[OGNL-102] Improves performance when null was returned

[lukaszlenart]

Improves performance of chained expressions in case if the root is null

Refs OGNL-102

[lukaszlenart]

@davoustp @harawata @quaff could you take a look? this should improve performance a bit, it's in relation to #138 and the JIRA ticket.

[harawata]

Hi @lukaszlenart ,

I'm sorry about the slow response (as always)!

So, is root the only concern here?

With the following test, for example, the for-loop is still evaluated for the second node and the similar exception is thrown :

ognl.OgnlException: source is null for getProperty(null, "key2")

public void testNullHnadling() throws Exception {
  OgnlContext context = (OgnlContext) Ognl.createDefaultContext(null, new DefaultMemberAccess(false));
  Map<String, Object> root = new HashMap<>();
  root.put("key1", null);
  String expr = "key1.key2.key3";
  assertNull(Ognl.getValue(expr, context, root));
}

[lukaszlenart]

Right, but if I did that on children level in the for loop a lot of tests have started to fail, especially this one

[harawata]

Yes, it will change the designed behavior and @davoustp seems to be aware.

I'll just show some tests that emphasizes the difference in behavior.
If these results match @davoustp 's expectation, this PR should be fine.

public void testNullValue() throws Exception {
  OgnlContext context = (OgnlContext) Ognl.createDefaultContext(null, new DefaultMemberAccess(false));
  Map<String, Object> root = new HashMap<>();
  root.put("key1", null);
  String expr = "key1.key2.key3";
  assertNull(Ognl.getValue(expr, context, root)); // FAIL : OgnlException
}

public void testEmptyRoot() throws Exception {
    OgnlContext context = (OgnlContext) Ognl.createDefaultContext(null, new DefaultMemberAccess(false));
    Map<String, Object> root = new HashMap<>();
    String expr = "key1.key2.key3";
    assertNull(Ognl.getValue(expr, context, root)); // FAIL : OgnlException
}

public void testNullRoot() throws Exception {
    OgnlContext context = (OgnlContext) Ognl.createDefaultContext(null, new DefaultMemberAccess(false));
    Map<String, Object> root = null;
    String expr = "key1.key2.key3";
    assertNull(Ognl.getValue(expr, context, root)); // PASS
}

[lukaszlenart]

Changes will be moved into #155