In this lab, we will create a small java program that gets data from MySQL and run it in Docker.

Estimated Time: 10 minutes

Java is a high-level, class-based, object-oriented programming language that is designed to have as few implementation dependencies as possible. It is a general-purpose programming language intended to let programmers write once, run anywhere (WORA), meaning that compiled Java code can run on all platforms that support Java without the need to recompile.

In this lab, you will:

• Create a Java program that gets data from MySQL
• Create a docker container
• Run it

This lab assumes you have:

• Followed the previous labs

Check the Dockerfile

<copy>cd oke_mysql_java_101/demo1
cat Dockerfile</copy>

FROM openjdk:11
COPY . /app
COPY lib /app/lib
WORKDIR /app
RUN javac QueryDB.java
CMD ["java", "-classpath",  "lib/*:.", "QueryDB", "jdbc:mysql://127.0.0.1/db1", "root", "Welcome___1"] 

Note: in the previous labs, we have forwarded the MySQL 3306 to localhost(127.0.0.1):3306.

Check the java program

<copy>cat QueryDB.java</copy>

import java.sql.*;
public class QueryDB {
  public static void main(String[] args) {
    try {
      Connection cnx = DriverManager.getConnection(args[0], args[1], args[2]);
      Statement stmt = cnx.createStatement();
      ResultSet rs = stmt.executeQuery("SELECT id, name FROM t1");
      while (rs.next()) {
        System.out.println(rs.getInt(1) + " " + rs.getString(2));
      }
      cnx.close();
    } catch (SQLException e) {
      e.printStackTrace();
    }
  }
} 

To build and run the docker container, do this:

<copy>bin/build.sh
docker run --net=host querydb</copy>

• Choose: docker.io/library/openjdk:xxxx
• The "-net=host" is needed because MySQL is accessed on 127.0.0.1.

You will see:

1 DOLPHIN
2 TIGER
3 PENGUIN
4 LION

To check what the container contains:

<copy>docker run -it --entrypoint /bin/bash querydb
ls
exit</copy>

• Marc Gueury - Application Development EMEA
• Stuart Davey - MySQL EMEA
• Mario Beck - MySQL EMEA
• Olivier Dasini - MySQL EMEA
• Last Updated <Feb 2022>