opt(test): avoid iterator resource leaks

Author: bladehan1

framework/src/test/java/org/tron/core/db/DBIteratorTest.java

@@ -84,43 +84,47 @@ public void testRocksDb() throws RocksDBException, IOException {
          RocksDB db = RocksDB.open(options, file.toString())) {
       db.put("1".getBytes(StandardCharsets.UTF_8), "1".getBytes(StandardCharsets.UTF_8));
       db.put("2".getBytes(StandardCharsets.UTF_8), "2".getBytes(StandardCharsets.UTF_8));
-      RockStoreIterator iterator = new RockStoreIterator(db.newIterator(), new ReadOptions());
-      iterator.seekToFirst();
-      Assert.assertArrayEquals("1".getBytes(StandardCharsets.UTF_8), iterator.getKey());
-      Assert.assertArrayEquals("1".getBytes(StandardCharsets.UTF_8), iterator.next().getValue());
-      Assert.assertTrue(iterator.hasNext());
-
-      Assert.assertArrayEquals("2".getBytes(StandardCharsets.UTF_8), iterator.getValue());
-      Assert.assertArrayEquals("2".getBytes(StandardCharsets.UTF_8), iterator.next().getKey());
-      Assert.assertFalse(iterator.hasNext());
-
-      try {
-        iterator.seekToLast();
-      } catch (Exception e) {
-        Assert.assertTrue(e instanceof  IllegalStateException);
+      try (RockStoreIterator iterator =
+               new RockStoreIterator(db.newIterator(), new ReadOptions())) {
+        iterator.seekToFirst();
+        Assert.assertArrayEquals("1".getBytes(StandardCharsets.UTF_8), iterator.getKey());
+        Assert.assertArrayEquals("1".getBytes(StandardCharsets.UTF_8), iterator.next().getValue());
+        Assert.assertTrue(iterator.hasNext());
+
+        Assert.assertArrayEquals("2".getBytes(StandardCharsets.UTF_8), iterator.getValue());
+        Assert.assertArrayEquals("2".getBytes(StandardCharsets.UTF_8), iterator.next().getKey());
+        Assert.assertFalse(iterator.hasNext());
+
+        try {
+          iterator.seekToLast();
+        } catch (Exception e) {
+          Assert.assertTrue(e instanceof IllegalStateException);
+        }
       }
-
-      iterator = new RockStoreIterator(db.newIterator(),  new ReadOptions());
-      iterator.seekToLast();
-      Assert.assertArrayEquals("2".getBytes(StandardCharsets.UTF_8), iterator.getKey());
-      Assert.assertArrayEquals("2".getBytes(StandardCharsets.UTF_8), iterator.getValue());
-      iterator.seekToFirst();
-      while (iterator.hasNext()) {
+      try (
+          RockStoreIterator iterator =
+              new RockStoreIterator(db.newIterator(), new ReadOptions())) {
+        iterator.seekToLast();
+        Assert.assertArrayEquals("2".getBytes(StandardCharsets.UTF_8), iterator.getKey());
+        Assert.assertArrayEquals("2".getBytes(StandardCharsets.UTF_8), iterator.getValue());
+        iterator.seekToFirst();
+        while (iterator.hasNext()) {
+          iterator.next();
+        }
+        Assert.assertFalse(iterator.hasNext());
+        try {
+          iterator.getKey();
+        } catch (Exception e) {
+          Assert.assertTrue(e instanceof IllegalStateException);
+        }
+        try {
+          iterator.getValue();
+        } catch (Exception e) {
+          Assert.assertTrue(e instanceof IllegalStateException);
+        }
+        thrown.expect(NoSuchElementException.class);
         iterator.next();
       }
-      Assert.assertFalse(iterator.hasNext());
-      try {
-        iterator.getKey();
-      } catch (Exception e) {
-        Assert.assertTrue(e instanceof  IllegalStateException);
-      }
-      try {
-        iterator.getValue();
-      } catch (Exception e) {
-        Assert.assertTrue(e instanceof  IllegalStateException);
-      }
-      thrown.expect(NoSuchElementException.class);
-      iterator.next();
     }
   }