spring how to manage lots connections to database?

Question

I created javafx apllication that connects to database and creates LineChart from data and i works fine except that when getting data im connecting to database in loop and that makes application slow when using h2 embedded database. I am using spring jdbcDaoSupport to make queries.

Making connection in loop is bad design, but i don't know how i would make it work differently. How should i manage connections like that?

I tried searching for answer but i didn't found anything relevant to my problem.

Here is relevant part of code:

public void cijenaVodePoGradovimaGraf(){
        ObservableList<Grad> gradList;
        ObservableList<String> gradNaziv;
        gradNaziv=FXCollections.observableArrayList();
        gradList=databaseService.getVodoopskrbaGradList();

        for (Grad grad : gradList) {
            gradNaziv.add(grad.getNaziv());
        }

        CategoryAxis xOs=new CategoryAxis(gradNaziv);
        xOs.setTickLabelRotation(270);
        xOs.setTickLabelFont(Font.font(14));

        NumberAxis yOs=new NumberAxis();
        yOs.setLabel("Cijena [kn/kubik]");
        yOs.setTickLabelFont(Font.font(14));

        XYChart.Series<String, Number> series=new XYChart.Series<>();
        series.setName("Varijabilni dio");
        XYChart.Series<String, Number> series2=new XYChart.Series<>();
        series2.setName("Fiksni dio");

        //this is where problem is
        for(int i=0;i<gradNaziv.size();i++){
            ObservableList<Vodoopskrba> v=databaseService.getVodoopskrbaList(gradNaziv.get(i));
            series.getData().add(new XYChart.Data<>(gradNaziv.get(i),v.get(0).getVodoOdvVar()));
            series2.getData().add(new XYChart.Data<>(gradNaziv.get(i),v.get(0).getVodoOdvFix()));
        }
        ObservableList<XYChart.Series<String, Number>> data=FXCollections.observableArrayList();
        data.add(series);
        data.add(series2);

        lcGraf=new LineChart<>(xOs,yOs,data);
        lcGraf.setTitle("Cijena vode");

        for(XYChart.Series<String, Number> s : lcGraf.getData()) {
            for (XYChart.Data<String, Number> d : s.getData()) {
                Tooltip tt=new Tooltip(d.getYValue().toString());
                Tooltip.install(d.getNode(), tt);
                d.getNode().setOnMouseEntered((event)->{
                    d.getNode().getStyleClass().add("onHover");
                });
                d.getNode().setOnMouseExited((event)->{
                    d.getNode().getStyleClass().remove("onHover");
                });
            }
        }

        AnchorPane root=((AnchorPane)this.getStage().getScene().getRoot());
        ((GridPane)root.getChildren().get(0)).add(lcGraf, 0, 1, 2, 1);
    }

I marked part of code where i am looping through list of cities and then i am making database connection to get water suply company from that town and then i add data about price of water in that city to chart.

Answer 1

@Kayaman suggested that i should use connection pool and after some research on internet i found how to set it and it solved speed problem, now stage loads immediately. I am posting solution here so if somebody else encounters this problem too.

<bean id="dataSource" class="org.apache.tomcat.jdbc.pool.DataSource"
        destroy-method="close">
        <property name="driverClassName" value="${jdbc.driver}" />
        <property name="url" value="${jdbc.url}" />
        <property name="username" value="${jdbc.user}" />
        <property name="password" value="${jdbc.pass}" />
        <property name="initialSize" value="5" />
        <property name="maxActive" value="10" />
        <property name="maxIdle" value="5" />
        <property name="minIdle" value="2" />
</bean>

its only thing that needs change.

<!--  tomcat jdbc dependency -->
<dependency>
    <groupId>org.apache.tomcat</groupId>
    <artifactId>tomcat-jdbc</artifactId>
    <version>7.0.35</version>
</dependency>

EDIT:

I found that its possible to use spring SingleConnectionDataSource to make JdbcDaoSupport to reuse same connection and thats exactly what i need.

Here is code:

<bean id="dataSource"
        class="org.springframework.jdbc.datasource.SingleConnectionDataSource">
        <property name="driverClassName" value="${jdbc.driver}" />
        <property name="username" value="${jdbc.user}" />
        <property name="password" value="${jdbc.pass}" />
        <property name="url" value="${jdbc.url}" />
        <property name="suppressClose" value="true" />
    </bean>

Because suppressClose=true connection will not be closed when code call close on datasource so we need to close it manually when we dont need it anymore. I did it the next way:

@Override
    public void stop() {
        SingleConnectionDataSource ds;
        ds=((SingleConnectionDataSource)AppUtil.getContext().getBean("dataSource"));
        ds.destroy();
        AppUtil.closeContext();
    }