Hi Andrea,
> I imagined it almost the way you proposed it, the only twist would
> be that the map would be stored in thread local to allow multiple
> value and that the function would also allow a default value to
> fall back to if the variable is not defined.
Thread-local values is a brilliant idea !
Would this do the trick ? (untested)
import java.util.LinkedHashMap;
import java.util.Map;
import org.geotools.filter.FunctionExpressionImpl;
import org.opengis.feature.simple.SimpleFeature;
public class VarLookupFunction extends FunctionExpressionImpl {
/**
* Provides a lookup table that is local to each thread.
*/
private static class Lookup extends ThreadLocal<Map<String, Object>> {
@Override
protected Map<String, Object> initialValue() {
return new LinkedHashMap<String, Object>();
}
/**
* Get a value from the lookup table by name.
*
* @param name name of the variable to look up
*
* @return value or {...@code null} if the name is not found
*/
public Object getValue(String name) {
return super.get().get(name);
}
/**
* Get the table of lookup values.
* Defined to make code using this class more obvious.
*
* @return the table of lookup values
*/
public Map<String, Object> getTable() {
return super.get();
}
};
private static final Lookup lookup = new Lookup();
/**
* Create a new instance of this function.
*/
public VarLookupFunction() {
super("VarLookup");
}
/**
* Set the table of lookup values, deleting any previously set table.
* The input {...@code Map} is copied.
*
* @param values the lookup table; if {...@code null} any existing lookup
* table will be cleared.
*/
public static void setValues(Map<String, Object> values) {
Map<String, Object> table = lookup.getTable();
table.clear();
if (values != null) {
table.putAll(values);
}
}
/**
* Add a named value to the lookup table. If the name is already present
* in the table it will be assigned the new value.
*
* @param name the name
* @param value the value
*/
public static void setValue(String name, Object value) {
lookup.getTable().put(name, value);
}
/**
* {...@inheritdoc}
* @return Always returns 1
*/
@Override
public int getArgCount() {
return 1;
}
/**
* {...@inheritdoc}
* If the result for this feature is {...@code null} a fallback value will
be
* returned if one has been set.
*
* @return the result for this feature
*
* @see #setFallbackValue
*/
@Override
public Object evaluate(SimpleFeature feature) {
String varName = getExpression(0).evaluate(feature, String.class);
Object value = lookup.getValue(name);
if (value != null) {
return value;
} else {
return this.getFallbackValue().getValue();
}
}
}
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