Loggers has mulitple levels for logging. If we are writing a real short program, just for learning purposes System.out.println is fine but when we are developing a quality software project, we should use professional logger and SOPs should be avoided.
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There are many java Api that are used for logging in java, some of the popular loggers that are used by professional developers are given here.
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Log4j is a popular logging package written in Java. Log4j is highly configurable through external configuration files at runtime.
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log4j is thread-safe, optimized for speed. Log4j supports internationalization and it is designed to handle Java Exceptions.
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There are various steps to configure Log4j in Eclipse. For configuring Log4j into Eclipse following given steps have to be followed-
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Logback is a higher version of Log4j project. It was developed by Ceki Gülcü, log4j's founder. Logback is faster and has a smaller footprint than all existing logging Api, sometimes by a wide margin. Just as importantly, logback offers unique and rather useful features missing in other logging systems.
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Faster implementation, extensive battery of tests, logback-classic speaks SLF4J natively, automatic reloading of configuration files are some features of Logback.
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Following steps have to follow for configuring Logback in Eclipse.
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As Logback is higher version it brings numerous improvement over log4j. Logback is conceptually very similar to log4j as both projects were founded by the same developer. If you are familiar with log4j, it will be easy to use logback.
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Both Logback and Log4j are logging framework, logback is conceptually very similar to log4j as both projects were founded by the same developer. If you are already familiar with log4j, you will feel quite familiar to logback.
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SLF4J (Simple Logging Facade) for java is an abstraction of different logging frameworks (eg. log4j, java.util.logging, commons logging, logback etc.). SLF4J provide plug-in to the end-user the desired logging framework at deployment time i.e we can choose the particular logging framework at application runtime.
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To use Log4j with SLF4J we need to follow some steps. Use of SLF4J with Log4j is given here -
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There are number of steps to use SLF4J with Logback. You have to follow the following steps to use both of them-
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Perf4J is used for calculating and displaying performance statistics for Java application. Perf4j is a set of utilities useful for developers those who are familiar with logging frameworks such as log4j, logback, JCL and JUL.
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A simple stop watch mechanism for succinct timing statements. Per4j is easy to integrate with common popular logging framework such as log4j, logback, JCl and Slf4j(facade) as well.
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To use Perf4j with SLF4J and Log4j we need to follow some steps. First download Per4j, Slf4j and Loj4j jar files and then add Perf4j, Slf4j and Log4j jars into classpath after that create java class.

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Here are some examples for Perf4j, SLF4J and Log4j.