If I have the following code:
let submitButton = document.getElementById("submitButton");
Is the following event handler correct?
submitButton.addEventListener("click", "");
Related
I'm using vert.x-web to implement a small service. One of my handlers for the end of the request (set via context.request().endHandler()) throws this NullPointerException:
2018-09-02 20:54:35,125 - ERROR [vert.x-eventloop-thread-1] (ContextImpl.java:345) - lambda$wrapTask$2()
Unhandled exception
java.lang.NullPointerException
at (My handler class)
at io.vertx.core.http.impl.HttpServerRequestImpl.handleEnd(HttpServerRequestImpl.java:417)
at io.vertx.core.http.impl.Http1xServerConnection.handleEnd(Http1xServerConnection.java:482)
at io.vertx.core.http.impl.Http1xServerConnection.handleContent(Http1xServerConnection.java:477)
at io.vertx.core.http.impl.Http1xServerConnection.processMessage(Http1xServerConnection.java:458)
at io.vertx.core.http.impl.Http1xServerConnection.handleMessage(Http1xServerConnection.java:144)
at io.vertx.core.http.impl.HttpServerImpl$ServerHandlerWithWebSockets.handleMessage(HttpServerImpl.java:712)
at io.vertx.core.http.impl.HttpServerImpl$ServerHandlerWithWebSockets.handleMessage(HttpServerImpl.java:619)
at io.vertx.core.net.impl.VertxHandler.lambda$channelRead$1(VertxHandler.java:146)
at io.vertx.core.impl.ContextImpl.lambda$wrapTask$2(ContextImpl.java:337)
at io.vertx.core.impl.ContextImpl.executeFromIO(ContextImpl.java:195)
at io.vertx.core.net.impl.VertxHandler.channelRead(VertxHandler.java:144)
Why doesn't this exception call my requests's exception handler? Why is it unhandled? I have the request's exception handler set to context.fail() (via context.request().exceptionHandler()). But it does not seem to have any effect.
Is there another exception handler I'm unaware of?
Edit: here is the minimal reproducing code:
Vertx vertx = Vertx.vertx();
Router router = Router.router(vertx);
router.route().handler(context -> {
context.request()
.exceptionHandler(context::fail)
.endHandler(nothing -> { throw new NullPointerException("null"); })
.handler(buffer -> {});
});
vertx.createHttpServer()
.requestHandler(router::accept)
.listen(8080);
Expected behavior: context.fail(e) gets called and the connection closes with HTTP ERROR 500.
Got behavior: context is not failed, connection "hangs".
The exceptionHandler applies to the HttpServerRequest object. The method is inherited from the ReadStream interface. This callback is invoked whenever a problem occurs in the Vert.x/Netty code handling HTTP requests, not user code.
If you want to execute some code before the actual request processing, I would suggest to register a route and invoke RoutingContext#next in the handler:
Router router = Router.router(vertx);
router.route("/somepath").handler(routingContext -> {
// Handler invoked first
// Execute pre-processing logic
// And then...
context.next();
});
router.route("/somepath").handler(routingContext -> {
// Handler invoked second
// Execute processing logic
});
Then any failure in pre-processing logic will be caught and managed normally by the router.
Two things need to be pointed out here:
The hang is caused by the response is not explicitly ended (see HttpServerResponse#end().
To handle exception happened during request handling, add failure handler at route level (see Route#failureHandler()). Handling exception on request will only caught exception when reading the stream.
For example:
Router router = Router.router(vertx);
router.route().failureHandler(handler -> handler.response().end());
router.route().handler(routingContext -> routingContext.request().endHandler(handler -> {
throw new NullPointerException("exception here!");
}));
vertx.createHttpServer().requestHandler(router::accept).listen(8085);
We have recently discovered the failureHandler in the Vertx router
We thought it could help us get rid of all the repetitive try-catch blocks we have. But alas, it seems that the exceptions that are thrown inside the callbacks are not caught by the failureHandler.
Example: below, the failureHandler is called only for the 3rd case:
// Get the user details
router.get("/user").handler(ctx -> {
ctx.response().headers().add("content-type", "application/json");
// some async operation
userApiImpl.getUser(ctx, httpClient, asyncResult -> {
// ctx.response().setStatusCode(404).end(); //1
// throw new RuntimeException("sth happened"); //2
ctx.fail(404); //3
});
});
// ============================
// ERROR HANDLER
// ============================
router.get("/user").failureHandler(ctx -> {
LOG.info("Error handler is in the action.");
ctx.response().setStatusCode(ctx.statusCode()).end("Error occurred in method");
});
Is this as expected?
Can we somehow declare a global try-catch in a router for the exceptions occurring in the async context?
It is expected that sending a response manually with an error code does not trigger the failure handler.
It should be triggered if:
the route path matches
a handler throws an exception or ctx.fail() is invoked
Here's an example:
Route route1 = router.get("/somepath/path1/");
route1.handler(routingContext -> {
// Let's say this throws a RuntimeException
throw new RuntimeException("something happened!");
});
Route route2 = router.get("/somepath/path2");
route2.handler(routingContext -> {
// This one deliberately fails the request passing in the status code
// E.g. 403 - Forbidden
routingContext.fail(403);
});
// Define a failure handler
// This will get called for any failures in the above handlers
Route route3 = router.get("/somepath/*");
route3.failureHandler(failureRoutingContext -> {
int statusCode = failureRoutingContext.statusCode();
// Status code will be 500 for the RuntimeException or 403 for the other failure
HttpServerResponse response = failureRoutingContext.response();
response.setStatusCode(statusCode).end("Sorry! Not today");
});
See the error handling section of the Vert.x Web documentation
I have following problem: I would like to send CAN messages out of a callback function. This callback function is called by an timerobject. Everytime when the callback function is executed it should send the CAN message.
I coded:
canch = canChannel('PEAK-System', 'PCAN_USBBUS1');
configBusSpeed(canch, 1000000)
start(canch)
canch.Database = canDatabase('\\psf\Home\Desktop\02 CAN DBC\CAN4.dbc');
message = canMessage (canch.Database,'IPSS_RX_1_1ms');
transmitPeriodic(canch,message, 'On', 0.01);
T= timer('ExecutionMode','fixedrate','Period',0.2,...
'TimerFcn',#TEST_timer_callback_fcn,'StopFcn','disp(''Timer has stopped'')');
start(T)
Callback function:
function TEST_timer_callback_fcn(src,event)
message.Signals.In_ti= 39;
The CAN Channel starts - but the message is not send.
Can somebody help?
It's likely that your timer function simply doesn't have access to the message object (i.e. it exists in a different scope). One option is to nest your timer function within a function where you initialize message. Alternatively, you can pass message to your timer function. You could do this by changing the timer creation line to this:
T = timer('ExecutionMode','fixedrate','Period',0.2,...
'TimerFcn',#(~,~) TEST_timer_callback_fcn(message),...
'StopFcn','disp(''Timer has stopped'')');
And the callback function to this:
function TEST_timer_callback_fcn(message)
message.Signals.In_ti= 39;
In ReactiveX an Observable might invoke
the following methods
onNext
onError
onCompleted
according to a very clear contract http://reactivex.io/documentation/contract.html
I am writing the code for the Observable and I have realized that under certain circumstances I might invoke onNext within the same thread of execution.
Is that a mistake ?
For example, if I have code like this:
// call onNext twice on the same thread execution.
o.onNext(event1);
o.onNext(event2);
Should I rewrite it like this:
// call onNext and then schedule the next call via setTimeout
o.onNext(event1);
setTimeout(function() { o.onNext(event2); },0);
= = = = = = = =
Clarification: why am I asking ?
In a browser, let's imagine the observer wants to update an HTML element with the content of onNext then if it is called serially that code would not work.
function onNext() {
count++;
htmlElement.innerHTML = 'count:'+count; // <-- this will work only if onNext is invoked on different thread of executions.
}
I'm using the below code to receive the messages using serial port event handler. But it dosent receives any.I am not getting errors. The code breaks in "string msg = comport.Readline()" Am i doing something wrong ?
public partial class SerialPortScanner : Form
{
private SerialPort comPort = new SerialPort();
public SerialPortScanner()
{
InitializeComponent();
comPort.Open();
comPort.DataReceived += new SerialDataReceivedEventHandler(comPort_DataReceived);
}
void comPort_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
if (comPort.IsOpen == true)
{
string msg = comPort.ReadLine();
MessageBox.Show(msg);
}
}
}
The DataReceived event is raised on a secondary thread when data is received from the SerialPort object. Because this event is raised on a secondary thread, and not the main thread, attempting to modify some elements in the main thread, such as UI elements, could raise a threading exception.
Source : Check this
ReadLine depends on having a NewLine character. You might have better luck with the Read method. See also the BytesToRead property.