Welcome!

Java IoT Authors: Elizabeth White, Pat Romanski, Yeshim Deniz, Liz McMillan, Stackify Blog

Related Topics: Java IoT

Java IoT: Article

Cover Story: Log4j vs java.util.logging

Which Logging Library Is Better For You?

Are your Java programs littered with a multitude of randomly placed System.out.println statements and stack traces? When you add debugging messages to a class in a project, are the outputs of your messages interleaved among dozens of messages from other developers, making your messages difficult to read? Do you use a simple, hand-rolled logging API, and fear that it may not provide the flexibility and power that you need once your applications are in production? If you answered yes to any of the above questions, it's time for you to pick an industrial-strength logging API and start using it.

This article will help you choose a logging API by evaluating two of the most widely used Java logging libraries: the Apache Group's Log4j and the java.util.logging package (referred to as "JUL"). This article examines how each library approaches logging, evaluates their differences and similarities, and offers a few simple guidelines that will help you decide which library to choose.

Introduction to Log4j
Log4j is an open source logging library developed as a subproject of the Apache Software Foundation's Logging Services Project. Based on a logging library developed at IBM in the late 1990s, its first versions appeared in 1999. Log4j is widely used in the open source community, including by some big name projects such as JBoss and Hibernate.

Log4j's architecture is built around three main concepts: loggers, appenders, and layouts. These concepts allow developers to log messages according to their type and priority, and to control where messages end up and how they look when they get there. Loggers are objects that your applications first call on to initiate the logging of a message. When given a message to log, loggers generate Logging-Event objects to wrap the given message. The loggers then hand off the LoggingEvents to their associated appenders. Appenders send the information contained by the LoggingEvents to specified output destinations - for example, a ConsoleAppender will write the information to System.out, or a FileApppender will append it to a log file. Before sending LoggingEvent information to its final output target, some appenders use layouts to create a text representation of the information in a desired format. For example, Log4j includes an XMLLayout class that can be used to format LoggingEvents as strings of XML.

In Log4j, LoggingEvents are assigned a level that indicates their priority. The default levels in Log4j are (ordered from highest to lowest): OFF, FATAL, ERROR, WARN, INFO, DEBUG, and ALL. Loggers and appenders are also assigned a level, and will only execute logging requests that have a level that is equal to or greater than their own. For example, if an appender whose level is ERROR is asked to write out a LoggingEvent that has a level of WARN, the appender will not write out the given LogEvent.

All loggers in Log4j have a name. Log4j organizes logger instances in a tree structure according to their names the same way packages are organized in the Java language. As Log4j's documentation succinctly states: "A logger is said to be an ancestor of another logger if its name followed by a dot is a prefix of the descendant logger name. A logger is said to be a parent of a child logger if there are no ancestors between itself and the descendant logger." For example, a logger named "org.nrdc" is said to be the child of the "org" logger. The "org.nrdc.logging" logger is the child of the "org.nrdc" logger and the grandchild of the "org" logger. If a logger is not explicitly assigned a level, it uses the level of its closest ancestor that has been assigned a level. Loggers inherit appenders from their ancestors, although they can also be configured to use only appenders that are directly assigned to them.

When a logger is asked to log a message, it first checks that the level of the request is greater than or equal to its effective level. If so, it creates a LoggingEvent from the given message and passes the LoggingEvent to its appenders, which format it and send it to its output destinations.

Introduction to JUL
The java.util.logging package, which Sun introduced in 2002 with Java SDK version 1.4, came about as a result of JSR 47, Logging API Specification. JUL is extremely similar to Log4j - it more or less uses exactly the same concepts, but renames some of them. For example, appenders are "handlers," layouts are "formatters," and LoggingEvents are "LogRecords." Figure 1 summarizes Log4j and JUL names and concepts. JUL uses levels the same way that Log4J uses levels, although JUL has nine default levels instead of seven. JUL organizes loggers in a hierarchy the same way Log4j organizes its loggers, and JUL loggers inherit properties from their parent loggers in more or less the same way that Log4j loggers inherit properties from their parents. Concepts pretty much map one-to-one from Log4j to JUL; though the two libraries are different in subtle ways, any developer familiar with Log4j needs only to adjust his or her vocabulary to generally understand JUL.

Functionality Differences
While Log4j and JUL are almost conceptually identical, they do differ in terms of functionality. Their difference can be summarized as, "Whatever JUL can do, Log4j can also do - and more." They differ most in the areas of useful appender/handler implementations, useful formatter/layout implementations, and configuration flexibility.

JUL contains four concrete handler implementations, while Log4j includes over a dozen appender implementations. JUL's handlers are adequate for basic logging - they allow you to write to a buffer, to a console, to a socket, and to a file. Log4j's appenders, on the other hand, probably cover every logging output destination that you could think of. They can write to an NT event log or a Unix syslog, or even send e-mail. Figure 2 provides a summary of JUL's handlers and Log4j's appenders.

JUL contains two formatter classes: the XMLFormatter and SimpleFormatter. Log4j includes the corresponding layouts: the XMLLayout and SimpleLayout. Log4j also offers the TTCCLayout, which formats LoggingEvents into content-rich strings, and the HTMLLayout, which formats LoggingEvents as an HTML table.

While the TTCCLayout and HTMLLayout are useful, Log4j really pulls ahead of JUL in the formatter/handler arena because of the PatternLayout. PatternLayout instances can be configured with an enormous amount of flexibility via string conversion patterns, similar to the conversion patterns used by the printf function in C. In PatternLayout conversion patterns, special conversion characters are used to specify the information included in layout's formatted output. For example, "%t" is used to specify the name of the thread that started the logging of the message; "%C" is used to specify the name of the class of the object that started the logging of the message; and "%m" specifies the message. "%t: %m" would result in output such as "main thread: This is my message." "%C - %t: %m" would result in output such as "org.nrdc.My-Class - main thread: This is my message." The Pattern-Layout is extremely useful, and JUL's two formatter classes don't come anywhere near to matching its versatility. It's not uncommon for JUL users to write their own custom formatter class, whereas most Log4j users generally need to just learn how to use PatternLayout conversion patterns.

While both Log4j and JUL can be configured with configuration files, Log4j allows for a broader range of configuration possibilities through configuration files than JUL does. JUL can be configured with .properties files, but until J2SE 5.0 the configuration of handlers was only on a per-class rather than a per-instance basis. This means that if you are going to be using a pre-Tiger SDK, you'll miss out on useful configuration options, such as the ability to set up different FileHandler instances to send their output to different files.

It's important to note that pre-Tiger JUL can easily be configured to write to multiple output files in code, just not through its default configuration mechanism. Log4j can be configured with .properties and/or XML files, and appenders can be configured on a per-instance basis. Also, Log4j allows developers to associate layout instances with appender instances, and configure layouts on a per-instance basis. This includes PatternLayout instances - you can set the conversion pattern each uses in the configuration file. During development, it usually isn't a problem to recompile an application to adjust its logging configuration; after deployment, however, you may want to be able to tweak or even completely reconfigure your application's logging without recompiling. In that case, Log4j offers more flexibility, especially pre-Tiger.

More Stories By Joe McNamara

Joe McNamara is a software developer and logging guru at Quantum Leap Innovations, an innovator of intelligent software. At Quantum Leap Innovations, he works on a revolutionary multiagent system technology for the seamless and dynamic integration of wide numbers of applications, systems, and human users.

Comments (1) View Comments

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


Most Recent Comments
Bengt Rodehav 03/11/05 03:18:56 AM EST

I agree with the conclusion that log4j can do anything that JUL can do plus more. In my opinion, log4j is the "de facto" standard for logging in Java. When a "de facto" standard exists there is no need to creata a JSR to solve a problem since it has already been solved. JUL should never have been created.
However, since we now have two rivaling "standards" (log4j and JUL) there is a need for another API on top of them. This does already exist in Apache commons logging. The article lacks a discussion of when commons logging is appropriate. Assume, for example, that you are developing a product that will be used in many different organisations. Those organisations might have standardised what kind of logging to use. In those cases commons logging make sense. Otherwise I would stick to log4j.

@ThingsExpo Stories
No hype cycles or predictions of zillions of things here. IoT is big. You get it. You know your business and have great ideas for a business transformation strategy. What comes next? Time to make it happen. In his session at @ThingsExpo, Jay Mason, Associate Partner at M&S Consulting, presented a step-by-step plan to develop your technology implementation strategy. He discussed the evaluation of communication standards and IoT messaging protocols, data analytics considerations, edge-to-cloud tec...
Announcing Poland #DigitalTransformation Pavilion
Digital Transformation is much more than a buzzword. The radical shift to digital mechanisms for almost every process is evident across all industries and verticals. This is often especially true in financial services, where the legacy environment is many times unable to keep up with the rapidly shifting demands of the consumer. The constant pressure to provide complete, omnichannel delivery of customer-facing solutions to meet both regulatory and customer demands is putting enormous pressure on...
DXWorldEXPO LLC announced today that All in Mobile, a mobile app development company from Poland, will exhibit at the 22nd International CloudEXPO | DXWorldEXPO. All In Mobile is a mobile app development company from Poland. Since 2014, they maintain passion for developing mobile applications for enterprises and startups worldwide.
CloudEXPO | DXWorldEXPO are the world's most influential, independent events where Cloud Computing was coined and where technology buyers and vendors meet to experience and discuss the big picture of Digital Transformation and all of the strategies, tactics, and tools they need to realize their goals. Sponsors of DXWorldEXPO | CloudEXPO benefit from unmatched branding, profile building and lead generation opportunities.
The best way to leverage your CloudEXPO | DXWorldEXPO presence as a sponsor and exhibitor is to plan your news announcements around our events. The press covering CloudEXPO | DXWorldEXPO will have access to these releases and will amplify your news announcements. More than two dozen Cloud companies either set deals at our shows or have announced their mergers and acquisitions at CloudEXPO. Product announcements during our show provide your company with the most reach through our targeted audienc...
@DevOpsSummit at Cloud Expo, taking place November 12-13 in New York City, NY, is co-located with 22nd international CloudEXPO | first international DXWorldEXPO and will feature technical sessions from a rock star conference faculty and the leading industry players in the world.
Everything run by electricity will eventually be connected to the Internet. Get ahead of the Internet of Things revolution. In his session at @ThingsExpo, Akvelon expert and IoT industry leader Sergey Grebnov provided an educational dive into the world of managing your home, workplace and all the devices they contain with the power of machine-based AI and intelligent Bot services for a completely streamlined experience.
DXWorldEXPO | CloudEXPO are the world's most influential, independent events where Cloud Computing was coined and where technology buyers and vendors meet to experience and discuss the big picture of Digital Transformation and all of the strategies, tactics, and tools they need to realize their goals. Sponsors of DXWorldEXPO | CloudEXPO benefit from unmatched branding, profile building and lead generation opportunities.
22nd International Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, and co-located with the 1st DXWorld Expo will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud ...
In his keynote at 19th Cloud Expo, Sheng Liang, co-founder and CEO of Rancher Labs, discussed the technological advances and new business opportunities created by the rapid adoption of containers. With the success of Amazon Web Services (AWS) and various open source technologies used to build private clouds, cloud computing has become an essential component of IT strategy. However, users continue to face challenges in implementing clouds, as older technologies evolve and newer ones like Docker c...
"MobiDev is a software development company and we do complex, custom software development for everybody from entrepreneurs to large enterprises," explained Alan Winters, U.S. Head of Business Development at MobiDev, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
JETRO showcased Japan Digital Transformation Pavilion at SYS-CON's 21st International Cloud Expo® at the Santa Clara Convention Center in Santa Clara, CA. The Japan External Trade Organization (JETRO) is a non-profit organization that provides business support services to companies expanding to Japan. With the support of JETRO's dedicated staff, clients can incorporate their business; receive visa, immigration, and HR support; find dedicated office space; identify local government subsidies; get...
Dion Hinchcliffe is an internationally recognized digital expert, bestselling book author, frequent keynote speaker, analyst, futurist, and transformation expert based in Washington, DC. He is currently Chief Strategy Officer at the industry-leading digital strategy and online community solutions firm, 7Summits.
Bill Schmarzo, author of "Big Data: Understanding How Data Powers Big Business" and "Big Data MBA: Driving Business Strategies with Data Science," is responsible for setting the strategy and defining the Big Data service offerings and capabilities for EMC Global Services Big Data Practice. As the CTO for the Big Data Practice, he is responsible for working with organizations to help them identify where and how to start their big data journeys. He's written several white papers, is an avid blogge...
In past @ThingsExpo presentations, Joseph di Paolantonio has explored how various Internet of Things (IoT) and data management and analytics (DMA) solution spaces will come together as sensor analytics ecosystems. This year, in his session at @ThingsExpo, Joseph di Paolantonio from DataArchon, added the numerous Transportation areas, from autonomous vehicles to “Uber for containers.” While IoT data in any one area of Transportation will have a huge impact in that area, combining sensor analytic...
Bill Schmarzo, author of "Big Data: Understanding How Data Powers Big Business" and "Big Data MBA: Driving Business Strategies with Data Science," is responsible for setting the strategy and defining the Big Data service offerings and capabilities for EMC Global Services Big Data Practice. As the CTO for the Big Data Practice, he is responsible for working with organizations to help them identify where and how to start their big data journeys. He's written several white papers, is an avid blogge...
Charles Araujo is an industry analyst, internationally recognized authority on the Digital Enterprise and author of The Quantum Age of IT: Why Everything You Know About IT is About to Change. As Principal Analyst with Intellyx, he writes, speaks and advises organizations on how to navigate through this time of disruption. He is also the founder of The Institute for Digital Transformation and a sought after keynote speaker. He has been a regular contributor to both InformationWeek and CIO Insight...
Michael Maximilien, better known as max or Dr. Max, is a computer scientist with IBM. At IBM Research Triangle Park, he was a principal engineer for the worldwide industry point-of-sale standard: JavaPOS. At IBM Research, some highlights include pioneering research on semantic Web services, mashups, and cloud computing, and platform-as-a-service. He joined the IBM Cloud Labs in 2014 and works closely with Pivotal Inc., to help make the Cloud Found the best PaaS.
It is of utmost importance for the future success of WebRTC to ensure that interoperability is operational between web browsers and any WebRTC-compliant client. To be guaranteed as operational and effective, interoperability must be tested extensively by establishing WebRTC data and media connections between different web browsers running on different devices and operating systems. In his session at WebRTC Summit at @ThingsExpo, Dr. Alex Gouaillard, CEO and Founder of CoSMo Software, presented ...