How to add Log4j2 JDBC Appender programmatically to an existing configuration in Spring Boot? - spring-boot

Question

A short rant at the beginning, just because it has to be said:
I'm getting tired of reading the terrible documentation of Log4j2 for the umpteenth time and still not finding any solutions for my problems. The documentation is completely outdated, sample code is torn uselessly out of a context that is needed but not explained further and the explanations are consistently insufficient. It shouldn't be that only Log4j2 developers can use Log4j2 in-depth. Frameworks should make the work of other developers easier, which is definitely not the case here. Period and thanks.
Now to my actual problem:
I have a Spring Boot application that is primarily configured with yaml files. The DataSource however is set programmatically so that we have a handle to its bean. Log4j2 is initially set up using yaml configuration as well.
log4j2-spring.yaml:
Configuration:
name: Default
status: warn
Appenders:
Console:
name: Console
target: SYSTEM_OUT
PatternLayout:
pattern: "%d{yyyy-MM-dd HH:mm:ss} %-5level [%t] %c: %msg%n"
Loggers:
Root:
level: warn
AppenderRef:
- ref: Console
Logger:
- name: com.example
level: debug
additivity: false
AppenderRef:
- ref: Console
What I want to do now is to extend this initial configuration programmatically with a JDBC Appender using the already existing connection-pool. According to the documentation, the following should be done:
The recommended approach for customizing a configuration is to extend one of the standard Configuration classes, override the setup method to first do super.setup() and then add the custom Appenders, Filters and LoggerConfigs to the configuration before it is registered for use.
So here is my custom Log4j2Configuration which extends YamlConfiguration:
public class Log4j2Configuration extends YamlConfiguration {
/* private final Log4j2ConnectionSource connectionSource; */ // <-- needs to get somehow injected
public Log4j2Configuration(LoggerContext loggerContext, ConfigurationSource configSource) {
super(loggerContext, configSource);
}
#Override
public void setup() {
super.setup();
}
#Override
protected void doConfigure() {
super.doConfigure();
LoggerContext context = (LoggerContext) LogManager.getContext(false);
Configuration config = context.getConfiguration();
ColumnConfig[] columns = new ColumnConfig[]{
//...
};
Appender jdbcAppender = JdbcAppender.newBuilder()
.setName("DataBase")
.setTableName("application_log")
// .setConnectionSource(connectionSource)
.setColumnConfigs(columns)
.build();
jdbcAppender.start();
config.addAppender(jdbcAppender);
AppenderRef ref = AppenderRef.createAppenderRef("DataBase", null, null);
AppenderRef[] refs = new AppenderRef[]{ref};
/* Deprecated, but still in the Log4j2 documentation */
LoggerConfig loggerConfig = LoggerConfig.createLogger(
false,
Level.TRACE,
"com.example",
"true",
refs,
null,
config,
null);
loggerConfig.addAppender(jdbcAppender, null, null);
config.addLogger("com.example", loggerConfig);
context.updateLoggers();
}
}
The ConnectionSource exists as an implementation of AbstractConnectionSource in the Spring context and still needs to be injected into the Log4j2Configuration class. Once I know how the configuration process works I can try to find a solution for this.
Log4j2ConnectionSource:
#Configuration
public class Log4j2ConnectionSource extends AbstractConnectionSource {
private final DataSource dataSource;
public Log4j2ConnectionSource(#Autowired #NotNull DataSource dataSource) {
this.dataSource = dataSource;
}
#Override
public Connection getConnection() throws SQLException {
return dataSource.getConnection();
}
}
And finally the ConfigurationFactory as described here in the documentation (It is interesting that the method getConfiguration calls with new MyXMLConfiguration(source, configFile) a constructor that doesn't exist. Is witchcraft at play here?).
Log4j2ConfigurationFactory:
#Order(50)
#Plugin(name = "Log4j2ConfigurationFactory", category = ConfigurationFactory.CATEGORY)
public class Log4j2ConfigurationFactory extends YamlConfigurationFactory {
#Override
public Configuration getConfiguration(LoggerContext context, ConfigurationSource configSource) {
return new Log4j2Configuration(context, configSource);
}
#Override
public String[] getSupportedTypes() {
return new String[]{".yml", "*"};
}
}
Now that the set up is more or less done, the running Log4j2 configuration needs somehow to be updated. So somebody should call doConfigure() within Log4j2Configuration. Log4j2 doesn't seem to do anything here on its own. Spring Boot doesn't do anything either. And I unfortunately don't have any plan what do at all.
Therefore my request:
Can anyone please explain to me how to get Log4j2 to update its configuration?
Many thanks for any help.