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Core components supporting the Micronaut Framework

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/*
 * Copyright 2017-2020 original authors
 *
 * Licensed 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 io.micronaut.management.health.indicator;

import io.micronaut.core.async.publisher.AsyncSingleResultPublisher;
import io.micronaut.health.HealthStatus;
import io.micronaut.scheduling.TaskExecutors;
import org.reactivestreams.Publisher;

import javax.inject.Inject;
import javax.inject.Named;
import java.util.concurrent.ExecutorService;

/**
 * A base health indicator class to extend from that catches exceptions thrown from the
 * {@link #getHealthInformation()} method and updates the {@link HealthResult} with the exception information.
 *
 * @param  The health indication type
 * @author James Kleeh
 * @since 1.0
 */
public abstract class AbstractHealthIndicator implements HealthIndicator {

    protected ExecutorService executorService;
    protected HealthStatus healthStatus;

    /**
     * @param executorService The executor service
     */
    @Inject
    public void setExecutorService(@Named(TaskExecutors.IO) ExecutorService executorService) {
        this.executorService = executorService;
    }

    @Override
    public Publisher getResult() {
        if (executorService == null) {
            throw new IllegalStateException("I/O ExecutorService is null");
        }
        return new AsyncSingleResultPublisher<>(executorService, this::getHealthResult);
    }

    /**
     * Provides information (typically a Map) to be returned. Set the {@link #healthStatus} field during execution,
     * otherwise {@link HealthStatus#UNKNOWN} will be used.
     *
     * @return Any details to be included in the response.
     */
    protected abstract T getHealthInformation();

    /**
     * Builds the whole health result.
     *
     * @return The health result to provide to the indicator.
     */
    protected HealthResult getHealthResult() {
        HealthResult.Builder builder = HealthResult.builder(getName());
        try {
            builder.details(getHealthInformation());
            builder.status(this.healthStatus);
        } catch (Exception e) {
            builder.status(HealthStatus.DOWN);
            builder.exception(e);
        }
        return builder.build();
    }

    /**
     * Used to populate the {@link HealthResult}. Provides a key to go along with the health information.
     *
     * @return The name of the indicator
     */
    protected abstract String getName();
}