Android: load native lib using ReLinker if it and Context available.

If ReLinker is available and BoxStore was built with an Android Context
will load the native JNI library using ReLinker.

Author: greenrobot-team

objectbox-java/src/main/java/io/objectbox/BoxStore.java

@@ -59,6 +59,9 @@
 @ThreadSafe
 public class BoxStore implements Closeable {
 
+    /** Android Context used for native library loading. */
+    @Nullable public static Object context;
+
     private static final String VERSION = "2.4.0-2019-01-08";
     private static BoxStore defaultStore;
 
@@ -186,6 +189,7 @@ public static boolean isObjectBrowserAvailable() {
     private final TxCallback failedReadTxAttemptCallback;
 
     BoxStore(BoxStoreBuilder builder) {
+        context = builder.context;
         NativeLibraryLoader.ensureLoaded();
 
         directory = builder.directory;

objectbox-java/src/main/java/io/objectbox/BoxStoreBuilder.java

@@ -66,6 +66,10 @@ public class BoxStoreBuilder {
     /** BoxStore uses this */
     File directory;
 
+    /** Android Context used for native library loading. */
+    @Nullable
+    Object context;
+
     /** Ignored by BoxStore */
     private File baseDirectory;
 
@@ -174,6 +178,8 @@ public BoxStoreBuilder androidContext(Object context) {
         if (context == null) {
             throw new NullPointerException("Context may not be null");
         }
+        this.context = context;
+
         File baseDir = getAndroidBaseDir(context);
         if (!baseDir.exists()) {
             baseDir.mkdir();

objectbox-java/src/main/java/io/objectbox/internal/NativeLibraryLoader.java

@@ -25,15 +25,21 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.lang.reflect.Method;
 import java.net.URL;
 import java.net.URLConnection;
 
+import io.objectbox.BoxStore;
+
 /**
  * Separate class, so we can mock BoxStore.
  */
 public class NativeLibraryLoader {
+
+    private static final String OBJECTBOX_JNI = "objectbox-jni";
+
     static {
-        String libname = "objectbox-jni";
+        String libname = OBJECTBOX_JNI;
         String filename = libname + ".so";
         boolean isLinux = false;
         // For Android, os.name is also "Linux", so we need an extra check
@@ -68,11 +74,15 @@ public class NativeLibraryLoader {
                 System.err.println("File not available: " + file.getAbsolutePath());
             }
             try {
-                System.loadLibrary(libname);
+                if (!android || !loadLibraryAndroid(libname)) {
+                    System.loadLibrary(libname);
+                }
             } catch (UnsatisfiedLinkError e) {
                 if (!android && isLinux) {
                     // maybe is Android, but check failed: try loading Android lib
-                    System.loadLibrary("objectbox-jni");
+                    if (!loadLibraryAndroid(OBJECTBOX_JNI)) {
+                        System.loadLibrary(OBJECTBOX_JNI);
+                    }
                 } else {
                     throw e;
                 }
@@ -113,6 +123,27 @@ private static void checkUnpackLib(String filename) {
         }
     }
 
+    @SuppressWarnings("BooleanMethodIsAlwaysInverted") // more readable
+    private static boolean loadLibraryAndroid(String libname) {
+        if (BoxStore.context == null) {
+            return false;
+        }
+
+        try {
+            Class<?> context = Class.forName("android.content.Context");
+            Class<?> relinker = Class.forName("com.getkeepsafe.relinker.ReLinker");
+            // ReLinker.loadLibrary(Context context, String library)
+            Method loadLibrary = relinker.getMethod("loadLibrary", context, String.class);
+
+            loadLibrary.invoke(null, BoxStore.context, libname);
+        } catch (ReflectiveOperationException e) {
+            // note: do not catch Exception as it will swallow ReLinker exceptions useful for debugging
+            return false;
+        }
+
+        return true;
+    }
+
     public static void ensureLoaded() {
     }
 }