Spring @ConfigurationProperty a Bean or not?

Semi-recently (“semi” because procrastination kept me from writing, so it’s more like two months ago, but blog posts have to start with “recently” when you try to explain yourself why you are writing what you are writing – but I’m getting sidetracked here, so let’s move on) I was wondering whether Java classes annotated with Spring’s @ConfigurationProperty should be declared as a bean, e.g. with @Component. I didn’t find a definitive answer, but I found three ways on how to do it – typical Spring, I guess.

Here’s a quick setup:

My configuration class.

package com.thecodeslinger.configpropsdemo;

import lombok.Data;
import org.springframework.boot.context.properties.ConfigurationProperties; 

@Data 
@ConfigurationProperties(prefix = "demo")
public class Configuration {

    private String elegy;
}

My main application:

package com.thecodeslinger.configpropsdemo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import javax.annotation.PostConstruct;

@SpringBootApplication
public class ConfigPropsDemoApplication {

   @Autowired
   private Configuration configuration;

   @PostConstruct
   public void postConstruct() {
      System.out.println(configuration.getElegy());
   }

   public static void main(String[] args) {
      SpringApplication.run(ConfigPropsDemoApplication.class, args);
   }
}

And finally, my properties file:

demo.elegy=R.I.P. Kobe

It’s not an elegant setup, but that’s not the point. It does the job for now.

If you run the application in this state, Spring will greet you with an error message.

APPLICATION FAILED TO START

Description:
Field configuration in com.thecodeslinger.configpropsdemo.ConfigPropsDemoApplication required a bean of type 'com.thecodeslinger.configpropsdemo.Configuration' that could not be found.
The injection point has the following annotations:
- @org.springframework.beans.factory.annotation.Autowired(required=true)
Action:
Consider defining a bean of type 'com.thecodeslinger.configpropsdemo.Configuration' in your configuration.

It obviously cannot find the configuration bean.

Option #1: Slap @Component to it.

package com.thecodeslinger.configpropsdemo;

import lombok.Data;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

@Data
@Component
@ConfigurationProperties(prefix = "demo")
public class Configuration {

    private String elegy;
}

Option #2: Use the @EnableConfigurationProperties annotation.

import org.springframework.boot.context.properties.EnableConfigurationProperties;

@SpringBootApplication
@EnableConfigurationProperties(Configuration.class)
public class ConfigPropsDemoApplication {

Option #3: Use @ConfigurationPropertiesScan to explicitly name the packages to scan for.

import org.springframework.boot.context.properties.ConfigurationPropertiesScan;

@SpringBootApplication
@ConfigurationPropertiesScan({"com.thecodeslinger.configpropsdemo"})
public class ConfigPropsDemoApplication {

All three options achieve what you’re aiming for, a running application.

:: Spring Boot :: (v2.2.4.RELEASE)
2020-02-03 19:57:43.562 INFO 4612 --- [ main] c.t.c.ConfigPropsDemoApplication : Starting ConfigPropsDemoApplication on DESKTOP-C0O3OKC with PID 4612 (D:\OneDrive\Code\Java\config-props-demo\target\classes started by lober in D:\OneDrive\Code\Java\config-props-demo)
2020-02-03 19:57:43.562 INFO 4612 --- [ main] c.t.c.ConfigPropsDemoApplication : No active profile set, falling back to default profiles: default
R.I.P. Kobe
2020-02-03 19:57:43.921 INFO 4612 --- [ main] c.t.c.ConfigPropsDemoApplication : Started ConfigPropsDemoApplication in 0.573 seconds (JVM running for 1.083)

So, is there any benefit of one over the other? The Spring documentation has the following to say:

Sometimes, classes annotated with @ConfigurationProperties might not be suitable for scanning, for example, if you’re developing your own auto-configuration or you want to enable them conditionally. In these cases, specify the list of types to process using the @EnableConfigurationProperties annotation. This can be done on any @Configuration class, as shown in the following example:

I’m not using a @Configuration class in my example, but if you were, you could leverage that to load your configuration classes based on @Profile annotations. Although @Component works too, it’s not mentioned in that part of the Spring documentation (“Type-safe Configuration Properties”).

For myself, I might go with @EnableConfigurationProperties and if it makes sense, even have dedicated @Configuration classes linked to @Profile. For little samples like this one it’s obviously overkill. In a remotely useful application, the additional overhead may be worth it for structural and documentational reasons.

Kotlin Object Expression – What more can object do?

In a previous post I explained what Kotlin Object Declarations are. This time around it’s about the declaration’s sibling, the Object Expression.

An object is not just a glorified static replacement or a singleton. object can be used where Java usually utilizes anonymous inner classes. Let’s look at a more realistic scenario: a JButton and an ActionListener or a MouseListener.

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Kotlin Object Declarations – The fake-static

Instead of implementing my own backup application as I had planned a long time ago, I’m wandering off (re)learning Kotlin after a long absence from that language. In my defense though, I’m doing it in the context of the backup app which will not be Java as originally intended (or maybe later for comparison, who knows, I obviously can’t be trusted with my plans). Putting that aside, the most confusing concept of Kotlin for a Java developer is the object. What is that thing doing that a class can’t do and how do we declare static fields and methods? I know it’s nothing new, but that part seems to have changed a bit since I used Kotlin about two (?) years ago. So, for me this is a refresh of old information and also something new and by writing about it I will engrave it in my brain once and for all. And your confusion will hopefully turn into some productive… fusion… of some sort… or so.

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Unwanted JUnit 4 Dependency with Kotlin and JUnit 5

I ran across this issue only by accident because I was investigating a completely different problem. I wrote a quick test to debug my issue and was wondering why custom serializers and deserializers are not registered with the Jackson ObjectMapper. I had a nice init() function that was annotated with @Before. So, what the hell?

Let’s back up a bit for some context.

  • Kotlin Project
  • Runs on Java 12
  • JUnit 5 as test engine
  • AssertK for assertions (just for the sake of completeness)

I’m used to JUnit 4, so in my test I used @Before to annotate a setup method. It was one of the many options IntelliJ presented to me.

@Before
fun init() {
    val module = SimpleModule()
    module.addDeserializer(Instant::class.java, InstantDeserializer())
    module.addSerializer(Instant::class.java, InstantSerializer())
    mapper.registerModule(module)
}

The method wasn’t called, however. But it’s annotated! Well, it’s the wrong annotation if you’re using JUnit 5. The correct one is @BeforeEach. This one and @BeforeClass (new name @BeforeAll) have been changed from version 4 to 5 to make their meaning more obvious.

But that’s besides the point. The question is: where does this @Before come from then?

A look at the dependency tree quickly reveals the culprit.

It’s the official JetBrains Kotlin JUnit test artifact. Although it doesn’t hurt me to have it in my project, it certainly caused some confusion and I’d like to avoid that in the future. Hence, I excluded the old version of JUnit in my POM file for this dependency.

<dependency>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-test-junit</artifactId>
    <version>${kotlin.version}</version>
    <scope>test</scope>
    <exclusions>
        <exclusion>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
        </exclusion>
    </exclusions>
</dependency>

Problem solved.

AdoptOpenJDK 8 NullPointerException sun.awt.FontConfiguration.getVersion(FontConfiguration.java:1264)

I recently had to deal with this little bugger as we moved from the OpenJDK 8 package supplied by the Linux distro of choice to AdoptOpenJDK 8. It is important to know that we completely uninstalled OpenJDK, including all its transient dependencies.

(And in due time we’ll uninstall Java 8 and replace that grandpa as well)

As a result, parts of our application didn’t work any longer, resulting in this nice and shiny Java stacktrace.

2019-05-03 08:22:07,345 ERROR [qtp1896708863-35] [PlotChartController] [/][/][/]- error while creating chart image
java.lang.NullPointerException
        at sun.awt.FontConfiguration.getVersion(FontConfiguration.java:1264)
        at sun.awt.FontConfiguration.readFontConfigFile(FontConfiguration.java:219)
        at sun.awt.FontConfiguration.init(FontConfiguration.java:107)
        at sun.awt.X11FontManager.createFontConfiguration(X11FontManager.java:774)
        at sun.font.SunFontManager$2.run(SunFontManager.java:431)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.font.SunFontManager.<init>(SunFontManager.java:376)
        at sun.awt.FcFontManager.<init>(FcFontManager.java:35)
        at sun.awt.X11FontManager.<init>(X11FontManager.java:57)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
        at java.lang.Class.newInstance(Class.java:442)
        at sun.font.FontManagerFactory$1.run(FontManagerFactory.java:83)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.font.FontManagerFactory.getInstance(FontManagerFactory.java:74)
        at java.awt.Font.getFont2D(Font.java:491)
        at java.awt.Font.defaultLineMetrics(Font.java:2176)
        at java.awt.Font.getLineMetrics(Font.java:2246)
        at org.jfree.chart.axis.DateAxis.estimateMaximumTickLabelWidth(DateAxis.java:1453)
        at org.jfree.chart.axis.DateAxis.selectHorizontalAutoTickUnit(DateAxis.java:1365)
        at org.jfree.chart.axis.DateAxis.selectAutoTickUnit(DateAxis.java:1340)
        at org.jfree.chart.axis.DateAxis.refreshTicksHorizontal(DateAxis.java:1616)
        at org.jfree.chart.axis.DateAxis.refreshTicks(DateAxis.java:1556)
        at org.jfree.chart.axis.ValueAxis.reserveSpace(ValueAxis.java:807)
        at org.jfree.chart.plot.CombinedDomainXYPlot.calculateAxisSpace(CombinedDomainXYPlot.java:364)
        at org.jfree.chart.plot.CombinedDomainXYPlot.draw(CombinedDomainXYPlot.java:442)
        at org.jfree.chart.JFreeChart.draw(JFreeChart.java:1235)
        at org.jfree.chart.JFreeChart.createBufferedImage(JFreeChart.java:1409)
        at org.jfree.chart.JFreeChart.createBufferedImage(JFreeChart.java:1389)
        at org.jfree.chart.ChartUtilities.writeChartAsPNG(ChartUtilities.java:183)

I obviously removed some (a lot) parts to make it more readable and to hide corporate IP 😉 But this is the relevant part.

I found this bug report on Github and for once, plowing through the comments, it helped me. As is mentioned there, the culprit is the missing “fontconfig” package. So, I added another Ansible task to our playbook to provision the server et voila, the problem is gone.

- name: Install fontconfig package
  package:
    name: fontconfig
    state: present
    tags:
      - java

As mentioned earlier, we had wiped all that was relevant to OpenJDK off the system and by doing so, also uninstalled the “fontconfig” package. Otherwise this error wouldn’t have surfaced. But that’s the benefit of starting with a clean slate. This way you know if something is missing and don’t get surprised by errors all of a sudden while, at the same time, it is working on another machine.

Micrometer and Spring (Non-Boot)

Almost all of the tutorials and blog posts I found on this topic were focused on Spring Boot because, starting with version 2, it uses Micrometer as its metrics framework. However, in a particular project at work we do not have access to Spring Boot let alone a recent Spring version. Therefore, I’m explaining how to include Micrometer in your non-Boot Spring application using XML configuration.

In this tutorial I will be using Spring 5 and Java 11, so not exactly the versions I’m dealing with at work, but the concepts are the same and everything can probably be copied exactly as shown here.

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A Java “DSL“ for Simple Unit Test Data Creation

I’m a person that usually writes tests before the implementation. In the context of my backup application project this has turned out to really slow me down. But it’s not just a problem of my personal projects. It also affects my professional work. 

Here’s the issue: for some tests you need test data and generating that test data can be a tedious task, depending on the complexity. This has caused me to procrastinate on my backup app. So, one evening, after having thought about this during a workout, I grabbed my laptop, sat down in my comfy bed and wrote a “DSL” that makes creating the data much simpler. Not only is it easier to create the data now, allowing me to continue at a faster pace, it’s also much more readable and the test setup doesn’t clutter the test case anymore. This is a very important aspect of a test. What good does it to have one if, after some time, you have to update it and don’t understand what it does anymore?

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