StarsServlet.java

package main.java;

import com.google.gson.JsonArray;
import com.google.gson.JsonObject;

import javax.naming.InitialContext;
import javax.naming.NamingException;
import jakarta.servlet.ServletConfig;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import javax.sql.DataSource;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.*;


// Declaring a WebServlet called StarsServlet, which maps to url "/api/stars"
@WebServlet(name = "StarsServlet", urlPatterns = "/api/stars")
public class StarsServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    // Create a dataSource which registered in web.
    private DataSource dataSource;

    public void init(ServletConfig config) {
        try {
            dataSource = (DataSource) new InitialContext().lookup("java:comp/env/master");
        } catch (NamingException e) {
            e.printStackTrace();
        }
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {

        response.setContentType("application/json"); // Response mime type

        // Output stream to STDOUT
        PrintWriter out = response.getWriter();

        // Get a connection from dataSource and let resource manager close the connection after usage.
        try (Connection conn = dataSource.getConnection()) {

            // Declare our statement
            Statement statement = conn.createStatement();

            String query = "SELECT * from stars";

            // Perform the query
            ResultSet rs = statement.executeQuery(query);

            JsonArray jsonArray = new JsonArray();

            // Iterate through each row of rs
            while (rs.next()) {
                String star_id = rs.getString("id");
                String star_name = rs.getString("name");
                String star_dob = rs.getString("birthYear");

                // Create a JsonObject based on the data we retrieve from rs
                JsonObject jsonObject = new JsonObject();
                jsonObject.addProperty("star_id", star_id);
                jsonObject.addProperty("star_name", star_name);
                jsonObject.addProperty("star_dob", star_dob);

                jsonArray.add(jsonObject);
            }
            rs.close();
            statement.close();

            // Log to localhost log
            request.getServletContext().log("getting " + jsonArray.size() + " results");

            // Write JSON string to output
            out.write(jsonArray.toString());
            // Set response status to 200 (OK)
            response.setStatus(200);

        } catch (Exception e) {

            // Write error message JSON object to output
            JsonObject jsonObject = new JsonObject();
            jsonObject.addProperty("errorMessage", e.getMessage());
            out.write(jsonObject.toString());

            // Set response status to 500 (Internal Server Error)
            response.setStatus(500);
        } finally {
            out.close();
        }

        // Always remember to close db connection after usage. Here it's done by try-with-resources

    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
        response.setContentType("application/json");

        PrintWriter out = response.getWriter();

        try (Connection conn = dataSource.getConnection()) {
            String starName = request.getParameter("star");
            String birthYear = request.getParameter("birth");

            String starIdQuery = "SELECT max(stars.id) FROM stars";

            PreparedStatement starIdStatement = conn.prepareStatement(starIdQuery);

            ResultSet starIdRS = starIdStatement.executeQuery();
            starIdRS.next();
            String maxId = starIdRS.getString("max(stars.id)");
            int maxIdNum = Integer.parseInt(maxId.replaceAll("\\D+", ""));
            int uniqueIdNum = maxIdNum + 1;
            String starId = "nm" + uniqueIdNum;

            String starInsert = "INSERT INTO stars (id, name, birthYear) VALUES(?, ?, ?)";
            PreparedStatement starInsertStatement = conn.prepareStatement(starInsert);

            starInsertStatement.setString(1, starId);
            starInsertStatement.setString(2, starName);
            if (!birthYear.isEmpty()) {
                starInsertStatement.setInt(3, Integer.parseInt(birthYear));
            } else {
                starInsertStatement.setNull(3, Types.INTEGER);
            }
            starInsertStatement.execute();

            JsonObject jsonObject = new JsonObject();
            jsonObject.addProperty("id", starId);

            out.write(jsonObject.toString());

        }
        catch (Exception e) {
            JsonObject jsonObject = new JsonObject();
            jsonObject.addProperty("errorMessage", e.getMessage());
            out.write(jsonObject.toString());

            request.getServletContext().log("Error:", e);

            response.setStatus(500);
        }
        finally {
            out.close();
        }
    }
}