On Thu, 29 May 2025 05:57:56 GMT, Jaikiran Pai <j...@openjdk.org> wrote:
> Can I please get a review of this doc-only change which proposes to add an > `@apiNote` on the constructors of `URLClassLoader` and `SecureClassLoader` to > explain the current implementation of these constructors? This addresses > https://bugs.openjdk.org/browse/JDK-8228773? > > As noted in that issue, this updated documentation is to help applications be > aware that a `null` value which represents the bootstrap class loader when > passed for `parent` class loader will mean that the constructed > `URLClassLoader` may not be able to load all platform classes. > > Specifically, only a specific set of modules are mapped (at JDK build time) > to the bootstrap class loader. Some modules like `java.sql` are visible to > the platform class loader but not to the bootstrap classloader. The > distinction between these class loaders is explained in the API documentation > of `ClassLoader` class > https://docs.oracle.com/en/java/javase/24/docs/api/java.base/java/lang/ClassLoader.html#builtinLoaders. > > Using `null` (which represents a bootstrap class loader) for `parent` when > constructing the `URLClassLoader` then means that the class loader would not > be able to load some of these platform classes. For example, consider: > > > import java.net.*; > > public class Test { > public static void main(String[] args) throws Exception { > System.out.println("testing against Java " + > System.getProperty("java.version")); > > final ClassLoader cl = new URLClassLoader(new URL[0], null); > final Class<?> klass = cl.loadClass("java.sql.ResultSet"); // load a > platform class that belongs to the java.sql module > System.out.println("loaded " + klass + " using classloader: " + > klass.getClassLoader()); > > } > } > > which constructs the `URLClassLoader` with the bootstrap class loader as its > parent and then attempts to load a platform class `java.sql.ResultSet`. Since > this class' module is mapped to the platform class loader and not the > bootstrap class loader, running this code against Java 9+ will result in a > `ClassNotFoundException`: > > > testing against Java 24 > Exception in thread "main" java.lang.ClassNotFoundException: > java.sql.ResultSet > at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:349) > at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:557) > at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:490) > at Test.main(Test.java:8) > > > No new tests have been introduced and existing tests in tier1, tier2 and > tier3 continue to pass. > > Once we settle on th... src/java.base/share/classes/java/net/URLClassLoader.java line 98: > 96: * Constructs a new URLClassLoader for the specified URLs using the > 97: * {@linkplain ClassLoader#getSystemClassLoader() default delegation > 98: * parent class loader}. The URLs will be searched in the order As we are changing it then maybe we could change this to "using the system class loader as the parent". I think that would be much clearer than "default delegation parent ...". Same thing in SecureClassLoader. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/25517#discussion_r2113431536
