Igor's Blog

I've recently discovered that on Mobile Safari the $(window).scrollTop() would not update during the scroll event animation. It appeared to only update after the scroll (the elastic scroll) had finished its animation. This was a rather annoying 'feature' for me because I needed to update my UI during the animation, so I went looking for a workaround and here's what I've come up with.

Below are two videos showing the before and after the workaround. The first video shows the default behaviour where scrollTop() is only updated after the scroll event completes, the second video shows a workaround that has continuous updates during scrolling.



This was my 'before' code:
 Before Code
<!DOCTYPE html>
<html lang="en">
<head>
<title>ScrollTop test</title>
<script src="https://code.jquery.com/jquery-2.2.4.min.js"></script>
<style>
div#message {
position: fixed;
right: 0;
top: 0;
color: red;
font-size: 300%;
}
</style>
</head>
<body>
<div id="body">
<div id="message"></div>
</div>
<div id="content" style="display: none; margin: 1em;"></div>
<script>
$(document).ready(function() {
/* generate some content */
for (var i = 0; i < 100; i++) {
$('#content').clone().text('Content item ' + i).show().appendTo($('#body'));
}
$(document).scroll(function(e) {
var scrollTop = $(window).scrollTop();
$('#message').text('Scroll Top: ' + scrollTop);
});
});
</script>
</body>
</html>


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Many of the plugins that would be used in a typical Maven setup provide an option to skip execution of that plugin via the <skip> configuration parameter or in the case of the Surefire plugin, the -DskipTests system property. Unfortunately some plugins, like the WebLogic Maven Plugin do not offer this facility.

I had a situation where I wanted each of the developers to be able to locally do a build and automatically deploy to WebLogic, but I didn't want jobs executed by the CI pipeline to do any automatic deployments. Since the WebLogic plugin didn't offer a skip option, I had to find another way.

What I ended up doing was changing the <phase> for the plugin to a variable instead of it being static. Something like this...
 Maven
<plugin>
...
<execution>
...
<phase>${skipPluginPhase}</phase>
...
</execution>
...
</plugin>


Then I could define the value for the skipPluginPhase property like...
 Maven
<properties>
<skipPluginPhase>none</skipPluginPhase>
</properties>


Leaving it as 'none' would skip plugin execution, whereas putting in a valid phase like 'install' would execute the plugin as expected. The only change each developer would need to do locally was update their version of the pom.xml file to reflect this.

To avoid unnecessary editing of the pom.xml file it is also possible to set up a number of different profiles in your Maven build. The default profile could then set skipPluginPhase to a valid phase name and a profile set up just for the CI pipeline could set skipPluginPhase to none, whereby skipping plugin execution.

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I've recently had a requirement to unmarshal an XML fragment that was passed into one of my services. This in itself is typically not and issue and I've written code that does that plenty a time, however in this case I was having to unmarshal a fragment for a complex type, not for an element. That's where it got a little bit more complicated.

Initially my code was throwing the following exception:
 Exception
javax.xml.bind.UnmarshalException: unexpected element (uri:"http://net.igorkromin/", local:"MyComplexType"). Expected elements are (none)


So that meant that the unmarshaller didn't recognise any valid elements in my XML string that I was trying to unmarshal. I checked the JAXB Context and it definitely had the complex type I was after so it was something else I was doing wrong.

Lets take a step back and look at the schema, my complex type, MyComplexType, was defined as:
 XSD
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<xsd:schema xmlns="http://net.igorkromin/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://net.igorkromin/" elementFormDefault="qualified">
...
<xsd:complexType name="MyComplexType">
<xsd:sequence>
...
</xsd:sequence>
</xsd:complexType>
...


That resulted in a JAXB generated class that looked like:
 Java Class
@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(
name = "MyComplexType",
propOrder = {...}
)
public class MyComplexType {
...
}


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I was implementing a custom entity provider in a Jersey REST service when I came across an error during deployment: "java.lang.IllegalStateException: Not inside a request scope." That struck me as a little odd since I was trying to inject a ContainerRequestContext into a MessageBodyWriter, which should have been within request scope. After some research and this Jersey issue I found a solution.

This is what I was trying to do in my class:
 MessageBodyWriter
@Context
ContainerRequestContext crc;


...which was throwing this exception...
 Exception
java.lang.IllegalStateException: Not inside a request scope."
weblogic.application.ModuleException: java.lang.IllegalStateException: Not inside a request scope.
at weblogic.application.internal.ExtensibleModuleWrapper.start(ExtensibleModuleWrapper.java:140)
...
Caused By: java.lang.IllegalStateException: Not inside a request scope.
at jersey.repackaged.com.google.common.base.Preconditions.checkState(Preconditions.java:173)
at org.glassfish.jersey.process.internal.RequestScope.current(RequestScope.java:233)
at org.glassfish.jersey.process.internal.RequestScope.findOrCreate(RequestScope.java:158)
at org.jvnet.hk2.internal.Utilities.createService(Utilities.java:2022)
at org.jvnet.hk2.internal.ServiceHandleImpl.getService(ServiceHandleImpl.java:114)
at org.jvnet.hk2.internal.ServiceHandleImpl.getService(ServiceHandleImpl.java:88)
at org.glassfish.jersey.internal.inject.ContextInjectionResolver.resolve(ContextInjectionResolver.java:126)
...


The solution was to inject a ResourceContext instead and then look up the ContainerRequestContext when needed.

So my injection code became:
 MessageBodyWriter
@Context
ResourceContext resourceContext;


...and then to get the ContainerRequestContext I simply got it from the ResourceContext like so:
 MessageBodyWriter
ContainerRequestContext crc =
resourceContext.getResource(ContainerRequestContext.class);


This worked with Jersey 2.x (2.25.1 in my case).

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