We Keep Coding

How to generate PDF documents from rpt in a multi-threaded approach?

I have a rpt file, using which i will be generating multiple reports in pdf format. Using the Engine class from inet clear reports. The process takes very long as I have nearly 10000 reports to be generated. Can I use the Mutli-thread or some other approach to speed up the process?
Any help of how it can be done would be helpful
My partial code.
//Loops
Engine eng = new Engine(Engine.EXPORT_PDF);
eng.setReportFile(rpt); //rpt is the report name
if (cn.isClosed() || cn == null ) {
cn = ds.getConnection();
}
eng.setConnection(cn);
System.out.println(" After set connection");
eng.setPrompt(data[i], 0);
ReportProperties repprop = eng.getReportProperties();
repprop.setPaperOrient(ReportProperties.DEFAULT_PAPER_ORIENTATION, ReportProperties.PAPER_FANFOLD_US);
eng.execute();
System.out.println(" After excecute");
try {
PDFExportThread pdfExporter = new PDFExportThread(eng, sFileName, sFilePath);
pdfExporter.execute();
} catch (Exception e) {
e.printStackTrace();
}
PDFExportThread execute
public void execute() throws IOException {
FileOutputStream fos = null;
try {
String FileName = sFileName + "_" + (eng.getPageCount() - 1);
File file = new File(sFilePath + FileName + ".pdf");
if (!file.getParentFile().exists()) {
file.getParentFile().mkdirs();
}
if (!file.exists()) {
file.createNewFile();
}
fos = new FileOutputStream(file);
for (int k = 1; k <= eng.getPageCount(); k++) {
fos.write(eng.getPageData(k));
}
fos.flush();
fos.close();
} catch (Exception e) {
e.printStackTrace();
} finally {
if (fos != null) {
fos.close();
fos = null;
}
}
}

This is a very basic code. A ThreadPoolExecutor with a fixed size threads in a pool is the backbone.
Some considerations:
The thread pool size should be equal or less than the DB connection pool size. And, it should be of an optimal number which is reasonable for parallel Engines.
The main thread should wait for sufficient time before killing all threads. I have put 1 hour as the wait time, but that's just an example.
You'll need to have proper Exception handling.
From the API doc, I saw stopAll and shutdown methods from the Engine class. So, I'm invoking that as soon as our work is done. That's again, just an example.
Hope this helps.
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.sql.Connection;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
public class RunEngine {
public static void main(String[] args) throws Exception {
final String rpt = "/tmp/rpt/input/rpt-1.rpt";
final String sFilePath = "/tmp/rpt/output/";
final String sFileName = "pdfreport";
final Object[] data = new Object[10];
ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newFixedThreadPool(10);
for (int i = 0; i < data.length; i++) {
PDFExporterRunnable runnable = new PDFExporterRunnable(rpt, data[i], sFilePath, sFileName, i);
executor.execute(runnable);
}
executor.shutdown();
executor.awaitTermination(1L, TimeUnit.HOURS);
Engine.stopAll();
Engine.shutdown();
}
private static class PDFExporterRunnable implements Runnable {
private final String rpt;
private final Object data;
private final String sFilePath;
private final String sFileName;
private final int runIndex;
public PDFExporterRunnable(String rpt, Object data, String sFilePath,
String sFileName, int runIndex) {
this.rpt = rpt;
this.data = data;
this.sFilePath = sFilePath;
this.sFileName = sFileName;
this.runIndex = runIndex;
}
#Override
public void run() {
// Loops
Engine eng = new Engine(Engine.EXPORT_PDF);
eng.setReportFile(rpt); // rpt is the report name
Connection cn = null;
/*
* DB connection related code. Check and use.
*/
//if (cn.isClosed() || cn == null) {
//cn = ds.getConnection();
//}
eng.setConnection(cn);
System.out.println(" After set connection");
eng.setPrompt(data, 0);
ReportProperties repprop = eng.getReportProperties();
repprop.setPaperOrient(ReportProperties.DEFAULT_PAPER_ORIENTATION,
ReportProperties.PAPER_FANFOLD_US);
eng.execute();
System.out.println(" After excecute");
FileOutputStream fos = null;
try {
String FileName = sFileName + "_" + runIndex;
File file = new File(sFilePath + FileName + ".pdf");
if (!file.getParentFile().exists()) {
file.getParentFile().mkdirs();
}
if (!file.exists()) {
file.createNewFile();
}
fos = new FileOutputStream(file);
for (int k = 1; k <= eng.getPageCount(); k++) {
fos.write(eng.getPageData(k));
}
fos.flush();
fos.close();
} catch (Exception e) {
e.printStackTrace();
} finally {
if (fos != null) {
try {
fos.close();
} catch (IOException e) {
e.printStackTrace();
}
fos = null;
}
}
}
}
/*
* Dummy classes to avoid compilation errors.
*/
private static class ReportProperties {
public static final String PAPER_FANFOLD_US = null;
public static final String DEFAULT_PAPER_ORIENTATION = null;
public void setPaperOrient(String defaultPaperOrientation, String paperFanfoldUs) {
}
}
private static class Engine {
public static final int EXPORT_PDF = 1;
public Engine(int exportType) {
}
public static void shutdown() {
}
public static void stopAll() {
}
public void setPrompt(Object singleData, int i) {
}
public byte[] getPageData(int k) {
return null;
}
public int getPageCount() {
return 0;
}
public void execute() {
}
public ReportProperties getReportProperties() {
return null;
}
public void setConnection(Connection cn) {
}
public void setReportFile(String reportFile) {
}
}
}

I will offer this "answer" as a possible quick & dirty solution to get you started on a parallelization effort.
One way or another you're going to build a render farm.
I don't think there is a trivial way to do this in java; I would love to have someone post an answer that show how to parallelize your example in just a few lines of code. But until that happens this will hopefully help you make some progress.
You're going to have limited scaling in the same JVM instance.
But... let's see how far you get with that and see if it helps enough.
Design challenge #1: restarting.
You will probably want a place to keep the status for each of your reports e.g. "units of work".
You want this in case you need to re-start everything (maybe your server crashes) and you don't want to re-run all of the reports thus far.
Lots of ways you can do this; database, check to see if a "completed" file exists in your report folder (not sufficient for the *.pdf to exist, as that may be incomplete... for xyz_200.pdf you could maybe make an empty xyz_200.done or xyz_200.err file to help with re-running any problem children... and by the time you code up that file manipulation/checking/initialization logic, seems like it may have been easier to add a column to your database which holds the list of work to-be-done).
Design consideration #2: maximizing throughput (avoiding overload).
You don't want to saturate you system and run one thousand reports in parallel.
Maybe 10.
Maybe 100.
Probably not 5,000.
You will need to do some sizing research and see what gets you near 80 to 90% system utilization.
Design consideration #3: scaling across multiple servers
Overly complex, outside the scope of a Stack Exchange answer.
You'd have to spin up JVM's on multiple systems that are running something like the workers below, and a report-manager that can pull work items from a shared "queue" structure, again a database table is probably easier here than doing something file-based (or a network feed).
Sample Code
Caution: None of this code is well tested, it almost certainly has an abundance of typos, logic errors and poor design. Use at your own risk.
So anyway... I do want to give you the basic idea of a rudimentary task runner.
Replace your "// Loops" example in the question with code like the following:
main loop (original code example)
This is more or less doing what your example code did, modified to push most of the work into ReportWorker (new class, see below). Lots of stuff seems to be packed into your original question's example of "// Loop", so I'm not trying to reverse engineer that.
fwiw, it was unclear to me where "rpt" and "data[i]" are coming from so I hacked up some test data.
public class Main {
public static boolean complete( String data ) {
return false; // for testing nothing is complete.
}
public static void main(String args[] ) {
String data[] = new String[] {
"A",
"B",
"C",
"D",
"E" };
String rpt = "xyz";
// Loop
ReportManager reportMgr = new ReportManager(); // a new helper class (see below), it assigns/monitors work.
long startTime = System.currentTimeMillis();
for( int i = 0; i < data.length; ++i ) {
// complete is something you should write that knows if a report "unit of work"
// finished successfully.
if( !complete( data[i] ) ) {
reportMgr.assignWork( rpt, data[i] ); // so... where did values for your "rpt" variable come from?
}
}
reportMgr.waitForWorkToFinish(); // out of new work to assign, let's wait until everything in-flight complete.
long endTime = System.currentTimeMillis();
System.out.println("Done. Elapsed time = " + (endTime - startTime)/1000 +" seconds.");
}
}
ReportManager
This class is not thread safe, just have your original loop keep calling assignWork() until you're out of reports to assign then keep calling it until all work is done, e.g. waitForWorkToFinish(), as shown above. (fwiw, I don't think you could say any of the classes here are especially thread safe).
public class ReportManager {
public int polling_delay = 500; // wait 0.5 seconds for testing.
//public int polling_delay = 60 * 1000; // wait 1 minute.
// not high throughput millions of reports / second, we'll run at a slower tempo.
public int nWorkers = 3; // just 3 for testing.
public int assignedCnt = 0;
public ReportWorker workers[];
public ReportManager() {
// initialize our manager.
workers = new ReportWorker[ nWorkers ];
for( int i = 0; i < nWorkers; ++i ) {
workers[i] = new ReportWorker( i );
System.out.println("Created worker #"+i);
}
}
private ReportWorker handleWorkerError( int i ) {
// something went wrong, update our "report" status as one of the reports failed.
System.out.println("handlerWokerError(): failure in "+workers[i]+", resetting worker.");
workers[i].teardown();
workers[i] = new ReportWorker( i ); // just replace everything.
return workers[i]; // the new worker will, incidentally, be avaialble.
}
private ReportWorker handleWorkerComplete( int i ) {
// this unit of work was completed, update our "report" status tracker as success.
System.out.println("handleWorkerComplete(): success in "+workers[i]+", resetting worker.");
workers[i].teardown();
workers[i] = new ReportWorker( i ); // just replace everything.
return workers[i]; // the new worker will, incidentally, be avaialble.
}
private int activeWorkerCount() {
int activeCnt = 0;
for( int i = 0; i < nWorkers; ++i ) {
ReportWorker worker = workers[i];
System.out.println("activeWorkerCount() i="+i+", checking worker="+worker);
if( worker.hasError() ) {
worker = handleWorkerError( i );
}
if( worker.isComplete() ) {
worker = handleWorkerComplete( i );
}
if( worker.isInitialized() || worker.isRunning() ) {
++activeCnt;
}
}
System.out.println("activeWorkerCount() activeCnt="+activeCnt);
return activeCnt;
}
private ReportWorker getAvailableWorker() {
// check each worker to see if anybody recently completed...
// This (rather lazily) creates completely new ReportWorker instances.
// You might want to try pooling (salvaging and reinitializing them)
// to see if that helps your performance.
System.out.println("\n-----");
ReportWorker firstAvailable = null;
for( int i = 0; i < nWorkers; ++i ) {
ReportWorker worker = workers[i];
System.out.println("getAvailableWorker(): i="+i+" worker="+worker);
if( worker.hasError() ) {
worker = handleWorkerError( i );
}
if( worker.isComplete() ) {
worker = handleWorkerComplete( i );
}
if( worker.isAvailable() && firstAvailable==null ) {
System.out.println("Apparently worker "+worker+" is 'available'");
firstAvailable = worker;
System.out.println("getAvailableWorker(): i="+i+" now firstAvailable = "+firstAvailable);
}
}
return firstAvailable; // May (or may not) be null.
}
public void assignWork( String rpt, String data ) {
ReportWorker worker = getAvailableWorker();
while( worker == null ) {
System.out.println("assignWork: No workers available, sleeping for "+polling_delay);
try { Thread.sleep( polling_delay ); }
catch( InterruptedException e ) { System.out.println("assignWork: sleep interrupted, ignoring exception "+e); }
// any workers avaialble now?
worker = getAvailableWorker();
}
++assignedCnt;
worker.initialize( rpt, data ); // or whatever else you need.
System.out.println("assignment #"+assignedCnt+" given to "+worker);
Thread t = new Thread( worker );
t.start( ); // that is pretty much it, let it go.
}
public void waitForWorkToFinish() {
int active = activeWorkerCount();
while( active >= 1 ) {
System.out.println("waitForWorkToFinish(): #active workers="+active+", waiting...");
// wait a minute....
try { Thread.sleep( polling_delay ); }
catch( InterruptedException e ) { System.out.println("assignWork: sleep interrupted, ignoring exception "+e); }
active = activeWorkerCount();
}
}
}
ReportWorker
public class ReportWorker implements Runnable {
int test_delay = 10*1000; //sleep for 10 seconds.
// (actual code would be generating PDF output)
public enum StatusCodes { UNINITIALIZED,
INITIALIZED,
RUNNING,
COMPLETE,
ERROR };
int id = -1;
StatusCodes status = StatusCodes.UNINITIALIZED;
boolean initialized = false;
public String rpt = "";
public String data = "";
//Engine eng;
//PDFExportThread pdfExporter;
//DataSource_type cn;
public boolean isInitialized() { return initialized; }
public boolean isAvailable() { return status == StatusCodes.UNINITIALIZED; }
public boolean isRunning() { return status == StatusCodes.RUNNING; }
public boolean isComplete() { return status == StatusCodes.COMPLETE; }
public boolean hasError() { return status == StatusCodes.ERROR; }
public ReportWorker( int id ) {
this.id = id;
}
public String toString( ) {
return "ReportWorker."+id+"("+status+")/"+rpt+"/"+data;
}
// the example code doesn't make clear if there is a relationship between rpt & data[i].
public void initialize( String rpt, String data /* data[i] in original code */ ) {
try {
this.rpt = rpt;
this.data = data;
/* uncomment this part where you have the various classes availble.
* I have it commented out for testing.
cn = ds.getConnection();
Engine eng = new Engine(Engine.EXPORT_PDF);
eng.setReportFile(rpt); //rpt is the report name
eng.setConnection(cn);
eng.setPrompt(data, 0);
ReportProperties repprop = eng.getReportProperties();
repprop.setPaperOrient(ReportProperties.DEFAULT_PAPER_ORIENTATION, ReportProperties.PAPER_FANFOLD_US);
*/
status = StatusCodes.INITIALIZED;
initialized = true; // want this true even if we're running.
} catch( Exception e ) {
status = StatusCodes.ERROR;
throw new RuntimeException("initialze(rpt="+rpt+", data="+data+")", e);
}
}
public void run() {
status = StatusCodes.RUNNING;
System.out.println("run().BEGIN: "+this);
try {
// delay for testing.
try { Thread.sleep( test_delay ); }
catch( InterruptedException e ) { System.out.println(this+".run(): test interrupted, ignoring "+e); }
/* uncomment this part where you have the various classes availble.
* I have it commented out for testing.
eng.execute();
PDFExportThread pdfExporter = new PDFExportThread(eng, sFileName, sFilePath);
pdfExporter.execute();
*/
status = StatusCodes.COMPLETE;
System.out.println("run().END: "+this);
} catch( Exception e ) {
System.out.println("run().ERROR: "+this);
status = StatusCodes.ERROR;
throw new RuntimeException("run(rpt="+rpt+", data="+data+")", e);
}
}
public void teardown() {
if( ! isInitialized() || isRunning() ) {
System.out.println("Warning: ReportWorker.teardown() called but I am uninitailzied or running.");
// should never happen, fatal enough to throw an exception?
}
/* commented out for testing.
try { cn.close(); }
catch( Exception e ) { System.out.println("Warning: ReportWorker.teardown() ignoring error on connection close: "+e); }
cn = null;
*/
// any need to close things on eng?
// any need to close things on pdfExporter?
}
}

Receiving "java.net.SocketException: Connection reset" when connecting from dotnet client to a java server

I have a server (written in java) that listens for a connection on a specific port.
I have a client (written in c#) that connects with java server and try to send some data but the connection get reset with following error at server side.
"java.net.SocketException: Connection reset"
Below is the client side code:-
public void ConnectServer()
{
try
{
if (Connect())
{
Broadcast("check");
}
}
catch (Exception ex)
{
Logger.Text = ex.Message;
}
}
private bool Connect()
{
bool flag = false;
try
{
if (!clientSocket.Connected)
{
clientSocket.Connect(ConfigurationManager.AppSettings["SMSRequestNotifierServer"].ToString(), Convert.ToInt32(ConfigurationManager.AppSettings["SMSRequestNotifierPort"].ToString()));
clientSocket.LingerState = new LingerOption(true,10);
isConnected = true;
flag = true;
}
else
{
flag = true;
}
}
catch (Exception ex)
{
Logger.Text = ex.Message;
flag = false; }
return flag;
}
private void Broadcast(String msg)
{
using (NetworkStream serverStream = clientSocket.GetStream())
{
byte[] outStream = System.Text.Encoding.ASCII.GetBytes(msg);
serverStream.Write(outStream, 0, outStream.Length);
serverStream.Flush();
serverStream.Close();
serverStream.Dispose();
clientSocket.Close();
}
}
Can anyone point me what am i doing wrong in this code that my connection is getting reset?
One more finding in code is that while I debug to this line, it should write the data in stream and server should receive it but nothing happens:-
serverStream.Write(outStream, 0, outStream.Length);
Executing below lines will throws "java.net.SocketException: Connection reset" on server side.
serverStream.Flush();
serverStream.Close();

You get this error when sending, not when connecting. It happens when you send to a connection that has already been closed by the peer, among other much less likely scenarios.
For example:
You send something that the peer didn't understand; it closes the connection; you keep writing; this is what happens next.
Or
The peer is sending something to you that you should be reading and you aren't, because you have already closed the socket.
Check the application protocol.

The original issue was in My Dotnet Client code the socket was close immediate after establishing.
For this I have use the
http://www.codeproject.com/Articles/19071/Quick-tool-A-minimalistic-Telnet-library
Below is the code that solved my problem
TelnetConnection oTelnetConnection = new TelnetConnection(ConfigurationManager.AppSettings["SMSRequestNotifierServer"].ToString(), Convert.ToInt32(ConfigurationManager.AppSettings["SMSRequestNotifierPort"].ToString()));
Logger.Text += oTelnetConnection.Read();
oTelnetConnection.WriteLine("check");
// minimalistic telnet implementation
// conceived by Tom Janssens on 2007/06/06 for codeproject
//
// http://www.corebvba.be
using System;
using System.Collections.Generic;
using System.Text;
using System.Net.Sockets;
namespace MinimalisticTelnet
{
enum Verbs {
WILL = 251,
WONT = 252,
DO = 253,
DONT = 254,
IAC = 255
}
enum Options
{
SGA = 3
}
class TelnetConnection
{
TcpClient tcpSocket;
int TimeOutMs = 100;
public TelnetConnection(string Hostname, int Port)
{
tcpSocket = new TcpClient(Hostname, Port);
}
public string Login(string Username,string Password,int LoginTimeOutMs)
{
int oldTimeOutMs = TimeOutMs;
TimeOutMs = LoginTimeOutMs;
string s = Read();
if (!s.TrimEnd().EndsWith(":"))
throw new Exception("Failed to connect : no login prompt");
WriteLine(Username);
s += Read();
if (!s.TrimEnd().EndsWith(":"))
throw new Exception("Failed to connect : no password prompt");
WriteLine(Password);
s += Read();
TimeOutMs = oldTimeOutMs;
return s;
}
public void WriteLine(string cmd)
{
Write(cmd + "\n");
}
public void Write(string cmd)
{
if (!tcpSocket.Connected) return;
byte[] buf = System.Text.ASCIIEncoding.ASCII.GetBytes(cmd.Replace("\0xFF","\0xFF\0xFF"));
tcpSocket.GetStream().Write(buf, 0, buf.Length);
}
public string Read()
{
if (!tcpSocket.Connected) return null;
StringBuilder sb=new StringBuilder();
do
{
ParseTelnet(sb);
System.Threading.Thread.Sleep(TimeOutMs);
} while (tcpSocket.Available > 0);
return sb.ToString();
}
public bool IsConnected
{
get { return tcpSocket.Connected; }
}
void ParseTelnet(StringBuilder sb)
{
while (tcpSocket.Available > 0)
{
int input = tcpSocket.GetStream().ReadByte();
switch (input)
{
case -1 :
break;
case (int)Verbs.IAC:
// interpret as command
int inputverb = tcpSocket.GetStream().ReadByte();
if (inputverb == -1) break;
switch (inputverb)
{
case (int)Verbs.IAC:
//literal IAC = 255 escaped, so append char 255 to string
sb.Append(inputverb);
break;
case (int)Verbs.DO:
case (int)Verbs.DONT:
case (int)Verbs.WILL:
case (int)Verbs.WONT:
// reply to all commands with "WONT", unless it is SGA (suppres go ahead)
int inputoption = tcpSocket.GetStream().ReadByte();
if (inputoption == -1) break;
tcpSocket.GetStream().WriteByte((byte)Verbs.IAC);
if (inputoption == (int)Options.SGA )
tcpSocket.GetStream().WriteByte(inputverb == (int)Verbs.DO ? (byte)Verbs.WILL:(byte)Verbs.DO);
else
tcpSocket.GetStream().WriteByte(inputverb == (int)Verbs.DO ? (byte)Verbs.WONT : (byte)Verbs.DONT);
tcpSocket.GetStream().WriteByte((byte)inputoption);
break;
default:
break;
}
break;
default:
sb.Append( (char)input );
break;
}
}
}
}
}

Removing users from chat (Java)

I have developed a client/server chat application using Java and I wish to know how can I remove a user from an array. When a specific client log-in the username is saved in username array and client ID in client array. To allow the server to accept multiple clients, I am using threads. Now can anyone guide me on how to remove a user from the array and also close the connection for that user.
Adding a new client and saving the ID in client array
public class AddClient implements Runnable {
Thread t;
AddClient(String tot) {
t = new Thread(this, tot);
t.start();
}
public void run() {
while (true) {
try {
try {
waitClient();
} catch (Exception ex) {
ex.printStackTrace();
}
for (int i = 0; i < client.length; i++) {
if (client[i] == 0) {
client[i] = i + 1;
id = i;
break;
}
}
//set stream to send and receive data
out[client[id]] = new ObjectOutputStream(connect.getOutputStream());
out[client[id]].flush();
in[client[id]] = new ObjectInputStream(connect.getInputStream());
The username is saved in the username array
username[client[id]] = cm.sender; //Add user in username[] array
Removing user
public synchronized void removeUser(int number) {
int position = number;
System.out.println("Server removing user " + username[number] + "which is client " + number);
for (int i = 0; i <= client.length; i++) {
if (position == client[i]) {
System.out.println("User to be remove found");
try {
client[i + 1] = client[i];
in[position].close();
out[position].close();
username[position] = null;
position = position - 1;
} catch (Exception e) {
e.printStackTrace();
}
}
}
I am trying to use HashTable to add and remove the client
public class ChatServerProtocol {
private String nick;
private AddClient a;
private Hashtable<String, AddClient> nicks = new Hashtable<String, AddClient>();
private boolean add_nick(String nick, AddClient a) {
if (nicks.containsKey(nick)) {
return false;
} else {
nicks.put(nick, a);
return true;
}
}
private boolean remove_nick(String nick, AddClient a) {
if (!(nicks.containsKey(nick))) {
return false;
} else {
nicks.remove(nick);
return true;
}
}
public ChatServerProtocol(AddClient a) throws IOException {
nick = null;
a = a;
}
But now how do I call the method add_nick. Whenever a client log-in the username is sent to the server and the server reads it as cm.sender. I also need to include the thread variable. So how to add the username so that later i can remove it.
ChatServerProtocol.add_nick(cm.sender);

No, saving in database won't be a good idea.. Remember you are saving details only for the length of the session and basic concept of database is to use it after the session. What happens if your session gets interruped because of network issues etc?
Just use Map instead of plain arrays, using key as client ID and value as username.. removing username will be a plain call such as map.remove(clientID);
EDIT AS YOU ASKED: Note that this code is not complete and only as much as you gave..
public class AddClient implements Runnable {
Thread t;
private Map<int, String> users = new HashMap <int, String>();
AddClient(String tot) {
t = new Thread(this, tot);
t.start();
}
public void run() {
while (true) {
try {
try {
waitClient();
} catch (Exception ex) {
ex.printStackTrace();
}
int clientId = users.size() + 1;
users.put(clientId, cm.sender);
//set stream to send and receive data
out[clientId] = new ObjectOutputStream(connect.getOutputStream());
out[clientId].flush();
in[clientId] = new ObjectInputStream(connect.getInputStream());
REMOVE USER METHOD
public synchronized void removeUser(int number) {
if(users.containsKey(number)) {
System.out.println("Server removing user " + users.get(number) + "which is client " + number);
users.remove(number);
} else {
System.out.println("User not in session");
}
}

Android JAVA: Reading variables that a thread is accessing

I've got an app with several screens. In addition, I have a globally-running timer that occasionally (every minute or so) attempts to refresh their transaction data from a website and store it in a JSONArray (static JSONArray jTransactions).
When you go to the Transaction screen, the first thing it does is populate a ListView with the contents of jTransactions, and it will refresh the displayed info every few seconds. However if the web-thread is currently running, I get null values for everything.
I've got enough coder savvy to know that it's a threading issue, but I'm not experienced enough with JAVA/Android development to know how to handle it. And my Google-fu may be weak but the only answers I found either didn't apply or involved heavy rewriting.
I guess my question is this - how can I alter my code so that there's no direct collision between my activity and the fetch thread?
Also I fully accept that my code is probably ugly; as I said, I'm still learning the platform.
Here's a pared-down version of the thread I'm running:
static int iRefreshTransactions = 30000;
static boolean bRefreshingTransactions = false;
static Calendar cLastRefreshTransactions = null;
final Runnable mRefreshTransactions = new Runnable() {
public void run() {
mHandler.removeCallbacks(this);
Thread T = new tRefreshTransactions();
T.start();
}
};
private class tRefreshTransactions extends Thread {
#Override
public void run() {
bRefreshingTransactions = true;
RetrieveTransactions();
bRefreshingTransactions = false;
handler.sendEmptyMessage(0);
}
private Handler handler = new Handler() {
#Override
public void handleMessage(Message msg) {
cLastRefreshTransactions = Calendar.getInstance();
ShowToast("cLastRefreshTransactions(): " + cLastRefreshTransactions.getTime().toLocaleString());
mHandler.postDelayed(mRefreshTransactions, iRefreshTransactions);
}
};
private Handler failhandler = new Handler() {
#Override
public void handleMessage(Message msg) {
// handle the failure somehow
}
};
}
Here's a pared-down version of the RetrieveTransactions() code:
// Retrieve the user's latest transactions from the website.
public boolean RetrieveTransactions() {
String result;
FailureReason = "";
iTransactions = 0;
// Retrieve the Page.
result = GetPage(Url);
// Strip the transactions from the page and convert them to a JSONArray.
try {
String sTransactions = textExtract(result, "var dataTable1Data=", ";\n", 0);
jTransactions = new JSONArray(sTransactions);
iTransactions = jTransactions.length();
return true;
} catch (JSONException e1) {
// Generally if it fails during this, there was no JSONArray to parse (hence no transactions).
FailureReason = "No Transactions Found";
return false;
}
}
And finally here's the pared-down code that displays the transactions in a listview, which is called at activity launch and every 5 seconds or so thereafter:
public void ShowTransactions() {
try {
if (!bRefreshingTransactions) {
if (iTransactions==0) {
return;
}
if (iTransactions==0) return;
List<String> listContents = new ArrayList<String>(iTransactions);
for (int i = 0; i < iTransactions; i++) {
listContents.add(jTransactions.getString(iTransactions - i - 1));
}
lvRecentTransactions.setAdapter(new ArrayAdapterTransactions(MyContext, listContents));
}
} catch (Exception e) {
// Do error stuff here
}
}
Thank you in advance. :)

It seems to be mutual exclusion problem. Make jTransaction synchronized or put the jTransaction variable in synchonized block.
synchronized(jTransactions ){
String sTransactions = textExtract(result, "var dataTable1Data=", ";\n", 0);
jTransactions = new JSONArray(sTransactions);
iTransactions = jTransactions.length();
}
I didn't test the code but I hope synchronization will help you.

getSnapshot not supported on Blackberry

I'm having problem when taking a picture using VideoControl.getSnapshot() method. It always throw the exception: getSnapshot not Supported. I'm using JRE 5.0.0 with Eclipse and BlackBerry® Java® SDK 5.0 Plugin.
What I do first is to list the encoding supported by Blackberry SmartPhone selected (bold 9700) with the command System.getProperty("video.snapshot.encodings") and select one encoding from the list and pass it as the getSnapshot argument.
I've tested on several Blackberry and the same exception is thrown.
Part of the code:
mPlayer = Manager.createPlayer("capture://video?encoding=video/3gpp");
mPlayer.realize();
mPlayer = Manager.createPlayer("capture://video?encoding=video/3gpp");
mPlayer.start();
videoControl = (VideoControl)mPlayer.getControl("VideoControl");
Field cameraView = (Field) videoControl.initDisplayMode(VideoControl.USE_GUI_PRIMITIVE, "net.rim.device.api.ui.Field");
Thread.sleep(1000);
UiApplication.getUiApplication().pushScreen(new TempScreen(cameraView));
byte[] snapShot = videoControl.getSnapshot("encoding=jpeg&width=480&height=360&quality=superfine");
Bitmap image = Bitmap.createBitmapFromBytes(snapShot, 0, snapShot.length, 1);
UiApplication.getUiApplication().pushScreen(new TempScreen(image));
}catch (MediaException e){
UiApplication.getUiApplication().pushScreen(new TempScreen("Exception: " + e.getMessage())); }
catch (IOException e){
UiApplication.getUiApplication().pushScreen(new TempScreen("IO Exception: " + e.getMessage()));
}
catch (InterruptedException e){UiApplication.getUiApplication().pushScreen(new TempScreen("Interrupted Exception: "+ e.getMessage()));}

Not sure is my answer is actual after more than a half of year, but may be it will be useful.
You may try to use Thread.sleep(1000); before getSnapshot() call.
The problem may be related with that fact: "viewfinder must actually be visible on the screen prior to calling getSnapShot()."
So if you call getSnapshot immediately after UiApplication.getUiApplication().pushScreen(new TempScreen(cameraView));
the camera isn't prepared for the next shot.
Also are you really sure that getSnapshot() API is supported exactly on your device? Some manufacturers may not support it, despite the API defines this method. Did you run System.getProperty("video.snapshot.encodings") exactly on the same device where you test getSnapshot()?

Player _p;
VideoControl _vc ;
RecordControl _rc ;
String PATH;
FileConnection fileconn;
Object canvas= new Object();
public static boolean SdcardAvailabulity() {
String root = null;
Enumeration e = FileSystemRegistry.listRoots();
while (e.hasMoreElements()) {
root = (String) e.nextElement();
if( root.equalsIgnoreCase("sdcard/") ) {
return true;
}else if( root.equalsIgnoreCase("store/") ) {
return false;
}
}
class MySDListener implements FileSystemListener {
public void rootChanged(int state, String rootName) {
if( state == ROOT_ADDED ) {
if( rootName.equalsIgnoreCase("sdcard/") ) {
}
} else if( state == ROOT_REMOVED ) {
}
}
}
return true;
}
protected boolean invokeAction(int action){
boolean handled = super.invokeAction(action);
if(SdcardAvailabulity()){
PATH = System.getProperty("fileconn.dir.memorycard.videos")+"Video_"+System.currentTimeMillis()+".3gpp";//here "str" having the current Date and Time;
} else {
PATH = System.getProperty("fileconn.dir.videos")+"Video_"+System.currentTimeMillis()+".3gpp";
}
if(!handled){
if(action == ACTION_INVOKE){
try{
if(_p!=null)
_p.close();
}catch(Exception e){
}
}
}
return handled;
}
public MyScreen(){
setTitle("Video recording demo");
ButtonField AddPhoto = new ButtonField("push",ButtonField.FOCUSABLE | ButtonField.FIELD_HCENTER | ButtonField.FIELD_VCENTER | DrawStyle.HCENTER | ButtonField.NEVER_DIRTY | Field.USE_ALL_WIDTH);
FieldChangeListener PhotoListener = new FieldChangeListener() {
public void fieldChanged(Field field, int context) {
ButtonField Button = (ButtonField) field;
if (Button.getLabel().equals("push")){
}
}
};
AddPhoto.setChangeListener(PhotoListener);
add(AddPhoto);
}
}