Java

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

The following WebFilter redirects incoming requests for / to a static HTML file, index.html. ToIndexPageRedirection.java package com.hascode.tutorial; import org.springframework.stereotype.Component; import org.springframework.web.server.ServerWebExchange; import org.springframework.web.server.WebFilter; import org.springframework.web.server.WebFilterChain; import reactor.core.publisher.Mono; @Component public class ToIndexPageRedirection implements WebFilter { @Override public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) { if (exchange.getRequest().getURI().getPath().equals("/")) { return chain.filter( exchange.mutate().request( exchange.getRequest().mutate().path("/index.html").build() ).build() ); } return chain.filter(exchange); } } Ressources: JavaDocs WebFilter

Sometimes this is useful for the diagnosis of configuration and network problems of ones Java application. This is our single-class HTTP client example without the need for external dependencies: HttpTest.java import javax.net.ssl.KeyManagerFactory; import javax.net.ssl.SSLContext; import javax.net.ssl.TrustManagerFactory; import java.io.FileInputStream; import java.io.IOException; import java.net.InetSocketAddress; import java.net.ProxySelector; import java.net.URI; import java.net.URISyntaxException; import java.net.http.HttpClient; import java.net.http.HttpRequest; import java.net.http.HttpRequest.BodyPublishers; import java.net.http.HttpResponse; import java.net.http.HttpResponse.BodyHandlers; import java.security.KeyManagementException; import java.security.KeyStore; import java.security.KeyStoreException; import java.security.NoSuchAlgorithmException; import java.security.UnrecoverableKeyException; import java.security.cert.CertificateException; import java.time.Duration; import java.time.temporal.ChronoUnit; public class HttpTest { public static void main(String[] args) throws URISyntaxException, NoSuchAlgorithmException, KeyManagementException, KeyStoreException, UnrecoverableKeyException, IOException, CertificateException { String bodyPayload = """ ourpayload, json, xml, ... """; String keyStorePath = "/opt/keystore.jks"; String keyStorePassword = "ABCDEFG"; String proxyHost = "ourproxy.proxy"; String uriString = "https://some-service/api"; int proxyPort = 8080; int timeoutInSeconds = 60; KeyStore keyStore = KeyStore.getInstance("JKS"); keyStore.load(new FileInputStream(keyStorePath), keyStorePassword.toCharArray()); KeyManagerFactory keyManagerFactory = KeyManagerFactory.getInstance("PKIX"); keyManagerFactory.init(keyStore, null); TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance("PKIX"); // using same keystore for both trustManagerFactory.init(keyStore); SSLContext sslContext = SSLContext.getInstance("TLS"); sslContext.init(keyManagerFactory.getKeyManagers(), trustManagerFactory.getTrustManagers(), null); HttpClient client = HttpClient.newBuilder() .proxy( ProxySelector.of(new InetSocketAddress(proxyHost, proxyPort))) .sslContext(sslContext) .build(); URI uri = new URI(uriString); HttpRequest request = HttpRequest.newBuilder(uri) .POST(BodyPublishers.ofString(bodyPayload)) .timeout(Duration.of(timeoutInSeconds, ChronoUnit.SECONDS)) .build(); System.out.printf("Sending POST request to %s, timeout: %ds%n", uri, timeoutInSeconds); try { HttpResponse response = client.send(request, BodyHandlers.ofString()); System.out.println("Response received..."); System.out.printf("\tResponse-Status: %d%n", response.statusCode()); System.out.printf("\tResponse-Body: %s%n", response.body()); System.out.println("-------------------------------------%n"); } catch (IOException e) { System.err.printf("IOException caught: %s%n", e.getMessage()); e.printStackTrace(System.err); } catch (InterruptedException e) { System.err.printf("IOException caught: %s%n", e.getMessage()); e.printStackTrace(System.err); } } } ...

Let’s say we would like to increase the limit t 10MB …​ Broker Configuration Apply the new limit either by modifying the server.properties like this…​ max.message.bytes=10485760 or apply it to a specific topic using kafka-configs.sh --bootstrap-server localhost:9092 \ --entity-type topics \ --entity-name thetopic \ --alter \ --add-config max.message.bytes=10485760 Producer Configuration for Spring Boot We simply need to add the following line to our application.properties: spring.kafka.producer.properties.max.request.size=spring.kafka.producer.properties.max.request.size The following proof-of-concept demonstrates that without the property, sending a large message fails, with the property it succeeds: ...

Sometimes it is nice to set up an embedded Kafka broker for testing without the need to have Docker installed (e.g. for using testcontainers-lib). The following snippet shows, how to set up an embedded Kafka instance for testing for a Spring Boot project. Setup Using Maven, this is our Spring Boot project with dependencies needed: 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 http://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>(1) <version>2.6.4</version> <relativePath/> <!-- lookup parent from repository --> </parent> <groupId>com.hascode.tutorial</groupId> <artifactId>kafka-testing</artifactId> <version>1.0.0-SNAPSHOT</version> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding> <java.version>17</java.version> <maven.compiler.source>${java.version}</maven.compiler.source> <maven.compiler.target>${java.version}</maven.compiler.target> <kafka.version>3.1.0</kafka.version>(2) </properties> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter</artifactId> </dependency> <dependency> <groupId>org.springframework.kafka</groupId> <artifactId>spring-kafka</artifactId>(3) </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency> <dependency> <groupId>org.springframework.kafka</groupId> <artifactId>spring-kafka-test</artifactId>(4) <scope>test</scope> </dependency> <dependency>(5) <groupId>org.junit.jupiter</groupId> <artifactId>junit-jupiter-api</artifactId> <scope>test</scope> </dependency> <dependency> <groupId>org.junit.jupiter</groupId> <artifactId>junit-jupiter-engine</artifactId> <scope>test</scope> </dependency> <dependency> <groupId>org.junit.platform</groupId> <artifactId>junit-platform-launcher</artifactId> <scope>test</scope> </dependency> [..] </project> ...

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 when accessing SOAP APIs, our SOAP client needs to sign the request. How this can be achieved using Spring Boot’s WebserviceTemplate within a few steps is the scope of this short article. This snippet only deals with the client side not with the security configuration on the server side. Also it assumes, that you have already set up your keystore/truststore and that you’re loading these with your Spring Boot application’s startup without errors. ...

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' ...

As technical documentation for my Java software projects often makes use of technologies like AsciiDoctor and PlantUML, having a tool to analyze existing structures and generating class diagrams from it, is a nice thing. Luckily, the Maven plugin from the Living Documentation Project does all the work for me here. Setup We just need to add the following Maven plugin to our project’s pom.xml: <plugin> <groupId>ch.ifocusit.livingdoc</groupId> <artifactId>livingdoc-maven-plugin</artifactId> <version>1.2</version> <executions> <execution> <id>class-diagram</id> <phase>package</phase> <goals> <goal>diagram</goal> <goal>glossary</goal> </goals> </execution> </executions> <configuration> <packageRoot>com.hascode</packageRoot> <interactive>true</interactive> </configuration> </plugin> ...