URLClassLoader是否正确遍历MANIFEST.MF类路径标头？

Question

UPDATE 1: Indeed, the URL format differences cause the error. Here is a unit test (cut and obfuscated by hand; hope I didn't miss anything) showing the problem:

@Test
public void wheresWaldo2() throws ClassNotFoundException, IllegalAccessException, InstantiationException, IOException, NoSuchMethodException {
  // Find Waldo from file:/someLocation/waldo.jar.  Prove that works.
  URL waldosJar = new File("/someLocation/waldo.jar").toURI().toURL();
  assertNotNull(waldosJar);
  assertEquals("file", waldosJar.getProtocol());
  String waldosPath = waldosJar.getPath();
  assertNotNull(waldosPath);
  assertTrue(waldosPath.endsWith("/waldo.jar"));

  ClassLoader cl = new URLClassLoader(new URL[] { waldosJar }, this.getClass().getClassLoader());

  Class<?> waldosClass = cl.loadClass("com.foobar.Waldo");
  assertNotNull(waldosClass);
  assertEquals("com.foobar.Waldo", waldosClass.getName());
  assertSame(cl, waldosClass.getClassLoader());

  Class<?> jimbosClass = cl.loadClass("com.foobar.Jimbo"); // Note: works
  assertNotNull(jimbosClass);

  // Find Waldo from jar:file:/someLocation/waldo.jar!/.  Prove that works.
  // This URL, when passed to a URLClassLoader, should result in the same
  // functionality as the first one.  But it doesn't.
  waldosJar = new URL("jar:" + waldosJar.toExternalForm() + "!/");
  assertEquals("jar", waldosJar.getProtocol());
  assertEquals("file:" + waldosPath + "!/", waldosJar.getPath());

  cl = new URLClassLoader(new URL[] { waldosJar }, this.getClass().getClassLoader());

  waldosClass = cl.loadClass("com.foobar.Waldo");
  assertNotNull(waldosClass);
  assertEquals("com.foobar.Waldo", waldosClass.getName());
  assertSame(cl, waldosClass.getClassLoader());

  jimbosClass = cl.loadClass("com.foobar.Jimbo"); // XXX FAILS
}

UPDATE 0: The problem may have to do with the supposed, but not actual, equivalence between two URL s referring to a jar file. For example, the following two URLs are supposed to refer to the same file:

• file:/myjar.jar
• jar:file:/myjar.jar!/

When I pass a URL built from the first format to my machinery, I think things are working. When I pass a URL built from the second format, I get the results described below. I am testing more to confirm all this beyond a doubt.

ORIGINAL QUESTION

(I am aware of this question .)

I have a jar file, waldo.jar , that contains a META-INF/MANIFEST.MF that looks like this:

Manifest-Version: 1.0
Class-Path: jimbo.jar

It also has a class at the following location within it:

com/foobar/Waldo.class

The class' source code is essentially:

package com.foobar;

public class Waldo {
  public Jimbo getJimbo() {
    return null;
  }
}

Next, in the same directory, I have a jar file, jimbo.jar , that contains a class at the following location within it:

com/foobar/Jimbo.class

That class' source code is essentially:

package com.foobar;

public class Jimbo {

}

Now I construct a URLClassLoader with a URL to waldo.jar . To review: jimbo.jar contains Jimbo and is "next to" waldo.jar , and is listed in waldo.jar 's META-INF/MANIFEST-MF 's Class-Path header appropriately. waldo.jar contains Waldo , that has a code reference to Jimbo . With me so far?

I can load com.foobar.Waldo just fine. But if I do something with Waldo that involves com.foobar.Jimbo , like, for example, calling Waldo.class.getDeclaredMethod("getJimbo") , I get a NoClassDefFoundError . Here is a sample stack:

java.lang.NoClassDefFoundError: com/foobar/Jimbo
    at java.lang.Class.getDeclaredMethods0(Native Method)
    at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
    at java.lang.Class.getDeclaredMethod(Class.java:2128)
    at com.foobar.TestClassLoadingProblems.wheresWaldo(TestClassLoadingProblems.java:115)

    Caused by:
    java.lang.ClassNotFoundException: com.foobar.Jimbo
        at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
        at com.foobar.MyClassLoader.findClass(...) // calls super.findClass()
        at java.lang.ClassLoader.loadClass(ClassLoader.java:424)

This suggests to me that URLClassLoader is not consulting the Class-Path header properly in all cases (I'm aware of how it works in general ).

Can anyone shed light on what is happening here?

Answer 1

这是由于JDK中的错误所致。