Logging in JDK11 HttpClient

Question

JDK11 introduced a new HTTP Client, with many features that lacks in traditional java.net.HttpURLConnection class. First question that I encountered with is how to properly enable logging in newly added HTTP Client?

Answer 1

The client uses java.util.logging, the easiest way is to use SLF4J. See JUL to SLF4J Bridge for more information.

3 steps are required:

1. Add jul-to-slf4j bridge to you classpath with runtime scope.
   Maven:

   <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>jul-to-slf4j</artifactId>
      <version>1.7.25</version>
      <scope>runtime</scope>
   </dependency>
   

Gradle:

`runtime group: 'org.slf4j', name: 'jul-to-slf4j', version: '1.7.25'`

2. Add in logback.xml (logback-test.xml), don't forget to add a STDOUT appender (or change it accordingly)

   <contextListener class="ch.qos.logback.classic.jul.LevelChangePropagator">
       <resetJUL>true</resetJUL>
   </contextListener>
   
   <logger name="jdk.internal.httpclient.debug" level="debug" additivity="false">
       <appender-ref ref="STDOUT" />
   </logger>
   
   <root level="DEBUG">
       <appender-ref ref="STDOUT"/>
   </root>
   

3. Add in your code:

    static {
    SLF4JBridgeHandler.removeHandlersForRootLogger();
    SLF4JBridgeHandler.install();
    }
   

Alternatively, for educational purposes it is possible to add a system property:
-Djdk.httpclient.HttpClient.log=all which will enable all logging printing to the console.