Tracing program execution during development

Debugging Providing an audit trail for a program Recording soft-errors (lost connections, etc.)

for monitoring performance and troubleshooting

A logging framework lets you use different logging levels◦ You can turn different types of messages on and off◦ You can send different types of messages to

different destinations

Replaces System.out.println() calls throughout

Don’t need to be removed Like adding System.out.println() calls, it’s

somewhat tedious to add logging code Utility of logging code is improved if it’s

consistent—logs can be searched with scripts, for example

Provides wizards that automate the addition of logging code

Add import and declaration for logger Insert logging at start and end of methods Insert logging of variables and method

parameters

Log4E does not provide a logging framework

Doesn’t configure your framework Doesn’t make a fresh pot of coffee

Log4E supports three logging frameworks:◦ Log4J◦ Java 1.4 Logging◦ Jakarta Commons Logging

Log4J is the original logging framework that Java 1.4 logging is modeled after

Jakarta Commons Logging is actually a wrapper for logging frameworks

We’ll use Log4J in this example because it’s mature, well-documented and supported, and easier to configure

Download a zip or compressed tarfile from: Apache.org website

Uncompress to a local directory In your Eclipse project’s properties

◦ Locate Java Build Path◦ On Libraries page, click on Add External Jars◦ Browse for your Log4J directory, and locate the

log4J Jar file in the /dist/lib directory◦ Press Open, followed by OK

The easiest way to configure Log4J is to add a log4j.properties file to your source directory.

There are many options available which we won’t cover here, but essentially you need to define:◦ A logger◦ An appender◦ A pattern layout

The following example uses the default root logger, appends to the console and prints the date, time, message priority, thread and message

# Loggerlog4j.rootLogger=DEBUG, ConApp

# Appenderlog4j.appender.ConApp=org.apache.log4j.ConsoleAppender

# PatternLayoutlog4j.appender.ConApp.layout=org.apache.log4j.PatternLayoutlog4j.appender.ConApp.layout.ConversionPattern=%d [%t] %-5p %c - %m%n

Create a simple Java application Ensure log4j is on class path Use Log4E to add several types of logging

messages Run program