package com.codahale.metrics.servlets;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectWriter;
import com.codahale.metrics.health.HealthCheck;
import com.codahale.metrics.health.HealthCheckRegistry;
import com.codahale.metrics.json.HealthCheckModule;
import javax.servlet.*;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Map;
import java.util.SortedMap;
import java.util.concurrent.ExecutorService;
public class HealthCheckServlet extends HttpServlet {
public static abstract class ContextListener implements ServletContextListener {
/**
* @return the {@link HealthCheckRegistry} to inject into the servlet context.
*/
protected abstract HealthCheckRegistry getHealthCheckRegistry();
/**
* @return the {@link ExecutorService} to inject into the servlet context, or {@code null}
* if the health checks should be run in the servlet worker thread.
*/
protected ExecutorService getExecutorService() {
// don't use a thread pool by default
return null;
}
@Override
public void contextInitialized(ServletContextEvent event) {
final ServletContext context = event.getServletContext();
context.setAttribute(HEALTH_CHECK_REGISTRY, getHealthCheckRegistry());
context.setAttribute(HEALTH_CHECK_EXECUTOR, getExecutorService());
}
@Override
public void contextDestroyed(ServletContextEvent event) {
// no-op
}
}
public static final String HEALTH_CHECK_REGISTRY = HealthCheckServlet.class.getCanonicalName() + ".registry";
public static final String HEALTH_CHECK_EXECUTOR = HealthCheckServlet.class.getCanonicalName() + ".executor";
private static final long serialVersionUID = -8432996484889177321L;
private static final String CONTENT_TYPE = "application/json";
private transient HealthCheckRegistry registry;
private transient ExecutorService executorService;
private transient ObjectMapper mapper;
public HealthCheckServlet() {
}
public HealthCheckServlet(HealthCheckRegistry registry) {
this.registry = registry;
}
@Override
public void init(ServletConfig config) throws ServletException {
super.init(config);
if (null == registry) {
final Object registryAttr = config.getServletContext().getAttribute(HEALTH_CHECK_REGISTRY);
if (registryAttr instanceof HealthCheckRegistry) {
this.registry = (HealthCheckRegistry) registryAttr;
} else {
throw new ServletException("Couldn't find a HealthCheckRegistry instance.");
}
}
final Object executorAttr = config.getServletContext().getAttribute(HEALTH_CHECK_EXECUTOR);
if (executorAttr instanceof ExecutorService) {
this.executorService = (ExecutorService) executorAttr;
}
this.mapper = new ObjectMapper().registerModule(new HealthCheckModule());
}
@Override
protected void doGet(HttpServletRequest req,
HttpServletResponse resp) throws ServletException, IOException {
final SortedMap<String, HealthCheck.Result> results = runHealthChecks();
resp.setContentType(CONTENT_TYPE);
resp.setHeader("Cache-Control", "must-revalidate,no-cache,no-store");
if (results.isEmpty()) {
resp.setStatus(HttpServletResponse.SC_NOT_IMPLEMENTED);
} else {
if (isAllHealthy(results)) {
resp.setStatus(HttpServletResponse.SC_OK);
} else {
resp.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
}
}
final OutputStream output = resp.getOutputStream();
try {
getWriter(req).writeValue(output, results);
} finally {
output.close();
}
}
private ObjectWriter getWriter(HttpServletRequest request) {
final boolean prettyPrint = Boolean.parseBoolean(request.getParameter("pretty"));
if (prettyPrint) {
return mapper.writerWithDefaultPrettyPrinter();
}
return mapper.writer();
}
private SortedMap<String, HealthCheck.Result> runHealthChecks() {
if (executorService == null) {
return registry.runHealthChecks();
}
return registry.runHealthChecks(executorService);
}
private static boolean isAllHealthy(Map<String, HealthCheck.Result> results) {
for (HealthCheck.Result result : results.values()) {
if (!result.isHealthy()) {
return false;
}
}
return true;
}
}