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App for external barcode scanner(use USB port)

Update: came up with new error about the provided java class
I have a tutorial for building an app for an external barcode scanner(use USB port) by using Java + provided Jar Library. I'm trying to build the same app by using the Xamarin.Forms and that Jar Library(through BindingsLibrary Project). However, I got an error
"Java.Lang.NoClassDefFoundError: " when I compiled my code. Does anybody have an idea about what I'm doing wrong?
This my java classes:
The USBScanFactory
package com.unistrong.qrcode;
import com.unistrong.pin.GOPOManager;
public class USBQRscanFactory {
private static USBQRscanFactory factory = new USBQRscanFactory();
static boolean mIsScanContinue = false;
private GOPOManager mGopoManager = GOPOManager.getInstance();
private OnScanListener mScanListener;
private QRScanManagerJNI qrScanManagerJNI;
private USBQRscanFactory() {
}
public static USBQRscanFactory createInstance() {
return factory;
}
public void init(OnScanListener onScanListener) {
this.mGopoManager.Pin11_High();
this.qrScanManagerJNI = new QRScanManagerJNI(onScanListener);
this.qrScanManagerJNI.callbackInit();
}
public void enableAddKeyValue(int i) {
QRScanManagerJNI.AddKeyValue(i);
}
public void open() {
this.mGopoManager.Pin11_Low();
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
QRScanManagerJNI.OpenDev();
}
public void powerOn() {
this.mGopoManager.Pin11_High();
this.mGopoManager.openPower5V_3V3();
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public void powerOff() {
this.mGopoManager.Pin11_High();
this.mGopoManager.closePower5V_3V3();
}
public void scan_start() {
QRScanManagerJNI.QRScan();
}
On ScanListener:
package com.unistrong.qrcode;
public interface OnScanListener {
void scanReport(byte[] bArr);
void statusReport(int i);
}
And here is my code on Xamain:
public class OnScanListener : Java.Lang.Object, IOnScanListener
{
H myH = new H();
public void ScanReport(byte[] byteArray)
{
lock (myH)
{
if (null != byteArray && byteArray.Length > 0)
{
myH.SendMessage(myH.ObtainMessage(0, byteArray));
}
}
}
public void StatusReport(int i)
{
lock (myH)
{
myH.SendEmptyMessage(i);
}
}
}
#endregion
public MainPage()
{
usbScan = USBQRscanFactory.CreateInstance();
InitializeComponent();
}
int count = 0;
private void scanBtn_Clicked(object sender, EventArgs e)
{
count++;
//usbScan.Init(OnScanListener);
OnScanListener myOnScanListener = new OnScanListener();
usbScan.PowerOn();
usbScan.Init(myOnScanListener);
Barcode.Text = "";
openScanner(true);
usbScan.Scan_start();
}
//Open Scanner
private void openScanner(bool open)
{
if (open == mWorkingStateFlag) return;
if (open)
{
try
{
Java.Lang.Thread.Sleep(50);
usbScan.Open();
usbScan.EnableAddKeyValue(0);
}
catch (Java.Lang.InterruptedException e)
{
// TODO Auto-generated catch block
e.PrintStackTrace();
}
}
}

ZuulFallbackProvider not getting invoked

I am trying to have a fallback if Zuul does not find a service. I have the a ZuulSever with the below code:
#SpringBootApplication
#EnableZuulProxy
#EnableDiscoveryClient
public class ZuulServerApplication {
public static void main(String[] args) {
SpringApplication.run(ZuulServerApplication.class, args);
}
#Bean
public ZuulFallbackProvider fallBackProvider() {
return new ZuulFallbackProvider() {
#Override
public ClientHttpResponse fallbackResponse() {
return new ClientHttpResponse() {
#Override
public HttpHeaders getHeaders() {
return null;
}
#Override
public InputStream getBody() throws IOException {
return new ByteArrayInputStream("Hello".getBytes());
}
#Override
public String getStatusText() throws IOException {
// TODO Auto-generated method stub
return "Service Down";
}
#Override
public HttpStatus getStatusCode() throws IOException {
// TODO Auto-generated method stub
return HttpStatus.OK;
}
#Override
public int getRawStatusCode() throws IOException {
// TODO Auto-generated method stub
return 200;
}
#Override
public void close() {
// TODO Auto-generated method stub
}
};
}
#Override
public String getRoute() {
// TODO Auto-generated method stub
return "*";
}
};
}
}
When the service in my route is up and running, I am able to get the output. But when I bring down the service in the route, I expected the fallback to kick in. But I still see an error message instead of the fallback message. Why is the fallback not invoked? I am using Dalston Release version.

If you configure Zuul to directly connect to an URL for your route, it will use SimpleHostRoutingFilter, which will (almost) always return a 500 in case of an error. Any FallbackProviders will not kick in.
I used a custom SimpleHostRoutingFilter instead:
public class CustomErrorHostRoutingFilter extends SimpleHostRoutingFilter {
public CustomErrorHostRoutingFilter(ProxyRequestHelper helper, ZuulProperties properties, ApacheHttpClientConnectionManagerFactory connectionManagerFactory, ApacheHttpClientFactory httpClientFactory) {
super(helper, properties, connectionManagerFactory, httpClientFactory);
}
#Override
protected ZuulException handleException(Exception ex) {
if (ex instanceof ConnectTimeoutException) {
return new ZuulException(ex, "Downstream timeout", HttpServletResponse.SC_GATEWAY_TIMEOUT, ex.getMessage());
}
if (ex instanceof IOException) {
return new ZuulException(ex, "Downstream I/O error", HttpServletResponse.SC_SERVICE_UNAVAILABLE, ex.getMessage());
}
return super.handleException(ex);
}
}
Some kind of configuration class is required as well:
#Configuration
#EnableZuulProxy
public class ZuulConfiguration {
#Bean
public SimpleHostRoutingFilter simpleHostRoutingFilter(ProxyRequestHelper helper,
ZuulProperties zuulProperties,
ApacheHttpClientConnectionManagerFactory connectionManagerFactory,
ApacheHttpClientFactory httpClientFactory) {
return new CustomErrorHostRoutingFilter(helper, zuulProperties, connectionManagerFactory, httpClientFactory);
}
}

JAVA RMI get pass ArrayList element

I have a server that contains an ArrayList in " ServerInfo " and when I try to take from ClientRMI an element of the ArrayList(in ServerInfo) for example adf.getSGM ( 0 ).incrementCount( ) ;
"count" does not increase it's as if every time I call it instantiates a new class SGM
in a few words I want to interact from ClientRMI with ArrayList that is on ServerInfo (SORRY FOR ENGLISH)
Hear are the classes :
SERVER
public class ServerRMI {
public static void main(String[] args) {
Registry registry = null;
String name = "ServerInfo";
try {
System.out.println("Init RMI");
ServerInfoInterface sir = ServerInfo.getInstance();
ServerInfoInterface stub = (ServerInfoInterface) UnicastRemoteObject.exportObject(sir, 0);
registry = LocateRegistry.createRegistry(9000);
registry.bind(name, stub);
System.out.println("RMI OK");
System.out.println("Init SGM...");
for(int i=0;i<3;i++){
ServerInfo.getInstance().addSGM(new SGM());
}
System.out.println("Init SGM OK");
} catch (Exception e) {
System.out.println("RMI Error"+e.toString());
registry = null;
}
}
}
public class ServerInfo implements ServerInfoInterface{
private ArrayList<SGM> sgmHandler = new ArrayList<SGM>();
// Singleton pattern
private static ServerInfo instance;
// Singleton pattern
public static ServerInfo getInstance() {
if (instance == null){
System.out.println("ServerInfo new instance");
instance = new ServerInfo();
}
return instance;
}
#Override
public synchronized void addSGM(SGM sgm) throws RemoteException {
sgmHandler.add(sgm);
}
#Override
public synchronized SGM getSGM(int i) throws RemoteException {
return sgmHandler.get(i);
}
}
public interface ServerInfoInterface extends Remote{
public void addSGM(SGM sgm) throws RemoteException;
public SGM getSGM(int i) throws RemoteException;
}
public class SGM implements Serializable{
/**
*
*/
private static final long serialVersionUID = -4756606091542270097L;
private int count=0;
public void incrementCount(){
count++;
}
public void decrementCount(){
count--;
}
public int getCount(){
return count;
}
}
CLIENT
public class ClientRMI {
private ServerInfoInterface sgmInterface;
public void startServer() {
String name = "ServerInfo";
Registry registry;
try {
registry = LocateRegistry.getRegistry(9000);
try {
sgmInterface = (ServerInfoInterface) registry.lookup(name);
sgmInterface.getSGM(0).incrementCount();
System.out.println(sgmInterface.getSGM(0).getCount()); // always 0
} catch (AccessException e) {
System.out.println("RIM AccessException"+ e.toString());
} catch (RemoteException e) {
System.out.println("RIM RemoteException"+ e.toString());
} catch (NotBoundException e) {
System.out.println("RIM NotBoundException"+ e.toString());
}
} catch (RemoteException e) {
System.out.println("RIM RemoteException registry"+ e.toString());
}
}
}

You're creating an SGM at the server, passing it via Serialization to the client, incrementing its count at the client, and then expecting that count to be magically increased at the server.
It can't work.
You will have to make SGM a remote object, with its own remote interface, or else provide a remote method in the original remote interface to increment the count of a GSM, specified by index.

Issue invoking WatchService inside a singleton bean

we wanted to watch a file periodically for changes, we are using jboss 7 . Following is my code snippet. I initialized the watcher in the postconstruct method of singleton bean and scheduled a method to poll watch events. I could observe the changes when i modify the file very first time, however the subsequent modifications to the file are not recieved . Can anyone please let me know what could be the issue
#Startup
#ConcurrencyManagement(ConcurrencyManagementType.BEAN)
#Interceptors(NonThrowingPostConstructInterceptor.class)
#Singleton
#Service
#LocalBinding(jndiBinding=IHeartBeatProducerService.JNDI_LOCAL_BINDING)
public class HeartBeatProducerService extends EMSingletonService implements IHeartBeatProducerService{
#EJB(mappedName=IMessageService.JNDI_LOCAL_BINDING)
public IMessageService messageService;
#EJB(mappedName=ICommandExecutionService.JNDI_LOCAL_BINDING)
public ICommandExecutionService commandService;
private final static String LAST_OPERATION_COMPLETED="Last Operation Completed";
private final static String STATUS="Status";
private WatchService watcher;
private Path dir;
private String concServer;
public static final String TOPIC="foo";
private IMLogger logger = new IMLogger("foo");
private String content=null;
#PostConstruct
#Override
public void init() {
// TODO Auto-generated method stub
super.init();
try {
watcher = FileSystems.getDefault().newWatchService();
dir=Paths.get("/shared/foo");
dir.register(watcher, StandardWatchEventKinds.ENTRY_MODIFY);
logger.entering(0, IHeartBeatProducerService.class.getSimpleName(), "Initializing Heart Beat", new String[]{"Entered"});
} catch (IOException e) {
e.printStackTrace();
}
}
#Schedule(second="*/10", minute = "*", hour="*")
private void checkStatus()
{
logger.entering(0, IHeartBeatProducerService.class.getSimpleName(), "Checking Status", new String[]{"Entered"});
final String[] command={"pidof","server"};
commandService.run(command, null, false);
concServer=(commandService.getExitCode()==0)?"UP":"DOWN";
if(concServer.equals("UP"))
{
watch();
}
else
{
content="foo:Failed";
}
produce();
}
public void watch()
{
logger.entering(0, IHeartBeatProducerService.class.getSimpleName(), "Entering watch()", new String[]{"Entered"});
WatchKey key = null;
try
{
key = watcher.take();
}
catch (InterruptedException e)
{
logger.error(HeartBeatProducerService.class.getSimpleName(),"Interupted Exception " + e.getMessage());
}
for ( WatchEvent<?> event: key.pollEvents())
{
WatchEvent.Kind kind = event.kind();
logger.info(HeartBeatProducerService.class.getSimpleName(),"Watch Event :" + kind.name());
if(kind.name().equals("OVERFLOW"))
{
continue;
}
if(kind.name().equals("ENTRY_MODIFY"))
{
Path concLog = (Path) event.context();
logger.info(HeartBeatProducerService.class.getSimpleName(),"Modified File Name:" + concLog.getFileName());
if(concLog.endsWith("current_status.txt"))
{
logger.info(HeartBeatProducerService.class.getSimpleName(), "Reading Status");
readStatus();
}
}
}
boolean valid = key.reset();
if ( !valid)
{
logger.error(HeartBeatProducerService.class.getSimpleName(),"Key Unregistered");
}
}
private void parse(String output)
{
// parse file contents
}
private void readStatus() {
//read status and parse()
}
private void produce()
{
try {
messageService.publish(TOPIC, content, PublishType.ASync);
} catch (MessageException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
There is already a link explaining the same with #Asynchronous tag (EJB 3.1 and NIO2: Monitoring the file system) . however I need to know what could be wrong in this approach.

Your watch method needs to run in an infinite loop. What's happening now is that after
try {
key = watcher.take();
}
you process the event and then the watch() method is finished. Try the effect of
for(;;) {
before the above lines, ending the for block after the validity check. Did you see the example at The Java Tutorials?

Decision to make a class static

I have the server project that I have seperated into 6 different classes:
ServerConnectionManager - is class is ment to be the hub for all other classes
Connection - This object is the created whenever a client connects and also starts a Thread
ServerListner - This is the Thread class that listens to input from the user
ServerSender - This is the class that sends messages to one or more users
ServerInformation - this class contains two list one of chat persons and one of connections this class also allows you to search through the list to find a specefic person and or connection
ChatPerson - This object is to contain the username of each person who connects to the server
As you no-doubt have guessed by now this is a server for a chat program!
My question to you is:
I want to use the Design patteren (Mediator) on this project and therefore the ServerConnectionManager contains all the key methods that each of the classes use. for example adding a connection to the connection list in the ServerInformation class.
But since the ServerInformation class cannot be called an object seeing as it only have alot of methods (functions) and no real purpose other than storing and searching Data would it be a good idea to make it static? or should i stick to the plan and make everything go through the ServerConnectionManager?
Here is a sample of my code:
ServerConnectionManager
public class ServerConnectionManager {
private static ServerSocket server;
private static Socket connection;
private static ServerInformation ai = new ServerInformation();
private static boolean connected = false;
private static final int portNumber = 7070;
private static int backLog = 100;
/**
* This method launches the server (and the application)!
* #param args
*/
public static void main(String[] args){
startServer();
waitForConnection();
}
/**
*This method sets the serverSocket to portNumber and also adds the backLog.
*/
private static void startServer() {
try {
server = new ServerSocket(portNumber, backLog);
connected = true;
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* This method waits for a connection aslong as the serverSocket is connected.
* When a new client connects it creates an Object of the connection and starts the individual procedure.
*/
private static void waitForConnection() {
while (connected) {
try {
connection = server.accept();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Connection c = new Connection(connection);
addConnection(c);
waitForConnection();
}
}
public static void closeMe(Socket con) {
for (Connection conn : ai.getConnectionList()) {
if (conn.getConnection() == con) {
ai.getList().remove(ai.getList().indexOf(ai.getChatPersonByConnection(con)));
ai.getConnectionList().remove(conn);
System.out.println(ai.getList());
System.out.println(ai.getConnectionList());
conn.close();
break;
}
}
}
public static void addConnection(Connection con){
ai.addToConnectionList(con);
}
public static void addChatPerson(ChatPerson p){
ai.add(p);
System.out.println(ai.getList());
}
}
Connection
public class Connection{
private Socket connection;
public Connection(Socket connection){
this.connection = connection;
ServerListner cl = new ServerListner(Connection.this);
cl.start();
}
public Socket getConnection(){
return this.connection;
}
public void close() {
try {
connection.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
ServerListner
public class ServerListner extends Thread {
private Socket connection;
private BufferedReader br;
private ChatPerson person;
private Connection con;
private ServerInformation ai = new ServerInformation();
private ServerSender sender = new ServerSender();
public ServerListner(Connection con){
this.con = con;
connection = con.getConnection();
try {
br = new BufferedReader(new InputStreamReader(connection.getInputStream()));
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public Socket getConnection(){
return this.connection;
}
public void run(){
System.out.println(con.getConnection().isConnected());
try {
String inString;
while ((inString = br.readLine()) != null) {
if (inString.equalsIgnoreCase("Disconnect")) {
System.out.println(inString);
break;
}else {
processInput(inString);
}
}
ServerConnectionManager.closeMe(connection);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public void processInput(String input){
if (input.equalsIgnoreCase("Connect")) {
sender.sendMessageToConnection(this.connection, "Accepted");
}
if (input.equalsIgnoreCase("UserInformation")) {
try {
String username = br.readLine();
person = new ChatPerson(username, connection);
ServerConnectionManager.addChatPerson(person);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if (input.equalsIgnoreCase("SearchByCon")) {
String name = ai.searchByConnection(connection);
System.out.println(name);
}
}
}
ServerSender
public class ServerSender {
private PrintWriter pw;
private ServerInformation ai = new ServerInformation();
public void addToList(){
}
public void sendToAll(String message){
for (Connection c : ai.getConnectionList()) {
try {
pw = new PrintWriter(c.getConnection().getOutputStream());
pw.print(message);
pw.flush();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
/**
*
* #param con
* #param message
*/
/*
* Note - Denne metode gør også at jeg kan hviske til folk!:)
*/
public void sendMessageToConnection(Socket con, String message){
try {
PrintWriter print = new PrintWriter(con.getOutputStream());
print.println(message);
print.flush();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
ServerInformation
public class ServerInformation{
private ArrayList<Connection> connectedClients = new ArrayList<Connection>();
private ArrayList<ChatPerson> list = new ArrayList<ChatPerson>();
public ArrayList<Connection> getConnectionList(){
return connectedClients;
}
public void addToConnectionList(Connection con){
connectedClients.add(con);
}
public String searchByConnection(Socket myConnection){
for (ChatPerson p : list) {
if (p.getConnection() == myConnection) {
return p.getName();
}
}
/*
* If none found!
*/
return null;
}
public ChatPerson getChatPersonByConnection(Socket myConnection){
for (ChatPerson p : list) {
if (p.getConnection() == myConnection) {
return p;
}
}
return null;
}
public void add(ChatPerson p){
list.add(p);
}
public void removeByName(String name){
for (ChatPerson p : list) {
if (p.getName().equalsIgnoreCase(name)) {
list.remove(p);
}
}
}
public String searchList(String name){
for (ChatPerson p : list) {
if (p.getName().equalsIgnoreCase(name)) {
return p.getName();
}
}
return null;
}
public ArrayList<ChatPerson>getList(){
return list;
}
}
ChatPerson
public class ChatPerson {
private String chatName;
private Socket connection;
/*
* This is for furture development
* private Integer adminLevel;
*/
public ChatPerson(String name, Socket connection){
this.chatName = name;
this.connection = connection;
}
public void setName(String name){
this.chatName = name;
}
public String getName(){
return chatName;
}
public String toString(){
return "Username: "+chatName;
}
public Socket getConnection(){
return connection;
}
}
Thank you in advance, by the way since i am a student it would be nice if you had time to rate my code aswell and come with suggestions on how i can improve (if there are any :))

You probably meant class with only static methods, not static class. Static inner classes are something different (you can google it).
Advantages of having non-static methods in your manager:
You can easily mock them with frameworks like Mockito during testing.
You can pull them up to some interface during refactoring of your code.
Using static methods is not object-oriented-programming as such method invocations are not associated with any instance (object) of your class.