Unable to expand/explode EnumSet and Guava Immutable Collections

[taa-autorola-com]

Problem

Using an EnumSet (or an Immutable Collection from Google Guava) to expand an exploded parameter in a template fails with a reflection exception.

Given the following test case:

import com.damnhandy.uri.template.UriTemplate;

import java.util.*;

public class DamnHandyBug {
	
	public enum Hello {
		World, 
		Universe
	}
	
	public static void main(String[] args) {
		// does NOT work
		final Set<Hello> someSet = EnumSet.of(Hello.World);

		// works fine
		// Set<Hello> someSet = new HashSet<>();
		// someSet.add(Hello.Universe);
		
		String template = "http://example.com{?someSet*}";
		Map<String, Object> map = new HashMap<>();
		map.put("someSet", someSet);
		
		String result = UriTemplate.fromTemplate(template)
			.expand(map);
			
		System.out.println(result);
	}
}

It fails with the following Exception:

Exception in thread "main" com.damnhandy.uri.template.VarExploderException: java.lang.IllegalAccessException: class com.damnhandy.uri.template.DefaultVarExploder cannot access a member of class java.util.RegularEnumSet (in module java.base) with modifiers "public"
        at com.damnhandy.uri.template.DefaultVarExploder.getValue(DefaultVarExploder.java:298)
        at com.damnhandy.uri.template.DefaultVarExploder.inspectGetters(DefaultVarExploder.java:199)
        at com.damnhandy.uri.template.DefaultVarExploder.initValues(DefaultVarExploder.java:141)
        at com.damnhandy.uri.template.DefaultVarExploder.setSource(DefaultVarExploder.java:115)
        at com.damnhandy.uri.template.DefaultVarExploder.<init>(DefaultVarExploder.java:94)
        at com.damnhandy.uri.template.impl.VarExploderFactory.getExploder(VarExploderFactory.java:54)
        at com.damnhandy.uri.template.UriTemplate.expandVariables(UriTemplate.java:664)
        at com.damnhandy.uri.template.UriTemplate.expressionReplacementString(UriTemplate.java:586)
        at com.damnhandy.uri.template.UriTemplate.expand(UriTemplate.java:422)
        at com.damnhandy.uri.template.UriTemplate.expand(UriTemplate.java:405)
        at DamnHandyBug.main(DamnHandyBug.java:25)
Caused by: java.lang.IllegalAccessException: class com.damnhandy.uri.template.DefaultVarExploder cannot access a member of class java.util.RegularEnumSet (in module java.base) with modifiers "public"
        at java.base/jdk.internal.reflect.Reflection.newIllegalAccessException(Reflection.java:361)
        at java.base/java.lang.reflect.AccessibleObject.checkAccess(AccessibleObject.java:591)
        at java.base/java.lang.reflect.Method.invoke(Method.java:558)
        at com.damnhandy.uri.template.DefaultVarExploder.getValue(DefaultVarExploder.java:290)
        ... 10 more

Likewise for guava's Immutable Collections.

It seems to be an invocation of Collection.isEmpty() that fails for some yet unknown reason. I haven't investigated further.

Workaround

Create a new collection before invoking expand, such as HashSet or ArrayList.

Versions

Tested in

• java 1.8.0_231 (version 2.1.6 and 2.1.8)
• java 11.0.7 (version 2.1.8)