MainView.java

package com.example.demo;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

import javax.annotation.PostConstruct;
import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Autowired;

import com.vaadin.flow.component.grid.Grid;
import com.vaadin.flow.component.orderedlayout.VerticalLayout;
import com.vaadin.flow.router.Route;

@Route
public class MainView extends VerticalLayout {

	@Autowired
	DataSource dataSource;
	private List<String> headers;
	private List<List<String>> queryResults;

	@PostConstruct
	void init() throws SQLException {

		initExampleDatabase();

		runTheQuery();

		// now do the actual grid and connect in to the Persons table

		Grid<List<String>> datagrid = new Grid<>();
		for (int i = 0; i < headers.size(); i++) {
			int columnIndex = i;
			datagrid.addColumn(listOfStrings -> listOfStrings.get(columnIndex)).setHeader(headers.get(columnIndex));
		}
		datagrid.setItems(queryResults);
		add(datagrid);
	}

	private void runTheQuery() {
		Connection con = null;
		Statement pstmt;
		try {
			// do the query and read the data to two-dim string array and headers to another
			// array
			con = dataSource.getConnection();
			pstmt = con.createStatement();
			// put your more complex query here
			ResultSet rs = pstmt.executeQuery("SELECT * FROM Persons");
			int columnCount = rs.getMetaData().getColumnCount();

			headers = new ArrayList<>();
			for (int i = 0; i < columnCount; i++) {
				String columnName = rs.getMetaData().getColumnName(i + 1);
				headers.add(columnName);
			}

			queryResults = new ArrayList<>();
			while (rs.next()) {
				ArrayList<String> row = new ArrayList<String>();
				for (int i = 0; i < columnCount; i++) {
					row.add(rs.getObject(i + 1).toString());
				}
				queryResults.add(row);
			}
			pstmt.close();
		} catch (SQLException e) {
			e.printStackTrace();
		} finally {
			if (con != null)
				try {
					con.close();
				} catch (SQLException e) {
				}
		}
	}

	private void initExampleDatabase() throws SQLException {
		Connection con = null;
		PreparedStatement pstmt;
		try {
			con = dataSource.getConnection();
			con.setAutoCommit(false);
			pstmt = con.prepareStatement(
					"CREATE TABLE Persons (PersonID int, LastName varchar(255), FirstName varchar(255), Address varchar(255),City varchar(255));");
			pstmt.executeUpdate();
			pstmt.close();

			pstmt = con.prepareStatement("INSERT INTO Persons VALUES(1,'Tahvonen','Matti','Ruukinkatu','Turku');");
			pstmt.executeUpdate();
			pstmt.close();
			con.commit();
			con.close();

		} catch (Exception e) {
			// NOP, table exists...
		} finally {
			if (con != null)
				con.close();
		}
	}

}