I am learning JAVA EE.

Before i created my Task servlet, and DBManager with methods like GetTaskList,AddTask with existing data:

Static { data }. Everything worked perfectly.

Now i connected MySql (created table there). In “DBManager.servlet” i wrote methods to get and add tasks to “DBManager”. Data imports from MySql successfully, i can see imported table database in Intelij Idea.

But i doesn’t show data in “Home.jsp”.

It writes:”java.lang.NullPointerException: Cannot invoke “java.sql.Connection.prepareStatement(String)” because “kz.bitlab.servlets.DBManager.connection” is null” ?

Home.jsp worked perfectly,showed data when i used static data from DBManager. But when connected MySql it doesn’t show anything….

Home.servlet:

package kz.bitlab.servlets;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.ArrayList;

@WebServlet(value = "/home")
public class home extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");

        String name = request.getParameter("name");
        String description = request.getParameter("description");
        String date = request.getParameter("date");
        String category = request.getParameter("category");

        DBManager.addTask(new Task(null, name, description, date, category));

        response.sendRedirect("/home");
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        request.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");

        ArrayList<Task> task = DBManager.getTaskList();
        request.setAttribute("task", task);
        request.getRequestDispatcher("/home.jsp").forward(request, response);
    }
}

DBManager.servlet

package kz.bitlab.servlets;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;

public class DBManager {

    private static Connection connection;

    static {
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            connection = DriverManager.getConnection(
                    "jdbc:mysql://localhost:3306/Tasks?useUnicode=true&serverTimezone=UTC","root", "");
        }catch (Exception e){
            e.printStackTrace();
        }
    }


    public static void addTask(Task task) {
        try {

            PreparedStatement statement = connection.prepareStatement(""+
            "INSERT INTO task_items(id,name,description,date,category)"+
                    "VALUES (NULL,?,?,?,?)"+
            "");

statement.setString(1,task.getName());
statement.setString(2,task.getDescription());
statement.setString(3,task.getDate());
statement.setString(4,task.getCategory());

int rows = statement.executeUpdate();
statement.close();

        }catch (Exception e){
            e.printStackTrace();
        }
    }

    public static ArrayList<Task> getTaskList() {
       ArrayList<Task>task = new ArrayList<>();

       try {
           PreparedStatement statement=connection.prepareStatement("SELECT * FROM task_items");

           ResultSet resultSet=statement.executeQuery();

           while(resultSet.next()){
               task.add(new Task(
                       resultSet.getLong("id"),
                       resultSet.getString("name"),
                       resultSet.getString("description"),
                       resultSet.getString("date"),
                       resultSet.getString("category")
               ));

               }
           statement.close();

       }catch (Exception e){
           e.printStackTrace();
       }

       return task;
    }


    public static Task getTask(Long getId) {
        Task task = null;
        try {
            PreparedStatement statement=connection.prepareStatement(""+
                    "SELECT id,name,description,date,category"+
                    " FROM task WHERE id=?");

            statement.setLong(1, getId);
            ResultSet resultSet=statement.executeQuery();

            if(resultSet.next()){
                task = new Task(
                        resultSet.getLong("id"),
                        resultSet.getString("name"),
                        resultSet.getString("description"),
                        resultSet.getString("date"),
                        resultSet.getString("category")
                );

            }
            statement.close();

        }catch (Exception e){
            e.printStackTrace();
        }

        return task;
    }

    public static void deleteTask(Long id) {}


    public static void saveTask(Task task) {}


}

Wanna show data from MySql to Home.jsp (Using Servlet in Java)