Develop Reference

how to avoid Infinite Recursion in a non-return method with Try catch

public class Sample {
public static void main(String[] args) {
method();
}
public static void method()
{
try {
System.out.println("function");
throw new StaleElementReferenceException("thih sexception occured");
}
catch (StaleElementReferenceException e) {
method();
}
catch (Exception e) {
System.out.println("AssertFail");
}
}
}
how to avoid Infinite Recursion in a non-return method with Try catch...For Example this code below...when the StaleElementException Occurs only once i want to execute "functions after Exception , if the Stale Element occurs the second time i want it to go to Exception catch and print Assert fail..how?

public class Sample {
public static void main(String[] args) {
method(false);
}
public static void method(boolean calledFromCatchBlock)
{
try {
System.out.println("function");
if(!calledFromCatchBlock) {
throw new StaleElementReferenceException("thih sexception occured");
} else {
throw new Exception();
}
} catch (StaleElementReferenceException e) {
method(true);
} catch (Exception e) {
System.out.println("AssertFail");
}
}
}

You should store somehow the state when you throw an exception (e.g. a boolean flag) outside method(), check this state and throw modified exception next time:
private static boolean alreadyThrown = false;
public static void method()
{
try {
System.out.println("function");
if (alreadyThrown) {
throw new RuntimeException("another exception occured");
} else {
alreadyThrown = true;
throw new StaleElementReferenceException("this exception occured");
}
}
catch (StaleElementReferenceException e) {
method();
}
catch (Exception e) {
System.out.println("AssertFail");
}
}
Or you could provide some argument to the method(int arg) and check its value in a similar way:
public static void main(String[] args) {
method(1);
}
public static void method(int arg)
{
try {
System.out.println("function");
if (arg > 1) {
throw new RuntimeException("another exception occured");
} else {
throw new StaleElementReferenceException("this exception occured");
}
}
catch (StaleElementReferenceException e) {
method(arg + 1);
}
catch (Exception e) {
System.out.println("AssertFail");
}
}

RMI chat over Internet

I managed to make the client send objects to the server and the server does reply correctly but only to the client who sent the object, I had to forward ports on the server side and allowed port connections on the server side, now I can't seem to send a reply/message to a specific client and always get a connection refused error, meddling with portforwardind/firewall on the client side is not possible since anyone should be able to use the chat(the client must stay a client and not become a server). Any ideas how to make this work ? I heard about http tunneling or rmi proxy but how does it work code-wise ?
here's my main code on the client side :
public class Main {
public static void main(String [] args) {
String input;
Scanner in = new Scanner(System.in);
input = in.nextLine();
try
{
Message b =(Message) Naming.lookup("//xx.xx.xx.xx:1099/Message");
Client c=new Client(input);
UnicastRemoteObject.exportObject(c, 1100);
b.addUser(c);
while(true)
{
input = in.nextLine();
if(input.contentEquals("deconnection"))
{
b.exit();
break;
}
else if(input.startsWith(">"))
{
b.broadcast(c,"test");
}
}
in.close();
}
catch (NotBoundException re) { System.out.println(re) ; }
catch (RemoteException re) { System.out.println(re) ; }
catch (MalformedURLException e) { System.out.println(e) ; }
}
}
on the server side :
public class Serveur
{
public static void main(String [] args) {
try {
MessageImpl objLocal = new MessageImpl();
Naming.rebind("rmi://localhost:"+1099+"/Message" , UnicastRemoteObject.exportObject(objLocal, 1100)) ;
System.out.println("Serveur pret");
}
catch (RemoteException re) { System.out.println(re) ; }
catch (MalformedURLException e) { System.out.println(e) ; }
}
}
with the MessageImpl.java where the clientlist is found :
public class MessageImpl
implements Message {
public Vector<ClientInterface> clientlist;
public MessageImpl () throws RemoteException {super();listec=new Vector<ClientInterface>();};
public String envoiMessage() throws RemoteException {
return( "message test" );
}
public boolean isNew(ClientInterface c) throws RemoteException
{
return false;
}
public String test() throws RemoteException
{
System.out.println("re");
return "test";
}
public void addUser(ClientInterface c) throws RemoteException
{
test();
clientlist.add(c);
}
public void broadcast(ClientInterface c,String message) throws RemoteException
{
int i;
for(i=0;i<clientlist.size();i++)
{
if(clientlist.elementAt(i).getUsername().equals(c.getUsername()))
{}
else
{
clientlist.elementAt(i).getMessage(c.getUsername()+" : "+message);
}
}
}
public String exit() throws RemoteException
{
try{
return "exiting messenger";
}
catch(Exception e){return "erreur deconnection";}
}
}

If 'meddling' with the client firewall isn't possible, your system is unimplementable as designed. You would have to use polling instead of callbacks on the client side.

Java application and AMD processor issues

We have a windows application, which was tested on Windows XP, 7, 8, 8.1. Application consists of 2 parts: Bootstrap and main application. Bootstrap assures updates of the main app, and updates main app at a particular point. But users were able to force stop Boostrap process via the Task Manager (Ctrl+Shift+ESC->processes) by killing a process named javaw. In that case main app would not update and elder version would be launched. To avoid such issue we introduced interface of Bootstrap with main application via Socket. Here are the VM parameters of Bootstrap when it starts:
javaw.exe -Xms75M -Xmx90M -Xincgc -jar bootstrap.jar
There is a class SocketServer in the bootstrap:
public class Provider {
ServerSocket providerSocket;
Socket connection = null;
ObjectOutputStream out;
ObjectInputStream in;
String message;
public Provider() {
}
public void run() {
try{
providerSocket = new ServerSocket(54345);
connection = providerSocket.accept();
out = new ObjectOutputStream(connection.getOutputStream());
out.flush();
in = new ObjectInputStream(connection.getInputStream());
sendMessage("Connection successful");
do {
try {
message = (String)in.readObject();
if (message.equals("bye")) {
sendMessage("bye");
}
} catch(ClassNotFoundException cnfe) {
cnfe.printStackTrace();
}
} while (!message.equals("bye"));
} catch(IOException ioe) {
ioe.printStackTrace();
} finally {
try {
in.close();
out.close();
providerSocket.close();
} catch(IOException ioef) {
ioef.printStackTrace();
}
}
}
public void sendMessage(String msg) {
try {
out.writeObject(msg);
out.flush();
} catch(IOException ioe) {
ioe.printStackTrace();
}
}
public void stop() {
if (providerSocket != null && in != null && out != null && !providerSocket.isClosed()) {
try {
in.close();
out.close();
providerSocket.close();
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
}
}
Main app is being started by Bootstrap via ProcessBuilder like so:
public static void communicate(Process process) {
final BufferedReader stdOut = new BufferedReader(new InputStreamReader(process.getInputStream(), Charset.forName("Windows-1251")));
final BufferedReader stdErr = new BufferedReader(new InputStreamReader(process.getErrorStream(), Charset.forName("Windows-1251")));
//InputStream
new Thread() {
#Override
public void run() {
String line;
try {
while ((line = stdOut.readLine()) != null) {
debugOut(line);
}
} catch (Exception e) {
e.printStackTrace();
}
try {
stdOut.close();
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
}.start();
//ErrorStream
new Thread() {
#Override
public void run() {
String line;
try {
while ((line = stdErr.readLine()) != null) {
debugOut(line);
}
} catch (Exception e) {
e.printStackTrace();
}
try {
stdErr.close();
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
}.start();
try {
final Provider provider = new Provider();
ExecutorService pEexec = Executors.newCachedThreadPool();
Future<Void> FPExec = pEexec.submit(new Callable<Void>() {
#Override
public Void call() throws Exception {
while (!Thread.currentThread().isInterrupted()) {
provider.run();
}
return null;
}
});
pEexec.shutdown();
process.waitFor();
debugOut("[MainApp] Exit");
provider.stop();
FPExec.cancel(true);
debug("Destroy process");
process.destroy();
} catch (Exception e) {
e.printStackTrace();
}
}
public static void startApp() {
try {
ArrayList<String> params = new ArrayList<String>();
...
params.add("-Xms32M");
params.add("-Xmx48M");
params.add("-Xincgc");
params.add("-cp");
params.add(new File(pathToJar, "mainapp.jar").getPath());
params.add("net.craftwork.mainapp.AppStart");
params.add(licCode());
ProcessBuilder procBuild = new ProcessBuilder(params);
debugOut("[MainApp] Start");
Process proc = procBuild.start();
communicate(proc);
} catch (Exception e) {
e.printStackTrace();
}
}
There is a class SocketClient in the main app:
public class Requester {
Socket requestSocket;
ObjectOutputStream out;
ObjectInputStream in;
String message;
static Future<Void> oExec;
Requester() {
}
void run() {
try {
requestSocket = new Socket("localhost", 54345);
out = new ObjectOutputStream(requestSocket.getOutputStream());
out.flush();
in = new ObjectInputStream(requestSocket.getInputStream());
do {
try {
message = (String)in.readObject();
sendMessage("bye");
} catch(ClassNotFoundException cnfe) {
cnfe.printStackTrace();
}
} while (!message.equals("bye"));
} catch(UnknownHostException uhe) {
uhe.printStackTrace();
} catch(IOException ioe) {
ioe.printStackTrace();
oExec.cancel(true);
CommonUtils.debug("Bootstrap not found. Exit.");
System.exit(0);
} finally {
try {
in.close();
out.close();
requestSocket.close();
} catch(IOException ioef) {
ioef.printStackTrace();
}
}
}
void sendMessage(String msg) {
try {
out.writeObject(msg);
out.flush();
} catch(IOException ioe) {
ioe.printStackTrace();
}
}
public static void main() {
final Requester client = new Requester();
ExecutorService exec = Executors.newCachedThreadPool();
oExec = exec.submit(new Callable<Void>() {
#Override
public Void call() throws Exception {
while (!Thread.currentThread().isInterrupted()) {
client.run();
Thread.sleep(1000);
}
return null;
}
});
exec.shutdown();
}
}
Socket Client is called when main application starts
public class AppStart {
public static void main(final String[] args) {
Requester.main();
EventQueue.invokeLater(new Runnable() {
public void run() {
...
}
});
}
}
This is all to it I do believe. Whole setup worked perfectly fine, even on slower computers. Problem is that after introduction of Socket interface we had major complaints from some users, reporting crashes. Took us some time to figure out the issue, but here is what we found: computers with Intel processors are perfectly fine, only ones with AMD processors crash. Crash normally happens within 3 to 15 minutes from the start of Bootstrap. When crash occurs resources of the computer are not fully used, processor workload is about 20-50% and RAM is quite free as well. When crash occurs user is only able to reset computer using hardware reset or power button, nothing else responds. All users have latest JAVA 1.7.0_51. Whether system is 32 or 64 bit does both crash (or not crash if it is Intel based). Please share your thoughts. May be someone had identical issues and could help me to figure this out.

Retrieve GPS DATA on a JTextArea with 2 different class

I have a a GPS receptor. I create a class to retrieve all the GPS data on my Eclipse Console.
(This is the code of makia42)
public class COM implements Runnable{
static Thread myThread=null;
static BufferedReader br;
static BufferedWriter wr;
static InputStreamReader isr;
static OutputStreamWriter osw;
static java.io.RandomAccessFile port;
public COM(){ /**Constructeur*/
myThread=new Thread(this);
}
public void start(){
try {
port=new java.io.RandomAccessFile("COM3","rwd");
port.writeBytes("\r\n");
port.writeBytes("c,31,0,0,5\r\n");
port.writeBytes("T,1000,1\r\n");
}
catch (Exception e) {
System.out.println("start "+e.toString());
}
myThread.start();
}
public void run() {
System.out.println("lecture COM...");
for(;;){
String st = null;
try {
st=port.readLine();
} catch (IOException e) {System.out.println(e.getMessage());}
System.out.println(st);
}
}
public static void main(String[] args) {
COM temp= new COM();
temp.start();
}
}
I have another class which is a frame containing a button and a JTextArea. This class is in communication with my first class COM.
When i click the button, COM is starting and show me the data in my Eclipse Console.
But now, I'd like to show it on my JTextArea.
How can I do it ?
Best regards,
Tofuw

Take a moment to read about this pattern.
Make the Thread a Subject. Before starting register the instance of the class that contains the JTextArea as the Observer with the instance of the Thread. At the run() instead of printing on the console, use the notify(String);
public void run() {
System.out.println("lecture COM...");
for(;;){
String st = null;
try {
st=port.readLine();
} catch (IOException e) {System.out.println(e.getMessage());}
System.out.println(st);
}
}
Change to
public void run() {
System.out.println("lecture COM...");
for(;;){
String st = null;
try {
st=port.readLine();
} catch (IOException e) {System.out.println(e.getMessage());}
notifyObservers(st); //Pass the data to the observers.
}
}
EDIT:
I suppose you can rewrite the Thread to a simple class. It will render the program unresponsive while it reads, that's why you have a Thread. I suppose you can implement a cleaner way using Future<String>
public class GpsReader {
public class GenericGPSException extends Exception {
public GenericGPSException(String message, Throwable cause) {
super(message, cause);
}
}
public static void main(String[] args) {
// Example of usage
GpsReader gpsReader = new GpsReader();
String messageFromDevice;
try {
// Try read it
messageFromDevice = gpsReader.getCoordinate();
} catch (GenericGPSException e) {
// Error, what does it says?
messageFromDevice = e.getMessage();
}
JTextArea mockArea = new JTextArea();
// Show to user anything that comes to it.
mockArea.setText(messageFromDevice);
}
private boolean isReady;
private RandomAccessFile port;
public GpsReader() {
}
public String getCoordinate() throws GenericGPSException {
if (!isReady) {
try {
port = new RandomAccessFile("COM3", "rwd");
port.writeBytes("\r\n");
port.writeBytes("c,31,0,0,5\r\n");
port.writeBytes("T,1000,1\r\n");
isReady = true;
} catch (FileNotFoundException e) {
throw new GenericGPSException(
"Error at starting communication to Device ", e);
} catch (IOException e) {
throw new GenericGPSException(
"Error at starting communication to Device ", e);
}
}
try {
return port.readLine();
} catch (IOException e) {
throw new GenericGPSException("Error at reading the Device ", e);
}
}
}

try-catch arround callback

public class Test {
public static void main(String[] args) {
try {
doSomething(new TestCallback() {
#Override
public void doCallback() {
throw new NullPointerException();
}
});
} catch (Exception e) {
e.printStackTrace();
}
}
public static void doSomething(TestCallback callback){
callback.doCallback();
}
interface TestCallback {
public void doCallback();
}
}
RESULT:
java.lang.NullPointerException
at managers.concurrency.Test$1.doCallback(Test.java:11)
at managers.concurrency.Test.doSomething(Test.java:20)
at managers.concurrency.Test.main(Test.java:8)
In the above code we will get NullPointerException because the callback code is executed in the different part of stack. Is there a way to catch the such exceptions locally?

You are already catching the exception. Try something as follows -
try {
doSomething(new TestCallback() {
#Override
public void doCallback() {
throw new NullPointerException();
}
});
} catch (Exception e) {
System.out.println("Exception caught !!!");
}
Output:
Exception caught !!!