io.dropwizard.health.core.HealthCheckServlet Maven / Gradle / Ivy

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Provides a health check implementation that performs ongoing monitoring of an application's dependencies and includes an endpoint that can be called by a load balancer to determine if the application is healthy and thus able to retrieve traffic.

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package io.dropwizard.health.core;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.concurrent.atomic.AtomicBoolean;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.ws.rs.core.HttpHeaders;

import static java.util.Objects.requireNonNull;

public class HealthCheckServlet extends HttpServlet {
    private static final String CHECK_TYPE_QUERY_PARAM = "type";
    private final HealthStatusChecker healthStatusChecker;
    private final boolean cacheControlEnabled;
    private final String cacheControlValue;
    private final String contentType;
    private final String healthyValue;
    private final String unhealthyValue;

    /**
     * @deprecated use {@link #HealthCheckServlet(HealthStatusChecker, boolean, String, String, String, String)} instead.
     */
    @Deprecated
    public HealthCheckServlet(final AtomicBoolean healthy,
                              final boolean cacheControlEnabled, final String cacheControlValue,
                              final String contentType, final String healthyValue, final String unhealthyValue) {
        this(new LegacyHealthStatusChecker(healthy), cacheControlEnabled, cacheControlValue, contentType,
                healthyValue, unhealthyValue);
    }

    public HealthCheckServlet(final HealthStatusChecker healthStatusChecker,
                              final boolean cacheControlEnabled, final String cacheControlValue,
                              final String contentType, final String healthyValue, final String unhealthyValue) {
        this.healthStatusChecker = requireNonNull(healthStatusChecker);
        this.cacheControlEnabled = cacheControlEnabled;
        this.cacheControlValue = requireNonNull(cacheControlValue);
        this.contentType = requireNonNull(contentType);
        this.healthyValue = requireNonNull(healthyValue);
        this.unhealthyValue = requireNonNull(unhealthyValue);
    }

    @Override
    protected void doGet(final HttpServletRequest req, final HttpServletResponse resp) throws ServletException, IOException {
        if (cacheControlEnabled) {
            resp.setHeader(HttpHeaders.CACHE_CONTROL, cacheControlValue);
        }
        resp.setContentType(contentType);

        final String typeValue = req.getParameter(CHECK_TYPE_QUERY_PARAM);

        final PrintWriter writer = resp.getWriter();
        if (healthStatusChecker.isHealthy(typeValue)) {
            writer.print(healthyValue);
        } else {
            writer.print(unhealthyValue);
            resp.setStatus(HttpServletResponse.SC_SERVICE_UNAVAILABLE);
        }
    }

    private static class LegacyHealthStatusChecker implements HealthStatusChecker {
        private final AtomicBoolean healthy;

        public LegacyHealthStatusChecker(final AtomicBoolean healthy) {
            this.healthy = healthy;
        }

        @Override
        public boolean isHealthy(final String type) {
            return healthy.get();
        }
    }
}