Imagine 2 jar files. One called helloworld.jar which contains just a single org.myapp.HelloWorld class which prints to System.out from its main method. The other jar called manifest-cp-test.jar. This manifest-cp-test.jar contains (only a) META-INF/MANIFEST.MF with the following content:
Manifest-Version: 1.0 Class-Path: /C:/helloworld.jar Main-Class: org.myapp.HelloWorld So this manifest-cp-test.jar has a Main-Class entry which points to the HelloWorld class that belongs in the other helloworld.jar file. Both the helloworld.jar and the manifest-cp-test.jar reside at C:\ on a Windows system. When run using Java 11, this runs correctly and prints the HelloWorld message: C:\>jdk-11.0.2\bin\java -jar manifest-cp-test.jar Hello World However, when run using Java 13 (and even latest upstream Java 14) on the same Windows system, this now runs into a ClassNotFoundException: Java 13: C:\>jdk-13.0.1\bin\java -jar manifest-cp-test.jar Error: Could not find or load main class org.myapp.HelloWorld Caused by: java.lang.ClassNotFoundException: org.myapp.HelloWorld Java 14: C:\>jdk-14\bin\java -jar manifest-cp-test.jar Error: Could not find or load main class org.myapp.HelloWorld Caused by: java.lang.ClassNotFoundException: org.myapp.HelloWorld Adding the "-Djdk.net.URLClassPath.showIgnoredClassPathEntries=true" debug flag to the java launch command shows: C:\>jdk-13.0.1\bin\java -Djdk.net.URLClassPath.showIgnoredClassPathEntries=true -jar manifest-cp-test.jar Class-Path entry: "/C:/helloworld.jar" ignored in JAR file file:/C:/manifest-cp- test.jar Error: Could not find or load main class org.myapp.HelloWorld Caused by: java.lang.ClassNotFoundException: org.myapp.HelloWorld So this Class-Path entry is being ignored starting Java 13. I compared the spec for Class-Path entry for Java 11[1] and Java 13[2] and I do changes in that section. The Java 13 version doc has those 3 rules mentioned under "A Class-Path entry is valid if the following conditions are true:". So all 3 rules should be satisfied? I guess that then means that this style of Class-Path entry will not satisfy the "It can be used to create a URL, by resolving it against the context JAR's URL"? I haven't yet had the time to look into the code or read up a bit more on what this rule actually means. Specifically what does resolve mean here? [1] https://docs.oracle.com/en/java/javase/11/docs/specs/jar/jar.html#class-path-attribute [2] https://docs.oracle.com/en/java/javase/13/docs/specs/jar/jar.html#class-path-attribute P.S: This is another case of Class-Path semantics which behave not just differently in different versions of Java but different in different subsystems of the same Java version itself. More about this has been discussed recently in https://mail.openjdk.java.net/pipermail/compiler-dev/2019-October/013766.html on compiler-dev. -Jaikiran
