Config file java logging

Log4j informed us that there is no configuration present. There are multiple ways we can configure our Log4j logging. We can do it programmatically — for example by including a static initialization block:. The above code configures Log4j to output the logs to the console in the default format.

The output of running our example application would look as follows:. The most common way would be to either use a properties file or an XML file. We can change our code and include the log4j. That way we told Log4j that we create the root logger, that will be used by default. We also gave our logger a name — MAIN. Next, we configure the logger, by setting its output to console and by using the pattern layout. We will talk about it more later in the blog post.

The output of running the above code would be as follows:. If we wish, we can also change the log4j. The same configuration using XML format would look as follows:.

If we would now change the log4j. So how does Log4j know which file to use? When it starts it looks for the log4j. That means that we can overwrite the Log4j configuration from the classpath by providing the -Dlog4j. For example, if we include a file called other. And then run out code with -Dlog4j. We already used appenders in our examples… well, really just one — the ConsoleAppender.

Its sole purpose is to write the log events to the console. Of course, with a large number of log events and systems running in different environments writing pure text data to the standard output may not be the best idea, unless you are running in containers. Here are a few common examples of Log4j appenders:.

For example, you can send logs to the console and to a file. The following log4j. The MAIN logger is the one that we already saw — the one that sends the data to the console. In our case, the log files should be called awesome.

If there are more files they will be removed from the file system as soon as log4j sees them. After running the code with the above configuration the console would print the following content:. The nice thing about Appenders is that they can have their level which should be taken into consideration when logging. What if we wanted to change that for all the classes in the com.

We would only have to modify our log4j. Look at the last line in the above configuration file. Our example application code looks like this:. With the above Log4j configuration the output of the logging looks as follows:.

As you can see, only the WARN level log was included. That is exactly what we wanted. Finally, the part of the Log4j logging framework that controls the way our data is structured in our log file — the layout. In most cases, you will encounter the PatternLayout. The idea behind this layout is that you can provide a variety of formatting options to define the structure of the logs.

Some of the examples are:. For more information on the available options head over to the official Log4j Javadocs for the PatternLayout. When using the PatternLayout we can configure which option we would like to use. We could use a pattern like this:. The full log4j. The output that is written to the console after running our example code looks as follows:. It is surrounded by a certain context. In addition, there are methods on LogManager that allow the configuration file to be re-read.

When this happens, the configuration file values will override any changes that have been made programatically. All of the logging class are in the java. Each logger may have a ResourceBundle name associated with it. The corresponding ResourceBundle can be used to map between raw message strings and localized message strings. Normally, formatters perform localization. As a convenience, the Formatter class provides a formatMessage method that provides some basic localization and formatting support.

All calls are intended to be local. However, it is expected that some handlers will want to forward their output to other systems. There are a variety of ways of doing this:. This provides a simple, standard, inter-change format that can be parsed and processed on a variety of systems. The LogRecord class is therefore serializable.

However, there is a problem in how to deal with the LogRecord parameters. Some parameters may not be serializable and other parameters may have been designed to serialize much more state than is required for logging.

To avoid these problems, the LogRecord class has a custom writeObject method that converts the parameters to strings using Object. Most of the logging classes are not intended to be serializable. Both loggers and handlers are stateful classes that are tied into a specific virtual machine. In this respect they are analogous to the java. This program relies on the root handlers that were established by the LogManager based on the configuration file. It creates its own Logger object and then makes calls to that Logger object to report various events.

Here's a small program that dynamically adjusts the logging configuration to send output to a specific file and to get lots of information on wombats. Here's a small program that sets up its own logging Handler and ignores the global configuration.

Overview of Control Flow Applications make logging calls on Logger objects. Figure Java Logging Control Flow. Log Levels Each log message has an associated log Level object. Loggers As stated earlier, client code sends log requests to Logger objects. In particular, a logger may inherit: Logging level : If a logger's level is set to be null, then the logger will use an effective Level that will be obtained by walking up the parent tree and using the first non-null Level.

Logging Methods The Logger class provides a large set of convenience methods for generating log messages. An example of this style is: void warning String sourceClass, String sourceMethod, String msg ; Second, there are a set of methods that do not take explicit source class or source method names.

MemoryHandler : A handler that buffers log records in memory. Formatters Java SE also includes two standard Formatter classes: SimpleFormatter : Writes brief "human-readable" summaries of log records. As with handlers, it is fairly straightforward to develop new formatters. This includes: A hierarchical namespace of named Loggers.

Configuration File The logging configuration can be initialized using a logging configuration file that will be read at startup. Default Configuration The default logging configuration that ships with the JRE is only a default and can be overridden by ISVs, system administrators, and end users. Dynamic Configuration Updates Programmers can update the logging configuration at run time in a variety of ways: FileHandler , MemoryHandler , and ConsoleHandler objects can all be created with various attributes.

Adding logging to our Java application is usually about configuring the library of choice and including the Logger.

That allows us to add logging into the parts of our application that we want to know about. The handler is used to export the LogRecord entity to a given destination. Those destinations can be the memory, console, files, and remote locations via sockets and various APIs. There are different standard handlers. Below are a few examples of such a handlers:. The ConsoleHandler is designed to send your log messages to the standard output. The FileHandler writes the log messages to a dedicated file and the SyslogHandler sends the data to the Syslog compatible daemon.

Turning any handler on and off is just a matter of including it in the configuration file for the logging library of your choice. You can also create your own handler by extending the Handler class. Java log levels are a set of standard severities of the logging message. Tells how important the log record is. For example, the following log levels are sorted from least to most important with some explanation on how I see them:. TRACE — Very fine-grained information only used in a rare case where you need the full visibility of what is happening.

In most cases, the TRACE level will be very verbose, but you can also expect a lot of information about the application. Use for annotating the steps in an algorithm that are not relevant in everyday use.

The DEBUG level should be used for information that can be useful for troubleshooting and is not needed for looking at the everyday application state. In most cases, if you are not looking into how your application performs you could ignore most if not all of the INFO level logs. WARN — Log level that usually indicates a state of the application that might be problematic or that it detected an unusual execution.

For example, a message was not parsed correctly, because it was not correct. The code execution is continuing, but we could log that with the WARN level to inform us and others that potential problems are happening. ERROR — Log level that indicates an issue with a system that prevents certain functionality from working. For example, if you provide login via social media as one way of logging into your system, the failure of such a module is an ERROR level log for sure.

FATAL — The log level indicating that your application encountered an event that prevents it from working or a crucial part of it from working. A FATAL log level is, for example, an inability to connect to a database that your system relies on or to an external payment system that is needed to check out the basket in your e-commerce system. The formatter supports the formatting of the LogRecord objects.

By default, two formatters are available:. Of course, your application can use the basic logging API provided out of the box by Java via the java. There is nothing wrong with that, but note that this will limit what you can do with your logs. Certain libraries provide easy to configure formatters, out-of-the-box industry standard destinations, and top-notch performance.

If you wish to use one of those frameworks and you would also like to be able to switch the framework in the future, you should look at the abstraction layer on top of the logging APIs. It provides bindings for common logging frameworks such as Log4j , Logback , and the out-of-the-box java.

You can imagine the process of writing the log message in the following, simplified way:. But how would that look from the code perspective? For example, if we would like to just start our application and print something to the log it would look as follows:. You can see that we initialize the static Logger class by using the class name. That way we can clearly identify where the log message comes from and we can reuse a single Logger for all the log messages that are generated by a given class.

This time, things are a bit different. We use the LoggerFactory class to retrieve the logger for our class and we use a dedicated info method of the Logger object to write the log message using the INFO level. Starting with SLF4J 2. The constructors of these classes can execute arbitrary configuration code. Replace the "logger" with a specific name of a Logger in your app e. Tweet Jakob Jenkov. Featured Videos Sponsored Ads.

All Trails. Trail TOC. Page TOC. A white space or comma separated list of handler class names to be added to the root Logger. A white space or comma separated list of class names which will be instantiated when the LogManager is initialized.