Welcome!

Java IoT Authors: Liz McMillan, Elizabeth White, Don MacVittie, Pat Romanski, Roger Strukhoff

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
Recently, REAN Cloud built a digital concierge for a North Carolina hospital that had observed that most patient call button questions were repetitive. In addition, the paper-based process used to measure patient health metrics was laborious, not in real-time and sometimes error-prone. In their session at 21st Cloud Expo, Sean Finnerty, Executive Director, Practice Lead, Health Care & Life Science at REAN Cloud, and Dr. S.P.T. Krishnan, Principal Architect at REAN Cloud, discussed how they built...
In his Opening Keynote at 21st Cloud Expo, John Considine, General Manager of IBM Cloud Infrastructure, led attendees through the exciting evolution of the cloud. He looked at this major disruption from the perspective of technology, business models, and what this means for enterprises of all sizes. John Considine is General Manager of Cloud Infrastructure Services at IBM. In that role he is responsible for leading IBM’s public cloud infrastructure including strategy, development, and offering m...
In his session at 21st Cloud Expo, Raju Shreewastava, founder of Big Data Trunk, provided a fun and simple way to introduce Machine Leaning to anyone and everyone. He solved a machine learning problem and demonstrated an easy way to be able to do machine learning without even coding. Raju Shreewastava is the founder of Big Data Trunk (www.BigDataTrunk.com), a Big Data Training and consulting firm with offices in the United States. He previously led the data warehouse/business intelligence and B...
With tough new regulations coming to Europe on data privacy in May 2018, Calligo will explain why in reality the effect is global and transforms how you consider critical data. EU GDPR fundamentally rewrites the rules for cloud, Big Data and IoT. In his session at 21st Cloud Expo, Adam Ryan, Vice President and General Manager EMEA at Calligo, examined the regulations and provided insight on how it affects technology, challenges the established rules and will usher in new levels of diligence arou...
Nordstrom is transforming the way that they do business and the cloud is the key to enabling speed and hyper personalized customer experiences. In his session at 21st Cloud Expo, Ken Schow, VP of Engineering at Nordstrom, discussed some of the key learnings and common pitfalls of large enterprises moving to the cloud. This includes strategies around choosing a cloud provider(s), architecture, and lessons learned. In addition, he covered some of the best practices for structured team migration an...
The 22nd International Cloud Expo | 1st DXWorld Expo has announced that its Call for Papers is open. Cloud Expo | DXWorld Expo, to be held June 5-7, 2018, at the Javits Center in New York, NY, brings together Cloud Computing, Digital Transformation, Big Data, Internet of Things, DevOps, Machine Learning and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding busin...
No hype cycles or predictions of a gazillion things here. IoT is here. 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, an Associate Partner of Analytics, IoT & Cybersecurity at M&S Consulting, presented a step-by-step plan to develop your technology implementation strategy. He also discussed the evaluation of communication standards and IoT messaging protocols, data...
Smart cities have the potential to change our lives at so many levels for citizens: less pollution, reduced parking obstacles, better health, education and more energy savings. Real-time data streaming and the Internet of Things (IoT) possess the power to turn this vision into a reality. However, most organizations today are building their data infrastructure to focus solely on addressing immediate business needs vs. a platform capable of quickly adapting emerging technologies to address future ...
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 ...
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 ...
DevOps at Cloud Expo – being held June 5-7, 2018, at the Javits Center in New York, NY – announces that its Call for Papers is open. Born out of proven success in agile development, cloud computing, and process automation, DevOps is a macro trend you cannot afford to miss. From showcase success stories from early adopters and web-scale businesses, DevOps is expanding to organizations of all sizes, including the world's largest enterprises – and delivering real results. Among the proven benefits,...
@DevOpsSummit at Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, is co-located with 22nd Cloud Expo | 1st DXWorld Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait...
Cloud Expo | DXWorld Expo have announced the conference tracks for Cloud Expo 2018. Cloud Expo will be held June 5-7, 2018, at the Javits Center in New York City, and November 6-8, 2018, at the Santa Clara Convention Center, Santa Clara, CA. Digital Transformation (DX) is a major focus with the introduction of DX Expo within the program. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive ov...
SYS-CON Events announced today that T-Mobile exhibited at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. As America's Un-carrier, T-Mobile US, Inc., is redefining the way consumers and businesses buy wireless services through leading product and service innovation. The Company's advanced nationwide 4G LTE network delivers outstanding wireless experiences to 67.4 million customers who are unwilling to compromise on qua...
SYS-CON Events announced today that Cedexis will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Cedexis is the leader in data-driven enterprise global traffic management. Whether optimizing traffic through datacenters, clouds, CDNs, or any combination, Cedexis solutions drive quality and cost-effectiveness. For more information, please visit https://www.cedexis.com.
SYS-CON Events announced today that Google Cloud has been named “Keynote Sponsor” of SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Companies come to Google Cloud to transform their businesses. Google Cloud’s comprehensive portfolio – from infrastructure to apps to devices – helps enterprises innovate faster, scale smarter, stay secure, and do more with data than ever before.
SYS-CON Events announced today that Vivint to exhibit at SYS-CON's 21st Cloud Expo, which will take place on October 31 through November 2nd 2017 at the Santa Clara Convention Center in Santa Clara, California. As a leading smart home technology provider, Vivint offers home security, energy management, home automation, local cloud storage, and high-speed Internet solutions to more than one million customers throughout the United States and Canada. The end result is a smart home solution that sav...
SYS-CON Events announced today that Opsani will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Opsani is the leading provider of deployment automation systems for running and scaling traditional enterprise applications on container infrastructure.
SYS-CON Events announced today that Nirmata will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Nirmata provides a comprehensive platform, for deploying, operating, and optimizing containerized applications across clouds, powered by Kubernetes. Nirmata empowers enterprise DevOps teams by fully automating the complex operations and management of application containers and its underlying ...
SYS-CON Events announced today that Opsani to exhibit at SYS-CON's 21st Cloud Expo, which will take place on October 31 through November 2nd 2017 at the Santa Clara Convention Center in Santa Clara, California. Opsani is creating the next generation of automated continuous deployment tools designed specifically for containers. How is continuous deployment different from continuous integration and continuous delivery? CI/CD tools provide build and test. Continuous Deployment is the means by which...