Maven

Figure 1. NATS Architecture Component Diagram NATS is a high-performance messaging system that offers simplicity, speed, and scalability. It is particularly suited for building distributed systems and microservices. This article demonstrates how to integrate NATS with Java, showcasing the essential steps to set up, connect, and publish/subscribe to messages. Prerequisites Before diving in, we should ensure to have the following installed: Java Development Kit (JDK) 11 or later. Maven or Gradle for dependency management. Docker (optional). ...

Just a quick snippet Maven Integration pom.xml <dependency> <groupId>org.javers</groupId> <artifactId>javers-core</artifactId> <version>${javers.version}</version> </dependency> Calculate Changes in Object Graph package io.hascode; import org.javers.core.Changes; import org.javers.core.Javers; import org.javers.core.JaversBuilder; import org.javers.core.diff.Diff; public <T> Changes diff(T snapshot, T latest) { Javers javers = JaversBuilder.javers().build(); Diff diff = javers.compare(snapshot, latest); return diff.getChanges(); } Resources Javers Website

MapStruct is a nice tool to generate mappers for converting one Java bean into another e.g. for projections, data-transfer-objects and so on …​ As long as fields in source and target beans do match, the mapper is able to generate the data setting automatically .. else we may specify which source fields to map into which target fields or to register custom converters with ease. Using Maven, we need to add dependencies and plugin integration to our pom.xml: ...

Sometimes one needs to derive a Google Protocol Buffers schema from an XML schema .. e.g. from an Enterprise Architect Export. Tool used here: schema2proto (GitLab project) Steps Download schema2proto-lib from the global Maven repository: https://search.maven.org/search?q=schema2proto Run Schema2Proto against a give XSD schema file and with a given output directory: java -jar schema2proto-lib-1.53.jar Schema2Proto --outputDirectory=src/main/protobuf input.xsd A yaml config file may be given instead of cli parameters: java -jar schema2proto-lib-1.53.jar Schema2Proto ----configFile=config.yaml input.xsd ...

Goals Setup Kafka and Zookeeper with Docker and docker-compose Create a message consumer and producer in Java Kafka Setup We’re using docker-compose to set up our message broker, zookeper and other stuff using confluent-platform. This is our docker-compose.yaml config file from Confluent’s following GitHub repository. docker-compose.yaml --- version: '2' services: zookeeper: image: confluentinc/cp-zookeeper:7.0.1 hostname: zookeeper container_name: zookeeper ports: - "2181:2181" environment: ZOOKEEPER_CLIENT_PORT: 2181 ZOOKEEPER_TICK_TIME: 2000 broker: image: confluentinc/cp-kafka:7.0.1 hostname: broker container_name: broker depends_on: - zookeeper ports: - "29092:29092" - "9092:9092" - "9101:9101" environment: KAFKA_BROKER_ID: 1 KAFKA_ZOOKEEPER_CONNECT: 'zookeeper:2181' KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: PLAINTEXT:PLAINTEXT,PLAINTEXT_HOST:PLAINTEXT KAFKA_ADVERTISED_LISTENERS: PLAINTEXT://broker:29092,PLAINTEXT_HOST://localhost:9092 KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1 KAFKA_TRANSACTION_STATE_LOG_MIN_ISR: 1 KAFKA_TRANSACTION_STATE_LOG_REPLICATION_FACTOR: 1 KAFKA_GROUP_INITIAL_REBALANCE_DELAY_MS: 0 KAFKA_JMX_PORT: 9101 KAFKA_JMX_HOSTNAME: localhost schema-registry: image: confluentinc/cp-schema-registry:7.0.1 hostname: schema-registry container_name: schema-registry depends_on: - broker ports: - "8081:8081" environment: SCHEMA_REGISTRY_HOST_NAME: schema-registry SCHEMA_REGISTRY_KAFKASTORE_BOOTSTRAP_SERVERS: 'broker:29092' SCHEMA_REGISTRY_LISTENERS: http://0.0.0.0:8081 connect: image: cnfldemos/kafka-connect-datagen:0.5.0-6.2.0 hostname: connect container_name: connect depends_on: - broker - schema-registry ports: - "8083:8083" environment: CONNECT_BOOTSTRAP_SERVERS: 'broker:29092' CONNECT_REST_ADVERTISED_HOST_NAME: connect CONNECT_GROUP_ID: compose-connect-group CONNECT_CONFIG_STORAGE_TOPIC: docker-connect-configs CONNECT_CONFIG_STORAGE_REPLICATION_FACTOR: 1 CONNECT_OFFSET_FLUSH_INTERVAL_MS: 10000 CONNECT_OFFSET_STORAGE_TOPIC: docker-connect-offsets CONNECT_OFFSET_STORAGE_REPLICATION_FACTOR: 1 CONNECT_STATUS_STORAGE_TOPIC: docker-connect-status CONNECT_STATUS_STORAGE_REPLICATION_FACTOR: 1 CONNECT_KEY_CONVERTER: org.apache.kafka.connect.storage.StringConverter CONNECT_VALUE_CONVERTER: io.confluent.connect.avro.AvroConverter CONNECT_VALUE_CONVERTER_SCHEMA_REGISTRY_URL: http://schema-registry:8081 CONNECT_PLUGIN_PATH: "/usr/share/java,/usr/share/confluent-hub-components" CONNECT_LOG4J_LOGGERS: org.apache.zookeeper=ERROR,org.I0Itec.zkclient=ERROR,org.reflections=ERROR ksqldb-server: image: confluentinc/cp-ksqldb-server:7.0.1 hostname: ksqldb-server container_name: ksqldb-server depends_on: - broker - connect ports: - "8088:8088" environment: KSQL_CONFIG_DIR: "/etc/ksql" KSQL_BOOTSTRAP_SERVERS: "broker:29092" KSQL_HOST_NAME: ksqldb-server KSQL_LISTENERS: "http://0.0.0.0:8088" KSQL_CACHE_MAX_BYTES_BUFFERING: 0 KSQL_KSQL_SCHEMA_REGISTRY_URL: "http://schema-registry:8081" KSQL_PRODUCER_INTERCEPTOR_CLASSES: "io.confluent.monitoring.clients.interceptor.MonitoringProducerInterceptor" KSQL_CONSUMER_INTERCEPTOR_CLASSES: "io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor" KSQL_KSQL_CONNECT_URL: "http://connect:8083" KSQL_KSQL_LOGGING_PROCESSING_TOPIC_REPLICATION_FACTOR: 1 KSQL_KSQL_LOGGING_PROCESSING_TOPIC_AUTO_CREATE: 'true' KSQL_KSQL_LOGGING_PROCESSING_STREAM_AUTO_CREATE: 'true' ksqldb-cli: image: confluentinc/cp-ksqldb-cli:7.0.1 container_name: ksqldb-cli depends_on: - broker - connect - ksqldb-server entrypoint: /bin/sh tty: true ksql-datagen: image: confluentinc/ksqldb-examples:7.0.1 hostname: ksql-datagen container_name: ksql-datagen depends_on: - ksqldb-server - broker - schema-registry - connect command: "bash -c 'echo Waiting for Kafka to be ready... && \ cub kafka-ready -b broker:29092 1 40 && \ echo Waiting for Confluent Schema Registry to be ready... && \ cub sr-ready schema-registry 8081 40 && \ echo Waiting a few seconds for topic creation to finish... && \ sleep 11 && \ tail -f /dev/null'" environment: KSQL_CONFIG_DIR: "/etc/ksql" STREAMS_BOOTSTRAP_SERVERS: broker:29092 STREAMS_SCHEMA_REGISTRY_HOST: schema-registry STREAMS_SCHEMA_REGISTRY_PORT: 8081 rest-proxy: image: confluentinc/cp-kafka-rest:7.0.1 depends_on: - broker - schema-registry ports: - 8082:8082 hostname: rest-proxy container_name: rest-proxy environment: KAFKA_REST_HOST_NAME: rest-proxy KAFKA_REST_BOOTSTRAP_SERVERS: 'broker:29092' KAFKA_REST_LISTENERS: "http://0.0.0.0:8082" KAFKA_REST_SCHEMA_REGISTRY_URL: 'http://schema-registry:8081' ...

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> ...

A lot of boilerplate code is written when developers need to test their applications with different connected systems like databases, stream platforms and other collaborators. Docker allows to handle those dependencies but there is still some glue code required to bind the container’s lifecycle and the configuration to the concrete integration test. Testcontainers is a testing library that offers lightweight throwaway instances of anything able to run in a Docker container, with bindings to configure the specific containers and also provides wrappers to manage our own custom containers. ...

The OpenAPI and Swagger API description format are becoming important standards to specify API contracts for RESTful web services and the Microservices trend pushes the need for such contracts even further. Therefore arises the need for software architects, testers and developers to write tests to verify if an exposed API follows such a specified contract. In the following tutorial I will demonstrate a setup with Java, Maven, JUnit and the designated contract-testing-library, assertj-swagger that verifies the validity of such a contract exposed by a Spring Boot application against a local stored definition. ...