BoxStore: add sizeOnDisk()

Author: greenrobot

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

@@ -332,6 +332,16 @@ static boolean isFileOpenSync(String canonicalPath, boolean runFinalization) {
         }
     }
 
+    /**
+     * The size in bytes occupied by the data file on disk.
+     *
+     * @return 0 if the size could not be determined (does not throw unless this store was already closed)
+     */
+    public long sizeOnDisk() {
+        checkOpen();
+        return nativeSizeOnDisk(handle);
+    }
+
     /**
      * Explicitly call {@link #close()} instead to avoid expensive finalization.
      */

tests/objectbox-java-test/src/test/java/io/objectbox/BoxStoreTest.java

@@ -215,4 +215,10 @@ private Callable<String> createTestCallable(final int[] countHolder) {
         };
     }
 
+    @Test
+    public void testSizeOnDisk() {
+        long size = store.sizeOnDisk();
+        assertTrue(size >= 8192);
+    }
+
 }