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Optimize with a SATA RAID Storage Solution
Range of capacities as low as $1250 per TB. Ideal if you currently rely on servers/disks/JBODs
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Listing 1 demonstrates how to use log4j. You create a
LoggergetLogger()
Then, when you want to log a message, you just send it to the logger. Logged messages typically fall into one of five categories:
debug, info, warn, error, or fatal, and methods named
debug()info()shutdown()main()shutdown()
Listing 1. Test.java: Using the log4j classes
1 import org.apache.log4j.Logger;
2 import org.apache.log4j.LogManager;
3
4 public class Test
5 {
6 private static final Logger log = Logger.getLogger( "com.holub.log4j.Test");
7
8 public static void main(String[] args) throws Exception
9 {
10 // For testing, give the client that will display the
11 // logged messages a moment to connect.
12 // (It's in a 50-ms wait loop, so pausing for
13 // 100 ms should do it).
14 Thread.currentThread().sleep( 100 );
15
16 log.debug("Debug Message");
17 log.warn ("Warning Message");
18 log.error("Error Message");
19
20 Thread.currentThread().sleep( 100 );
21 LogManager.shutdown();
22 }
23 }
The only other piece of the puzzle is a simple configuration file, which (thankfully) is not in XML format. It's a simple properties file, like the one in Listing 2.
To understand the file, you need to know a little about the logger architecture. Loggers form a runtime hierarchy of objects, organized by name. The "root" logger is at the root of the hierarchy, and the loggers you create are beneath the root (and each other), depending on their names. For example, a logger named a.b is beneath the logger named a, which is beneath the root.
Loggers write strings using two main helper classes called appenders and layouts. An appender object does the actual writing, and a layout object formats the message. Appenders are bound to a logger at runtime using information in the configuration file—this way, you can change them without recompiling. A particular logger can use several appenders, in which case, each appender sends the message somewhere, thus duplicating messages in several places. Log4j comes with several appenders that do things like console and file output and send logging messages using email or JMS (Java Message Service). Log4j also includes a socket-based appender similar to the one I illustrate in this article.
Layout objects, which control message formatting, are bound to appenders at runtime in a manner similar to loggers and appenders.
Log4J comes with several layout classes, which format in XML, HTML, and by means of a printf-like format string. I've found these to be adequate for most of my needs.
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