How to run jul-to-slf4j bridge once per JVM?

Question

I'd like to run Surefire in parallel mode (multiple JVMs) where each JVM must run:

SLF4JBridgeHandler.removeHandlersForRootLogger();
SLF4JBridgeHandler.install();

exactly once before the first test. How can this be done?

Answer 1

There are various ways to make some code run at the beginning of a test suite.

Here are 4 (I'm sure there are more):

1. JUnit via RunWith Suite with Suite.SuiteClasses and BeforeClass (adapted from examples in SuiteTest):

   @RunWith(Suite.class)
   @SuiteClasses({FirstTest.class, SecondTest.class/*, ...*/, LastTest.class})
   public static class AllWithSLF4JBridgeHandler {
       @BeforeClass
       public static void registerRootLoggerHandlers() {
           SLF4JBridgeHandler.removeHandlersForRootLogger();
           SLF4JBridgeHandler.install();
       }
   }
   

2. TestNG with BeforeSuite:

   /**
    * Base class for each test class (i.e. every test class should extend this class).
    */
   public abstract class BaseTest {
       @BeforeSuite
       public void registerRootLoggerHandlers() {
           SLF4JBridgeHandler.removeHandlersForRootLogger();
           SLF4JBridgeHandler.install();
       }
   }
   

3. TestNG with Guice:

   /**
    * Test module. Each test class should be annotated with `@Guice(TestModule.class)`.
    */
   public class TestModule implements Module {
       @Override
       public void configure(Binder binder) {
           SLF4JBridgeHandler.removeHandlersForRootLogger();
           SLF4JBridgeHandler.install();
       }
   }
   

4. Static initialization blocks (test-framework independent):

   /**
    * Base class for each test class (i.e. every test class should extend this class).
    */
   public abstract class BaseTest {
       static {
           SLF4JBridgeHandler.removeHandlersForRootLogger();
           SLF4JBridgeHandler.install();
       }
   }
   

I'm not sure how all of these methods work with Surefire's parallel mode. Methods 1 and 2 may not work there but I believe methods 3 and 4 should.

---

Another option would be to not use the programmatic installation of the SLF4JBridgeHandler but to use a java.util.logging.config file or class (see LogManager):

1. "java.util.logging.config.file":

   logging.properties file:

   // register SLF4JBridgeHandler as handler for the j.u.l. root logger
   handlers = org.slf4j.bridge.SLF4JBridgeHandler
   

   System property assignment:

   java -Djava.util.logging.config.file=/path/to/logging.properties ...
   

   This works well if you know the path to your logging file beforehand.

2. "java.util.logging.config.class":

   Using a file may not be a good option if you're deploying a WAR and don't know where the file will be, etc. so alternatively you can create a logging config class:

   public class SLF4JBridgeHandlerInitializer {
       public SLF4JBridgeHandlerInitializer() throws IOException {
           String loggingConfigurationString = "handlers = " + SLF4JBridgeHandler.class.getName();
           InputStream inputStream = new ByteArrayInputStream(loggingConfigurationString.getBytes());
           LogManager.getLogManager().readConfiguration(inputStream);
       }
   }
   

   System property assignment:

   java -Djava.util.logging.config.class=package.SLF4JBridgeHandlerInitializer ...
   

   I've done this before and it has worked well for me (SLF4JBridgeHandler.Initializer by mfulton26 · Pull Request #57 · qos-ch/slf4j).

These final two options should initialize each JVM instance as long as the appropriate system property is set.