JavaKit: add CustomJavaClassLoader protocol

Swift projections of Java classes can conform to CustomJavaClassLoader, to
provide a custom class loader to be used when initializing new instances. This
is useful for platforms such as Android which modify class and class loader
visibility depending on the call stack.

Fixes: #154

Author: lhoward

Sources/JavaKit/AnyJavaObject.swift

@@ -49,6 +49,19 @@ public protocol AnyJavaObject {
   var javaHolder: JavaObjectHolder { get }
 }
 
+/// Protocol that allows Swift types to specify a custom Java class loader on
+/// initialization. This is useful for platforms (e.g. Android) where the default
+/// class loader does not make all application classes visible.
+public protocol CustomJavaClassLoader: AnyJavaObject {
+  static func getJavaClassLoader(in environment: JNIEnvironment) throws -> JavaClassLoader!
+}
+
+/// Add getClassLoader() to JavaObject as it is otherwise recursively defined
+extension JavaObject {
+  @JavaMethod
+  public func getClassLoader() throws -> JavaClassLoader!
+}
+
 extension AnyJavaObject {
   /// Retrieve the underlying Java object.
   public var javaThis: jobject {
@@ -81,13 +94,41 @@ extension AnyJavaObject {
     JavaClass(javaThis: jniClass!, environment: javaEnvironment)
   }
 
-  /// Retrieve the Java class for this type.
-  public static func getJNIClass(in environment: JNIEnvironment) throws -> jclass {
-    try environment.translatingJNIExceptions {
+  /// Retrieve the Java class for this type using the default class loader.
+  private static func _withJNIClassFromDefaultClassLoader<Result>(
+    in environment: JNIEnvironment,
+    _ body: (jclass) throws -> Result
+  ) throws -> Result {
+    let resolvedClass = try environment.translatingJNIExceptions {
       environment.interface.FindClass(
         environment,
         fullJavaClassNameWithSlashes
       )
     }!
+    return try body(resolvedClass)
+  }
+
+  /// Retrieve the Java class for this type using a specific class loader.
+  private static func _withJNIClassFromCustomClassLoader<Result>(
+    _ classLoader: JavaClassLoader,
+    in environment: JNIEnvironment,
+    _ body: (jclass) throws -> Result
+  ) throws -> Result {
+    let resolvedClass = try classLoader.findClass(fullJavaClassName)
+    return try body(resolvedClass!.javaThis)
+  }
+
+  /// Retrieve the Java class for this type and execute body().
+  @_spi(Testing)
+  public static func withJNIClass<Result>(
+    in environment: JNIEnvironment,
+    _ body: (jclass) throws -> Result
+  ) throws -> Result {
+    if let customJavaClassLoader = self as? CustomJavaClassLoader.Type,
+       let customClassLoader = try customJavaClassLoader.getJavaClassLoader(in: environment) {
+      try _withJNIClassFromCustomClassLoader(customClassLoader, in: environment, body)
+    } else {
+      try _withJNIClassFromDefaultClassLoader(in: environment, body)
+    }
   }
 }

Sources/JavaKit/Exceptions/ExceptionHandling.swift

@@ -39,10 +39,8 @@ extension JNIEnvironment {
     }
 
     // Otherwise, create a exception with a message.
-    _ = interface.ThrowNew(
-      self,
-      try! JavaClass<Exception>.getJNIClass(in: self),
-      String(describing: error)
-    )
+    _ = try! JavaClass<Exception>.withJNIClass(in: self) { exceptionClass in
+      interface.ThrowNew(self, exceptionClass, String(describing: error))
+    }
   }
 }

Sources/JavaKit/Java2Swift.config

@@ -5,6 +5,7 @@
     "java.lang.Byte" : "JavaByte",
     "java.lang.Character" : "JavaCharacter",
     "java.lang.Class" : "JavaClass",
+    "java.lang.ClassLoader" : "JavaClassLoader",
     "java.lang.Double" : "JavaDouble",
     "java.lang.Error" : "JavaError",
     "java.lang.Exception" : "Exception",

Sources/JavaKit/JavaClass+Initialization.swift

@@ -21,9 +21,11 @@ extension JavaClass {
   @_nonoverride
   public convenience init(environment: JNIEnvironment? = nil) throws {
     let environment = try environment ?? JavaVirtualMachine.shared().environment()
-    self.init(
-      javaThis: try ObjectType.getJNIClass(in: environment),
-      environment: environment
-    )
+    var javaClassHolder: JavaObjectHolder!
+
+    javaClassHolder = try ObjectType.withJNIClass(in: environment) { javaClass in
+      JavaObjectHolder(object: javaClass, environment: environment)
+    }
+    self.init(javaHolder: javaClassHolder)
   }
 }

Sources/JavaKit/JavaObject+Inheritance.swift

@@ -22,19 +22,17 @@ extension AnyJavaObject {
   private func isInstanceOf<OtherClass: AnyJavaObject>(
     _ otherClass: OtherClass.Type
   ) -> jclass? {
-    guard let otherJavaClass = try? otherClass.getJNIClass(in: javaEnvironment) else {
-      return nil
-    }
+    try? otherClass.withJNIClass(in: javaEnvironment) { otherJavaClass in
+      if javaEnvironment.interface.IsInstanceOf(
+       javaEnvironment,
+       javaThis,
+       otherJavaClass
+     ) == 0 {
+       return nil
+     }
 
-    if javaEnvironment.interface.IsInstanceOf(
-      javaEnvironment,
-      javaThis,
-      otherJavaClass
-    ) == 0 {
-      return nil
+     return otherJavaClass
     }
-
-    return otherJavaClass
   }
 
   /// Determine whether this object is an instance of a specific

Sources/JavaKit/JavaObject+MethodCalls.swift

@@ -253,23 +253,23 @@ extension AnyJavaObject {
     in environment: JNIEnvironment,
     arguments: repeat each Param
   ) throws -> jobject {
-    let thisClass = try Self.getJNIClass(in: environment)
-
-    // Compute the method signature so we can find the right method, then look up the
-    // method within the class.
-    let methodID = try Self.javaMethodLookup(
-      thisClass: thisClass,
-      methodName: javaConstructorName,
-      parameterTypes: repeat (each Param).self,
-      resultType: .void,
-      in: environment
-    )
+    try Self.withJNIClass(in: environment) { thisClass in
+      // Compute the method signature so we can find the right method, then look up the
+      // method within the class.
+      let methodID = try Self.javaMethodLookup(
+        thisClass: thisClass,
+        methodName: javaConstructorName,
+        parameterTypes: repeat (each Param).self,
+        resultType: .void,
+        in: environment
+      )
 
-    // Retrieve the constructor, then map the arguments and call it.
-    let jniArgs = getJValues(repeat each arguments, in: environment)
-    return try environment.translatingJNIExceptions {
-      environment.interface.NewObjectA!(environment, thisClass, methodID, jniArgs)
-    }!
+      // Retrieve the constructor, then map the arguments and call it.
+      let jniArgs = getJValues(repeat each arguments, in: environment)
+      return try environment.translatingJNIExceptions {
+        environment.interface.NewObjectA!(environment, thisClass, methodID, jniArgs)
+      }!
+    }
   }
 
   /// Retrieve the JNI field ID for a field with the given name and type.

Sources/JavaKit/Optional+JavaObject.swift

@@ -70,8 +70,9 @@ extension Optional: JavaValue where Wrapped: AnyJavaObject {
 
   public static func jniNewArray(in environment: JNIEnvironment) -> JNINewArray {
     return { environment, size in
-      let jniClass = try! Wrapped.getJNIClass(in: environment)
-      return environment.interface.NewObjectArray(environment, size, jniClass, nil)
+      try! Wrapped.withJNIClass(in: environment) { jniClass in
+        environment.interface.NewObjectArray(environment, size, jniClass, nil)
+      }
     }
   }
 

Sources/JavaKit/generated/JavaClassLoader.swift

@@ -0,0 +1,72 @@
+// Auto-generated by Java-to-Swift wrapper generator.
+import JavaRuntime
+
+@JavaClass("java.lang.ClassLoader")
+open class JavaClassLoader: JavaObject {
+  @JavaMethod
+  open func getName() -> String
+
+  @JavaMethod
+  open func loadClass(_ arg0: String, _ arg1: Bool) throws -> JavaClass<JavaObject>!
+
+  @JavaMethod
+  open func loadClass(_ arg0: String) throws -> JavaClass<JavaObject>!
+
+  @JavaMethod
+  open func setSigners(_ arg0: JavaClass<JavaObject>?, _ arg1: [JavaObject?])
+
+  @JavaMethod
+  open func getClassLoadingLock(_ arg0: String) -> JavaObject!
+
+  @JavaMethod
+  open func findLoadedClass(_ arg0: String) -> JavaClass<JavaObject>!
+
+  @JavaMethod
+  open func findClass(_ arg0: String) throws -> JavaClass<JavaObject>!
+
+  @JavaMethod
+  open func findClass(_ arg0: String, _ arg1: String) -> JavaClass<JavaObject>!
+
+  @JavaMethod
+  open func resolveClass(_ arg0: JavaClass<JavaObject>?)
+
+  @JavaMethod
+  open func defineClass(_ arg0: [Int8], _ arg1: Int32, _ arg2: Int32) throws -> JavaClass<JavaObject>!
+
+  @JavaMethod
+  open func defineClass(_ arg0: String, _ arg1: [Int8], _ arg2: Int32, _ arg3: Int32) throws -> JavaClass<JavaObject>!
+
+  @JavaMethod
+  open func findLibrary(_ arg0: String) -> String
+
+  @JavaMethod
+  open func findSystemClass(_ arg0: String) throws -> JavaClass<JavaObject>!
+
+  @JavaMethod
+  open func isRegisteredAsParallelCapable() -> Bool
+
+  @JavaMethod
+  open func getParent() -> JavaClassLoader!
+
+  @JavaMethod
+  open func setDefaultAssertionStatus(_ arg0: Bool)
+
+  @JavaMethod
+  open func setPackageAssertionStatus(_ arg0: String, _ arg1: Bool)
+
+  @JavaMethod
+  open func setClassAssertionStatus(_ arg0: String, _ arg1: Bool)
+
+  @JavaMethod
+  open func clearAssertionStatus()
+}
+extension JavaClass<JavaClassLoader> {
+  @JavaStaticMethod
+  public func getPlatformClassLoader() -> JavaClassLoader!
+
+  @JavaStaticMethod
+  public func getSystemClassLoader() -> JavaClassLoader!
+
+  @JavaStaticMethod
+  public func registerAsParallelCapable() -> Bool
+}

Tests/Java2SwiftTests/Java2SwiftTests.swift

@@ -12,6 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+@_spi(Testing)
 import JavaKit
 import Java2SwiftLib
 import XCTest // NOTE: Workaround for https://github.com/swiftlang/swift-java/issues/43
@@ -661,24 +662,27 @@ func assertTranslatedClass<JavaClassType: AnyJavaObject>(
   translator.translatedClasses[javaType.fullJavaClassName] = (swiftTypeName, nil)
   translator.nestedClasses = nestedClasses
   translator.startNewFile()
-  let translatedDecls = try translator.translateClass(
-    JavaClass<JavaObject>(
-      javaThis: javaType.getJNIClass(in: environment),
-      environment: environment)
-  )
-  let importDecls = translator.getImportDecls()
 
-  let swiftFileText = """
-    // Auto-generated by Java-to-Swift wrapper generator.
-    \(importDecls.map { $0.description }.joined())
-    \(translatedDecls.map { $0.description }.joined(separator: "\n"))
-    """
+  try javaType.withJNIClass(in: environment) { javaClass in
+    let translatedDecls = try translator.translateClass(
+      JavaClass<JavaObject>(
+        javaThis: javaClass,
+        environment: environment)
+    )
+    let importDecls = translator.getImportDecls()
 
-  for expectedChunk in expectedChunks {
-    if swiftFileText.contains(expectedChunk) {
-      continue
-    }
+    let swiftFileText = """
+      // Auto-generated by Java-to-Swift wrapper generator.
+      \(importDecls.map { $0.description }.joined())
+      \(translatedDecls.map { $0.description }.joined(separator: "\n"))
+      """
 
-    XCTFail("Expected chunk '\(expectedChunk)' not found in '\(swiftFileText)'", file: file, line: line)
+    for expectedChunk in expectedChunks {
+      if swiftFileText.contains(expectedChunk) {
+        continue
+      }
+
+      XCTFail("Expected chunk '\(expectedChunk)' not found in '\(swiftFileText)'", file: file, line: line)
+    }
   }
 }