Java

Java Joy: Getting Multiple Results From One Stream With Teeing Collector

Posted on by  
Hubert Klein Ikkink

If we want to get two types of information from a Stream of objects we can consume the Stream twice and collect the results. But that is not very efficient, especially when the stream has a lot of objects. Since Java 12 we can use the teeing method of the java.util.stream.Collectors class to get multiple results while consuming the stream of objects only once. The teeing method takes two collectors as argument each returning a separate result for the stream items. As third argument we must pass a function that will merge the results of the two collectors into a new object.

Continue reading →

Follow through GitLab deployments with Slack

Posted on by  
Tim te Beek

Our team has a (not so) slight tendency to not immediately follow through with our deployments to production. We’ll create and review our changes, merge and deploy to staging, and dilligently test the changes there. And then…​ nothing happens.

It could be that something else needs our immediate attention, or someone else wants to confirm an issue is fixed; Or we might want to deploy at a different point in time as to not disrupt an ongoing process by a service restart. Any which way the result is the same: changes accumulate in staging, and with that the risk involved with the next production deployment.

To nudge ourselves to deploy to production more often we created a Slack App that gives us a daily report of such pending deployments. In this post I’ll showcase the code we use, and how to set up something similar yourself.

Continue reading →

Java Joy: Formatting A String Value With Formatted Method

Posted on by  
Hubert Klein Ikkink

Java 15 introduced the multi-line string value referred to as a text block. With this introduction also the formatted method was added to the String class. The method can be invoked on a String value directly and function exactly as the static String.format method. The nice thing is that now we directly can use a method on the value instead of having to use a static method where the value is passed as argument.

Continue reading →

Java Joy: Apply Function To String With Transform

Posted on by  
Hubert Klein Ikkink

In Java 12 the transform method was add to the String class. This method accepts a Function as argument. The function must have a single parameter of type String and can return any other type. The nice thing is that it works on a String instance, so we can directly use the transform method when we have a String value. We don’t have to pass the String object to another method to tranform it, but we can define the tranformation function close to the String value.

Continue reading →

Java Joy: Format Numbers In Compact Form

Posted on by  
Hubert Klein Ikkink

Since Java 12 we can format numbers in a compact style with the CompactNumberFormat class in the java.text package. A number like 23000 is formatted as 23K for the English locale. Instead of the short representation of K for 1000 we can also use a longer style where K is transformed as thousand for the English locale. We can use the same class to parse a String value that is in the compact style into a number.

Continue reading →

Java Joy: Merge Maps Using Stream API

Posted on by  
Hubert Klein Ikkink

In Java we can merge a key/value pair into a Map with the merge method. The first parameter is the key, the second the value and the third parameter of the merge method is a remapping function that is applied when the key is already present in the Map instance. The remapping function has the value of the key in the original Map and the new value. We can define in the function what the resulting value should be. If we return null the key is ignored.

Continue reading →

Java Joy: Composing Functions

Posted on by  
Hubert Klein Ikkink

In Java we can write single argument functions that implement the java.util.function.Function interface. We can combine multiple functions into a new function using the andThen and compose methods from the Function interface. We need to give another function as argument to these methods. When we use the andThen method the output of the original function will be input of the function passed as argument. With the compose method our function will get as input the output of the function that is passed as argument. It is important to know the difference, because it can change the result of the function we are composing. The andThen and compose methods are also available on the IntUnaryOperator, LongUnaryOperator and DoubleUnaryOperator interface.

Continue reading →

Java Joy: Partition Stream By Predicate

Posted on by  
Hubert Klein Ikkink

The Java Stream API has many useful methods. If we want to partition a stream of objects by a given predicate we can use the partitioningBy() method from the java.util.stream.Collectors package. We must use this method in the collect() method of the stream. The result is a Map with the keys true and false. The objects from the stream that are true for the predicate will end up in the true value list and if the result of the predicate is false the value will end up in the list of values for the false key. The partitionBy method accepts a collector as second parameter. This collector will be applied to the values before they are put in the true or false keys in the result.

Continue reading →

Java Joy: Turn Stream Into An Array

Posted on by  
Hubert Klein Ikkink

The Java Stream API has many useful methods. If we want to transform a Stream to a Java array we can use the toArray method. Without an argument the result is an object array (Object[]), but we can also use an argument to return an array of another type. The easiest way is to use the contructor of the array type we want as method reference. Then the result is an array of the given type with the elements of the stream.

Continue reading →

Java Joy: Optional orElse orElseGet That Is The Question

Posted on by  
Hubert Klein Ikkink

The Optional class has the orElse and orElseGet methods to return a value when the Optional object is empty. This is useful to return a default value for example. But there is a small difference between the two methods. The orElseGet method needs a Supplier argument that returns a value of the type of the Optional value. The Supplier is only invoked when the Optional value is empty. The statement passed as argument to the orElse method is always executed, even when the Optional value is not empty. Preferrably we should use orElseGet as it will only invoke statements if needed.

Continue reading →

Custom SSLContext with Apaches fluent HttpClient5

Posted on by  
Sjoerd During

Apaches fluent httpclient API is a facade API to simplify the httpclients usage for standard use cases. It’s also better readable and results in cleaner code. In this post we’ll see how to use a custom SSLContext with the fluent API. We’ll use the new 5.0 version because it contains some changes compared to 4.x.

Continue reading →

Automatic Switching Of Java Versions With SDKMAN!

Posted on by  
Hubert Klein Ikkink

SDKMAN! is a very useful tool to manage versions of so-called software development kits. There are a lot of SDKs supported by SDKMAN!: Java, Groovy, Kotlin, Scala, Gradle, Maven, Leiningen, Micronaut, Grails, Vert.x, JBake, AsciidoctorJ and more. When we look at Java we can use a simple install java <version> command from the command-line to install a version of Java on our computer. SDKMAN! will take care of downloading the Java version and setting all the correct system variables to use that Java version. With the use command we can switch between version in the current shell we are working in. But we can even automatically switch to a specific installed Java version when we enter a directory. This is very useful when we have to work on multiple projects on our computer and each project requires a specific Java version to be used.

Continue reading →

shadow-left