In Java we can define capturing groups in regular expression. We can refer to these groups (if found) by the index from the group as defined in the regular expression. Instead of relying on the index of the group we can give a capturing group a name and use that name to reference the group. The format of the group name is ?<name> as first element of the group definition. The name of the group can be used with the group method of the Matcher class. Also we can use the name when we want to reference the capturing group for example with the replaceAll method of a Matcher object. The format is ${name} to reference the group by name. Finally we can use a named capturing group also as backreference in a regular expression using the syntax \k<name>.

In the following example we define a regular expression with named groups and use them with several methods:

This week at work a colleague showed a nice feature of the Pattern class in Java: we can easily turn a Pattern into a Predicate with the asPredicate and asMatchPredicate methods. The asPredicate method return a predicate for testing if the pattern can be found given string. And the asMatchPredicate return a predicate for testing if the pattern matches a given string.

In the following example code we use both methods to create predicates:

When using Springfox you can annotate your endpoints to automatically generate OpenAPI docs for your clients.
This blogpost will show how you can prevent Springfox generating a model on an endpoint with ResponseEntity as return type.
I’ll also cover how to prevent generating default responses.

Using the Stream API and the map method we can transform elements in a stream to another object. Instead of using the map method we can also write a custom Collector and transform the elements when we use the collect method as terminal operation of the stream.

First we have an example where we transform String values using the map method:

I have seen the following pattern appear quite a lot:

Here the function is called with a nullable argument, and if the argument was null, the function will return null, and if not it will return a proper value. I do not like this, and here is why.

In Java we can use a Predicate to test if something is true or false. This is especially useful when we use the filter method of the Java Stream API. We can use lambda expressions to define our Predicate or implement the Predicate interface. If we want to combine different Predicate objects we can use the or, and and negate methods of the Predicate interfaces. These are default methods of the interface and will return a new Predicate.

Let’s start with an example where we have a list of String values. We want to filter all values that start with Gr or with M. In our first implementation we use a lambda expression as Predicate and implements both tests in this expression:

There are those moments you wish you could just start up a real database or system for your (integration) test. In many tests I’ve written I used H2 or HSQLDB to have a data storage for my tests. It starts up quickly and almost supports everything you need to do your repository test or any other test needing data storage. But when your project progresses you start using other ways to store your data other than standard SQL or you use dialect specifics to create your database. This is the moment you discover H2 or HSQLDB is not supporting your database vendor specific features and you can’t get your test running. For example the support for PostgreSQL in H2 or HSQLDB isn’t great, using TIMESTAMP in a SQL script already makes H2 or HSQLDB break. Yes, there are workarounds, but you rather not apply them to keep your code clean and simple. This is the moment you wish it is cheap to start up a real database instance you can test against, so you’re sure your code works in your production environment. You could install the database software locally, make some scripts to initialise the database and clean up afterwards. Or you can make scripts to do this in a Docker container. But what if there’s something which makes this even cheaper to setup?

There are a few ways to get your application version with Spring Boot. One approach is using Maven resource filtering to add the version number as an enviroment variable in the application.yml during the build. Another approach is to use the Implementation-Version stored in the manifest file.

Although Java has always been awesome, Java 8 has brought the language several features the language was in dire need of. Apart from the long-awaited improved DateTime-API and the introduction of Optionals, Java 8 finally gave behaviour the attention it deserves by incorporating (a form of) functional programming into the language using lambdas.

The opportunities that Java 8 brought the language and the platform have long since been taken and functional styles of programming are part of our day-to-day routines as Java Developers. For-loops are a thing of the past for most of us, and although it had quite the learning curve, passing streams around and chaining operations on them to create some very readable code is common sense for us now.