Java

Create a custom converter This class converts the well known log levels to a custom format CustomLogLevelConverter.java package com.hascode; public class CustomLogLevelConverter extends ClassicConverter { @Override public String convert(ILoggingEvent event) { switch (event.getLevel().toInt()) { case Level.ERROR_INT: return "ERROR!!!"; case Level.WARN_INT: return "WARN!!"; case Level.INFO_INT: return "INFO!"; case Level.TRACE_INT: return "DEBUG"; default: return event.getLevel().toString(); } } } Register the converter The following Logback config includes some defaults and registers our custom converter. ...

Goals Set up Maven build pipeline for a Java 11 app Release Maven artifact on GitHub using GitHub actions Setup Maven Assuming that we have a project named sample-app released for my hascode GitHub account: We’re adding some release information to our project’s pom.xml: pom.xml <?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.hascode</groupId> <artifactId>sample-app</artifactId> <version>1.0.0-SNAPSHOT</version>bookmark-manager <name>sample-app</name> <description>hasCode.com Bookmark Manager</description> <scm> <developerConnection>scm:git:https://github.com/hascode/sample-app.git </developerConnection> </scm> <distributionManagement> <repository> <id>github</id> <name>GitHub</name> <url>https://maven.pkg.github.com/hascode/sample-app</url> </repository> </distributionManagement> <properties> <java.version>11</java.version> <project.scm.id>github</project.scm.id> </properties> [..] </project> ...

Goals Use JUnit Maven BOM for version alignment Add minimal dependencies for JUnit5 Java Projekt Setup Excerpt from the Maven project’s pom.xml: <dependencyManagement> <dependencies> <dependency> <groupId>org.junit</groupId> <artifactId>junit-bom</artifactId> <version>5.7.1</version> <type>pom</type> <scope>import</scope> </dependency> </dependencies> </dependencyManagement> <dependencies> <dependency> <groupId>org.junit.jupiter</groupId> <artifactId>junit-jupiter</artifactId> <scope>test</scope> </dependency> </dependencies> JUnit5 does not work with older versions of the Maven Compiler Plugin and the Surefire Plugin used for test execution. Setting their versions in the pom.xml is done like this: ...

Goals Package a Spring Boot Service as RPM Package Configure systemd integration Add install/uninstall hooks to create users, directories etc. Maven Setup <?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.4.2</version> <relativePath/> </parent> <groupId>com.hascode</groupId> <artifactId>sample-app</artifactId> <version>1.0.0-SNAPSHOT</version> <name>sample-app</name> <properties> <java.version>11</java.version> </properties> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-actuator</artifactId> </dependency> </dependencies> <build> <plugins> <plugin> (1) <groupId>de.dentrassi.maven</groupId> <artifactId>rpm</artifactId> <version>1.5.0</version> <executions> <execution> <goals> <goal>rpm</goal> </goals> </execution> </executions> <configuration> <packageName>sample-app</packageName> <skipSigning>true</skipSigning> <group>Application/Misc</group> <requires> <require>java-11-openjdk-headless</require> (2) </requires> <entries> <entry> (3) <name>/opt/sample-app</name> <directory>true</directory> <user>root</user> <group>root</group> <mode>0755</mode> </entry> <entry> (4) <name>/opt/sample-app/log</name> <directory>true</directory> <user>sample-app</user> <group>sample-app</group> <mode>0750</mode> </entry> <entry> (5) <name>/opt/sample-app/sample-app.jar</name> <file>${project.build.directory}/${project.build.finalName}.jar</file> <user>root</user> <group>root</group> <mode>0644</mode> </entry> <entry> (6) <name>/usr/lib/systemd/system/sample-app.service</name> <file>${project.basedir}/src/main/dist/sample-app.service</file> <mode>0644</mode> </entry> </entries> <beforeInstallation> (7) <file>${project.basedir}/src/main/dist/preinstall.sh</file> </beforeInstallation> <afterInstallation> <file>${project.basedir}/src/main/dist/postinstall.sh</file> </afterInstallation> <beforeRemoval> <file>${project.basedir}/src/main/dist/preuninstall.sh</file> </beforeRemoval> <license>All rights reserved</license> </configuration> </plugin> </plugins> </build> </project> ...

Reactive design or reactive architecture has an impact on how modern software systems are implemented. RSocket is a project that aims to adapt the benefits of the patterns described in the Reactive Manifesto and resulting tools like Reactive Streams or Reactive Extensions to a formal new communication protocol. RSocket works with TCP, WebSockets and Aeron transport layers and offers additional features like session resumption. In the following tutorial I’m going to demonstrate how to implement simple client-server communication over TCP and Websockets for different interaction models like request-response, request-stream, fire-and-forget and event subscription. ...

Capacity planning is an important task when trying to anticipate resources and scaling factors for our applications. The usl4j library offers us an easy abstraction for Neil J. Gunther’s Universal Scalability Law and allows us to build up a predictive model based on the parameters throughput, latency and concurrent operations. With a basic input set of two of these parameters, we are able to predict how these values change if we change one input parameter so that we can build our infrastructure or systems according to our SLAs. ...

When implementing distributed systems, client-server architectures and simple applications with network related functionalities, everything is fine when we’re in the development or in the testing stage because the network is reliable and the communicating systems are not as stressed as they are in production. But to sleep well we want to validate how resilient we have implemented our systems, how they behave when the network fails, the latency rises, the bandwidth is limited, connections time out and so on. ...

JetstreamDB is a in-memory database engine for Java that claims to be built for ultra-high speed and the ability of managing complex data structures by storing real Java objects instead of serializing data structures to other database specific formats. In the following short example I would like to demonstrate how to create and read items from such a database by building a small article management sample app. ...

When we need to investigate the cause for a dysfunctional Java application we have a plethora of tools available that on the one hand help us in gathering information, artifacts and statistics and on the other hand help us in processing this information and identifying possible problems. The following list of tools, snippets, workflows and information about specific artifacts could provide a starting point for analyzing such problems and covers topics like heap-dumps, thread-dumps, heap-histograms, heap-regions, garbage-collection-logs, hotspot-compiler/codecache-logs, debugging native-memory, tools for heap-dump-analysis, JVM unified logging and more.. ...

When writing test for applications that interact with Kafka brokers we often need to setup a decent environment including an instance of Kafka and ZooKeeper. Though Kafka ships with some classes for testing, setting up a simple testing environment is quite easier with the kafka-unit library that offers JUnit test rule support or a fast programmatic setup within no time. In the following short example, I’d like to show how create a simple setup using Maven, Surefire and kafka-unit. ...