jextract: fix protocol threading

Sources/SwiftJava/AnyJavaObject.swift

@@ -110,10 +110,10 @@ extension AnyJavaObject {
   private static func _withJNIClassFromCustomClassLoader<Result>(
     _ classLoader: JavaClassLoader,
     in environment: JNIEnvironment,
-    _ body: (jclass) throws -> Result
+    _ body: (jclass?) throws -> Result
   ) throws -> Result {
-    let resolvedClass = try classLoader.findClass(fullJavaClassName)
-    return try body(resolvedClass!.javaThis)
+    let resolvedClass = try? classLoader.findClass(fullJavaClassName)
+    return try body(resolvedClass?.javaThis)
   }
 
   /// Retrieve the Java class for this type and execute body().
@@ -124,7 +124,14 @@ extension AnyJavaObject {
   ) throws -> Result {
     if let AnyJavaObjectWithCustomClassLoader = self as? AnyJavaObjectWithCustomClassLoader.Type,
        let customClassLoader = try AnyJavaObjectWithCustomClassLoader.getJavaClassLoader(in: environment) {
-      try _withJNIClassFromCustomClassLoader(customClassLoader, in: environment, body)
+      try _withJNIClassFromCustomClassLoader(customClassLoader, in: environment) { clazz in
+        guard let clazz else {
+          // If the custom class loader did not find the class
+          // let's look in the default class loader.
+          return try _withJNIClassFromDefaultClassLoader(in: environment, body)
+        }
+        return try body(clazz)
+      }
     } else {
       try _withJNIClassFromDefaultClassLoader(in: environment, body)
     }

Sources/SwiftJava/JavaObject+Inheritance.swift

@@ -25,9 +25,10 @@ extension AnyJavaObject {
     guard let this: jobject = javaThisOptional else {
       return nil 
     }
+    let environment = try! JavaVirtualMachine.shared().environment()
 
-    return try? otherClass.withJNIClass(in: javaEnvironment) { otherJavaClass in
-      if javaEnvironment.interface.IsInstanceOf(javaEnvironment, this, otherJavaClass) == 0 { 
+    return try? otherClass.withJNIClass(in: environment) { otherJavaClass in
+      if environment.interface.IsInstanceOf(environment, this, otherJavaClass) == 0 {
         return nil
       }
 

Sources/SwiftJavaRuntimeSupport/generated/JavaJNISwiftInstance.swift

@@ -15,7 +15,11 @@
 import SwiftJava
 
 @JavaInterface("org.swift.swiftkit.core.JNISwiftInstance")
-public struct JavaJNISwiftInstance {
+public struct JavaJNISwiftInstance: AnyJavaObjectWithCustomClassLoader {
   @JavaMethod("$memoryAddress")
   public func memoryAddress() -> Int64
+
+  public static func getJavaClassLoader(in environment: JNIEnvironment) throws -> JavaClassLoader! {
+    JNI.shared.applicationClassLoader
+  }
 }