JSF Expression Language Operations and sum values fields

Question

I need to make calculations of amounts received in the jsf datatable and display in columns sum of these fields.

A) I need sum all items calculated in EL Expression of value1 and show in total1 field.

B) I need sum all items calculated in EL Expression of value2 and show in total2 field.

C) I need sum total1 + total2 and show in field Total.

Obs.: I receive values from DatabaseBean.

<p:dataTable id="table" value="#{valueBean.values}" var="item">
<p:column >
<h:outputText id="value1" value="#{(item[0]*160)/100}" />
<f:facet name="footer">
   <h:outputText id="total1" value="#...????" />
</f:facet>
</p:column >
<p:column >
<h:outputText id="value2" value="#{(item[1]*160)/100}" />
<f:facet name="footer">
   <h:outputText id="total2" value="#...????" />
</f:facet>   
</p:column >
<h:outputText id="total" value="#...????" />
...
</p:dataTable>

Answer 1

1. Things to point out first. Doing thing such as value="#{(item[0]*160)/100}" is bad programming practice. For various reasons but obviously for maintainability, future developers will find it had to understand why 160 or 100 let alone figure out how to change these values safely if they change
2. Depending on whether item in values are valid "numerical" values you might have errors that can be easily handled server side rather than on the UI layer

Safest Strategy is to employ beans to use to calculate and to hold all the values you need to display on the UI

-You sound like a green programmer so I will give you a leg up. But the code below can still use some improvements if you think carefully.

-I have defined the Item bean as an inner class below but you can always break it out into its own class if you feel comfortable with that.

-Also this strategy allows you to add checks where needed and error handling where needed which i have not included.

-I have also assumed that the initial data comes from a list of DatabaseBean that holds some 2 values in an array.

import java.util.ArrayList;
import java.util.List;

public class BagOfItems {

    private static int COMMON_MULTIPLIER = 160;//here document where this comes from
    private static int COMMON_DIVISOR = 100; //here document where this comes from

    private class Item{
        private int value1;
        private int value2;
        private int calculatedValue1;
        private int calculatedValue2;

        public Item(int[] values){
            value1 = values[0];
            value2 = values[1];
            calculateValues();
        }

        public int getValue1() {
            return value1;
        }
        public void setValue1(int value1) {
            this.value1 = value1;
        }
        public int getValue2() {
            return value2;
        }
        public void setValue2(int value2) {
            this.value2 = value2;
        }

        public int getCalculatedValue1() {
            return calculatedValue1;
        }

        public void setCalculatedValue1(int calculatedValue1) {
            this.calculatedValue1 = calculatedValue1;
        }

        public int getCalculatedValue2() {
            return calculatedValue2;
        }

        public void setCalculatedValue2(int calculatedValue2) {
            this.calculatedValue2 = calculatedValue2;
        }

        public void calculateValues(){
            calculatedValue1 = (value1 * COMMON_MULTIPLIER)/COMMON_DIVISOR;
            calculatedValue2 = (value2 * COMMON_MULTIPLIER)/COMMON_DIVISOR;
        }
    }


    private int totalValues1 = 0;
    private int totalValues2 = 0;

    private List<Item> items = new ArrayList<Item>();

    public BagOfItems(List<DatabaseBean> databaseBeans){
        initItems(databaseBeans);
    }

    private void initItems(List<DatabaseBean> databaseBeans){
        for(DatabaseBean databaseBean : databaseBeans){
            Item item = new Item(databaseBean.values);
            items.add(item);
        }
    }

    protected void sum(){
        for(Item item : items){
            totalValues1 += item.getCalculatedValue1();
            totalValues2 += item.getCalculatedValue2();
        }
    }

    public int getTotalValues1() {
        return totalValues1;
    }

    public void setTotalValues1(int totalValues1) {
        this.totalValues1 = totalValues1;
    }

    public int getTotalValues2() {
        return totalValues2;
    }

    public void setTotalValues2(int totalValues2) {
        this.totalValues2 = totalValues2;
    }

    public List<Item> getItems() {
        return items;
    }

    public void setItems(List<Item> items) {
        this.items = items;
    }

    public int getTotal(){
        return (totalValues1 + totalValues2);
    }

}

The UI would then look something like this

<p:dataTable id="table" value="#{bagOfItems.items}" var="item">
<p:column >
<h:outputText id="value1" value="#{item.calculatedValue1}" />
<f:facet name="footer">
   <h:outputText id="total1" value="#{bagOfItems.totalValues1}" />
</f:facet>
</p:column >
<p:column >
<h:outputText id="value2" value="#{item.calculatedValue2}" />
<f:facet name="footer">
   <h:outputText id="total2" value="#{bagOfItems.totalValues2}" />
</f:facet>   
</p:column >
<h:outputText id="total" value="#{bagOfItems.total}" />
...
</p:dataTable>