com.codahale.metrics.servlets.MetricsServlet Maven / Gradle / Ivy
package com.codahale.metrics.servlets;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Locale;
import java.util.concurrent.TimeUnit;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.codahale.metrics.MetricFilter;
import com.codahale.metrics.MetricRegistry;
import com.codahale.metrics.json.MetricsModule;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectWriter;
import com.fasterxml.jackson.databind.util.JSONPObject;
/**
* A servlet which returns the metrics in a given registry as an {@code application/json} response.
*/
public class MetricsServlet extends HttpServlet {
/**
* An abstract {@link ServletContextListener} which allows you to programmatically inject the
* {@link MetricRegistry}, rate and duration units, and allowed origin for
* {@link MetricsServlet}.
*/
public static abstract class ContextListener implements ServletContextListener {
/**
* @return the {@link MetricRegistry} to inject into the servlet context.
*/
protected abstract MetricRegistry getMetricRegistry();
/**
* @return the {@link TimeUnit} to which rates should be converted, or {@code null} if the
* default should be used.
*/
protected TimeUnit getRateUnit() {
// use the default
return null;
}
/**
* @return the {@link TimeUnit} to which durations should be converted, or {@code null} if
* the default should be used.
*/
protected TimeUnit getDurationUnit() {
// use the default
return null;
}
/**
* @return the {@code Access-Control-Allow-Origin} header value, if any.
*/
protected String getAllowedOrigin() {
// use the default
return null;
}
/**
* Returns the name of the parameter used to specify the jsonp callback, if any.
*/
protected String getJsonpCallbackParameter() {
return null;
}
/**
* Returns the {@link MetricFilter} that shall be used to filter metrics, or {@link MetricFilter#ALL} if
* the default should be used.
*/
protected MetricFilter getMetricFilter() {
// use the default
return MetricFilter.ALL;
}
@Override
public void contextInitialized(ServletContextEvent event) {
final ServletContext context = event.getServletContext();
context.setAttribute(METRICS_REGISTRY, getMetricRegistry());
context.setAttribute(METRIC_FILTER, getMetricFilter());
if (getDurationUnit() != null) {
context.setInitParameter(MetricsServlet.DURATION_UNIT, getDurationUnit().toString());
}
if (getRateUnit() != null) {
context.setInitParameter(MetricsServlet.RATE_UNIT, getRateUnit().toString());
}
if (getAllowedOrigin() != null) {
context.setInitParameter(MetricsServlet.ALLOWED_ORIGIN, getAllowedOrigin());
}
if (getJsonpCallbackParameter() != null) {
context.setAttribute(CALLBACK_PARAM, getJsonpCallbackParameter());
}
}
@Override
public void contextDestroyed(ServletContextEvent event) {
// no-op
}
}
public static final String RATE_UNIT = MetricsServlet.class.getCanonicalName() + ".rateUnit";
public static final String DURATION_UNIT = MetricsServlet.class.getCanonicalName() + ".durationUnit";
public static final String SHOW_SAMPLES = MetricsServlet.class.getCanonicalName() + ".showSamples";
public static final String METRICS_REGISTRY = MetricsServlet.class.getCanonicalName() + ".registry";
public static final String ALLOWED_ORIGIN = MetricsServlet.class.getCanonicalName() + ".allowedOrigin";
public static final String METRIC_FILTER = MetricsServlet.class.getCanonicalName() + ".metricFilter";
public static final String CALLBACK_PARAM = MetricsServlet.class.getCanonicalName() + ".jsonpCallback";
private static final long serialVersionUID = 1049773947734939602L;
private static final String CONTENT_TYPE = "application/json";
private String allowedOrigin;
private String jsonpParamName;
private transient MetricRegistry registry;
private transient ObjectMapper mapper;
public MetricsServlet() {
}
public MetricsServlet(MetricRegistry registry) {
this.registry = registry;
}
@Override
public void init(ServletConfig config) throws ServletException {
super.init(config);
final ServletContext context = config.getServletContext();
if (null == registry) {
final Object registryAttr = context.getAttribute(METRICS_REGISTRY);
if (registryAttr instanceof MetricRegistry) {
this.registry = (MetricRegistry) registryAttr;
} else {
throw new ServletException("Couldn't find a MetricRegistry instance.");
}
}
final TimeUnit rateUnit = parseTimeUnit(context.getInitParameter(RATE_UNIT),
TimeUnit.SECONDS);
final TimeUnit durationUnit = parseTimeUnit(context.getInitParameter(DURATION_UNIT),
TimeUnit.SECONDS);
final boolean showSamples = Boolean.parseBoolean(context.getInitParameter(SHOW_SAMPLES));
MetricFilter filter = (MetricFilter) context.getAttribute(METRIC_FILTER);
if (filter == null) {
filter = MetricFilter.ALL;
}
this.mapper = new ObjectMapper().registerModule(new MetricsModule(rateUnit,
durationUnit,
showSamples,
filter));
this.allowedOrigin = context.getInitParameter(ALLOWED_ORIGIN);
this.jsonpParamName = context.getInitParameter(CALLBACK_PARAM);
}
@Override
protected void doGet(HttpServletRequest req,
HttpServletResponse resp) throws ServletException, IOException {
resp.setContentType(CONTENT_TYPE);
if (allowedOrigin != null) {
resp.setHeader("Access-Control-Allow-Origin", allowedOrigin);
}
resp.setHeader("Cache-Control", "must-revalidate,no-cache,no-store");
resp.setStatus(HttpServletResponse.SC_OK);
final OutputStream output = resp.getOutputStream();
try {
if (jsonpParamName != null && req.getParameter(jsonpParamName) != null) {
getWriter(req).writeValue(output, new JSONPObject(req.getParameter(jsonpParamName), registry));
} else {
getWriter(req).writeValue(output, registry);
}
} 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 TimeUnit parseTimeUnit(String value, TimeUnit defaultValue) {
try {
return TimeUnit.valueOf(String.valueOf(value).toUpperCase(Locale.US));
} catch (IllegalArgumentException e) {
return defaultValue;
}
}
}