Interface Predicate

public interface Predicate

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 int[] lo;
       private int[] hi;
       private int[] idx;

       public Range(int[] lo, int[] hi, int[] idx) {
          this.lo = lo;
          this.hi = hi;
          this.idx = idx;
       }

      public boolean evaluate(RowSet rs) {

          // Check the present row determine if it lies
          // within the filtering criteria.

          for (int i = 0; i < idx.length; i++) {
             int value;
             try {
                 value = (Integer) rs.getObject(idx[i]);
             } catch (SQLException ex) {
                 Logger.getLogger(Range.class.getName()).log(Level.SEVERE, null, ex);
                 return false;
             }

             if (value < lo[i] && value > hi[i]) {
                 // outside of filter constraints
                 return false;
             }
         }
         // Within filter constraints
        return true;
      }
   }

The example above implements a simple range predicate. Note, that implementations should but are not required to provide String and integer index based constructors to provide for JDBC RowSet Implementation applications that use both column identification conventions.

Methods

evaluate

boolean evaluate(RowSet rs)

This method is typically called a FilteredRowSet object internal methods (not public) that control the RowSet object's cursor moving from row to the next. In addition, if this internal method moves the cursor onto a row that has been deleted, the internal method will continue to ove the cursor until a valid row is found.

Parameters:

rs - The RowSet to be evaluated

Returns:

true if there are more rows in the filter; false otherwise

evaluate

boolean evaluate(Object value,
                 int column)
          throws SQLException

Parameters:

value - An Object value which needs to be checked, whether it can be part of this FilterRowSet object.

column - a int object that must match the SQL index of a column in this RowSet object. This must have been passed to Predicate as one of the columns for filtering while initializing a Predicate

Returns:

true if row value lies within the filter; false otherwise

Throws:

SQLException - if the column is not part of filtering criteria

evaluate

boolean evaluate(Object value,
                 String columnName)
          throws SQLException

Parameters:

value - An Object value which needs to be checked, whether it can be part of this FilterRowSet.

columnName - a String object that must match the SQL name of a column in this RowSet, ignoring case. This must have been passed to Predicate as one of the columns for filtering while initializing a Predicate

Returns:

true if value lies within the filter; false otherwise

Throws:

SQLException - if the column is not part of filtering criteria