package returnitRest;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;

import java.io.IOException;
import java.util.Map;

public class MapBarPlot extends JsonSerializer<Map<?, ?>> {

    @Override
    public void serialize(Map<?, ?> value, JsonGenerator generator,
                          SerializerProvider serializers) throws IOException,
            JsonProcessingException {
        generator.writeStartArray();
        for (Map.Entry<?, ?> entry : value.entrySet()){
            generator.writeStartObject();
            generator.writeObjectField("key", entry.getKey());
            generator.writeObjectField("value", entry.getValue());
            generator.writeEndObject();
        }
        generator.writeEndArray();
    }
}
=========================================================================================
package returnitRest;

import com.fasterxml.jackson.databind.annotation.JsonSerialize;

import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.time.LocalDateTime;
import java.util.HashMap;
import java.util.Map;

public class DbReport implements AutoCloseable {

    private static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
    private static final String DB_URL = "jdbc:mysql://localhost/returnit";

    private static final String USER = "returnit";
    private static final String PASS = "returnit";

    private java.sql.Connection conn = null;

    @JsonSerialize(using = MapBarPlot.class)
    private Map<String, Integer> recipes;

    public DbReport() throws SQLException {
        try {
            Class.forName(JDBC_DRIVER);
            conn = DriverManager.getConnection(DB_URL, USER, PASS);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void close() {
        try {
            this.conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public Map<String, Integer> ereturnsPerClient(LocalDateTime from , LocalDateTime to) throws SQLException {

        Map<String, Integer> bpData = new HashMap<String, Integer>();

        String sql = "SELECT firstName \"client\", COUNT(client) \"num_ereturns\" " +
                "FROM ereturn, user " +
                "WHERE client = idUser GROUP BY client";

        PreparedStatement stmt = conn.prepareStatement(sql);

        ResultSet rs = stmt.executeQuery();

        while (rs.next()) {
            bpData.put(rs.getString("client"), rs.getInt("num_ereturns"));
        }

        return bpData;
    }
}
====================================================================================
package returnitRest;

import javax.ws.rs.*;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
import java.sql.SQLException;
import java.util.Map;
import java.util.logging.Logger;

@Path("/report")
public class ReportResource {

    private static final Logger logger = Logger.getLogger(UserResource.class.getName());

    @POST
    @Path("/numEreturnAllClients")
    @Produces(MediaType.APPLICATION_JSON)
    public Response numEreturnAllClients() throws SQLException {

        logger.info("Getting number of ereturn per client for all clients (numEreturnAllClients) ... ");

        try{
            DbReport q = new DbReport();

            Map<String, Integer> balPlotData = q.ereturnsPerClient(null, null);

            return Response.ok(balPlotData).build();

        }catch (SQLException e){

            return Response.serverError().entity(e).build();
        }
    }
}