Jetty Server
The Jetty Server
object is the central component that links protocol connectors to web applications.
The Server
component is defined by the server
Jetty module, that in turn depends on other Jetty modules that provide key functionalities, in particular:
Logging
You can configure two types of logging in Jetty: server logging and request logging.
-
Server logging refers to the console output produced by Jetty itself.
-
Request logging refers to the information that Jetty can capture about incoming HTTP requests and responses.
Server Logging
Jetty uses the SLF4J API for its logging. SLF4J is a generic abstraction layer that is supported by many different logging frameworks (or SLF4J bindings).
Jetty provides a default binding via the jetty-slf4j-impl
Maven artifact, but you can plug in the SLF4J binding of your choice provided by other logging frameworks.
Jetty’s server logging is enabled by default with the logging
Jetty module.
You typically won’t have to enable the logging
module directly, since it is a transitive dependency of the server
module, and thus pulled in by many of the most commonly used modules.
The logging
module is a virtual module and its default implementation is provided by the logging-jetty
Jetty module, which uses the Jetty SLF4J binding.
Default Configuration
Jetty’s default SLF4J binding uses an appender (org.eclipse.jetty.logging.StdErrAppender
) to format a logging message with metadata (like a timestamp) before sending it to System.err
.
The default StdErrAppender
format is:
<datetime>:<level>:<logger name>:<thread name>:<message>
where <datetime>
is a timestamp with the format yyyy-MM-dd HH:mm:ss.SSS
.
You can configure the appender via a file named jetty-logging.properties
, which must be found in the server class-path.
When you enable the logging-jetty
module — either directly or by transitive dependency, as in the following example — Jetty automatically generates a jetty-logging.properties
file in $JETTY_BASE/resources/
:
$ java -jar $JETTY_HOME/start.jar --add-modules=http
INFO : mkdir ${jetty.base}/start.d INFO : server transitively enabled, ini template available with --add-modules=server INFO : logging-jetty transitively enabled INFO : http initialized in ${jetty.base}/start.d/http.ini INFO : resources transitively enabled INFO : threadpool transitively enabled, ini template available with --add-modules=threadpool INFO : logging/slf4j dynamic dependency of logging-jetty INFO : bytebufferpool transitively enabled, ini template available with --add-modules=bytebufferpool INFO : mkdir ${jetty.base}/resources INFO : copy ${jetty.home}/modules/logging/jetty/resources/jetty-logging.properties to ${jetty.base}/resources/jetty-logging.properties INFO : Base directory was modified
You can specify the following configuration options in jetty-logging.properties
:
org.eclipse.jetty.LEVEL=
<logging level>-
Sets the logging level for the logger tree based at
org.eclipse.jetty
. You can specify any of the usual SLF4J logging levels —TRACE
,DEBUG
,INFO
(default),WARN
andERROR
— plus two additional levels:ALL
(an alias forTRACE
) andOFF
(disables logging entirely). You can also configure a default logging level for specific loggers, or arbitrary logger trees:-
com.example.MyComponent.LEVEL=DEBUG
(sets logging level of loggercom.example.MyComponent
toDEBUG
) -
com.example.LEVEL=DEBUG
(sets logging level of treecom.example.*
toDEBUG
)
-
com.example.STACKS=
<boolean>-
Specifies whether to hide stack traces for some arbitrary logger tree
com.example.*
. The exception type and message are logged normally; only stack traces are hidden. Default value isfalse
org.eclipse.jetty.logging.appender.NAME_CONDENSE=
<boolean>-
Specifies whether to condense logger names, so that for example
org.eclipse.jetty.util.QueuedThreadPool
becomesoeju.QueuedThreadPool
. Default value istrue
. org.eclipse.jetty.logging.appender.MESSAGE_ALIGN=
<integer>-
Specifies the column at which the logging
<message>
should be printed. The value0
specifies no alignment. Default value is0
. org.eclipse.jetty.logging.appender.MESSAGE_ESCAPE=
<boolean>-
Specifies whether to escape ISO control characters such as
\r
or\n
present in the message. Character\r
is replaced with<
and character\n
is replaced with|
; all other ISO control characters are replaced with?
. Default value isfalse
. org.eclipse.jetty.logging.appender.ZONE_ID=
<timezone id>-
Specifies the timezone ID (such as
PST
, orAmerica/Los_Angeles
orGMT-8:00
) for the<datetime>
part of the logging line. The empty string specifies theUTC
timezone. Default value is the local timezone.
When using the Jetty SLF4J binding, the logging levels can be dynamically changed via JMX, see the troubleshooting section for more information.
Capturing Logs to a Rolling File
Logging to System.err
may be fine at development time, but you will typically want to capture logs on disk for later inspection, or if you don’t have a terminal access (for example, if you started Jetty as a service).
The console-capture
Jetty module allows you to capture what is written to System.out
and System.err
and write it to a log file.
By default, console-capture
logs to a file in the $JETTY_BASE/logs/
directory.
See the console-capture
module documentation for details on configuring how logs are written to the log
directory.
The |
Custom Configuration
You can use a different SLF4J binding if you are more familiar with other logging libraries, or if you need custom logging appenders. There are a number of out-of-the-box Jetty modules that you can use:
Logging with LogBack
To enable the logging-logback
module, run:
$ java -jar $JETTY_HOME/start.jar --add-modules=logging-logback,http
Since LogBack is released under a license that is different from Jetty’s, you will be prompted to accept the LogBack license.
Once you accept the LogBack license, your $JETTY_BASE
directory will have the following structure.
$JETTY_BASE ├── lib │ └── logging │ ├── logback-classic-<version>.jar │ └── logback-core-<version>.jar ├── resources │ └── logback.xml └── start.d ├── http.ini └── logging-logback.ini
Jetty downloaded the required LogBack *.jar
files, and created a $JETTY_BASE/resources/logback.xml
file for configuring your LogBack logging.
Please refer to the LogBack configuration manual for more information about how to configure LogBack.
Logging with Log4j2
To enable the logging-log4j2
module, run:
$ java -jar $JETTY_HOME/start.jar --add-modules=logging-log4j2,http
After accepting the Log4j2 license, you will have the following directory structure:
$JETTY_BASE ├── lib │ └── logging │ ├── log4j-api-<version>.jar │ ├── log4j-core-<version>.jar │ └── log4j-slf4j2-impl-<version>.jar ├── resources │ └── log4j2.xml └── start.d ├── http.ini └── logging-log4j2.ini
Jetty downloaded the required Log4j2 *.jar
files, and created a $JETTY_BASE/resources/log4j2.xml
file that you can configure to customize your Log4j2 logging.
Please refer to the Log4j2 configuration manual for more information about how to configure Log4j2.
Bridging Logging to SLF4J
When you use libraries that provide the features you need (for example, JDBC drivers), it may be possible that those libraries use a different logging framework than SLF4J.
SLF4J provides bridges for legacy logging APIs that allows you to bridge logging from one of these legacy logging frameworks to SLF4J. Once the logging is bridged to SLF4J, you can use Jetty’s default configuration or a custom configuration so that your logging is centralized in one place.
Jetty provides the logging-jul-capture
module for bridging from java.util.logging
to SLF4J.
The modules logging-jcl-capture and logging-log4j1-capture similarly provide bridges from Jakarta Commons Logging (JCL) and Apache Log4j, respectively; however, these modules are obsolete and should not be used anymore.
|
Bridging from java.util.logging
For libraries that use java.util.logging
as their logging framework, you can enable Jetty’s logging-jul-capture
module:
$ java -jar $JETTY_HOME/start.jar --add-modules=logging-jul-capture
The logging-jul-capture
module implies --exec
and therefore spawns a second JVM because it needs to provide the system property java.util.logging.config.file
(so that java.util.logging
can read the configuration from the specified file), and because it needs to make available on the System ClassLoader the class org.slf4j.bridge.SLF4JBridgeHandler
.
For example, a library that uses java.util.logging
as its logging library is the Postgresql JDBC driver.
With the logging-jul-capture
Jetty module, the logging follows this diagram:
Note how Jetty logs directly to SLF4J, while the Postgresql JDBC driver logs to SLF4J through the SLF4JBridgeHandler
.
They both arrive to the SLF4J binding, in this case the Jetty SLF4J binding (but could be any other SLF4J binding such as LogBack).
Request Logging
HTTP requests and responses can be logged to provide data that can be later analyzed with other tools, that can provide information such as the most frequently accessed request URIs, the response status codes, the request/response content lengths, geographical information about the clients, etc.
Request logging is enabled by enabling the requestlog
Jetty module.
In the example below, both the http
Jetty module and the requestlog
module are enabled, so that you can make HTTP requests to the server and have them logged:
$ cd $JETTY_BASE $ java -jar $JETTY_HOME/start.jar --add-modules=http,requestlog
The $JETTY_BASE
directory looks like this:
$JETTY_BASE
├── logs
├── resources
│ └── jetty-logging.properties
└── start.d
├── http.ini
└── requestlog.ini
The $JETTY_BASE/start.d/requestlog.ini
file is the Jetty module configuration file that allows you to configure the requestlog
module, see this section for more details.
By default the requestlog
Jetty module produces the $JETTY_BASE/logs/yyyy_MM_dd.request.log
, where the pattern yyyy_MM_dd
is replaced with the current date, for example 2020_01_31
.
The format of the request log lines is the result of a format string that uses formatting symbols to log relevant request/response data.
The default format is the NCSA Format extended with referrer data and user-agent data. A typical log line looks like this:
192.168.0.100 - - [31/Jan/2020:20:30:40 +0000] "GET / HTTP/1.1" 200 6789 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/97.0.4692.71 Safari/537.36"
The line above (that uses fake values) shows 192.168.0.100
for the client IP address, a hard-coded -
for the identity, -
for the authenticated user name, [31/Jan/2020:20:30:40 +0000]
for the date and time with timezone, "GET / HTTP/1.1"
for the HTTP request line, 200
for the HTTP response status code, 6789
for the HTTP response content length, "-"
for the referrer and "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/97.0.4692.71 Safari/537.36"
for the user-agent.
The format string can be customized as described in this section. Request log files are rolled every day, and retained for customizable number of days, by default 90 days.
When Jetty is behind a load balancer, you want to log the remote client IP address, not the load balancer IP address. Refer to this section to configure the load balancer and Jetty to retain the remote client IP address information. |
Thread Pooling
Jetty uses thread pooling to efficiently execute tasks that provide Jetty functionalities.
Like any other component, the Jetty thread pool is configured and enabled via the threadpool
Jetty module, that is transitively enabled by the server
Jetty module which, in turn, is transitively enabled by a protocol module such as the http
Jetty module:
$ java -jar $JETTY_HOME/start.jar --add-modules=http
The command above gives you the default configuration for the thread pool.
If you want to explicitly configure the thread pool, it is enough to explicitly specify the threadpool
module:
$ java -jar $JETTY_HOME/start.jar --add-modules=threadpool,http
After the command above, the $JETTY_BASE
directory looks like this:
$JETTY_BASE
├── resources
│ └── jetty-logging.properties
└── start.d
├── http.ini
└── threadpool.ini
Now you can customize the threadpool.ini
file to explicitly configure the thread pool.
Virtual Threads Support
Virtual threads have been introduced as a preview feature in Java 19 and Java 20, and have become an official feature since Java 21.
The threadpool-virtual-preview
Jetty module provides support for virtual threads in Java 19 and Java 20, and it is mutually exclusive with the threadpool
Jetty module.
When using Java 21, there are two Jetty modules available:
Both are mutually exclusive with the threadpool
Jetty module.
If you have already enabled the threadpool
Jetty module, it is sufficient to remove it by removing the $JETTY_BASE/start.d/threadpool.ini
file.
The threadpool-virtual
Jetty module provides a mixed thread mode, where platform threads are used to run internal Jetty tasks, but application code is invoked using virtual threads.
The threadpool-all-virtual
Jetty module provides a thread mode where all threads are virtual threads, including those used internally by Jetty.
You can enable either module using:
$ java -jar $JETTY_HOME/start.jar --add-modules=threadpool-virtual,http
or
$ java -jar $JETTY_HOME/start.jar --add-modules=threadpool-all-virtual,http
After the command above, the $JETTY_BASE/start.d/
directory will contain the corresponding threadpool-virtual.ini
or threadpool-all-virtual.ini
file.
You can now explicitly configure the thread pool module properties inside the *.ini
file and then start Jetty.