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         http://www.apache.org/licenses/LICENSE-2.0

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    distributed under the License is distributed on an "AS IS" BASIS,
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:jpl-link: https://openjdk.org/jeps/264[JPL (Java Platform Logging)]
:jul-link: https://docs.oracle.com/javase/{java-target-version}/docs/technotes/guides/logging/overview.html[JUL (Java Logging)]

= Installation

In this page we will elaborate on various ways to install Log4j in your library or application.

[#shortcuts]
== Shortcuts

Below we share some shortcuts for the impatient.

[WARNING]
====
We strongly advise you to skim through this page to get a grip on fundamental logging concepts and understand which recipe fits your bill best.
====

Are you a library developer?::
You just need to log against <<logging-api,a logging API>>.
See <<api>>.

Are you an application developer?::
Your code and libraries it depends on are most probably already logging against a logging API, you just need to install <<logging-impl,a logging implementation>>.
See <<impl-core>>.

Are you a Spring Boot application developer?::
See <<impl-core-spring-boot>>.

Are you migrating from...::
xref:migrate-from-log4j1.adoc[Log4j 1], xref:migrate-from-logback.adoc[Logback], or xref:migrate-from-slf4j.adoc[SLF4J]?

[#concepts]
== Concepts (APIs, Implementations, and Bridges)

It is crucial to understand certain concepts in logging to be able to talk about the installation of them.

include::partial$concepts.adoc[]

[#requirements]
== Requirements

The Log4j 2 runtime requires a minimum of Java {java-target-version}.
See xref:download.adoc#older[the Download page] for older releases supporting Java 6 and 7.

[#build-tool]
== Configuring the build tool

The easiest way to install Log4j is through a build tool such as Maven or Gradle.
The rest of the instructions in this page assume you use one of these.

[#bom]
=== Importing the Bill-of-Materials (aka. BOM)

To keep your Log4j module versions in sync with each other, a BOM (Bill of Material) file is provided for your convenience.
You can import the BOM in your build tool of preference:

include::partial$components/log4j-bom.adoc[]

Once you import the BOM, you don't need to explicitly provide the versions of the Log4j artifacts managed by it.

In the rest of the explanations, we will assume that the Log4j BOM is imported.

[#snapshots]
=== Using snapshots

[%collapsible]
.Do you want to test the latest (**unstable!**) development version? Click here details.
====

You can access the latest development snapshots by using the `https://repository.apache.org/content/groups/snapshots/` repository.

[WARNING]
=====
Snapshots are published for development and testing purposes; **they should not be used at production!**
=====

[tabs]
=====
Maven::
+
[source,xml]
----
<repositories>
  <repository>
    <id>apache.snapshots</id>
    <name>Apache Snapshot Repository</name>
    <url>https://repository.apache.org/snapshots</url>
    <releases>
      <enabled>false</enabled>
    </releases>
  </repository>
</repositories>
----

Gradle::
+
[source,groovy]
----
repositories {
  mavenCentral()
  maven { url 'https://repository.apache.org/snapshots' }
}
----
=====
====

[#api]
== Installing Log4j API

The easiest way to install Log4j API is through a dependency management tool such as Maven or Gradle, by adding the following dependency:

include::partial$components/log4j-api.adoc[]

[#impl]
== Installing a logging implementation

Log4j provides several modules to facilitate the deployment of different logging implementations:

`log4j-core`::
The reference implementation.
Log4 Core primarily accepts input from Log4j API.
Refer to <<impl-core>> for the installation instructions.

`log4j-to-jul`::
The bridge that translates Log4j API calls to {jul-link}.
See <<impl-jul>> for the installation instructions.

`log4j-to-slf4j`::
The bridge that translates Log4j API calls to {slf4j-url}[SLF4J].
Since currently only
{logback-url}[Logback] implements SLF4J natively, refer to <<impl-logback>> for the installation instructions.

[IMPORTANT]
====
To ensure that your code does not directly depend on a particular logging implementation, the logging backend should be put in the appropriate scope of your dependency manager:

[cols="2,1m,1m"]
|===
.2+h| Software type
2+^h| Build tool

h| Maven
h| Gradle

| Application
| runtime
| runtimeOnly

| Library
| test
| testRuntimeOnly
|===
====

[#impl-core]
=== Installing Log4j Core

Log4j Core is the reference logging implementation of the Log4j project.
It primarily accepts input from Log4j API.

[TIP]
====
Do you have a Spring Boot application?
You can directly skip to <<impl-core-spring-boot>>.
====

To install Log4j Core as your logging implementation, you need to add the following dependency to your application:

[tabs]
====
Maven::
+
[source,xml]
----
<dependencies>

  <!-- Logging implementation (Log4j Core) -->
  <dependency>
      <groupId>org.apache.logging.log4j</groupId>
      <artifactId>log4j-core</artifactId>
      <scope>runtime</scope>
  </dependency>

  <!-- Logging bridges will follow... -->

</dependencies>
----

Gradle::
+
[source,groovy]
----
runtimeOnly 'org.apache.logging.log4j:log4j-core'
// Logging bridges will follow...
----
====

[#impl-core-bridges]
==== Installing bridges

If either your application or one of its dependencies logs against a logging API that is different from Log4j API, you need to <<logging-bridge,bridge>> that API to Log4j API.

[TIP]
====
**Do you need bridges?
And if so, which ones?**

* If you have any direct or transitive dependency on `org.slf4j:slf4j-api`, you need <<impl-core-bridge-slf4j,the SLF4J-to-Log4j bridge>>.
* If you have any direct or transitive dependency on `commons-logging:commons-logging`, you need <<impl-core-bridge-jcl,the JCL-to-Log4j bridge>>.
* If it is a standalone application (i.e., not running in a Java EE container), you will probably need <<impl-core-bridge-jul,JUL-to-Log4j>> and <<impl-core-bridge-jpl,JPL-to-Log4j>> bridges.
====

The following sections explain the installation of Log4j-provided bridges.

[#impl-core-bridge-slf4j]
===== Installing SLF4J-to-Log4j bridge

You can translate {slf4j-url}[SLF4J] calls to Log4j API using the `log4j-slf4j2-impl` artifact:

include::partial$components/log4j-slf4j2-impl.adoc[]

.Are you still using SLF4J 1.x?
[%collapsible]
=====
Add this example instead:

include::partial$components/log4j-slf4j-impl.adoc[]
=====

[#impl-core-bridge-jul]
===== Installing JUL-to-Log4j bridge

You can translate {jul-link} calls to Log4j API using the `log4j-jul` artifact:

include::partial$components/log4j-jul.adoc[]

In order to activate the bridge from JUL to Log4j API, you also need to add:

[source]
----
-Djava.util.logging.manager=org.apache.logging.log4j.jul.LogManager
----

to the JVM parameters in your application launcher.

The JUL-to-Log4j bridge supports additional configuration and installation methods.
See xref:log4j-jul.adoc[] for more information.

[#impl-core-bridge-jpl]
===== Installing JPL-to-Log4j bridge

You can translate {jpl-link} calls to Log4j API using the `log4j-jpl` artifact:

include::partial$components/log4j-jpa.adoc[]

[#impl-core-bridge-jcl]
===== Installing JCL-to-Log4j bridge

Since version `1.3.0` https://commons.apache.org/proper/commons-logging/[Apache Commons Logging] natively supports Log4j API.

You can enforce the version of a transitive dependency using the dependency management mechanism appropriate to your build tool:

[tabs]
====
Maven::
Maven users should add an entry to the `<dependencyManagement>` section of their POM file:
+
[source,xml,subs="+attributes"]
----
<dependencyManagement>
  <dependency>
    <groupId>commons-logging</groupId>
    <artifactId>commons-logging</artifactId>
    <version>{commons-logging-version}</version>
  </dependency>
</dependencyManagement>
----

Gradle::
+
Gradle users should refer to the https://docs.gradle.org/current/userguide/platforms.html#sub:using-platform-to-control-transitive-deps[Using a platform to control transitive versions] of the Gradle documentation.
====

.Are you using Commons Logging 1.2.0 or earlier?
[%collapsible]
=====
You need to install the following dependency instead:

include::partial$components/log4j-jcl.adoc[]
=====

[#impl-core-bridge-jboss-logging]
===== Installing JBoss Logging-to-Log4j bridge

JBoss Logging is shipped with an integrated bridge to Log4j API and requires no steps on your part.
See https://github.com/jboss-logging/jboss-logging/blob/main/README.adoc#supported-log-managers[Supported Log Managers] for more information.

[#impl-core-spring-boot]
==== Installing Log4j Core for Spring Boot applications

Spring Boot users should replace the `spring-boot-starter-logging` dependency with `spring-boot-starter-log4j2`:

[tabs]
====

Maven::
+
[source,xml]
----
<dependencies>

  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter</artifactId>
    <exclusions>
      <exclusion>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-logging</artifactId>
      </exclusion>
    </exclusions>
  </dependency>

  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-log4j2</artifactId>
    <scope>runtime</scope>
  </dependency>

</dependencies>
----

Gradle::
+
[source,groovy]
----
configurations {
  all.exclude group: 'org.springframework.boot', module: 'spring-boot-starter-logging'
}

dependencies {
  runtimeOnly group: 'org.springframework.boot', module: 'spring-boot-starter-log4j2'
}
----

====

The `spring-boot-starter-log4j2` artifact will automatically install Log4j Core, <<impl-core-bridge-jul,JUL-to-Log4j bridge>>, and configure them.
You don't need to add any other dependency or configure JUL anymore.
See https://docs.spring.io/spring-boot/reference/features/logging.html[Spring Boot Logging documentation] for further information.

[#impl-core-config]
==== Configuring Log4j Core

As with any other logging implementation, Log4j Core needs to be properly configured.
Log4j Core supports many different configuration formats: JSON, XML, YAML, and Java properties.
To configure Log4j Core, see xref:manual/configuration.adoc[].
A basic configuration can be obtained by adding one of these files to your application's classpath:

[tabs]
====

log4j2.xml::
+
[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration xmlns="https://logging.apache.org/xml/ns"
               xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
               xsi:schemaLocation="https://logging.apache.org/xml/ns
                                   https://logging.apache.org/xml/ns/log4j-config-2.xsd">

  <appenders>
    <Console name="CONSOLE">
      <PatternLayout pattern="%d [%t] %5p %c{1.} - %m%n"/><!--1-->
    </Console>
  </appenders>

  <loggers>
    <root level="INFO">
      <AppenderRef ref="CONSOLE"/>
    </root>
  </loggers>

</Configuration>
----

log4j2.json::
+
[source,json]
----
{
  "Configuration": {
    "Appenders": {
      "Console": {
        "name": "CONSOLE",
        "PatternLayout": {
          "pattern": "%d [%t] %5p %c{1.} - %m%n" // <1>
        }
      }
    },
    "Loggers": {
      "Root": {
        "level": "INFO",
        "AppenderRef": {
          "ref": "CONSOLE"
        }
      }
    }
  }
}
----

log4j2.yaml::
+
[source,yaml]
----
Configuration:
  Appenders:
    Console:
      name: CONSOLE
      PatternLayout:
        pattern: "%d [%t] %5p %c{1.} - %m%n" # <1>
  Loggers:
    Root:
      level: INFO
      AppenderRef:
        ref: CONSOLE
----

log4j2.properties::
+
[source,properties]
----
appender.0.type = Console
appender.0.name = CONSOLE
appender.0.layout = PatternLayout # <1>
appender.0.layout.pattern = %d [%t] %5p %c{1.} - %m%n
rootLogger.level = INFO
rootLogger.appenderRef.0.ref = CONSOLE
----

====

<1> While xref:manual/pattern-layout.adoc[] is a good first choice and preferable for tests, we recommend using a structured format such as xref:manual/json-template-layout.adoc[] for production deployments.

To use these formats, the following additional dependencies are required:

include::partial$configuration-file-format-deps.adoc[]

[#impl-jul]
=== Installing JUL

[TIP]
====
Are you using https://github.com/jboss-logging/jboss-logmanager[JBoss Log Manager] as your JUL implementation?
You can skip this section and use the https://github.com/jboss-logging/log4j2-jboss-logmanager[`log4j2-jboss-logmanager`] and https://github.com/jboss-logging/slf4j-jboss-logmanager[`slf4j-jboss-logmanager`] bridges from the JBoss Logging project instead.
====

Java Platform contains a very simple logging API and its implementation called {jul-link}.
Since it is embedded in the platform, it only requires the addition of bridges from Log4j API and SLF4J:

[tabs]
====

Maven::
+
[source,xml,subs="+attributes"]
----
<dependencies>

    <!-- Log4j-to-JUL bridge -->
  <dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-to-jul</artifactId>
    <scope>runtime</scope>
  </dependency>

  <!-- SLF4J-to-JUL bridge -->
  <dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-jdk14</artifactId>
    <version>{slf4j-version}</version>
    <scope>runtime</scope>
  </dependency>

  <!-- ... -->

</dependencies>
----

Gradle::
+
[source,groovy,subs="+attributes"]
----
runtimeOnly 'org.apache.logging.log4j:log4j-to-jul' // Log4j-to-JUL bridge
runtimeOnly 'org.slf4j:slf4j-jdk14:{slf4j-version}' // SLF4J-to-JUL bridge
----

====

See also:

* https://docs.oracle.com/javase/{java-target-version}/docs/api/java/util/logging/LogManager.html[`java.util.logging.LogManager`], to learn more about JUL configuration,
* xref:log4j-to-jul.adoc[] to learn more about the `log4j-to-jul` artifact.

[#impl-logback]
=== Installing Logback

To install {logback-url}[Logback] as the logging implementation, you only need to add a Log4j-to-SLF4J bridge:

[tabs]
====

Maven::
+
[source,xml]
----
<dependencies>

  <!-- Logging implementation (Logback) -->
  <dependency>
    <groupId>ch.qos.logback</groupId>
    <artifactId>logback-classic</artifactId>
    <version>{logback-version}</version>
    <scope>runtime</scope>
  </dependency>

  <!-- Log4j-to-SLF4J bridge -->
  <dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-to-slf4j</artifactId>
    <scope>runtime</scope>
  </dependency>

</dependencies>
----

Gradle::
+
[source,groovy,subs="+attributes"]
----
runtimeOnly 'ch.qos.logback:logback-classic:{logback-version}'
runtimeOnly 'org.apache.logging.log4j:log4j-to-slf4j' // Log4j-to-SLF4J bridge
----

====

To configure Logback, see {logback-url}/manual/configuration.html[Logback's configuration documentation].
