my project consists of 2 parts: server side and client side. When I start server side everything is OK, but when I start client side from time to time I get this error:
java.io.IOException: stream active
at java.io.ObjectOutputStream.reset(Unknown Source)
at client.side.TcpConnection.sendUpdatedVersion(TcpConnection.java:77)
at client.side.Main.sendCharacter(Main.java:167)
at client.side.Main.start(Main.java:121)
at client.side.Main.main(Main.java:60)
When I tried to run this project on the other pc this error occurred even more frequently. In Java docs I found this bit.
Reset may not be called while objects are being serialized. If called
inappropriately, an IOException is thrown.
And this is the function where error is thrown
void sendUpdatedVersion(CharacterControlData data) {
try {
ServerMessage msg = new ServerMessage(SEND_MAIN_CHARACTER);
msg.setCharacterData(data);
oos.writeObject(msg);
oos.reset();
} catch (IOException e) {
e.printStackTrace();
}
}
I tried to put flush() but that didn't help. Any ideas? Besides, no errors on server side.
I think you're misunderstanding what reset() does. It resets the stream to disregard any object instances previously written to it. This is pretty clearly not what you want in your case, since you're sending an object to the stream and then resetting straight away, which is pointless.
It looks like all you need is a flush(); if that's insufficient then the problem is on the receiving side.
I think you are confusing close() with reset().
use
oos.close();
instead of oos.reset();
calling reset() is a perfectly valid thing to want to do. It is possible that 'data' is reused, or some field in data is reused, and the second time he calls sendUpdatedVersion, that part is not sent. So those who complain that the use is invalid are not accurate. Now as to why you are getting this error message
What the error message is saying is that you are not at the top level of your writeObject call chain. sendUpdatedVersion must be being called from an method that was called from another writeObject.
I'm assuming that some object is implementing a custom writeObject() and that method, is calling this method.
So you have to differentiate when sendUpdatedVersion is being called at the top level of the call chain and only use reset() in those cases.
Related
So if I have a socket server, I can accept each socket and pass it to a executory
while(true){
Socket conn = socketServ.accept();
Runnable task = new Runnable() {
#Override
public void run() {
try{
server.executor(conn);
} catch(IOException e){
}
}
};
exec1.execute(task);
}
Doing this allows my server to run on my threads and does not block the same thread. Because I also have reference to that socket... called "conn" I can successfully return messages as well.
Now I have an RMI interface, which basically lets me call methods back and forth.
for example if I had this method:
public MusicServerResponseImpl CreatePlayerlist(String Name, UserObjectImpl uo) throws RemoteException {
MusicServerResponseImpl res = new MusicServerResponseImpl();
return res;
}
Which returns a serializable object. My concern is when this message gets called, I think it is going to get called in the main thread of the server, and thus will block that thread and slow down parallelism.
What I think is the solution is to have every single RMI method also create a task for an executor.. to speed up the execution of everything...this issue I am seeing however is unlike the socket where I have an object to send information back to, I am unsure how I would return a response from the RMI method, without somehow having to block the thread.
Does that make sense? Basically I am asking how I can execute in parallel with RMI methods while still being able to return results!
Thanks for the help!
Does that make sense?
No. Concurrent calls are natively supported.
See this documentation page and look for the property named maxConnectionThreads.
You could also have tested your assumptions by, for example, printing the current thread name in your server code, and trying to execute concurrent calls and see what happens.
The code directly below attempts to send a message through a Java websocket; however, it occasionally produces the error (shown in the error stack below). Could anyone suggest what the problem'solution?
Code:
if(currSession != null && currSession.isOpen()) {
try {
currSession.sendMessage(new BinaryMessage(flowTable.getBytes()));
} catch (IOException e) {
e.printStackTrace();
}
Error Stack:
java.lang.IllegalStateException: The remote endpoint was in state [BINARY_PARTIAL_WRITING] which is an invalid state for called method
at org.apache.tomcat.websocket.WsRemoteEndpointImplBase$StateMachine.checkState(WsRemoteEndpointImplBase.java:1015)
at org.apache.tomcat.websocket.WsRemoteEndpointImplBase$StateMachine.binaryPartialStart(WsRemoteEndpointImplBase.java:963)
at org.apache.tomcat.websocket.WsRemoteEndpointImplBase.sendPartialBytes(WsRemoteEndpointImplBase.java:140)
at org.apache.tomcat.websocket.WsRemoteEndpointBasic.sendBinary(WsRemoteEndpointBasic.java:56)
at org.springframework.web.socket.adapter.standard.StandardWebSocketSession.sendBinaryMessage(StandardWebSocketSession.java:202)
at org.springframework.web.socket.adapter.AbstractWebSocketSession.sendMessage(AbstractWebSocketSession.java:107)
at com.hp.fucms.impl.TopoRestController.setFlowTable(TopoRestController.java:147)
Wrap your code in a synchronized method and funnel all calls through this new method. It appears the tomcat web socket cannot handle multiple messages being placed on the same websocket session at the same time. I have code which has been running flawlessly under Glassfish and fell apart instantly when I moved to Tomcat. I then altered my code as explained above and all my problems went away....and there was much rejoicing.
I try to get a connection to multiple clients using the Sockets in Java. Everything seems to work, but the problem is, that the server just listens to the first client. If there are multiple clients, the server can send them all messages, but he can just listen to the messages that came from the first client. I tried this all out (I'm at this problem since yesterday). So I'm pretty sure, that the fault has to be in the class "ClientListener".
Explanation:
There is a List with clients (connection to communicate with Strings). In the GUI there is a list, where I can choose, with which client I'd like to communicate. If I change the client, the variable currentClient (int) switches to another number
networkClients is an ArrayList, where all the different connections are "stored".
The first connected client is exactly the same as the other clients, there is nothing special about him. He is called, when the variable currentClient is set to 0 (per default). The variable-switching is working. Like I said, all the clients give me a response if I send them an order, but just networkClients.get(0) is heard by the server (ClientListener).
class ClientListener implements Runnable {
String request;
#Override
public void run() {
try {
while (networkClients.size() < 1) {
Thread.sleep(1000);
}
//***I'm pretty sure, that the problem is in this line
while ((request = networkClients.get(currentClient).getCommunicationReader().readLine()) != null) {
//***
myFileList.add(new MyFile(request));
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
I hope someone can help me. I tried many things, but nothing worked.
EDIT: Like I wrote in the code example, is it possible that the while-loop isn't able to switch the number of "currentClient" (which is handled by another Thread)? I tested/simulated something similar in a testclass and the result was, that a while-loop of course can can update the state in it (meaning, that if a variable changes in the () of a while loop, it will of course be checked after every repeat).
You should take a look at multithreading.
Your server program should be made out of:
- The main thread
- A thread that handles new connections.
(Upon creating a new connection, start a new thread and pass the connection on to that thread)
- A thread for each connected client, listening to the each client separately
Take a look at some examples like: (1) (2)
I found the solution:
The Thread sits in the declared method I mentioned in the starting post (in the code snippet) and waits unlimited time for a new response of the client.
So changing the index of the list "networkClients" won't do anything, because nothing will happen there, until there is a new order sent by the client (which lets the thread go further).
So you need to implement an extra listener for each client.
I am working on a relatively simple packet capture application, and I am using the Jpcap library. Everything has been working until I added in the save feature to my program.
My write function
public void write() {
try {
writer = JpcapWriter.openDumpFile(captor, fileName);
} catch (IOException e) {e.printStackTrace();}
for (Packet packet : this.packets) {
writer.writePacket(packet);
}
writer.close();
}
It correctly gets the captor and filepath, loops through all the packets successfully, but when it tries to write at the end of the code block, the JVM crashes.
My question is, why does my application crash when trying to close the JpcapWriter?
UPDATE: The weird thing I just discovered, is it IS actually writing to the file. It just crashes after the write. I added a print statement after the close, and it never reaches it.
I found several other people with the same issue as me. I'm not sure why but removing the call to close the writer fixed my problem. The file now writes correctly, and has no issues. For now, I am content with it working, but I may come back to this issue at a later date.
UPDATE: It turns out the the file closes when a call is made to stop the capture. When the capture thread is closed it closes the captor, which in turn closes the writer for me. It essence, I was trying to tell it to close the writer, as the writer was already closing, which caused the JVM to crash.
I am using the Javamail API connecting to my IMAP server. Everything is working great with the javax.mail.Folder.idle() method. My listener gets called when a new mail comes in. However the problem is idle blocks forever, how do I interrupt it? How do I actually stop the listening without killing my Java program?
I've tried calling Thread.interrupt() on the idle'd thread. Nothing happens. I am running out of ideas.
Performing any operation on that folder (from another thread) will cause idle() method to return immediately. So if you want to forcefully interrupt it, just call close() from a new thread.
If you read the documentation properly, and read the source code, you'll realise that you have to create a new thread for calling .idle().
Allocate that thread to a variable, and whenever you want call the interrupt() on that thread, or just ignore notifications!
If you need to get idle() going again, just rerun the thread!
I created something similar, so you might wanna check it out.
https://github.com/mofirouz/JavaPushMail/blob/master/src/main/java/com/mofirouz/javapushmail/JavaPushMailAccount.java
Good luck
A proper way to abort IDLE command is the following snippet. Note that the Folder instance should be the same as the one used to start idling. I've tested the other solutions proposed on this thread but they didn't work in my case.
IMAPFolder folder = store.getFolder("INBOX");
try {
folder.doOptionalCommand("Abort IDLE error mesage", new IMAPFolder.ProtocolCommand() {
#Override
public Object doCommand(IMAPProtocol p) throws ProtocolException {
p.idleAbort();
return Boolean.TRUE;
}
});
} catch (MessagingException e) {
e.printStackTrace();
}