UpdatingAllowableValues.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.nifi.reporting.ambari;

import org.apache.nifi.annotation.lifecycle.OnScheduled;
import org.apache.nifi.annotation.lifecycle.OnUnscheduled;
import org.apache.nifi.components.PropertyDescriptor;
import org.apache.nifi.processor.AbstractProcessor;
import org.apache.nifi.processor.ProcessContext;
import org.apache.nifi.processor.ProcessSession;
import org.apache.nifi.processor.exception.ProcessException;

import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;

public class UpdatingAllowableValues extends AbstractProcessor {

    // How often to refresh values from external system
    static final long REFRESH_MS = 60000;
    
    private final AtomicReference<Set<String>> allowableVales = new AtomicReference<>(Collections.emptySet());
    private final ScheduledExecutorService executorService = Executors.newSingleThreadScheduledExecutor();

    @OnScheduled
    public void onScheduled(final ProcessContext context) {
        executorService.scheduleAtFixedRate(() -> {
            
            // TODO replace with call to fetch new values from an external service
            final Set<String> values = new LinkedHashSet<>();
            values.add("Choice #1");
            values.add("Choice #2");
            values.add("Choice #3");
            
            // set the new values into the holder to be used later
            allowableVales.set(values);
            
        }, REFRESH_MS, REFRESH_MS, TimeUnit.MILLISECONDS);
    }

    @OnUnscheduled
    public void onUnscheduled(final ProcessContext context) {
        try {
            executorService.shutdownNow();
        } catch (Exception e) {
            getLogger().error("Error shutting down allowable values refresh task", e);
        }
    }

    @Override
    protected List<PropertyDescriptor> getSupportedPropertyDescriptors() {
        final List<PropertyDescriptor> properties = new ArrayList<>();
        
        // dynamically create a new descriptor using the values that were refreshed in the background
        properties.add(new PropertyDescriptor.Builder()
                .name("My Property")
                .description("This is my property")
                .allowableValues(allowableVales.get())
                .build());
        
        return properties;
    }

    @Override
    public void onTrigger(ProcessContext context, ProcessSession session) throws ProcessException {
        // TODO fill in processing
    }
}