[improve][ml] Optimization method getNumberOfEntries

Author: hanmz

Diff for: managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedCursorImpl.java

@@ -1149,7 +1149,7 @@ public boolean hasMoreEntries() {
 
     @Override
     public long getNumberOfEntries() {
-        if (readPosition.compareTo(ledger.getLastPosition().getNext()) > 0) {
+        if (readPosition.compareTo(ledger.getLastPosition()) > 0) {
             if (log.isDebugEnabled()) {
                 log.debug("[{}] [{}] Read position {} is ahead of last position {}. There are no entries to read",
                         ledger.getName(), name, readPosition, ledger.getLastPosition());

Diff for: managed-ledger/src/test/java/org/apache/bookkeeper/mledger/impl/ManagedCursorTest.java

@@ -444,6 +444,10 @@ void readFromClosedLedger() throws Exception {
     void testNumberOfEntries() throws Exception {
         ManagedLedger ledger = factory.open("my_test_ledger", new ManagedLedgerConfig().setMaxEntriesPerLedger(2));
 
+        ManagedCursor c0 = ledger.openCursor("c0");
+        assertEquals(c0.getNumberOfEntries(), 0);
+        assertFalse(c0.hasMoreEntries());
+
         ManagedCursor c1 = ledger.openCursor("c1");
         ledger.addEntry("dummy-entry-1".getBytes(Encoding));
         ManagedCursor c2 = ledger.openCursor("c2");