Develop Reference

How do I load and save an arrayList<String> into a text class in java?

I am trying to implement a save and load function in my program that saves an arrayList to a textfile and then can later load all of the past lists I have saved and print them out. I am currently using these two methods:
public static void save(Serializable data, String fileName) throws Exception {
try (ObjectOutputStream oos = new ObjectOutputStream((Files.newOutputStream(Paths.get(fileName))))) {
oos.writeObject(data);
}
}
public static Object load(String fileName) throws Exception {
try (ObjectInputStream oos = new ObjectInputStream((Files.newInputStream(Paths.get(fileName))))) {
return oos.readObject();
}
}
As well as a class that represents a list as serializable data.
The problem with this is that it won't save the data after I terminate the program, and when it loads data it prints it with a great deal of extra text besides the list I want it to return. Is there a better or easier way of doing this?

I once had a same problem. So I will show you how to do it ...
Be the below Level class is what is to be saved:
public class Level implements Serializable {
private int level = 1;
private int star;
private int point;
// Constructor
public Level() {
}
public void setLevel(int level) {
this.level = level;
}
public int getLevel() {
return level;
}
public void setStar(int stars) {
this.star = stars;
}
public int getStar() {
return star;
}
public void setPoint(int points) {
this.point = points;
}
public int getPoint() {
return point;
}
#Override
public String toString() {
return "Level-" + level + " " +
(star > 1 ? star + " stars": star + " star") + " " +
(point > 1 ? point + " points" : point + " point") + "\n";
}
}
We will save the list into this file:
private static final String FILENAME = "data.level";
This is the List of our objects:
List<Level> mLevels;
Call this method to save the list into the file:
private void save() {
if(mLevels.isEmpty()) {
return;
}
try
{
ObjectOutputStream oos = new ObjectOutputStream(mContext.openFileOutput(FILENAME, Context.MODE_PRIVATE));
oos.writeObject(mLevels);
}
catch (IOException e)
{
//Toast.makeText(mContext,e.getMessage(),Toast.LENGTH_SHORT).show();
}
}
Use this method to load the list from saved file. Notice, we cast the list of our object with this (List<Level>) ois.readObject(); in the method:
private void load() {
try
{
ObjectInputStream ois = new ObjectInputStream(mContext.openFileInput(FILENAME));
mLevels = (List<Level>) ois.readObject();
}
catch (IOException e)
{
//Toast.makeText(mContext,e.getMessage(),Toast.LENGTH_SHORT).show();
}
catch (ClassNotFoundException e)
{
//Toast.makeText(mContext,e.getMessage(),Toast.LENGTH_SHORT).show();
}
if(mLevels == null) {
mLevels = new ArrayList<>();
//Toast.makeText(mContext,"List created",Toast.LENGTH_SHORT).show();
}
}
By now, you should get the idea of how to save your own list.

NotSerializableException in Third-Party Graphics Library

I have created a clone of Atari Breakout game using the ACM graphics library and just finished adding a highscore interface and functionality. The player's name and score should be displayed on the GUI window (it is successfully) and also be written to a .dat binary file.
However, when the code attempts to load the existing file I get the following error.
writing aborted; java.io.NotSerializableException: acm.graphics.GCanvasListener
I've researched this error online and it seems it can be solved by editing the class to implement Serializable. However, the class throwing this error is not one of my own but rather a class that belongs to the third-party ACM graphics library. How do I solve this?
I'm not even sure why this error is being caused in the first place since the data I'm attempting to serialize is only a name and score, I'm not trying to serialize a canvas of objects or anything like that.
Main class (called Breakout)
public class Breakout extends GraphicsProgram {
... // game variables
public void run() {
... // this if clause runs when game ends
if (brickCounter > 0) {
removeAll(); // clears screen
printGameOver(); // displays game over message
HighscoreManager hm = new HighscoreManager();
String name = getHighScoreName();
hm.addScore(name, score);
hm.displayHighscores();
}
}
... // game functionality methods
private String getHighScoreName(){
IODialog dialog = new IODialog();
String name = dialog.readLine("Enter your name: ");
return name;
}
Score class
private class Score implements Serializable {
private int score;
private String name;
public Score(String name, int score) {
this.score = score;
this.name = name;
}
public int getScore() { return score; }
public String getName() { return name; }
}
ScoreComparator class
private class ScoreComparator implements Comparator<Score> {
public int compare(Score score1, Score score2) {
int sc1 = score1.getScore();
int sc2 = score2.getScore();
if (sc1 > sc2) {
return -1;
} else if (sc1 < sc2) {
return 1;
} else {
return 0;
}
}
}
HighscoreManager class
private class HighscoreManager {
private ArrayList<Score> scores;
private static final String HIGHSCORE_FILE = ".//bin//scores.dat";
ObjectOutputStream outputStream = null;
ObjectInputStream inputStream = null;
public HighscoreManager() {
scores = new ArrayList<Score>(10);
}
public ArrayList<Score> getScores() {
loadScoreFile();
sort();
return scores;
}
private void sort() {
ScoreComparator comparator = new ScoreComparator();
Collections.sort(scores, comparator);
}
public void addScore(String name, int score) {
loadScoreFile();
scores.add(new Score(name, score));
updateScoreFile();
}
public void loadScoreFile() {
try {
inputStream = new ObjectInputStream(new FileInputStream(HIGHSCORE_FILE));
scores = (ArrayList<Score>) inputStream.readObject();
}
catch (FileNotFoundException e) {
System.out.println("[Load] File Not Found Error: " + e.getMessage());
}
catch (IOException e) {
System.out.println("[Load] Input/Output Error: " + e.getMessage());
}
catch (ClassNotFoundException e) {
throw new RuntimeException("[Load] Class Not Found Error: " + e.getMessage());
}
finally {
try {
if (outputStream != null) {
outputStream.flush();
outputStream.close();
}
} catch (IOException e) {
System.out.println("[Load] Input/Output Error: " + e.getMessage());
}
}
}
public void updateScoreFile() {
try {
outputStream = new ObjectOutputStream(new FileOutputStream(HIGHSCORE_FILE));
outputStream.writeObject(scores);
}
catch (FileNotFoundException e) {
System.out.println("[Update] File Not Found Error: " + e.getMessage());
}
catch (IOException e) {
System.out.println("[Update] Input/Output Error: " + e.getMessage());
}
finally {
try {
if (outputStream != null) {
outputStream.flush();
outputStream.close();
}
} catch (IOException e) {
System.out.println("[Update] Input/Output Error: " + e.getMessage());
}
}
}
public void displayHighscores() {
int max = 10;
ArrayList<Score> scores;
scores = getScores();
int x = scores.size();
if (x > max) {
x = max;
}
removeAll(); // clears screen
int npos = 160;
int spos = 160;
for (int i = 0; i < x; i++) {
GLabel showName = new GLabel(scores.get(i).getName(), (getWidth() / 2.0) - 100, (getHeight() / 2.0) - npos);
showName.move(-showName.getWidth() / 2, -showName.getHeight());
showName.setColor(Color.WHITE);
add(showName);
npos -= 40;
}
for (int i = 0; i < x; i++) {
GLabel showScore = new GLabel(Integer.toString(scores.get(i).getScore()), (getWidth() / 2.0) + 100, (getHeight() / 2.0) - spos);
showScore.move(-showScore.getWidth() / 2, -showScore.getHeight());
showScore.setColor(Color.WHITE);
add(showScore);
spos -= 40;
}
}
After running the application:
[Load] Input/Output Error: writing aborted; java.io.NotSerializableException: acm.graphics.GCanvasListener
[Update] Input/Output Error: acm.graphics.GCanvasListener
[Load] Input/Output Error: writing aborted; java.io.NotSerializableException: acm.graphics.GCanvasListener

Your task will be to find a hidden reference from your name and score structure to the UI components. Many GUI applications use a lot of inner classes, and this might be the missing link.
When you have a class something like this:
class MyGame {
private SomeUIWidget widget;
class TopScore implements Serializable {
String name;
int score;
...
}
...
}
There is a hidden member in TopScore that references the "enclosing instance" of MyGame, including its SomeUIWidget member. When you try to serialize a TopScore instance, all the rest gets dragged in with it.
You could simply declare TopScore as a static nested class. This means that there is no enclosing instance, and serves only to hide the TopScore class from other code. But, I would suggest just making TopScore a top-level class, in its own file, because it's likely that other objects will want to use those objects in different ways—that is, it seems like a likely candidate for part of your public API.
This is an educated guess, in the absence of any actual code. To get a better answer, reduce your code to the minimum required to demonstrate the problem, and include that in your question.

You should go to the class where the fields name and score are, and add for example public class nameclass implements Serializable. I hope it works for you.

Interactive Brokers API - Executing multiple trades

I'm trying to create a program for an API to place multiple trades at once, and then get prices for the stocks, and then rebalance every so often. I used a tutorial from online to get some of this code, and made a few tweaks.
However, when I run the code, it often connects and will place an order if I restart IB TWS. But if I go to run the code again it does not work, or show any indication that it will connect. Can anyone help me figure out how to keep the connection going, so that I can run the main.java file, and it will execute multiple trades and then end the connection? Do I need to change the client id number in either the code, or the settings of TWS?
There are three files:
Ordermanagement.java:
package SendMarketOrder;
//import statements//
class OrderManagement extends Thread implements EWrapper{
private EClientSocket client = null; //IB API client Socket Object
private Stock stock = new Stock();
private Order order = new Order();
private int orderId;
private double limitprice;
private String Ticker;
//method to create connection class. It's the constructor
public OrderManagement() throws InterruptedException, ClassNotFoundException, SQLException {
// Create a new EClientSocket object
System.out.println("////////////// Creating a Connection ////////////");
client = new EClientSocket(this); //Creation of a socket to connect
//connect to the TWS Demo
client.eConnect(null,7497,1);
try {
Thread.sleep(3000); //waits 3 seconds for user to accept
while (!(client.isConnected()));
} catch (Exception e) {
e.printStackTrace();
}
System.out.println("///////// Connected /////////");
}
public void sendMarketOrder(String cusip, String buyorSell, int shares) throws SQLException, ClassNotFoundException{
//New Order ID
orderId++;
order.m_action = buyorSell;
order.m_orderId = orderId;
order.m_orderType = "MKT";
order.m_totalQuantity = shares;
order.m_account = "DU33xxxxx"; //write own account
order.m_clientId = 1;
//Create a new contract
stock.createContract(cusip);
client.placeOrder(orderId, stock.contract, order);
//Show order in console
SimpleDateFormat time_formatter = new SimpleDateFormat("HH:mm:ss");
String current_time_str = time_formatter.format(System.currentTimeMillis());
System.out.println("////////////////////////////////////////////////\n" +
"#Limit Price: " + order.m_lmtPrice + "///////////////////////////\n" +
"#Client number: " + order.m_clientId + "///////////////////////////\n" +
"#OrderType: " + order.m_orderType + "///////////////////////////\n" +
"#Order Quantity: " + order.m_totalQuantity + "///////////////////////////\n" +
"#Account number: " + order.m_account + "///////////////////////////\n" +
"#Symbol: " + stock.contract.m_secId + "///////////////////////////\n" +
"///////////////////////////////////////"
);
}
Stock.java
public class Stock{
private int StockId; //we can identify the stock
private String Symbol; //Ticker
public Stock() { //default constructor
}
public Stock(int StockId, String Symbol) { //constructor
this.StockId = StockId;
this.Symbol = Symbol;
}
//getter and setters
public int getStockId() {
return StockId;
}
public String getSymbol() {
return Symbol;
}
Contract contract = new Contract ();
public void createContract(String cusip){
contract.m_secId = cusip;
contract.m_secIdType = "CUSIP";
contract.m_exchange = "SMART";
contract.m_secType = "STK";
contract.m_currency = "USD";
}
}
Main.java:
package SendMarketOrder;
import java.sql.SQLException;
public class Main {
public static void main(String[] args) throws InterruptedException, ClassNotFoundException, SQLException {
OrderManagement order = new OrderManagement();
order.sendMarketOrder("922908363","BUY", 100);
order.sendMarketOrder("92204A504","BUY", 50);
order.sendMarketOrder("92204A702","BUY", 100);
System.exit(0);
}
}
These are my current settings TWS settings if that helps:
Thanks in advance for the help!

I changed a few things around in the code and added comments.
package sendmarketorder;//usually lower case pkg names
public class Main {
//you throw a bunch of exceptions that are never encountered
public static void main(String[] args) {
//since there's a Thread.sleep in this class
//it will block until ready
OrderManagement order = new OrderManagement();
//obviously you need some logic to buy/sell
//you can use command line args here if you want
order.sendMarketOrder("922908363", "BUY", 100);
order.sendMarketOrder("92204A504", "BUY", 50);
order.sendMarketOrder("92204A702", "BUY", 100);
//the socket creates a reader thread so this will stop it.
//if you didn't have this line the non-daemon thread would keep a
//connection to TWS and that's why you couldn't reconnect
//System.exit(0);//use better exit logic
}
}
.
package sendmarketorder;
import com.ib.client.*;
import java.text.SimpleDateFormat;
import java.util.HashMap;
import java.util.Map;
//doesn't extend thread and if you implement EWrapper you have to implement all methods
//in API 9.72 you can extend DefaultWrapper and just override the methods you need
public class OrderManagement implements EWrapper{
private EClientSocket client = null; //IB API client Socket Object
private int orderId = -1;//use as flag to send orders
//private double limitprice;
//private String Ticker;
//keep track of all working orders
private Map<Integer, Order> workingOrders = new HashMap<>();
//method to create connection class. It's the constructor
public OrderManagement(){
// Create a new EClientSocket object
System.out.println("////////////// Creating a Connection ////////////");
client = new EClientSocket(this); //Creation of a socket to connect
//connect to the TWS Demo
client.eConnect(null, 7497, 123);//starts reader thread
try {
while (orderId < 0){ //not best practice but it works
System.out.println("waiting for orderId");
Thread.sleep(1000);
}
} catch (Exception e) {
e.printStackTrace();
}
System.out.println("///////// Connected /////////");
}
public void sendMarketOrder(String cusip, String buyorSell, int shares) {
//make new stock and order for each stock
Stock stock = new Stock();
Order order = new Order();
//New Order ID, but get from API as you have to increment on every run for life
orderId++;
order.m_action = buyorSell;
order.m_orderId = orderId;
order.m_orderType = "MKT";
order.m_totalQuantity = shares;
//I don't think you're supposed to use these fields
//order.m_account = "DU33xxxxx"; //write own account
//order.m_clientId = 1;
//Create a new contract
stock.createContract(cusip);
//remember which orders are working
workingOrders.put(orderId, order);
client.placeOrder(orderId, stock.contract, order);
//Show order in console
SimpleDateFormat time_formatter = new SimpleDateFormat("HH:mm:ss");
String current_time_str = time_formatter.format(System.currentTimeMillis());
System.out.println("////////////////////////////////////////////////\n"
+ "#Limit Price: " + order.m_lmtPrice + "///////////////////////////\n"
+ "#Client number: " + order.m_clientId + "///////////////////////////\n"
+ "#OrderType: " + order.m_orderType + "///////////////////////////\n"
+ "#Order Quantity: " + order.m_totalQuantity + "///////////////////////////\n"
+ "#Account number: " + order.m_account + "///////////////////////////\n"
+ "#Symbol: " + stock.contract.m_secId + "///////////////////////////\n"
+ "///////////////////////////////////////"
);
}
//always impl the error callback so you know what's happening
#Override
public void error(int id, int errorCode, String errorMsg) {
System.out.println(id + " " + errorCode + " " + errorMsg);
}
#Override
public void nextValidId(int orderId) {
System.out.println("next order id "+orderId);
this.orderId = orderId;
}
#Override
public void orderStatus(int orderId, String status, int filled, int remaining, double avgFillPrice, int permId, int parentId, double lastFillPrice, int clientId, String whyHeld) {
//so you know it's been filled
System.out.println(EWrapperMsgGenerator.orderStatus(orderId, status, filled, remaining, avgFillPrice, permId, parentId, lastFillPrice, clientId, whyHeld));
//completely filled when remaining == 0, or possible to cancel order from TWS
if (remaining == 0 || status.equals("Cancelled")){
//remove from map, should always be there
if (workingOrders.remove(orderId) == null) System.out.println("not my order!");
}
//if map is empty then exit program as all orders have been filled
if (workingOrders.isEmpty()){
System.out.println("all done");
client.eDisconnect();//will stop reader thread
//now is when you stop the program, but since all
//non-daemon threads have finished, the jvm will close.
//System.exit(0);
}
}
//impl rest of interface...
}

GridSim: how to send message among peer nodes through a router?

I'm a new user to the Gridsim, and currently wish to use it for my work. I wish to connect users (say 2) through a router. I followed example01 (sends pkt directly from sender to recipient), and included one router, attach it with both users. But I don't know how to start communication between both entities through router. It returns null values. On the other hand, when I use link.attach, both users bypass the router and directly communicate.
Example03 works fine but sends msg from users to the resource, but not to peer user.
I hope you could help me to sort out this issue.
Any help in this regard would be highly appreciated.
Thanks.

I find out the solution. Here is the code:
Program_name: FlowNetEx01.java
package network.flow.example01;
import gridsim.*;
import gridsim.net.*;
import gridsim.net.flow.*;
import java.util.*;
public class FlowNetEx01
{
public static void main(String[] args)
{
System.out.println("Starting network example ...");
try
{
int num_user = 2; // number of grid users
Calendar calendar = Calendar.getInstance();
boolean trace_flag = false; // mean trace GridSim events
System.out.println("Initializing GridSim package");
GridSim.initNetworkType(GridSimTags.NET_FLOW_LEVEL);
GridSim.init(num_user, calendar, trace_flag);
// In this example, the topology is:
// user(s) --10Mb/s-- r1 --1.5Mb/s-- r2 --10Mb/s-- GridResource(s)
Router r1 = new FlowRouter("router1", trace_flag); // router 1
Router r2 = new FlowRouter("router2", trace_flag); // router 2
String sender1 = "user1";
String receipient1 = "test1";
// these entities are the senders
FlowNetUser user1 = new FlowNetUser(sender1, receipient1, 5.0);
// these entities are the receipients
FlowTest test1 = new FlowTest(receipient1, sender1);
// The schedulers are redundent and will be stripped out soon
FIFOScheduler userSched1 = new FIFOScheduler("NetUserSched_0");
r1.attachHost(user1, userSched1);
FIFOScheduler testSched1 = new FIFOScheduler("FlowTestSched_0");
r2.attachHost(test1, testSched1);
double baud_rate = 1572864; // bits/sec (baud) [1.5Mb/s]
double propDelay = 200; // propagation delay in millisecond
int mtu = Integer.MAX_VALUE;; // max. transmission unit in byte
Link link = new FlowLink("r1_r2_link", baud_rate, propDelay, mtu);
FIFOScheduler r1Sched = new FIFOScheduler("r1_Sched");
FIFOScheduler r2Sched = new FIFOScheduler("r2_Sched");
r1.attachRouter(r2, link, r1Sched, r2Sched);
GridSim.startGridSimulation();
System.out.println("\nFinish ...");
}
catch (Exception e)
{
e.printStackTrace();
System.err.print(e.toString());
System.out.println("Unwanted errors happen");
}
}
}
Program_name: FlowNetUser.java
package network.flow.example01;
import gridsim.*;
import gridsim.net.*;
import gridsim.net.flow.*;
import eduni.simjava.*;
import java.util.*;
public class FlowNetUser extends GridSim
{
private int myID_; // my entity ID
private String name_; // my entity name
private String destName_; // destination name
private int destID_; // destination id
private double wait_; // Delay until I begin sending
/** Custom tag that denotes sending a message */
public static final int SEND_MSG = 1;
public static final int ACK_MSG = 2;
/**
* Creates a new NetUser object
* #param name this entity name
* #param destName the destination entity's name
* #param link the physical link that connects this entity to destName
* #throws Exception This happens when name is null or haven't
* initialized GridSim.
*/
public FlowNetUser(String name, String destName, Link link, double wait) throws Exception
{
super(name, link);
// get this entity name from Sim_entity
this.name_ = super.get_name();
// get this entity ID from Sim_entity
this.myID_ = super.get_id();
// get the destination entity name
this.destName_ = destName;
// get the waiting time before sending
this.wait_ = wait;
}
public FlowNetUser(String name, String destName, double wait) throws Exception
{
// 10,485,760 baud = 10Mb/s
super(name, new FlowLink(name+"_link",10485760,450,Integer.MAX_VALUE));
// get this entity name from Sim_entity
this.name_ = super.get_name();
// get this entity ID from Sim_entity
this.myID_ = super.get_id();
// get the destination entity name
destName_ = destName;
// get the waiting time before sending
this.wait_ = wait;
}
/**
* The core method that handles communications among GridSim entities.
*/
public void body()
{
int packetSize = 524288000; // packet size in bytes [5MB]
//int packetSize = 52428800; // packet size in bytes [50MB]
//int packetSize = 524288000; // packet size in bytes [500MB]
//int packetSize = 5242880000; // packet size in bytes [5000MB]
int size = 3; // number of packets sent
int i = 0;
// get the destination entity ID
this.destID_ = GridSim.getEntityId(destName_);
//super.sim_pause(this.wait_);
this.gridSimHold(this.wait_);
// sends messages over the other side of the link
for (i = 0; i < size; i++)
{
String msg = "Message_" + i;
IO_data data = new IO_data(msg, packetSize, destID_);
System.out.println(name_ + ".body(): Sending " + msg +
", at time = " + GridSim.clock() );
// sends through Output buffer of this entity
super.send(super.output, GridSimTags.SCHEDULE_NOW,
GridSimTags.FLOW_SUBMIT, data);
//super.sim_pause();
super.sim_pause(10.0);
//this.gridSimHold((Math.random()*10)+1.0);
}
////////////////////////////////////////////////////////
// get the ack back
Object obj = null;
for (i = 0; i < size; i++)
{
// waiting for incoming event in the Input buffer
obj = super.receiveEventObject();
System.out.println(name_ + ".body(): Receives Ack for " + obj);
}
// Wait for other FlowNetUser instances to finish
this.gridSimHold(1000.0);
super.send(destID_, GridSimTags.SCHEDULE_NOW,
GridSimTags.END_OF_SIMULATION);
////////////////////////////////////////////////////////
// shut down I/O ports
shutdownUserEntity();
terminateIOEntities();
System.out.println(this.name_ + ":%%%% Exiting body() at time " +
GridSim.clock() );
}
} // end class
Program_name: FlowTest.java
package network.flow.example01;
import java.util.*;
import gridsim.*;
import gridsim.net.*;
import gridsim.net.flow.*;
import gridsim.util.SimReport;
import eduni.simjava.*;
public class FlowTest extends GridSim
{
private int myID_; // my entity ID
private String name_; // my entity name
private String destName_; // destination name
private int destID_; // destination id
private SimReport report_; // logs every activity
public FlowTest(String name, String destName, Link link) throws Exception
{
super(name, link);
this.name_ = super.get_name();
this.myID_ = super.get_id();
this.destName_ = destName;
report_ = new SimReport(name);
report_.write("Creates " + name);
}
public FlowTest(String name, String destName) throws Exception
{
super(name, new FlowLink(name+"_link",10485760,250,Integer.MAX_VALUE));
this.name_ = super.get_name();
this.myID_ = super.get_id();
this.destName_ = destName;
report_ = new SimReport(name);
report_.write("Creates " + name);
}
public void body()
{
this.destID_ = GridSim.getEntityId(destName_);
int packetSize = 1500; // packet size in bytes
Sim_event ev = new Sim_event(); // an event
// a loop waiting for incoming events
while ( Sim_system.running() )
{
// get the next event from the Input buffer
super.sim_get_next(ev);
// if an event denotes end of simulation
if (ev.get_tag() == GridSimTags.END_OF_SIMULATION)
{
System.out.println();
write(super.get_name() + ".body(): exiting ...");
break;
}
// if an event denotes another event type
else if (ev.get_tag() == GridSimTags.FLOW_SUBMIT)
{
System.out.println();
write(super.get_name() + ".body(): receive " +
ev.get_data() + ", at time = " + GridSim.clock());
// No need for an ack, it is handled in FlowBuffer now on our behalf
// sends back an ack
IO_data data = new IO_data(ev.get_data(), packetSize, destID_);
write(name_ + ".body(): Sending back " +
ev.get_data() + ", at time = " + GridSim.clock() );
// sends through Output buffer of this entity
super.send(super.output, GridSimTags.SCHEDULE_NOW,
GridSimTags.FLOW_ACK, data);
}
else if (ev.get_tag() == GridSimTags.INFOPKT_SUBMIT)
{
processPingRequest(ev);
}
}
shutdownUserEntity();
terminateIOEntities();
// don't forget to close the file
if (report_ != null) {
report_.finalWrite();
}
System.out.println(this.name_ + ":%%%% Exiting body() at time " +
GridSim.clock() );
}
/**
* Handles ping request
* #param ev a Sim_event object
*/
private void processPingRequest(Sim_event ev)
{
InfoPacket pkt = (InfoPacket) ev.get_data();
pkt.setTag(GridSimTags.INFOPKT_RETURN);
pkt.setDestID( pkt.getSrcID() );
// sends back to the sender
super.send(super.output, GridSimTags.SCHEDULE_NOW,
GridSimTags.INFOPKT_RETURN,
new IO_data(pkt,pkt.getSize(),pkt.getSrcID()) );
}
private void write(String msg)
{
System.out.println(msg);
if (report_ != null) {
report_.write(msg);
}
}
} // end class

Java object LinkedList attribute: only receiving the first element on server-side using TCP

A little bit of context: the client is sending to the server a SOSPFPacket object (via TCP) that has various attributes, such as a Vector<LSA> lsaArray. The LSA itself has a LinkedList<LinkDescription> links attribute. In my test case, there are two messages being sent. In both messages, there is only one LSA in the vector. In the first message, the LSA has one LinkDescription, in the second, it has two. When I send a message, I increment the messageId.
The server receives both messages with proper ids, but in the second message, the links only contain one link instead of two. I'm clueless...
Here are the object implementations:
import java.io.*;
import java.util.Vector;
public class SOSPFPacket implements Serializable {
public final static short HELLO = 0;
public final static short LSU = 1;
public final static short OVER_BURDENED = 2;
public static int id = Integer.MIN_VALUE;
public String srcProcessIP;
public short srcProcessPort;
public String srcIP;
public String dstIP;
public short sospfType; //0 - HELLO, 1 - LinkState Update, 2 - Over Burdened
public String routerID;
public int messageId = id++;
public String neighborID; //neighbor's simulated IP address
public Vector<LSA> lsaArray = new Vector<>();
public String lsaInitiator = null;
}
import java.io.Serializable;
import java.util.LinkedList;
public class LSA implements Serializable {
public String linkStateID;
public int lsaSeqNumber = Integer.MIN_VALUE;
public LinkedList<LinkDescription> links = new LinkedList<LinkDescription>();
#Override
public String toString() {
StringBuffer sb = new StringBuffer();
sb.append(linkStateID + ":").append(lsaSeqNumber + "\n");
for (LinkDescription ld : links) {
sb.append(ld);
}
sb.append("\n");
return sb.toString();
}
}
import java.io.Serializable;
public class LinkDescription implements Serializable {
public String linkID;
public int portNum;
public int tosMetrics;
public LinkDescription() {}
public LinkDescription(String linkID, int portNum, int tosMetrics) {
this.linkID = linkID;
this.portNum = portNum;
this.tosMetrics = tosMetrics;
}
public String toString() {
return linkID + "," + portNum + "," + tosMetrics;
}
}
To send the message, I do it via a Client.java thread implementing Runnable. Here are the relevant methods:
public void run() {
try {
_outputStream = new ObjectOutputStream(_clientSocket.getOutputStream());
sendMessage(SOSPFPacket.HELLO);
_inputStream = new ObjectInputStream(_clientSocket.getInputStream());
SOSPFPacket message = Util.receiveMessage(_inputStream);
if (message.sospfType == SOSPFPacket.OVER_BURDENED) {
System.out.println("Removing link with router " + message.srcIP + "...");
_router.removeLink(_remoteRouterIP);
return;
}
_remoteRouterDescription.setStatus(RouterStatus.TWO_WAY);
_router.addLinkDescriptionToDatabase(_remoteRouterDescription, _link.getWeight());
sendMessage(SOSPFPacket.HELLO);
message = Util.receiveMessage(_inputStream);
if (message.sospfType == SOSPFPacket.LSU) {
_router.synchronize(message.lsaArray);
}
_router.propagateSynchronization(message.lsaInitiator, message.srcIP);
} catch (IOException e) {
e.printStackTrace();
}
}
private void sendMessage(short messageType) {
try {
SOSPFPacket message = Util.makeMessage(_rd, _remoteRouterDescription, messageType, _router);
_outputStream.writeObject(message);
_outputStream.flush();
} catch (IOException e) {
e.printStackTrace();
}
}
public class Util {
public static SOSPFPacket makeMessage(RouterDescription local, RouterDescription external, short messageType, Router rd) {
SOSPFPacket message = new SOSPFPacket();
message.srcProcessIP = local.getProcessIPAddress();
message.srcProcessPort = local.getProcessPortNumber();
message.srcIP = local.getSimulatedIPAddress();
message.dstIP = external.getSimulatedIPAddress();
message.sospfType = messageType;
message.routerID = local.getSimulatedIPAddress();
message.neighborID = external.getSimulatedIPAddress();
rd.getLsd().getStore().forEach((k, v) -> message.lsaArray.addElement(v));
message.lsaInitiator = messageType == SOSPFPacket.LSU ? message.srcIP : null;
return message;
}
public static SOSPFPacket receiveMessage(ObjectInputStream inputStream) {
SOSPFPacket receivedMessage = null;
try {
receivedMessage = (SOSPFPacket) inputStream.readObject();
String messageType;
switch (receivedMessage.sospfType) {
case SOSPFPacket.HELLO:
messageType = "HELLO";
break;
case SOSPFPacket.LSU:
messageType = "LINKSTATEUPDATE";
break;
case SOSPFPacket.OVER_BURDENED:
messageType = "OVER_BURDENED";
break;
default:
messageType = "UNKNOWN_STATE";
break;
}
System.out.println("received " + messageType + " from " + receivedMessage.srcIP + ";");
} catch (ClassNotFoundException e) {
System.out.println("No message received.");
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return receivedMessage;
}
}
And the server instantiates a private ClientServiceThread when it receives a new connection, which is in charge of receiving the message.
private class ClientServiceThread implements Runnable {
Socket _clientSocket;
Thread _runner;
ClientServiceThread(Socket s) {
_clientSocket = s;
_runner = new Thread(this);
}
public Thread getRunner() { return _runner; }
public void run() {
ObjectInputStream inputStream = null;
ObjectOutputStream outputStream = null;
try {
inputStream = new ObjectInputStream(_clientSocket.getInputStream());
outputStream = new ObjectOutputStream(_clientSocket.getOutputStream());
while (true) {
try {
SOSPFPacket receivedMessage = Util.receiveMessage(inputStream);
//some logic not relevant since the receivedMessage is already not correct
}
}
}
}
}
Again, all SOSPFPacket fields are correctly received, except for the Vector<LSA> lsaArray...
Edit: I also tried sending a third sendMessage(SOSPFPacket.HELLO) after _router.propagateSynchronization(message.lsaInitiator, message.srcIP);. This time, the message being sent contains two LSA, the first one having two LinkDescription, the second one having one. Both LSA are received by the server, but still, only the first LinkDescription is received in the first LSA. The message id is correct in all three messages.
If I run everything a second time (i.e. I create a new Client and a new ClientService Thread for the already running routers), only then does the server finally receive two LinkDescription in the first LSA.

Java sends references to objects that have already been serialized, to preserve the integrity of object graphs.
You should call ObjectOutputStream.reset() after each writeObject().
Or use ObjectOutputStream.writeUnshared(), but note that it still shares referenced objects, i.e. if you try to send a list with both added and changed element objects, it will send the new list and new element objects, but not the element objects which have been changed.

Finally figured it out. Somehow it seems like the problem was the following line of code in Util.makeMessage: rd.getLsd().getStore().forEach((k, v) -> message.lsaArray.addElement(v));. I replaced it with rd.getLsd().getStore().forEach((k, v) -> message.lsaArray.add(new LSA(v))); with the following LSA constructor:
public LSA(LSA lsa) {
linkStateID = lsa.linkStateID;
lsaSeqNumber = lsa.lsaSeqNumber;
links = new LinkedList<>();
for (LinkDescription ld : lsa.links) {
LinkDescription linkD = new LinkDescription();
linkD.linkID = ld.linkID;
linkD.portNum = ld.portNum;
linkD.tosMetrics = ld.tosMetrics;
links.add(linkD);
}
}
In other words, I needed to deep copy the object contained in my message.