Custom Logging in Jetty

Posted on April 25, 2020  |  

There’re times when an out-of-the-box solution for access log is not enough and one has to customize the logging output for various reasons, including security. Recently, I had to redact a part of the request URL for requests matching certain. In the request log example shown in Figure 1, the word rosemont in the URL had to be substituted with the word REDACTED. - - [25/Apr/2020:21:01:23 +0000] "GET /health HTTP/1.1" 200 383 "-" "kube-probe/1.17" - - [25/Apr/2020:21:01:28 +0000] "GET /myservice/tokens/zipcode/97068/rosemont HTTP/1.1" 200 40 "-" "insomnia/7.1.1"

Figure 1. Request logs before redaction

In a Spring Boot application running an embedded Jetty, one has to enable the access log property, as shown in Figure 2, to generate request logs.

      enabled: true

Figure 2. Property to enable Jetty access log

It used to be a relatively easy task to customize the request log in a Jetty web server by modifying the JettyServletWebServerFactory. As shown in Figure 3, one had to set the custom request log by adding a server customizer.

public JettyServletWebServerFactory jettyEmbeddedServletContainerFactory(
        @Value("${server.port:8080}") final String port) {
    final JettyServletWebServerFactory factory =
        new JettyServletWebServerFactory(Integer.valueOf(port));

    factory.addServerCustomizers(server -> {
        server.setRequestLog(new MyCustomRequestLog(new RequestLogWriter(),

    return factory;

Figure 3. Setting a custom request log inside a Jetty customizer

The changes shown in Figure 3, no longer works in 2.3.0-M4 version of Spring Boot library. It stopped working as the Jetty dependency in the new Spring Boot version overwrites the custom requst log set in the customizer. The built-in Jetty customizer, JettyWebServerFactoryCustomizer, gets loaded last thus overwriting any changes I made to add a custom request log.

However, there’s an alternative approach that I have came across which solved my dilemma. Instead of setting the request log directly on the server from the customizer, add a custom configuration and make it the last configuration that gets loaded by Jetty. The custom configuration is added to the WebAppContext. The new approach introduced a new CustomRequestLogConfiguration class which instantiates and sets my request log, MyCustomRequestLog. The new approach, as shown in Figure 4, still needs a Jetty customizer.

public class CustomJettyConfiguration {

    public JettyServletWebServerFactory jettyEmbeddedServletContainerFactory(
            @Value("${server.port:8080}") final String port) {
        final JettyServletWebServerFactory factory =
                new JettyServletWebServerFactory(Integer.valueOf(port));

        factory.addServerCustomizers(server -> {
            WebAppContext context = (WebAppContext) server.getHandler();
            org.eclipse.jetty.webapp.Configuration[] configs = context.getConfigurations();
            org.eclipse.jetty.webapp.Configuration[] modifiedConfigs =
                    new org.eclipse.jetty.webapp.Configuration[configs.length + 1];
            System.arraycopy(configs, 0, modifiedConfigs, 0, configs.length);
            modifiedConfigs[configs.length] = new CustomRequestLogConfiguration();

        return factory;

    private static class CustomRequestLogConfiguration extends AbstractConfiguration {

        public void configure(WebAppContext context) {
                    new MyCustomRequestLog(new RequestLogWriter(),

Figure 4. A new approach to setting a custom Jetty request log

Figure 5 shows the content of my custom request log which extends from Jetty’s CustomRequestLog. This class matches a GET request having a /myservice/tokens/** URL pattern. If the request matches the criteria, it substitutes the last segment of the request URL with the word REDACTED. My custom log delegates it to its super class if the request doesn’t match the criteria.

    private static class MyCustomRequestLog extends CustomRequestLog {
        private static final ThreadLocal<StringBuilder> buffers =
                ThreadLocal.withInitial(() -> new StringBuilder(256));

        private static final String MY_URL = "/myservice/tokens/**";

        private final Writer writer;

        private final PathPattern pattern;

        private final DateCache dateCache;

        public MyCustomRequestLog(Writer writer, String formatString) {
            super(writer, formatString);
            this.writer = writer;

            PathPatternParser pp = new PathPatternParser();
            pattern = pp.parse(MY_URL);

            TimeZone timeZone = TimeZone.getTimeZone("GMT");
            Locale locale = Locale.getDefault();
            dateCache = new DateCache(DEFAULT_DATE_FORMAT, locale, timeZone);

        public void log(Request request, Response response) {
            String requestURI = request.getRequestURI();
            if ( &&
                    pattern.matches(PathContainer.parsePath(requestURI))) {
                try {
                    requestURI = requestURI.substring(0, requestURI.lastIndexOf('/'))
                            + "/REDACTED";
                    StringBuilder sb = buffers.get();

                            .append(" - - [")
                            .append("] \"")
                            .append(" ")
                            .append(" ")
                            .append("\" ")
                            .append(" ")
                            .append(" \"-\" \"")

                } catch (Exception e) {
                    LOG.warn("Unable to log request", e);
            } else {
                super.log(request, response);

        protected void stop(LifeCycle lifeCycle) throws Exception {

Figure 5. A custom Jetty request log

After adding the custom request log, the log from Figure 1 looks like the one shown below, - - [25/Apr/2020:21:01:03 +0000] "GET /health HTTP/1.1" 200 383 "-" "kube-probe/1.17" - - [25/Apr/2020:21:01:13 +0000] "GET /health HTTP/1.1" 200 383 "-" "kube-probe/1.17" - - [25/Apr/2020:21:01:23 +0000] "GET /health HTTP/1.1" 200 383 "-" "kube-probe/1.17" - - [25/Apr/2020:21:01:28 +0000] "GET /myservice/tokens/zipcode/97068/REDACTED HTTP/1.1" 200 40 "-" "insomnia/7.1.1" - - [25/Apr/2020:21:01:31 +0000] "GET /myservice/strings/zipcode/97068/Ao6bQf1QuJAxw5LovOpGioKnwDKNAR4Dyp5myQ HTTP/1.1" 200 7 "-" "insomnia/7.1.1"

Figure 6. Redacted request logs