IT-SDK-Java

Ref.

• https://dev.java/
• http://tutorials.jenkov.com/
• Books: https://www.manning.com/
• Tutorial: https://www.javatpoint.com/java-tutorial
• Tutorial: https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/object-oriented-programming
• Tutorial: https://www.tutorialspoint.com/design_pattern/index.htm
• Tutorial: https://howtodoinjava.com/
• Patterns: https://en.wikipedia.org/wiki/Facade_pattern
• Patterns: https://www.baeldung.com/java-core-structural-patterns
• https://www.jrebel.com/blog/what-is-jrebel
• Hibernate: http://hibernate.org/

Tools

• https://sdkman.io/

Setting

* JAVA_HOME=C:\sdk\Java\jdk_1.8.0_65
* JDK_HOME=%JAVA_HOME%
* JRE_HOME=%JAVA_HOME%
* ----------------------------------
* Windows: PATH=%JAVA_HOME%/bin
* Linux: PATH=$PATH:$JAVA_HOME/bin

taskkill /f /im jqs.exe
taskkill /f /im javaw.exe
taskkill /f /im java.exe

Installing Java

• https://www.adoptium.net/
• https://www.graalvm.org/
• https://aws.amazon.com/corretto/
• https://learn.microsoft.com/en-us/java/openjdk/download

Releases

• GA (General-Availability)
• LTS (Long-Term-Support)
• https://en.wikipedia.org/wiki/Java_version_history

* JDK 25 (GA 2025.09.16) LTS <<<
* JDK 24 (GA 2025.03.18)
* JDK 23 (GA 2024.09.17) 
* JDK 22 (GA 2024.03.19) 
* JDK 21 (GA 2023.09.19) LTS 
* JDK 20 (GA 2023.03.21) 
* JDK 19 (GA 2022.09.20) 
* JDK 18 (GA 2022.03.22) 
* JDK 17 (GA 2021.09.14) LTS
* JDK 16 (GA 2021.03.16) 
* JDK 15 (GA 2020.09.15) 
* JDK 14 (GA 2020.03.17) 
* JDK 13 (GA 2019.09.17) 
* JDK 12 (GA 2019.03.19) 
* JDK 11 (GA 2018.09.25) LTS
* JDK 10 (GA 2018.03.20) 
* JDK 09 (GA 2017.09.21) 
* JDK 08 (GA 2014.03.18) LTS

Settings

sudo update-alternatives --config java
sudo update-alternatives --config javac

fedora

sudo dnf install java-17-openjdk-devel       ## JDK
sudo dnf install java-17-openjdk-headless    ## JRE-Min
sudo dnf install java-17-openjdk             ## JRE-Full

Ubuntu

sudo apt install default-jre      ### JRE
sudo apt install default-jdk      ### JDK
----
sudo apt install openjdk-17-jre   ### JRE
sudo apt install openjdk-17-jdk   ### JDK

macOS

rm -rf /opt/homebrew/opt/openjdk@21
rm -rf /opt/homebrew/Cellar/openjdk@21
brew cleanup && brew doctor
#########################################
brew install openjdk@21
brew install openjdk@17
brew install openjdk@11
brew install --cask corretto
#########################################
sudo ln -sfn /opt/homebrew/opt/openjdk@21/libexec/openjdk.jdk /Library/Java/JavaVirtualMachines/openjdk-21.jdk
echo 'export PATH="/opt/homebrew/opt/openjdk@21/bin:$PATH"' >> ~/.zshrc
export CPPFLAGS="-I/opt/homebrew/opt/openjdk@21/include"
#########################################
brew list --versions openjdk@21
brew unlink openjdk@21
brew link --force --overwrite openjdk@21

Settings

-Xms1g                   ### Setting the initial and minimum heap size for 1G.
-Xmx1g                   ### Setting the maximum heap size for 1G.
-XX:+PrintGCDetails      ### Detaillierte GC Logging.
-XX:+PrintGCDateStamps   ### Jeder Zeile eine absolute Datums- und Zeitangabe vorangestellt.
-Xloggc:file.log         ### Das GC Log wird in der Datei <file.log> geschrieben.

Maven

• ref: https://maven.apache.org/guides/mini/guide-multiple-repositories.html
• ref: https://www.vogella.com/tutorials/ApacheMaven/article.html

wget https://www-us.apache.org/dist/maven/maven-3/3.6.3/binaries/apache-maven-3.6.3-bin.tar.gz
sudo tar xzf apache-maven-3.6.3-bin.tar.gz
sudo ln -s apache-maven-3.6.3 maven
sudo vi /etc/profile.d/maven.sh
-------------------------------------
export MAVEN_HOME=/opt/maven
export PATH=${MAVEN_HOME}/bin:${PATH}
-------------------------------------
source /etc/profile.d/maven.sh
mvn -version

mvn archetype:generate 
-DgroupId=net.samerhijazi 
-DartifactId=maven-startup 
-DarchetypeArtifactId=maven-archetype-quickstart 
-DinteractiveMode=false

mvn clean
mvn compile
mvn package
mvn dependency:list-repositories
mvn dependency:tree
mvn dependency:analyze
mvn dependency:copy-dependencies
mvn dependency:get -Dartifact=com.google.protobuf:protobuf-java:3.19.1
mvn dependency:get -Dartifact=org.apache.maven.plugins:maven-downloader-plugin:1.0

Code-Collections

import java.util.concurrent.TimeUnit;
---------------------------------------------
try {
    TimeUnit.SECONDS.sleep(secondsToSleep);
} catch (InterruptedException ie) {
    Thread.currentThread().interrupt();
}
---------------------------------------------

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import io.agroal.api.AgroalDataSource;

public class SettingDatabase{

  AgroalDataSource dataSource;
  String db = "jdbc:db2://localhost:5245/DATABASE:user=db2;password=db2;";
  String sql = "SELECT * FROM users";

  public void init_DriverManager()throws SQLException{
    try{		
      Connection connection = DriverManager.getConnection(db); //Connection connection = AgroalDataSource.getConnection(db);
      PreparedStatement ps = connection.prepareStatement(sql);
      ResultSet rs = ps.executeQuery();
    }
  }	
}

Architekture

Database

• JDBC is a low level standard for interaction with databases. JPA is higher level standard for the same purpose.
• JDBC allows you to do more things with the Database directly. JPA allows you to use an object model in your application.
• Datasource & Pooling (JDBC) >> Agroal
• Datasource & Pooling (Reactive) >> Vert.x
• Agroal is a datasource connection pool implementation with integration with transaction, security and other systems.
• Agroal library allows the definition of java.sql.DataSource with connection pooling.
• JPA (Java Persistence API) & Hibernate ORM (Object-relational mapping). JPA is only a specification. Hibernate is an implementation of JPA.

---

• JDBC: https://quarkus.io/guides/datasource
• Reactive: https://quarkus.io/guides/reactive-sql-clients
• Oracle: https://blogs.oracle.com/developers/configuring-the-oracle-jdbc-drivers-with-quarkus

RESTFul

• RESTEasy is an implementation of JAX-RS and it is used to implement RestFul-services.
• Microservices communicating either synchronously via REST or asynchronously using Kafka.

---

• https://quarkus.io/guides/rest-json
• https://quarkus.io/guides/rest-client
• https://quarkus.io/guides/resteasy-reactive
• https://lankydan.dev/building-a-rest-api-with-quarkus
• https://dzone.com/articles/building-a-rest-api-with-quarkus

Sprin Boot

• https://www.baeldung.com/spring-boot-start