RFR: 8262277: java.net.URLClassLoader.getResource throws undocumented IllegalArgumentException

[Craig Andrews]

On Sat, 20 Feb 2021 19:22:10 GMT, Craig Andrews <github.com+194713+candrews at openjdk.org> wrote:

>> _NOTE_: I've reported this issue at https://bugreport.java.com/ (internal review ID : 9069151)
>> 
>> `java.net.URLClassLoader.getResource` can throw an undocumented `IllegalArgumentException`.
>> 
>> According to the javadoc for the `getResource` and `findResource` methods, neither should be throwing `IllegalArgumentException` - they should return null if the resource can't be resolved.
>> 
>> Quoting the javadoc for [`URLClassLoader.html#findResource`](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/net/URLClassLoader.html#findResource(java.lang.String))
>>> Returns:
>>>     a URL for the resource, or null if the resource could not be found, or if the loader is closed.
>> 
>> And quoting the javadoc for [`ClassLoader.html#getResource`](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/ClassLoader.html#getResource(java.lang.String))
>>> Returns:
>>>     URL object for reading the resource; null if the resource could not be found, a URL could not be constructed to locate the resource, the resource is in a package that is not opened unconditionally, or access to the resource is denied by the security manager.
>> 
>> Neither mentions throwing `IllegalArgumentException` and both are clear that when URL can't be constructed, `null` should be returned.
>> 
>> Here's a stack trace:
>> java.lang.IllegalArgumentException: name
>>         at java.base/jdk.internal.loader.URLClassPath$Loader.findResource(URLClassPath.java:600)
>>         at java.base/jdk.internal.loader.URLClassPath.findResource(URLClassPath.java:291)
>>         at java.base/java.net.URLClassLoader$2.run(URLClassLoader.java:655)
>>         at java.base/java.net.URLClassLoader$2.run(URLClassLoader.java:653)
>>         at java.base/java.security.AccessController.doPrivileged(Native Method)
>>         at java.base/java.net.URLClassLoader.findResource(URLClassLoader.java:652)
>> 
>> Looking at [`URLClassPath.findResource`](https://github.com/openjdk/jdk/blob/2b00367e1154feb2c05b84a11d62fb5750e46acf/src/java.base/share/classes/jdk/internal/loader/URLClassPath.java#L603)
>>         URL findResource(final String name, boolean check) {
>>             URL url;
>>             try {
>>                 url = new URL(base, ParseUtil.encodePath(name, false));
>>             } catch (MalformedURLException e) {
>>                 throw new IllegalArgumentException("name");
>>             }
>> 
>> Instead of throwing `IllegalArgumentException`, that line should simply return `null`.
>> 
>> A similar issue exists at [`URLClassPath.getResource`](https://github.com/openjdk/jdk/blob/2b00367e1154feb2c05b84a11d62fb5750e46acf/src/java.base/share/classes/jdk/internal/loader/URLClassPath.java#L639)
>>         URL findResource(final String name, boolean check) {
>>             URL url;
>>             try {
>>                 url = new URL(base, ParseUtil.encodePath(name, false));
>>             } catch (MalformedURLException e) {
>>                 throw new IllegalArgumentException("name");
>>             }
>> 
>> Instead of throwing `IllegalArgumentException`, that line should simply return `null`.
>
> Submitted a bug report at https://bugreport.java.com/
> Received internal review ID : 9069151

This one liner will reproduce this issue (you can easily use `jshell` to run it and see the problem):
new java.net.URLClassLoader(new java.net.URL[]{new java.net.URL("https://repo1.maven.org/anything-that-ends-with-slash/")}).findResource("c:/windows");

The key parts to reproduce the issue are:
1. The `URLClassLoader` URL must not start with `file:` or `jar:` and must end in `/`. See https://github.com/openjdk/jdk/blob/2b00367e1154feb2c05b84a11d62fb5750e46acf/src/java.base/share/classes/jdk/internal/loader/URLClassPath.java#L493
2. The string passed to `findResource` must not be a valid URL component. Windows paths (which include a `:` making them invalid URL components) are a common and easy way to see this error.

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PR: https://git.openjdk.java.net/jdk/pull/2662