Category Archives: How To

Docker How To

SSH into a Docker Container

November 30, 2018 – 5:03 pm

Just sometimes, it’s useful to SSH into a Docker Container. While docker exec or docker attach are usually sufficient to run commands in a container, sometimes you specifically need SSH. For example, to connect directly from a remote machine or when an application needs to run commands on your container. Most Docker images don’t come with the SSHd service installed so it is not possible to SSH to them. This post demonstrates how to install and run the SSHd service to an existing image so that you can connect to it.

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How To Testing

Unit test time based logic

October 23, 2018 – 7:57 pm

A standard unit testing problem is how to unit test code that has a dependency on dates or times. Consider a method that returns a greeting according to the time of day. If we were to call this method from a test fixture (say JUnit), it would return different values depending on when the test was run. This is not ideal. Unit tests should pass or fail consistently.

Here’s a simple solution for testing time based code.

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How To Testing

Test log4j2 with JUnit using a custom appender

April 29, 2018 – 6:57 pm

In previous articles, I’ve described how to test System.out with JUnit and how to test log4j with JUnit. This article describes how to test log4j2 logging with JUnit. This largely follows the same technique as testing log4j logging but using the the newer log4j2 APIs. Differences between log4j and log4j2 log4j2 follows a similar design read more »

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How To Testing

Test log4j with JUnit using a custom appender

January 15, 2018 – 8:21 pm

Following a recent article on how to Test System.out with JUnit, here’s a follow up on how to test log4J with JUnit. This article describes a technique to test log4J output in a JUnit test by adding a custom appender. This allows us to verify that log4j output contains expected Strings.

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How To

Validate JSPs at build time

November 13, 2017 – 7:44 pm

JSPs compile to Java code at run time. This is helpful if we want to test code changes without a build and deploy. However, if errors are introduced, they may not be spotted till it’s too late. A useful compromise is to validate JSPs at build time to verify that they will compile. The validator catches syntax errors before the application deploys and starts. This speeds up our build and test cycle and prevents silly mistakes slipping through to production code.

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How To Security Spring Boot

Thymeleaf and Spring Security

June 29, 2017 – 10:05 pm

Thymeleaf is a popular templating engine, particularly with Spring projects. Spring Boot has chosen Thymeleaf as the view technology of choice, largely replacing the need for JSP. With old JSPs, custom tag libraries provided integration with various technologies, including Spring Security. A similar library exists to integrate Thymeleaf and Spring Security – the Thymeleaf Spring read more »

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How To Testing

Test System.out with JUnit

May 12, 2017 – 3:54 pm

It can be useful to verify output to System.out in a unit test. For example, if you’re testing application logging or if you’re using log output to sense some other behaviour. It can be tricky to properly mock behaviour of System.out but fortunately, it is possible to test System.out using JUnit.

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How To Spring Boot

Spring Boot Actuator Trace: Logging HTTP requests

April 14, 2017 – 1:28 pm

Spring Boot Actuator provides assistance for application monitoring. Out of the box it provides information on application health, configuration and logging. It’s trivial to enable: simply add the spring-boot-starter-actuator dependency to a Spring Boot project in Maven or Gradle and it just works! The monitoring information is provided as JSON from HTTP endpoints or via JMX.

The Spring Boot Actuator trace endpoint is particularly handy. By default it shows the last 100 HTTP requests made to the application. This article walks through an Actuator demo and shows some of the configuration options to get the best from this feature.

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Docker How To

Tomcat debugging in Docker

March 12, 2017 – 7:42 pm

Like a many things in Tomcat, there are a number of ways to enable remote debugging. Here’s the easiest way I’ve found to enable remote debugging in a Docker container running Tomcat.

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Docker How To

Activate the Docker Maven plugin when Docker is present

February 28, 2017 – 10:33 pm

The wonderful docker-maven-plugin from Spotify is a great way to build Docker images from Maven. If you bind it to Maven phases, it can be used to make a one-step build of a project artifact and its Docker image. For example, if you bind the Docker Maven plugin’s build goal to the Maven package phase, read more »

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