I have a method which tries to get the current message in an arraylist of mesages and if there are none then it returns null, however I get an index out of bounds exception and I can't understand why
public Message getCurrent() {
if(this.size() <= 0) {
return null;
}else {
return this.get(currentMessageIndex);
}
}
The following calls the above method in another class and throws the exception:
public void run() {
while (running) {
//Message msg = clientQueue.getLast(); // Matches EEEEE in ServerReceiver
Message msg = clientQueue.getCurrent();
System.out.flush();
if (msg != null) {
if (msg.getSent() == false) {
client.println(msg);// Matches FFFFF in ClientReceiver
client.flush();
msg.setSent();
}
}
}
return;
}
public Message getCurrent() {
if(this.size() <= 0) {
return null;
}else {
return (this.size() > currentMessageIndex) ? this.get(currentMessageIndex) : null;
}}
Can you try with this, I have handled fail over case.
Just use
this.size()-1
Instead of
this.size()
Related
The fact is that I need to simultaneously pull in data from the local database, from the server, while checking the connection to the Internet.
Without checking the internet is easy. But when I turn off mobile data, crashes.
I do not understand how to combine and decided to do this:
private void getCategories() {
composite.add(getDataFromLocal(context)
.observeOn(AndroidSchedulers.mainThread()).flatMap(new Function<PromoFilterResponse, ObservableSource<List<FilterCategory>>>() {
#Override
public ObservableSource<List<FilterCategory>> apply(PromoFilterResponse promoFilterResponse) throws Exception {
if (promoFilterResponse != null) {
PreferencesHelper.putObject(context, PreferencesKey.FILTER_CATEGORIES_KEY, promoFilterResponse);
return combineDuplicatedCategories(promoFilterResponse);
} else {
return Observable.empty();
}
}
})
.subscribe(new Consumer<List<FilterCategory>>() {
#Override
public void accept(List<FilterCategory> categories) throws Exception {
if (mView != null) {
mView.hideConnectingProgress();
if (categories != null && categories.size() > 0) {
mView.onCategoriesReceived(categories);
}
}
}
}));
composite.add(InternetUtil.isConnectionAvailable().subscribe(isOnline -> {
if (isOnline) {
composite.add(
getDataFromServer(context)
.flatMap(new Function<PromoFilterResponse, ObservableSource<List<FilterCategory>>>() {
#Override
public ObservableSource<List<FilterCategory>> apply(PromoFilterResponse promoFilterResponse) throws Exception {
if (promoFilterResponse != null) {
PreferencesHelper.putObject(context, PreferencesKey.FILTER_CATEGORIES_KEY, promoFilterResponse);
return combineDuplicatedCategories(promoFilterResponse);
} else {
return Observable.empty();
}
}
})
.observeOn(AndroidSchedulers.mainThread())
.subscribe(categories -> {
if (mView != null) {
mView.hideConnectingProgress();
if (categories != null && categories.size() > 0) {
mView.onCategoriesReceived(categories);
} else {
mView.onCategoriesReceivingFailure(errorMessage[0]);
}
}
}, throwable -> {
if (mView != null) {
if (throwable instanceof HttpException) {
ResponseBody body = ((HttpException) throwable).response().errorBody();
if (body != null) {
errorMessage[0] = body.string();
}
}
mView.hideConnectingProgress();
mView.onCategoriesReceivingFailure(errorMessage[0]);
}
}));
} else {
mView.hideConnectingProgress();
mView.showOfflineMessage();
}
}));
}
private Single<Boolean> checkNetwork(Context context) {
return InternetUtil.isConnectionAvailable()
.subscribeOn(Schedulers.io())
.doOnSuccess(new Consumer<Boolean>() {
#Override
public void accept(Boolean aBoolean) throws Exception {
getDataFromServer(context);
}
});
}
private Observable<PromoFilterResponse> getDataFromServer(Context context) {
return RetrofitHelper.getApiService()
.getFilterCategories(Constants.PROMO_FILTER_CATEGORIES_URL)
.subscribeOn(Schedulers.io())
.retryWhen(BaseDataManager.isAuthException())
.publish(networkResponse -> Observable.merge(networkResponse, getDataFromLocal(context).takeUntil(networkResponse)))
.doOnNext(new Consumer<PromoFilterResponse>() {
#Override
public void accept(PromoFilterResponse promoFilterResponse) throws Exception {
PreferencesHelper.putObject(context, PreferencesKey.FILTER_CATEGORIES_KEY, promoFilterResponse);
}
})
.doOnError(new Consumer<Throwable>() {
#Override
public void accept(Throwable throwable) throws Exception {
LogUtil.e("ERROR", throwable.getMessage());
}
});
}
private Observable<PromoFilterResponse> getDataFromLocal(Context context) {
PromoFilterResponse response = PreferencesHelper.getObject(context, PreferencesKey.FILTER_CATEGORIES_KEY, PromoFilterResponse.class);
if (response != null) {
return Observable.just(response)
.subscribeOn(Schedulers.io());
} else {
return Observable.empty();
}
}
As you can see, connect the local database separately, simultaneously check the Internet and upload data from the server.
But it seems to me not quite right. Moreover, the subscriber is duplicated and so on.
I saw a lot of tutorials, where the combination of the local database with the API is described, but I did not see it at the same time processing the connection error with the Internet.
I think many people faced such a problem and how did you solve it?
Suppose You have two Obsevable: one from server and another from database
You can merge them into one stream like below:
public Observable<Joke> getAllJokes() {
Observable<Joke> remote = mRepository.getAllJokes()
.subscribeOn(Schedulers.io());
Observable<Joke> local = mRepository.getAllJokes().subscribeOn(Schedulers.io());
return Observable.mergeDelayError(local, remote).filter(joke -> joke != null);
}
Im' not android developer, but in my mind methods return types should be something like this:
//just for demonstration
static boolean isOnline = false;
static class NoInternet extends RuntimeException {
}
private static Completable ensureOnline() {
if (isOnline)
return Completable.complete();
else
return Completable.error(new NoInternet());
}
private static Single<String> getDataFromServer() {
return Single.just("From server");
}
private static Maybe<String> getDataFromLocal() {
return Maybe.just("From local");//or Maybe.never()
}
We can run all in parallel with Observable.merge. But what if error NoIternet happens? Merged observable will fail. We can use materialisation - transform all emission and errors to onNext value.
private static void loadData() {
Observable<Notification<String>> fromServer = ensureOnline().andThen(getDataFromServer()).toObservable().materialize();
Observable<Notification<String>> fromLocaldb = getDataFromLocal().toObservable().materialize();
Observable.merge(fromLocaldb, fromServer)
.subscribe(notification -> {
if (notification.isOnNext()) {
//calls one or two times(db+server || db || server)
//show data in ui
} else if (notification.isOnError()) {
if (notification.getError() instanceof NoInternet) {
//show no internet
} else {
//show another error
}
} else if (notification.isOnComplete()){
//hide progress bar
}
});
}
Have method for insert elements in array.
public boolean insertElementToSlot(Element element, int index) {
checkArray(index);
try {
if (element != null && mas[index] == null) {
mas[index] = element;
return true;
} else {
throw new ElementValidationException("Element.insertElementToSlot", device);
}
} catch (ElementValidationException d) {
logger.log(Level.SEVERE, ""+d);
}
return false;
}
And own exception class with method:
public ElementValidationException(String operation, Element element) {
super("Element is not valid for operation" + checkOperation(operation));
this.element = element;
}
When testing method insertElementToSlot, I have error
java.lang.AssertionError: Expected exception: com.inventory.exception.ElementValidationException
Why is the error related and how to solve it?
If you have a unit test which expects an exception, it has to be thrown out of the test. It doesn't check that this exception is thrown anywhere in the code but caught.
NOTE: your exception isn't being used as an exception and could be replaced with a log message
Your code is basically the same as
public boolean insertElementToSlot(Element element, int index) {
checkArray(index);
if (element != null && mas[index] == null) {
mas[index] = element;
return true;
}
logger.log(Level.SEVERE, "some.package.ElementValidationException");
return false;
}
Actually I make an update through Bluetooth. In first time I erase the memory bank and then I write an hexa File on it.
But half the time an update will don't work correctly, for every data I transfer the first writeCharacteristic will return false.
It happen on an entire update half the time.
I try in debug mode but the method never return false in that case, of course it's probably a delay problem, but I can't increase the time.
This is my code for send my data :
public void sendTX(final byte[] sMessage) {
BluetoothGattService service = mBluetoothGatt.getService(UUID_SERVICE_SERIAL);
if (service != null && sMessage != null) {
Log.d(TAG,"sMessage : " + sMessage);
final BluetoothGattCharacteristic characteristic = service.getCharacteristic(UUID_TX);
if (characteristic != null) {
Thread thread = new Thread() {
public void run() {
if (sMessage.length > 20) {
for (int i = 0; i < sMessage.length; i += 20) {
byte[] byteArraySplit = Arrays.copyOfRange(sMessage, i, i + 20 < sMessage.length ? i + 20 : sMessage.length);
characteristic.setWriteType(BluetoothGattCharacteristic.WRITE_TYPE_NO_RESPONSE);
characteristic.setValue(byteArraySplit);
while(!mBluetoothGatt.writeCharacteristic(characteristic)) {
try {
TimeUnit.MILLISECONDS.sleep(15);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
} else {
characteristic.setWriteType(BluetoothGattCharacteristic.WRITE_TYPE_NO_RESPONSE);
characteristic.setValue(sMessage);
while(!mBluetoothGatt.writeCharacteristic(characteristic)){
try {
TimeUnit.MILLISECONDS.sleep(15);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
};
thread.start();
} else {
Log.d(TAG, "UUID TX null");
}
} else {
Log.d(TAG, "Service BLE null");
}
}
And this is the code of the native writeCharacteristic method :
public boolean writeCharacteristic(BluetoothGattCharacteristic characteristic) {
if ((characteristic.getProperties() & BluetoothGattCharacteristic.PROPERTY_WRITE) == 0
&& (characteristic.getProperties() &
BluetoothGattCharacteristic.PROPERTY_WRITE_NO_RESPONSE) == 0) return false;
if (VDBG) Log.d(TAG, "writeCharacteristic() - uuid: " + characteristic.getUuid());
if (mService == null || mClientIf == 0 || characteristic.getValue() == null) return false;
BluetoothGattService service = characteristic.getService();
if (service == null) return false;
BluetoothDevice device = service.getDevice();
if (device == null) return false;
synchronized(mDeviceBusy) {
if (mDeviceBusy) return false;
mDeviceBusy = true;
}
try {
mService.writeCharacteristic(mClientIf, device.getAddress(),
characteristic.getInstanceId(), characteristic.getWriteType(),
AUTHENTICATION_NONE, characteristic.getValue());
} catch (RemoteException e) {
Log.e(TAG,"",e);
mDeviceBusy = false;
return false;
}
return true;
}
Never use timeouts to try to workaround this issue. The proper way is to wait for the callback and then perform the next request. See Android BLE BluetoothGatt.writeDescriptor() return sometimes false.
I need to see the result as a boolean result: true. But there's a catch I need to do it in a non-ordinary way.
import java.io.IOException;
public class FlashLight {
private Bulb bulb;
private Battery[] batteries;
public void on() {
try {
if (this.IsThereEnoughPower()) {
this.bulb.setOn(true);
for (Battery b : batteries) {
b.setPower(b.getPower() - this.bulb.getBrightness());
}
}
} catch (IOException e) {
System.out.println(e.getMessage());
this.setBatteries(new Battery[4]);
}
}
I need to catch the exception in method on() but i can only modify method: DetermineIfFlashlightCanBeTurnedOn
public boolean DetermineIfFlashlightCanBeTurnedOn() throws IOException {
return bulb != null && DetermineIfBatteriesAreInstalled() && IsThereEnoughPower();
}
private boolean DetermineIfBatteriesAreInstalled() throws IOException {
if (batteries.length < 4) {
throw new IOException(Math.abs(-4 + batteries.length));
}
for (Battery b : batteries) {
if (b == null) {
return false;
}
}
return true;
}
private boolean IsThereEnoughPower() {
for (Battery b : batteries) {
if (b.getPower() < MIN_BATTERY_POWER) {
return false;
}
}
return true;
}
private static void testLatarki(String... args) {
FlashLight flashlight = new Flashlight();
System.out.println(flashlight.DetermineIfFlashlightCanBeTurnedOn());
}
}
Exception can be caught only in on() method.
DetermineIfBatteriesAreInstalled() DetermineIfFlashlightCanBeTurnedOn
must be signed as: throws IOException.
You can use try{}catch(){} instead :
public boolean DetermineIfFlashlightCanBeTurnedOn() {
try {
return bulb != null && DetermineIfBatteriesAreInstalled() && IsThereEnoughPower();
} catch (Exception e) {
//log your exception
}
return false;
}
I forgot to tell you guys i can use try/catch blocks only in on()
method
In this case you can use RuntimeException you don't need to use throws IOException in your method:
if (batteries.length < 4) {
throw new RuntimeException(Math.abs(-4 + batteries.length)+"");
}
So :
public boolean DetermineIfFlashlightCanBeTurnedOn() {
//--not need to use throw throws IOException-------^
return bulb != null && DetermineIfBatteriesAreInstalled() && IsThereEnoughPower();
}
private boolean DetermineIfBatteriesAreInstalled() {
//--not need to use throw throws IOException------^
if (batteries.length < 4) {
throw new RuntimeException(Math.abs(-4 + batteries.length) + "");
//----------^^
}
for (Battery b : batteries) {
if (b == null) {
return false;
}
}
return true;
}
You can read more here Is there a way to throw an exception without adding the throws declaration?
We have a java socket program where the server gets data from many devices and works fine. At times the server needs to send some command to the devices. When it sends individual commands it works fine. The problem comes when it sends multiple commands, only the first one is successful. We cant figure out why the rest fails. Below is the snippet showing how the message is sent. Should I set a delay after a message is sent?
public static void main(String[] args) {
new sServer7888();
}
sServer7888() {
try{
final ServerSocket serverSocketConn = new ServerSocket(7888);
while (true){
try{
Socket socketConn1 = serverSocketConn.accept();
new Thread(new ConnectionHandler(socketConn1)).start();
}
catch(Exception e){
e.printStackTrace(System.out);
}
}
}
catch (Exception e) {
e.printStackTrace(System.out);
}
}
class ConnectionHandler implements Runnable {
private Socket receivedSocketConn1;
ConnectionHandler(Socket receivedSocketConn1) {
this.receivedSocketConn1=receivedSocketConn1;
}
public void run() {
while ((nextChar=readIn1.read()) != -1) {
completeMessage += (char) nextChar;
if (nextChar == '*')
{
String[] splitResult = completeMessage .split(",");
String header=splitResult[0].trim().substring(0,4);
if((header.equals("$ACK")){
//update the message sent from the server as already acknowledge.
}
else{
//run query to find if there are any message to be sent out to the devices
while(rsOC1.next()){
commandText = rsOC1.getString("commandText");
writeOut1.write(commandText);
writeOut1.write("\r\n");
writeOut1.flush();
}
//now process the normal message receive from the devices.
}
completeMessage="";
}
}
}
}
If your device is sending ACK on Every message and Server is able to receive it then you can proceed in following way with your server side program.
EDIT
I have updated the code as per the requirement analysis. Let me know if any discrepancy is found after implementing it.
Thread.sleep(1000) is not the reliable solution for above case because
we are not knowing how long the device might take to execute previous
command sent by Server .
public void run()
{
int i = -1;
ArrayList<String> list = new ArrayList<String>();
while ((nextChar=readIn1.read()) != -1)
{
boolean isCompleteMessage = readMessage(nextChar);
if (isCompleteMessage)
{
String[] splitResult = completeMessage .split(",");
String header=splitResult[0].trim().substring(0,4);
if((header.equals("$ACK"))
{
String id = null;
if (i != -1)
{
id = list.get(i);
id = id.substring(0,id.indexOf("^"));
}
//update the message sent from the server as already acknowledge using id extracted above.
if ( i == 0)
{
list.remove(i);
if (list.size() == 0)
{
i = -1;
}
else
{
commandText = list.get(i);
writeOut1.write(commandText.substring((commandText.indexOf("^")) + 1));
writeOut1.write("\r\n");
writeOut1.flush();
}
}
}
else
{
//process here the normal message receive from the devices.
if (i == -1)
{
list = getRecords();
if (list.size() > 0)
{
i = 0;
commandText = list.get(i);
writeOut1.write(commandText.substring((commandText.indexOf("^")) + 1));
writeOut1.write("\r\n");
writeOut1.flush();
}
}
else
{
commandText = list.get(i);
writeOut1.write(commandText.substring((commandText.indexOf("^")) + 1));
writeOut1.write("\r\n");
writeOut1.flush();
}
}
completeMessage = "";
}
}
}
public boolean readMessage(int nextChar)
{
completeMessage += (char)nextChar;
if (((char)nextChar) == '*')
{
return true;
}
else
{
return false;
}
}
//Retreive all commands from database and returns the ArrayList containing those commands.
public ArrayList<String> getRecords()
{
ArrayList<String> list = new ArrayList<String>();
Statement stat = null;
ResultSet rsOC1 = null;
try
{
stat = con.createStatement();
rsOC1 = stat.executeQuery("Query for message retrieval from database");
while (rsOC1.next())
{
String sElement = rs0C1.getString("commandID") + "^" + rs0C1.getString("commandText");
list.add(sElement);
}
}
catch (Exception ex){}
finally
{
if (rs0C1 != null)
{
try
{
rs0C1.close();
} catch () {}
}
if (stat != null)
{
try
{
stat.close();
} catch () {}
}
return list;
}
}