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Add Logging to a Native Executable
By default, a native executable produced by Native Image supports logging via the java.util.logging.*
API.
Default Logging Configuration
The default logging configuration in a native executable is based on the logging.properties
file found in the JDK.
This file configures a java.util.logging.ConsoleHandler
which will only show messages at the INFO
level and above.
Custom logging configuration can be loaded either at build time or at runtime as described below.
If you require additional logging handlers, you must register the corresponding classes for reflection.
For example, if you use java.util.logging.FileHandler
then provide the following reflection configuration:
{
"name" : "java.util.logging.FileHandler",
"methods" : [
{ "name" : "<init>", "parameterTypes" : [] },
]
}
For more details, see Reflection Support.
The usage of the logger is shown in the following example:
-
Save the following Java code into a file named LoggerRunTimeInit.java, and compile it:
import java.io.IOException; import java.util.logging.Level; import java.util.logging.LogManager; import java.util.logging.Logger; public class LoggerRunTimeInit { public static void main(String[] args) throws IOException { LogManager.getLogManager().readConfiguration(LoggerRunTimeInit.class.getResourceAsStream("/logging.properties")); Logger logger = Logger.getLogger(LoggerRunTimeInit.class.getName()); logger.log(Level.WARNING, "Danger, Will Robinson!"); } }
javac LoggerRunTimeInit.java
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Download the logging.properties resource file and save it in the same directory as LoggerRunTimeInit.java.
-
Build and run the native executable
native-image LoggerRunTimeInit -H:IncludeResources="logging.properties"
./loggerruntimeinit
It should produce output that looks similar to:
WARNING: Danger, Will Robinson! [Wed May 18 17:22:40 BST 2022]
In this case, the logging.properties file needs to be available for runtime processing so it must be included into the reachability-metadata.json file under the _META-INF/native-image/
_ folder. For more details on how to do this, see [Use of Resources in a Native Executable](/dev/reference-manual/native-image/metadata/#resources).