Android: Use the application's class loader when loading Java classes.

Previously the system class loader was used, which meant only system
Java classes where available. With this change it's no longer necessary
to add a JNI_OnLoad() to get a handle to application specific classes.

Change-Id: Ic8fe35b4e525bfeb1d317d5ba6b496e39bf9bb30
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>

src/corelib/kernel/qjni.cpp

@@ -70,16 +70,24 @@ static jclass getCachedClass(JNIEnv *env, const char *className)
     QString key = QLatin1String(className);
     QHash<QString, jclass>::iterator it = cachedClasses->find(key);
     if (it == cachedClasses->end()) {
-        jclass c = env->FindClass(className);
+        QJNIObjectPrivate classLoader = QtAndroidPrivate::classLoader();
+        if (!classLoader.isValid())
+            return 0;
+
+        QJNIObjectPrivate stringName = QJNIObjectPrivate::fromString(QLatin1String(className));
+        QJNIObjectPrivate classObject = classLoader.callObjectMethod("loadClass",
+                                                                     "(Ljava/lang/String;)Ljava/lang/Class;",
+                                                                     stringName.object());
         if (env->ExceptionCheck()) {
-            c = 0;
 #ifdef QT_DEBUG
             env->ExceptionDescribe();
 #endif // QT_DEBUG
             env->ExceptionClear();
         }
-        if (c)
-            clazz = static_cast<jclass>(env->NewGlobalRef(c));
+
+        if (classObject.isValid())
+            clazz = static_cast<jclass>(env->NewGlobalRef(classObject.object()));
+
         cachedClasses->insert(key, clazz);
     } else {
         clazz = it.value();

src/corelib/kernel/qjnihelpers.cpp

@@ -45,6 +45,7 @@ QT_BEGIN_NAMESPACE
 
 static JavaVM *g_javaVM = Q_NULLPTR;
 static jobject g_jActivity = Q_NULLPTR;
+static jobject g_jClassLoader = Q_NULLPTR;
 
 static inline bool exceptionCheck(JNIEnv *env)
 {
@@ -79,6 +80,20 @@ jint QtAndroidPrivate::initJNI(JavaVM *vm, JNIEnv *env)
     if (exceptionCheck(env))
         return JNI_ERR;
 
+
+
+    jmethodID classLoaderMethodID = env->GetStaticMethodID(jQtNative,
+                                                           "classLoader",
+                                                           "()Ljava/lang/ClassLoader;");
+
+    if (exceptionCheck(env))
+        return JNI_ERR;
+
+    jobject classLoader = env->CallStaticObjectMethod(jQtNative, classLoaderMethodID);
+    if (exceptionCheck(env))
+        return JNI_ERR;
+
+    g_jClassLoader = env->NewGlobalRef(classLoader);
     g_jActivity = env->NewGlobalRef(activity);
     g_javaVM = vm;
 
@@ -96,4 +111,9 @@ JavaVM *QtAndroidPrivate::javaVM()
     return g_javaVM;
 }
 
+jobject QtAndroidPrivate::classLoader()
+{
+    return g_jClassLoader;
+}
+
 QT_END_NAMESPACE

src/corelib/kernel/qjnihelpers_p.h

@@ -63,6 +63,7 @@ namespace QtAndroidPrivate
     Q_CORE_EXPORT jobject activity();
     Q_CORE_EXPORT JavaVM *javaVM();
     Q_CORE_EXPORT jint initJNI(JavaVM *vm, JNIEnv *env);
+    jobject classLoader();
 }
 
 QT_END_NAMESPACE