Load Conscrypt method via reflection only once

Motivation:

The code did reflection every method call which made the code slower and
harder to read with additional cases to consider.

Modifications:

Instead of loading the method and then throwing it away, save the Method
reference instead of the Class reference. Then also use more precise
exception handling for the method invocation.

Result:

Simpler, speedier code.

handler/src/main/java/io/netty/handler/ssl/Conscrypt.java

@@ -18,6 +18,7 @@
 import io.netty.util.internal.PlatformDependent;
 
 import javax.net.ssl.SSLEngine;
+import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 
 /**
@@ -26,44 +27,39 @@
 final class Conscrypt {
     // This class exists to avoid loading other conscrypt related classes using features only available in JDK8+,
     // because we need to maintain JDK6+ runtime compatibility.
-    private static final Class<?> CONSCRYPT_CLASS = getConscryptClass();
+    private static final Method IS_CONSCRYPT_SSLENGINE = loadIsConscryptEngine();
 
-    /**
-     * Indicates whether or not conscrypt is available on the current system.
-     */
-    static boolean isAvailable() {
-        return CONSCRYPT_CLASS != null && PlatformDependent.javaVersion() >= 8;
-    }
-
-    static boolean isEngineSupported(SSLEngine engine) {
-        return isAvailable() && isConscryptEngine(engine, CONSCRYPT_CLASS);
-    }
-
-    private static Class<?> getConscryptClass() {
+    private static Method loadIsConscryptEngine() {
         try {
             Class<?> conscryptClass = Class.forName("org.conscrypt.Conscrypt", true,
                     ConscryptAlpnSslEngine.class.getClassLoader());
-            // Ensure that it also has the isConscrypt method.
-            getIsConscryptMethod(conscryptClass);
-            return conscryptClass;
+            return conscryptClass.getMethod("isConscrypt", SSLEngine.class);
         } catch (Throwable ignore) {
             // Conscrypt was not loaded.
             return null;
         }
     }
 
-    private static boolean isConscryptEngine(SSLEngine engine, Class<?> conscryptClass) {
+    /**
+     * Indicates whether or not conscrypt is available on the current system.
+     */
+    static boolean isAvailable() {
+        return IS_CONSCRYPT_SSLENGINE != null && PlatformDependent.javaVersion() >= 8;
+    }
+
+    static boolean isEngineSupported(SSLEngine engine) {
+        return isAvailable() && isConscryptEngine(engine);
+    }
+
+    private static boolean isConscryptEngine(SSLEngine engine) {
         try {
-            Method method = getIsConscryptMethod(conscryptClass);
-            return (Boolean) method.invoke(null, engine);
-        } catch (Throwable ignore) {
+            return (Boolean) IS_CONSCRYPT_SSLENGINE.invoke(null, engine);
+        } catch (IllegalAccessException ignore) {
             return false;
+        } catch (InvocationTargetException ex) {
+            throw new RuntimeException(ex);
         }
     }
 
-    private static Method getIsConscryptMethod(Class<?> conscryptClass) throws NoSuchMethodException {
-        return conscryptClass.getMethod("isConscrypt", SSLEngine.class);
-    }
-
     private Conscrypt() { }
 }