Logging

Overview

The web and underlying HTTP layers log through a swappable LoggerFactory. When you don’t configure one, Web uses WebPrintStreamLoggerFactory.FACTORY by default. That factory always returns a single shared WebPrintStreamLogger that writes to System.out, prefixing each line with an ISO-8601 offset date-time formatted in the system default time zone (e.g. 2026-04-27T13:45:23.689-04:00).

Once the server is up, Web logs a single line announcing where the application is reachable:

Web application is available at [http://localhost:8080]

The URL is built from the bind address and port, so it points at localhost when bound to any-local, or the actual host/port otherwise.

Setting the log level

Web.logLevel(Level) sets the level applied to the logger that Web retrieves from its LoggerFactory. The Level type lives in org.lattejava.http.log and has four values: Trace, Debug, Info, and Error.

import module org.lattejava.http;
import module org.lattejava.web;

void main() {
  new Web()
      .logLevel(Level.Debug)
      .get("/", ctx -> ctx.write("Hello"))
      .start(8080);
}

logLevel must be called before start(int). Calling it after the server has started throws IllegalStateException.

Swapping the LoggerFactory

Web.loggerFactory(LoggerFactory) replaces the factory used by this Web instance and the underlying HTTP server. Provide your own implementation to route web and HTTP logs into your application’s logging system:

import module org.lattejava.http;
import module org.lattejava.web;

void main() {
  LoggerFactory factory = klass -> myLoggerAdapterFor(klass);

  new Web()
      .loggerFactory(factory)
      .get("/", ctx -> ctx.write("Hello"))
      .start(8080);
}

Like logLevel, loggerFactory must be called before start(int) and throws IllegalStateException if called afterward.

Capturing logs in tests

WebPrintStreamLoggerFactory has a WebPrintStreamLoggerFactory(PrintStream) constructor that lets you point the logger at any stream instead of System.out. Wrap a ByteArrayOutputStream to capture log output in a test without redirecting System.out:

import module java.base;
import module org.lattejava.http;
import module org.lattejava.web;
import org.lattejava.web.log.WebPrintStreamLoggerFactory;

void main() throws Exception {
  var captured = new ByteArrayOutputStream();
  var factory = new WebPrintStreamLoggerFactory(new PrintStream(captured, true));

  var web = new Web()
      .loggerFactory(factory)
      .logLevel(Level.Debug)
      .get("/", ctx -> ctx.write("Hello"))
      .start(8080);

  // ... exercise the server, then assert against captured.toString()

  web.close();
}