HOW-TO Create Custom Expressions

Custom Expressions are a way we provide to let the developer make complex arranging of the data to be displayed in the report such as a concatenation of 2 or more fields from the data source, a math calculation, etc. Custom Expressions classes must implement the ar.com.fdvs.dj.domain.CustomExpression interface, which has a single method: evaluate(Object object) , the parameter is a java.util.Map wich contains the elements of the current row.

Custom Expression may be defined in-line (they are like closures) Lets see an example.

AbstractColumn columnaCustomExpression = ColumnBuilder.getNew()
.setCustomExpression( 
        new CustomExpression() {
                public Object evaluate(Object object) {
                        Map map = (Map) object;
                        String state = (String) map.get("state");
                        String branch = (String) map.get("branch");
                        String productLine = (String) map.get("productLine");
                        return state.toUpperCase() + " / " + branch.toUpperCase() + " / " + productLine;
                }
        } 
).build();      

As you can see, the keys of the map are the properties defined at the moment of the creation of the columns.

If we need to use fields from the data source that are not directly shown on any column, we must register them like this:

drb.addField("productLine", String.class.getName());
drb.addField("branch", String.class.getName());

The resulting report would be something like this