The manifest (MANIFEST.MF) in log4j-1.2.15.jar now uses: Name: org.apache.log4j instead of Name: org/apache/log4j/ in previous versions (1.2.14, 1.2.13, etc) Note the dot '.' instead of the slash '/'. This means that the following piece of code: String implementationVersion = org.apache.log4j.Appender.class.getPackage().getImplementationVersion(); System.out.println('"' + implementationVersion + '"'); now returns "null" instead of "1.2.15" as it would have done with previous releases. Changing the MANIFEST.MF line "Name: org.apache.log4j" into "Name: org/apache/log4j/" solves the issue.
Proposed patch for MANIFEST.MF: Manifest-Version: 1.0 Archiver-Version: Plexus Archiver Created-By: Apache Maven Built-By: ubuntu Build-Jdk: 1.6.0 Name: org/apache/log4j/ Implementation-Title: log4j Implementation-Vendor: "Apache Software Foundation" Implementation-Version: 1.2.15
I've confirmed it is a change from log4j 1.2.14 and earlier. It may have been a mistake when writing the Maven POM file, but it may have been intentional and needs a bit more research to see if there was a motivation behind the change. From http://java.sun.com/j2se/1.4.2/docs/guide/jar/jar.html#Manifest%20Specification The individual sections define various attributes for packages or files contained in this JAR file. Not all files in the JAR file need to be listed in the manifest as entries, but all files which are to be signed must be listed. The manifest file itself must not be listed. Each section must start with an attribute with the name as "Name", and the value must be a relative path to the file, or an absolute URL referencing data outside the archive. So the name definitely should be separated with slashes. MANIFEST.MF is generated from the specification in pom.xml. Any patch would be against pom.xml. Also, it would be good to try to coordinate this with any changes related to http://issues.apache.org/bugzilla/show_bug.cgi?id=43282
Should be clarified before 1.2.16
fixed with rv1344711 Manifest shows: Name: org/apache/log4j/ Implementation-Vendor: "Apache Software Foundation" DynamicImport-Package: * Implementation-Title: log4j Implementation-Version: 1.2.18-SNAPSHOT