Java Logging: Filters

Jakob Jenkov
Last update: 2014-06-23

You can set a Filter on a Logger. A Filter can filter out log messages, meaning decide if the message gets logged or not. Filters are represented by the Java interface java.util.logging.Filter

Here is an example of setting a Filter on a Logger:

Filter filter = new MyFilter();

logger1.setFilter(filter);

The Filter interface is defined like this:

public interface Filter {
    public boolean isLoggable(LogRecord record);
}

If the isLoggable() method returns false, the LogRecord is not logged. If the method returns true, the LogRecord is forwarded to the Handler's of the given Logger.

To create a Filter you must implement that interface. Here is a very simple example implementation:

public class MyFilter implements Filter {
    public boolean isLoggable(LogRecord record) {
        return false;
    }
}

This filter rejects all messages. Of course this is not a very useful filter. You would probably inspect the LogRecord and make a decision based on that. You can learn more about the LogRecord in the text on the LogRecord, and in the JavaDoc too.

For a discussion of how Filter's work within the Logger hierarchy, see the text on the Logger hierarchy.

Jakob Jenkov

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