Showing posts from 2017

Using web component polyfills with template tags

I've been playing around with using <template> tags  and how well they work with the current Web Component ( Custom Elements ) polyfills. My main motivation for going for Web Components instead of something like React or Angular is that I'm currently developing a chrome extension. I wanted the code base to be as small so that it didn't slow down devtools and increase the frequency of hands. Plus I think it's going to be the natural progression from the current React/Angular/etc components - especially with HTTP 2.0's server push of dependant files removing the need for tools like webpack by allow all dependant files to be automatically sent in response to one request. I immediately hit problems using custom elements in a chrome extension as they're disabled by default. So in order to use them I had to forcefully polyfill the existing API, it took a bit of fiddling  but now works with both libraries I looked at. Next, using template tags an import li

How to chain an ES6 Promise

Node.js uses async functions extensively, as it based around non-blocking I/O. Each function takes a callback function parameter, which can result in some messy, deeply nested callback functions if you have to call a bunch of async functions in sequence. Promises make these callbacks a lot cleaner. ES6 (or ES2016)  Promise s are a great way of chaining together asynchronous functions so that they read like a series of synchronous statements. There's already some great posts on Promises, 2ality has a good intro to async then detail of the api , so I won't rehash that article. However, after starting to use them for cases more complicated than most examples, it easy to make a few mistaken assumptions or make things difficult for yourself. So here is a more complicated example showing a pattern I like to follow. In this example, I'll use the new Javascript Fetch API , which is an API that returns a Promise, allowing you to make async HTTP calls without having to muck a

Adding MDC headers to every Spring MVC request

Mapped Diagnostic Context ( MDC ) logging allows you to set attributes associated with current thread, so that SLF4J (via your logger implementation library) can log those attributes with each logging statement without it having to be specified. For example you could configure logback to log the sessionId on every statement, which is really handy when using a log indexer such as Splunk. This would allow you to easily see all the requests made by a user, for a given session. To use with logback, you'd set the pattern to %-4r [%thread] %-5level sessionId=%X{sessionId} - %msg%n Setting these attributes for each entry point would be a pain so one way would be to implement a ServletRequestListener , which would allow setting the attributes at the start of the request and removing them again at the end of the request. ( Note: It's important to remove the attributes afterwards, as threads are re-used by application servers and will give misleading logging statements) If you&#

Populating stored procs into a HSQL DB

I recently encountered a problem trying to load stored procedures into a HSQL DB used for testing. The problem was caused by the script runner provided by spring which separates each statement to be executed in a script file by a semicolon. If a stored proc has statements inside it (which most do), then the proc isn't executed as a single statement. This is further compounded by each statement executed must be understandable by JDBC. For example the following stored proc causes issues: CREATE PROCEDURE MY_PROC(IN param1 VARCHAR(30), OUT out_param VARCHAR(100)) READS SQL DATA BEGIN ATOMIC SELECT the_value INTO out_param FROM my_table WHERE field = param1; END .; This problem is solved by using the script runners provided by HSQL in the "org.hsqldb:sqltool" dependency as they parse can correctly parse the scripts containing stored procedures. Here is a Spring Boot test, using an in memory database but using HSQL's script runners: @RunWith(SpringRunner.class

Dev Setup of a Mac

After working in my 2nd consecutive company that uses Mac's for developers and having forgot everything I used the first time, I thought I better write down all the tweaks, work arounds and config changes that got me using my mac efficiently. Remap Fn-C to copy Mac's use Mac-C instead of Ctrl-C to copy (and X, V to cut and paste). This is really annoying if you switch between a mac and Windows machine a lot. Fortunately you can use Karabiner  to map Fn-C to copy as the Fn key is located where Ctrl is on a windows keyboard. If your on OSX Sierra you'll need to use Karabiner Elements for now. Git Just run git from the command line and it will prompt you to install xcode tools. homebrew This needs to be installed first as it installs most dev tools. Note: if your behind a corporate proxy you'll need to run export HTTPS_PROXY=http://yourproxy:port first. /usr/bin/ruby -e "$(curl -fsSL