first and only hunch was the timezone settings, but that seems to be OK!
I use git as my SCM and I use both Ubuntu and Mac OSX. The home directory of the two operating systems are different and there lies the problem. When I commit the .classpath to version control, it looks something like this:
Now when I update my project on Ubuntu. I have to change the build path again because it is referencing paths on OSX. And this goes back and forth. Rather than remove this file from git with .gitignore, I'd prefer to use a global environment variable like as follows:
I am attempting to use JLists to complete a program that models how operating systems manage processes. A quick synopsis of what it is supposed to do. Each process is to have a priority level (I chose to do 1 -3 with 3 being the most important) and there are supposed to be three lists. One for ready processes, blocked processes, and a running process.
My issues:
1) when I block a process it does indeed switch lists but when it is copied into the blocked list it pulls the element number instead of what the actual process number is. For ex: Say the ready list has 5 processes / I delete 2 / Leaving process 1, 2, 5. When I block 5, it gets registered in the blocked list as process 2.
2) I can't figure out how to give a label to each of my scroll panels (JLists) to signify which box is ready / blocked / and running
3) My switch button - I have commented in what I need to do but don't know how I am going to do it.
Below are my files:
Main
import java.util.Comparator; import java.util.PriorityQueue; import java.util.Queue; import javax.swing.JFrame; import javax.swing.JTextArea; public class PQueue { public static void main(String[] args) throws InterruptedException {
I've been trying to send a file(text & image files) from one system to another. somewhat I did, but file is not send originally in destination system. It shows AccessDeniedException on the destination system. What should do to avoid this exception.
I'm writing a small program in Java to simulate a shopping cart. A shopping cart has an array og objects Item. As a console application, my program runs.But, in the GUI version, I have some issues. In class MainMenu I create a ShoppingCart object, named "cart"(line 103)In class AddItemMenu I create an Item object, and I want to add it in my ShoppingCart object "cart".BUT, AddItemMenu cannot "see" variable "cart".
//MainMenu.java package shoppingcartgui; public class MainMenu extends javax.swing.JFrame { public MainMenu() { initComponents();
My primary question is about which method is the best for having an applet of mine communication with a backend database of mine. In other words, I don't want to try learning a technology that is out of date or not a good fit for my goal. I purchased the O'Reilly title "Java Servlet Programming", but it seems to be very old and out of date (referencing Netscape 4, etc.) and I see a Java RMI O'Reilly title on Amazon, but it was written in 2001.
My basic goal is to allow my applet to have access to a back-end database for reading and writing. I understand that direct Applet to DB (via JDBC) access is a bad idea so my thought is to create a servlet (much like web service for lack of a better term) or an actual web service (RESTful would be my first guess) to broker the requests. I already have a very basic servlet running that has access to my database server so now I want to focus on the best method for making calls from the applet to the servlet but having said that I don't want to go down this road too far if a servlet is not the right tool for the job.
My reading has been leading me to RMI, but as I said, I don't want to focus on that if there is a better option. In a non-Java environment, I'd use a web service (REST, SOAP, etc.) and perhaps that's what I should do here as well and not even bother with a servlet per se and just go with a web service.I know there can be some subjectivity with regard to these choices and I don't need to know what the "best" one is.I don't want to use RMI if it's dead or has been surpassed by something else, for example.
Should I use a servlet? Should I use a web service? My needs are rather modest; query the database, send updates to the database, etc. Nothing too crazy.
We have this website that is run on two web applications. The first web application hosts the home page and clicking certain links in the home page would forward it to pages of the second web application where certain functionalities can be done. Now, there has been an initiative to redesign the site to have a login page and only logged in users could browse it. This would mean a login page being created in the first app, and when links to the second application are clicked, the pages are supposed to forward to it with the same session of the user that logged in.
We have already creating handling to pass the session from the first app to the second. Logging out from the first application would also invalidate the same user session in the second application. My questions is, is this a bad idea? would it be better to combine the two apps even if it would mean a huge impact?
or is there are better way to do this? like set it in web.xml. I have read that you cannot use two context for it.
I would like users in an application to be able to access and edit their user profiles (Application A). The problem is that the user objects (entities, dao, beans) are handled in a separate application (Application B) which is specifically for managing user accounts. Importing the java sources for App B into App A could be messy and might need configuration of the persistence unit and connection. I'm thinking it would be better to inject an EJB from App B to App A to query the user DB and return the results so a user profile form is rendered in App A.
I know how to inject EJBs within the same application, but I'm not so sure about how it's done across different applications or even if that's the most advisable way to achieve what I want. it's better practice to inject an external EJB into App A or simply import the classes from App B and use those.
@Stateless public class UsersDaoImpl implements UsersDAO { @PersistenceContext private EntityManager em;
I question this as I have not yet succeeded in deploying a working ruleset for use with intranet based applications. I have verified the ruleset is working with external internet java apps so it is being deployed correctly just doesn't steer Intranet based apps to the correct version.
Generally sessions in web applications expire after a stipulated max inactive interval. To my knowledge primarily the reason is if the session objects are not invalidated they keep exhausting the memory. So my question is
A. Is there any other reason other why web applications timeout the user session after an inactive interval?
B. Social sites never timeout the user session even if you just leave them for the entire day. How do they manage sessions? Don't the active sessions exhaust memory on their servers or JVM to be specific?
