Data communications by example for developers
In this section I discuss communication protocols; we start with a grounding on the basics and move through to some worked examples. To start with let’s look at some of the simplest cases and understand how communications between computer systems work in practise. There are many methods of communicating between two computers, be they embedded, mobile, desktop or server. Protocols range...
Filtered extraction from zip file using ZipInputStream and Java 8
In the example below we build on the Reading a zip file from java using ZipInputStream page to provide basic filtering. This filtering is provided by the filteredExpandZipFile method taking a Predicate. Every ZipEntry is passed to the predicate, but only ones that match (predicate returns true) are included. Note that the size of an entry cannot be accurately determined in...
Using Future and ConcurrentMap for a lazy cache
In this example I demonstrate how to use ConcurrentMap along with Future to generate a lazy cache. Concurrent maps are a good choice in some situations, where absolute atomicity can be traded off for performance, some level of control over ordering of events has been traded for performance. Let's assume for the sake of example that we have an object that...
Writing a zip file in java using ZipOutputStream.
Following on from one of our popular articles on Reading a zip file from java using ZipInputStream we've put together a new article on how to create a zip archive using Java. The below example uses ZipOutputStream to create a zip file from all the items in a directory. Zip files are written slightly differently to a normal stream in that...
Old Generation GC and cache performance?
This is a question as much as a discussion, I can’t find a lot of detail on the state of play in this area and would really welcome any feedback or corrections. Please don’t read this as a negative article as that is not how it is intended; it’s in the optimisation section but I’m not sure what impact it really...
Simple uses of CountDownLatch
CountDownLatch provides a means of waiting for a number of asynchronous events before proceeding. In order to do this one constructs a latch providing the event count. Then one thread would normally call whilst the other thread calls . Once the count reaches zero the call returns and the latch is set. If the call to happens after...
Formatting dates in Java with DateFormat
There are several ways to format dates in Java, but by far the easiest is to use DateFormat. Creating a DateFormat is very similar to NumberFormat that we saw on the previous page. Here are the static factory methods called directly on the DateFormat class: getDateInstance(..) getDateTimeInstance(..) getTimeInstance(..) There are several overloaded versions of each method above. We will not cover...
The background, string formatting in java
Over the years there have been no shortage of ways to format a string in java. What with the + operator, , , and various specialised formatters for numbers and dates we sometimes feel a little spoilt for choice. But how do they all work and what are their advantanges / disadvantages? StringBuffer - a hang up from times gone...
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