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

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):
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();
}
}
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();
}
}
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();
}
}
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):
"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.
"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.