Remove support for Log4j

Apache Log4j 1.x is EOL and has now been replaced by log4j 2. This commit
removes the deprecated support for Log4j 1.x

See gh-4905

spring-boot-docs/src/main/asciidoc/howto.adoc

@@ -1313,12 +1313,11 @@ You also need to add `logging.file` to your `application.properties`:
 
 [[howto-configure-log4j-for-logging]]
 === Configure Log4j for logging
-Spring Boot also supports either http://logging.apache.org/log4j/1.2[Log4j] or
-http://logging.apache.org/log4j/2.x[Log4j 2] for logging configuration, but only if one
-of them is on the classpath. If you are using the starter poms for assembling
-dependencies that means you have to exclude Logback and then include your chosen version
-of Log4j instead. If you aren't using the starter poms then you need to provide
-`commons-logging` (at least) in addition to your chosen version of Log4j.
+Spring Boot supports http://logging.apache.org/log4j/2.x[Log4j 2] for logging
+configuration if it is on the classpath. If you are using the starter poms for
+assembling dependencies that means you have to exclude Logback and then include log4j 2
+instead. If you aren't using the starter poms then you need to provide `commons-logging`
+(at least) in addition to Log4j 2.
 
 The simplest path is probably through the starter poms, even though it requires some
 jiggling with excludes, .e.g. in Maven:
@@ -1341,17 +1340,14 @@ jiggling with excludes, .e.g. in Maven:
 	</dependency>
 	<dependency>
 		<groupId>org.springframework.boot</groupId>
-		<artifactId>spring-boot-starter-log4j</artifactId>
+		<artifactId>spring-boot-starter-log4j2</artifactId>
 	</dependency>
 ----
 
-To use Log4j 2, simply depend on `spring-boot-starter-log4j2` rather than
-`spring-boot-starter-log4j`.
-
-NOTE: The use of one of the Log4j starters gathers together the dependencies for
-common logging requirements (e.g. including having Tomcat use `java.util.logging` but
-configuring the output using Log4j or Log4j 2). See the Actuator Log4j or Log4j 2
-samples for more detail and to see it in action.
+NOTE: The use of the Log4j starters gathers together the dependencies for common logging
+requirements (e.g. including having Tomcat use `java.util.logging` but configuring the
+output using Log4j 2). See the Actuator Log4j 2 samples for more detail and to see it in
+action.
 
 
 

spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -983,9 +983,9 @@ Spring Boot uses http://commons.apache.org/logging[Commons Logging] for all inte
 logging, but leaves the underlying log implementation open. Default configurations are
 provided for
 http://docs.oracle.com/javase/7/docs/api/java/util/logging/package-summary.html[Java Util Logging],
-http://logging.apache.org/log4j/[Log4J], http://logging.apache.org/log4j/2.x/[Log4J2] and
-http://logback.qos.ch/[Logback]. In each case loggers are pre-configured to use console
-output with optional file output also available.
+http://logging.apache.org/log4j/2.x/[Log4J2] andhttp://logback.qos.ch/[Logback]. In each
+case loggers are pre-configured to use console output with optional file output also
+available.
 
 By default, If you use the '`Starter POMs`', Logback will be used for logging. Appropriate
 Logback routing is also included to ensure that dependent libraries that use
@@ -1182,9 +1182,6 @@ Depending on your logging system, the following files will be loaded:
 |Logback
 |`logback-spring.xml`, `logback-spring.groovy`, `logback.xml` or `logback.groovy`
 
-|Log4j
-|`log4j-spring.properties`, `log4j-spring.xml`, `log4j.properties` or `log4j.xml`
-
 |Log4j2
 |`log4j2-spring.xml` or `log4j2.xml`
 

spring-boot-docs/src/main/asciidoc/using-spring-boot.adoc

@@ -517,8 +517,8 @@ swap specific technical facets.
 |`spring-boot-starter-jetty`
 |Imports the Jetty HTTP engine (to be used as an alternative to Tomcat).
 
-|`spring-boot-starter-log4j`
-|Support the Log4J logging framework.
+|`spring-boot-starter-log4j2`
+|Support the Log4J 2 logging framework.
 
 |`spring-boot-starter-logging`
 |Import Spring Boot's default logging framework (Logback).