storm-client/src/jvm/org/apache/storm/trident/operation/builtin/Negate.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The ASF licenses this file to you under the Apache License, Version
 * 2.0 (the "License"); you may not use this file except in compliance with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions
 * and limitations under the License.
 */

package org.apache.storm.trident.operation.builtin;

import java.util.Map;
import org.apache.storm.trident.operation.Filter;
import org.apache.storm.trident.operation.TridentOperationContext;
import org.apache.storm.trident.tuple.TridentTuple;

/**
 * A `Filter` implementation that inverts another delegate `Filter`.
 *
 * <p>The `Negate.isKeep()` method simply returns the opposite of the delegate's `isKeep()` method:
 *
 * <p>```java public boolean isKeep(TridentTuple tuple) { return !this.delegate.isKeep(tuple); } ```
 *
 * <p>The `Negate` filter is useful for dividing a Stream in two based on some boolean condition.
 *
 * <p>Suppose we had a Stream named `userStream` containing information about users, and a custom `Filter` implementation,
 * `RegisteredUserFilter` that filtered out unregistered users. We could divide the `userStream` Stream into two separate Streams -- one for
 * registered users, and one for unregistered users -- by doing the following:
 *
 * <p>```java Stream userStream = ...
 *
 * <p>Filter registeredFilter = new ResisteredUserFilter(); Filter unregisteredFilter = new Negate(registeredFilter);
 *
 * <p>Stream registeredUserStream = userStream.each(userStream.getOutputFields(), registeredFilter); Stream unregisteredUserStream =
 * userStream.each(userStream.getOutputFields(), unregisteredFilter); ```
 */
public class Negate implements Filter {

    Filter delegate;

    public Negate(Filter delegate) {
        this.delegate = delegate;
    }

    @Override
    public boolean isKeep(TridentTuple tuple) {
        return !delegate.isKeep(tuple);
    }

    @Override
    public void prepare(Map<String, Object> conf, TridentOperationContext context) {
        delegate.prepare(conf, context);
    }

    @Override
    public void cleanup() {
        delegate.cleanup();
    }

}