DATACMNS-991 - Support Java 9 compatible MethodHandle lookup.

DefaultMethodInvokingMethodInterceptor now contains two alternative implementations, one compatible to Java 8, one for Java 9.

Original pull request: #223.

src/main/java/org/springframework/data/projection/DefaultMethodInvokingMethodInterceptor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2015 the original author or authors.
+ * Copyright 2015-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,7 +15,10 @@
  */
 package org.springframework.data.projection;
 
+import java.lang.invoke.MethodHandle;
 import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodHandles.Lookup;
+import java.lang.invoke.MethodType;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.Method;
 
@@ -27,6 +30,7 @@ import org.springframework.aop.ProxyMethodInvocation;
  * Method interceptor to invoke default methods on the repository proxy.
  *
  * @author Oliver Gierke
+ * @author Jens Schauder
  */
 public class DefaultMethodInvokingMethodInterceptor implements MethodInterceptor {
 
@@ -36,15 +40,27 @@ public class DefaultMethodInvokingMethodInterceptor implements MethodInterceptor
 	 * Creates a new {@link DefaultMethodInvokingMethodInterceptor}.
 	 */
 	public DefaultMethodInvokingMethodInterceptor() {
+		constructor = tryToGetLookupConstructor();
+	}
+
+	private static Constructor<Lookup> tryToGetLookupConstructor() {
 
 		try {
-			this.constructor = MethodHandles.Lookup.class.getDeclaredConstructor(Class.class);
 
-			if (!constructor.isAccessible()) {
-				constructor.setAccessible(true);
+			Constructor<Lookup> accessibleConstructor = Lookup.class.getDeclaredConstructor(Class.class);
+
+			if (!accessibleConstructor.isAccessible()) {
+				accessibleConstructor.setAccessible(true);
+			}
+
+			return accessibleConstructor;
+		} catch (Exception ex) {
+			// this is the signal that we are on Java 9 and can't use the accessible constructor approach.
+			if (ex.getClass().getName().equals("java.lang.reflect.InaccessibleObjectException")) {
+				return null;
+			} else {
+				throw new IllegalStateException(ex);
 			}
-		} catch (Exception o_O) {
-			throw new IllegalStateException(o_O);
 		}
 	}
 
@@ -65,7 +81,24 @@ public class DefaultMethodInvokingMethodInterceptor implements MethodInterceptor
 		Class<?> declaringClass = method.getDeclaringClass();
 		Object proxy = ((ProxyMethodInvocation) invocation).getProxy();
 
-		return constructor.newInstance(declaringClass).unreflectSpecial(method, declaringClass).bindTo(proxy)
-				.invokeWithArguments(arguments);
+		return getMethodHandle(method, arguments, declaringClass, proxy).bindTo(proxy).invokeWithArguments(arguments);
+	}
+
+	private MethodHandle getMethodHandle(Method method, Object[] arguments, Class<?> declaringClass, Object proxy)
+			throws Throwable {
+
+		if (constructor != null) {
+			// java 8 variant
+			return constructor.newInstance(declaringClass).unreflectSpecial(method, declaringClass);
+		}
+
+		// java 9 variant
+		return MethodHandles.lookup() //
+				.findSpecial( //
+						method.getDeclaringClass(), //
+						method.getName(), //
+						MethodType.methodType(method.getReturnType(), method.getParameterTypes()), //
+						method.getDeclaringClass() //
+		);
 	}
 }