Java logging thread name

Printing Thread Info in Log File Using Log4j2

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The Jet Profiler was built for MySQL only, so it can do things like real-time query performance, focus on most used tables or most frequent queries, quickly identify performance issues and basically help you optimize your queries.

Critically, it has very minimal impact on your server’s performance, with most of the profiling work done separately — so it needs no server changes, agents or separate services.

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1. Overview

This tutorial will show the idea and examples of logging thread information using the Log4j2 library.

2. Logging and Threads

Logs are a powerful tool to provide the context about what was happening in the system when some error or flow occurred. Logging helps us capture and persist relevant information to be analyzed at any time.

Threads allow our application to execute multiple things simultaneously to handle more requests and make our jobs more efficient.

Many Java applications use logging and threads to control their process in this scenario. However, as the logs usually concentrate on a specific file, the logs mess up from different threads, and the user cannot identify and understand the sequence of the events. We will use one of the most popular Java logging frameworks, Log4j2, to show relevant information about our thread to solve this problem.

3. Log4j2 Usage

Forward, we have an example of using some parameters in Log4j2 to show information about our thread:

 %d --- thread_id="%tid" thread_name="%tn" thread_priority="%tp" --- [%p] %m%n 

Log4j2 uses parameters in its pattern to refer to data. All parameters start with a % in their beginner. Here are some examples of thread parameters:

• tid: Thread identifier is a positive long number generated when the thread is created.
• tn: It’s a sequence of characters that names a thread.
• tp: Thread priority is an integer number between 1 and 10 where more significant numbers mean higher priority.

First, as it suggests, we are adding the information’s about the id, name, and priority of our thread. Therefore, to visualize it, we need to create a simple application that makes new threads and log some info:

public class Log4j2ThreadInfo < private static final Logger logger = LogManager.getLogger(Log4j2ThreadInfo.class); public static void main(String[] args) < IntStream.range(0, 5).forEach(i -> < Runnable runnable = () ->logger.info("Logging info"); Thread thread = new Thread(runnable); thread.start(); >); > >

In other words, we are simply running a forEach in a range of 0 to 5 with the help of Java Streams and then starting a new thread with some logging. As a result, we’re going to have:

2022-01-14 23:44:56.893 --- thread_id="22" thread_name="Thread-2" thread_priority="5" --- [INFO] Logging info 2022-01-14 23:44:56.893 --- thread_id="21" thread_name="Thread-1" thread_priority="5" --- [INFO] Logging info 2022-01-14 23:44:56.893 --- thread_id="20" thread_name="Thread-0" thread_priority="5" --- [INFO] Logging info 2022-01-14 23:44:56.893 --- thread_id="24" thread_name="Thread-4" thread_priority="5" --- [INFO] Logging info 2022-01-14 23:44:56.893 --- thread_id="23" thread_name="Thread-3" thread_priority="5" --- [INFO] Logging info

4. Conclusion

This article shows a simple way to add thread information in your Java Project using Log4j2 Parameters. If you want to check the code up, it is available over on GitHub.

Slow MySQL query performance is all too common. Of course it is. A good way to go is, naturally, a dedicated profiler that actually understands the ins and outs of MySQL.

The Jet Profiler was built for MySQL only, so it can do things like real-time query performance, focus on most used tables or most frequent queries, quickly identify performance issues and basically help you optimize your queries.

Critically, it has very minimal impact on your server’s performance, with most of the profiling work done separately — so it needs no server changes, agents or separate services.

Basically, you install the desktop application, connect to your MySQL server, hit the record button, and you’ll have results within minutes:

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Printing thread name using java.util.logging

Embarrassingly, but looks like java.util.logging can’t do this.

The default java.util.logging.SimpleFormatter doesn’t have the ability to log thread name at all. The java.util.logging.FileHandler supports few template placeholders, none of them is thread name.

java.util.logging.XMLFormatter is the closest one, but only logs thread id:

 2011-07-31T13:15:32 1312110932680 0 INFO java.util.logging.LogManager$RootLogger log 10 Test  

If you think we’re getting close — we’re not. LogRecord class only holds the thread ID, not its name — not very useful.

Solution 2

With a custom Formatter

Luckily, LogRecord contains the ID of the thread that produced the log message. We can get hold of this LogRecord when writing a custom Formatter . Once we have that, we only need to get the thread name via its ID.

There are a couple of ways to get the Thread object corresponding to that ID, here’s mine:

static Optional getThread(long threadId) < return Thread.getAllStackTraces().keySet().stream() .filter(t ->t.getId() == threadId) .findFirst(); > 

The following is a minimal Formatter that only prints the thread name and the log message:

private static Formatter getMinimalFormatter() < return new Formatter() < @Override public String format(LogRecord record) < int threadId = record.getThreadID(); String threadName = getThread(threadId) .map(Thread::getName) .orElseGet(() ->"Thread with ID " + threadId); return threadName + ": " + record.getMessage() + "\n"; > >; > 

To use your custom formatter, there are again different options, one way is to modify the default ConsoleHandler :

public static void main(final String. args) < getDefaultConsoleHandler().ifPresentOrElse( consoleHandler ->consoleHandler.setFormatter(getMinimalFormatter()), () -> System.err.println("Could not get default ConsoleHandler")); Logger log = Logger.getLogger(MyClass.class.getName()); log.info("Hello from the main thread"); SwingUtilities.invokeLater(() -> log.info("Hello from the event dispatch thread")); > static Optional getDefaultConsoleHandler() < // All the loggers inherit configuration from the root logger. See: // https://docs.oracle.com/javase/8/docs/technotes/guides/logging/overview.html#a1.3 var rootLogger = Logger.getLogger("") // The root logger's first handler is the default ConsoleHandler return first(Arrays.asList(rootLogger.getHandlers())); >static Optional first(List list)

Your minimal Formatter should then produce the folowing log messages containing the thread name:

main: Hello from the main thread

AWT-EventQueue-0: Hello from the event dispatch thread

This is a Formatter that shows how to log more than thread name and log message:

private static Formatter getCustomFormatter() < return new Formatter() < @Override public String format(LogRecord record) < var dateTime = ZonedDateTime.ofInstant(record.getInstant(), ZoneId.systemDefault()); int threadId = record.getThreadID(); String threadName = getThread(threadId) .map(Thread::getName) .orElse("Thread with ID " + threadId); // See also: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Formatter.html var formatString = "%1$tF %1$tT %2$-7s [%3$s] %4$s.%5$s: %6$s %n%7$s"; return String.format( formatString, dateTime, record.getLevel().getName(), threadName, record.getSourceClassName(), record.getSourceMethodName(), record.getMessage(), stackTraceToString(record) ); >>; > private static String stackTraceToString(LogRecord record) < final String throwableAsString; if (record.getThrown() != null) < var stringWriter = new StringWriter(); var printWriter = new PrintWriter(stringWriter); printWriter.println(); record.getThrown().printStackTrace(printWriter); printWriter.close(); throwableAsString = stringWriter.toString(); >else < throwableAsString = ""; >return throwableAsString; > 

That Formatter produces log messages like these:

2019-04-27 13:21:01 INFO [AWT-EventQueue-0] package.ClassName.method: The log message

Solution 3

Some application servers implicitly log the thread ID (I know of WebSphere). You can create your own LogFormatter. The records passed to the formatter contain the Thread ID, see here. I implemented that approach for Tomcat several times, but it’ll work in Java SE environments as well.

BTW: The Thread name is not available to LogRecord.

Solution 4

java.util.logging has many curious peculiarities. you can add a facade API to tweak its behaviors

public class Log Logger logger; static public Log of(Class clazz) return new Log( Logger.getLogger( clazz.getName() )); public void error(Throwable thrown, String msg, Object. params) < log(ERROR, thrown, msg, params); >void log(Level level, Throwable thrown, String msg, Object. params) < if( !logger.isLoggable(level) ) return; // bolt on thread name somewhere LogRecord record = new LogRecord(. ); record.setXxx(. ); . logger.log(record); >---- static final Log log = Log.of(Foo.class); . log.error(. ); 

People use java’s logging mostly because they don’t want to have 3rd party dependencies. That’s also why they can’t depend on existing logging facades like apache’s or slf4j.

Solution 5

I had similar problem. As answered here How to align log messages using java.util.logging you can extend java.util.logging.Formatter but instead getting LogRecord#getThreadID() you can get thread name by invoking Thread.currentThread().getName() like this:

public class MyLogFormatter extends Formatter < private static final MessageFormat messageFormat = new MessageFormat("[  ] \n"); public MyLogFormatter() < super(); >@Override public String format(LogRecord record) < Object[] arguments = new Object[6]; arguments[0] = record.getLoggerName(); arguments[1] = record.getLevel(); arguments[2] = Thread.currentThread().getName(); arguments[3] = new Date(record.getMillis()); arguments[4] = record.getMessage(); arguments[5] = record.getSourceMethodName(); return messageFormat.format(arguments); >> 

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Printing thread name using java.util.logging

Embarrassingly, but looks like java.util.logging can’t do this.

The default java.util.logging.SimpleFormatter doesn’t have the ability to log thread name at all. The java.util.logging.FileHandler supports few template placeholders, none of them is thread name.

java.util.logging.XMLFormatter is the closest one, but only logs thread id:

 2011-07-31T13:15:32 1312110932680 0 INFO java.util.logging.LogManager$RootLogger log 10 Test  

If you think we’re getting close — we’re not. LogRecord class only holds the thread ID, not its name — not very useful.

With a custom Formatter

Luckily, LogRecord contains the ID of the thread that produced the log message. We can get hold of this LogRecord when writing a custom Formatter . Once we have that, we only need to get the thread name via its ID.

There are a couple of ways to get the Thread object corresponding to that ID, here’s mine:

static Optional getThread(long threadId) < return Thread.getAllStackTraces().keySet().stream() .filter(t ->t.getId() == threadId) .findFirst(); > 

The following is a minimal Formatter that only prints the thread name and the log message:

private static Formatter getMinimalFormatter() < return new Formatter() < @Override public String format(LogRecord record) < int threadId = record.getThreadID(); String threadName = getThread(threadId) .map(Thread::getName) .orElseGet(() ->"Thread with ID " + threadId); return threadName + ": " + record.getMessage() + "\n"; > >; > 

To use your custom formatter, there are again different options, one way is to modify the default ConsoleHandler :

public static void main(final String. args) < getDefaultConsoleHandler().ifPresentOrElse( consoleHandler ->consoleHandler.setFormatter(getMinimalFormatter()), () -> System.err.println("Could not get default ConsoleHandler")); Logger log = Logger.getLogger(MyClass.class.getName()); log.info("Hello from the main thread"); SwingUtilities.invokeLater(() -> log.info("Hello from the event dispatch thread")); > static Optional getDefaultConsoleHandler() < // All the loggers inherit configuration from the root logger. See: // https://docs.oracle.com/javase/8/docs/technotes/guides/logging/overview.html#a1.3 var rootLogger = Logger.getLogger("") // The root logger's first handler is the default ConsoleHandler return first(Arrays.asList(rootLogger.getHandlers())); >static Optional first(List list)

Your minimal Formatter should then produce the folowing log messages containing the thread name:

main: Hello from the main thread

AWT-EventQueue-0: Hello from the event dispatch thread

This is a Formatter that shows how to log more than thread name and log message:

private static Formatter getCustomFormatter() < return new Formatter() < @Override public String format(LogRecord record) < var dateTime = ZonedDateTime.ofInstant(record.getInstant(), ZoneId.systemDefault()); int threadId = record.getThreadID(); String threadName = getThread(threadId) .map(Thread::getName) .orElse("Thread with ID " + threadId); // See also: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Formatter.html var formatString = "%1$tF %1$tT %2$-7s [%3$s] %4$s.%5$s: %6$s %n%7$s"; return String.format( formatString, dateTime, record.getLevel().getName(), threadName, record.getSourceClassName(), record.getSourceMethodName(), record.getMessage(), stackTraceToString(record) ); >>; > private static String stackTraceToString(LogRecord record) < final String throwableAsString; if (record.getThrown() != null) < var stringWriter = new StringWriter(); var printWriter = new PrintWriter(stringWriter); printWriter.println(); record.getThrown().printStackTrace(printWriter); printWriter.close(); throwableAsString = stringWriter.toString(); >else < throwableAsString = ""; >return throwableAsString; > 

That Formatter produces log messages like these:

2019-04-27 13:21:01 INFO [AWT-EventQueue-0] package.ClassName.method: The log message

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