A Filter expects a single argument Tuple and returns a boolean value stating whether or not the current Tuple in the tuple stream should be discarded.

A Filter may only be used with a Each pipe, and it may follow any other pipe type.

To create a custom Filter, subclass the class cascading.operation.BaseOperation and implement the interfacecascading.operation.Filter. Because BaseOperation has been subclassed, the isRemove method, as defined on the Filter interface, is the only method that must be implemented.

public class SomeFilter extends BaseOperation implements Filter
  {
  public boolean isRemove( FlowProcess flowProcess, FilterCall filterCall )
    {
    // get the arguments TupleEntry
    TupleEntry arguments = filterCall.getArguments();

    // initialize the return result
    boolean isRemove = false;

    // test the argument values and set isRemove accordingly

    return isRemove;
    }
  }

Filters should declare the number of argument values they expect.

Filters must accept 1 or more values in a Tuple as arguments, by default they will accept any number ( Operation.ANY) of values. Cascading will verify the number of arguments selected match the number of arguments expected.

The number of arguments declarations must be done on the constructor, either by passing a default value to the super constructor, or by accepting the value from the user via a constructor implementation.

public class StringLengthFilter extends BaseOperation implements Filter
  {
  public StringLengthFilter()
    {
    // expects 2 arguments, fail otherwise
    super( 2 );
    }

  public boolean isRemove( FlowProcess flowProcess, FilterCall filterCall )
    {
    // get the arguments TupleEntry
    TupleEntry arguments = filterCall.getArguments();

    // filter out the current Tuple if the first argument length is greater
    // than the second argument integer value
    return arguments.getString( 0 ).length() > arguments.getInteger( 1 );
    }
  }

The example above implements a fully functional Filter that accepts two arguments and filters out the current Tuple if the first argument String length is greater than the integer value of the second argument.