PV Display is an Android app to view data on the PV Output website. You can view live solar panel data and browse through historical data. The data is presented in five different tabs in both graphical and tabular form. It works in portrait mode: And in landscape mode: […]
Category Archives: Programming
Monitoring hosts with CollectD, InfluxDB and Grafana
In this article we will install a monitoring solution on CentOS 7 consisting of CollectD, InfluxDB and Grafana. The first step is to install CollectD: yum -y install epel-release yum -y install collectd At the time of writing, this resulted in the installation of CollectD version 5.5.0. If you are using an older version of […]
Serialize and deserialize a list of polymorphic objects with GSON
GSON is a great Java library for serializing and deserializing objects to and from JSON strings. When you have a list of polymorphic objects you want to serialize and deserialize, things get a bit more difficult. You have to tell GSON which type of object you expect when deserializing. When you have a list of […]
Storm in pictures
We’ve been using Storm for some time now. It is quite easy to start using it in a local environment (e.g. your IDE), but it can be a bit daunting to install a cluster and then really understand what Storm is actually doing to execute your topology. The documentation has improved over time, and some […]
Changing the number of columns in WordPress dashboard
The latest version of WordPress sets the number of columns in its dashboard to 4. This gives ugly results with some plugins that expect more horizontal room for their content, such as the Google Analytics plugin. Until the WordPress team decides on a solution to this problem or the plugin developers adapt to the new […]
Getting metrics from the Java Virtual Machine (JVM)
Sometimes it is useful to see what the Java Virtual Machine (JVM) is doing when it is running your program. In this blog we will see how to get metrics about memory, buffers, threads and the garbage collection (gc) process from the JVM. The metrics-core and the metrics-jvm package from Codahale is all we need. […]
WebSocket tutorial with Java server (Jetty) and JavaScript client
WebSocket is a web technology providing full-duplex communications channels over a single TCP connection. WebSocket is designed to be implemented in web browsers and web servers, but it can be used by any client or server application. In this tutorial we will use a Java server and a JavaScript client. We start with the Java […]
Running dynamic Java code
Using a Java library called Javassist it is possible to create class files on the fly and use them in the same program that created them. Sounds funky, and it is… First download the jar file from the JBoss download website. Then write a sample class file that will be edited by the Javassist library […]
Installing a Storm cluster on CentOS hosts
Storm is a distributed, realtime computation system to reliably process unbounded streams of data. The following picture shows how data is processed in Storm: This tutorial will show you how to install Storm on a cluster of CentOS hosts. A Storm cluster contains the following components: Nimbus is the name for the master node. Nimbus […]
Installing Apache Libcloud on CentOS
Apache Libcloud is a standard Python library that abstracts away differences among multiple cloud provider APIs. At the moment it can be used to manage four different kinds of cloud services: servers, storage, loadbalancers and DNS. Here are the steps to install Libcloud on a machine running CentOS 6: rpm -Uvh http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm yum install python-pip […]