The standard interface that provides the framework for all
FilteredRowSet objects to describe their filters.
1.0 Background
The Predicate interface is a standard interface that
applications can implement to define the filter they wish to apply to a
a FilteredRowSet object. A FilteredRowSet
object consumes implementations of this interface and enforces the
constraints defined in the implementation of the method evaluate.
A FilteredRowSet object enforces the filter constraints in a
bi-directional manner: It outputs only rows that are within
the constraints of the filter; and conversely, it inserts, modifies, or updates
only rows that are within the constraints of the filter.
2.0 Implementation Guidelines
In order to supply a predicate for the FilteredRowSet.
this interface must be implemented. At this time, the JDBC RowSet
Implementations (JSR-114) does not specify any standard filters definitions.
By specifying a standard means and mechanism for a range of filters to be
defined and deployed with both the reference and vendor implementations
of the FilteredRowSet interface, this allows for a flexible
and application motivated implementations of Predicate to emerge.
A sample implementation would look something like this:
public class Range implements Predicate {
private Object lo[];
private Object hi[];
private int idx[];
public Range(Object[] lo, Object[] hi, int[] idx) {
this.lo = lo;
this.hi = hi;
this.idx = idx;
}
public boolean evaluate(RowSet rs) {
CachedRowSet crs = (CachedRowSet)rs;
boolean bool1,bool2;
// Check the present row determine if it lies
// within the filtering criteria.
for (int i = 0; i < idx.length; i++) {
if ((rs.getObject(idx[i]) >= lo[i]) &&
(rs.getObject(idx[i]) >= hi[i]) {
bool1 = true; // within filter constraints
} else {
bool2 = true; // outside of filter constraints
}
}
if (bool2) {
return false;
} else {
return true;
}
}
The example above implements a simple range predicate. Note, that
implementations should but are not required to provider String
and integer index based constructors to provide for JDBC RowSet Implementation
applications that use both column identification conventions. |
