MySQL Bugs: #59977: ResultSet.getObject(String columnLabel) returns corrupted object when casting

Bug #59977	ResultSet.getObject(String columnLabel) returns corrupted object when casting
Submitted:	7 Feb 2011 3:54	Modified:	26 Feb 2011 14:09
Reporter:	Anthony Cosgrove	Email Updates:
Status:	Closed	Impact on me:	None
Category:	Connector / J	Severity:	S3 (Non-critical)
Version:	5.1.14	OS:	MacOS (10.6.6)
Assigned to:		CPU Architecture:	Any
Tags:	ResultSet.getObect()

Description:
I serialized a number of classes which appear to write correctly to the designated blob field of my db using either PreparedStatement.setObject() or a combination of ObjectOutputStream and PreparedStatement.setBytes(). However when calling the getObject() method the returned de-serialized object is corrupted. The weird thing is ClassNotFoundException is not thrown but ClassCastException is. If I use the old method of using an ObjectInputStream with a ByteArrayInputStream then I get the correct results.

expected results: de-serialization of a Class type object

actual results: java.lang.ClassCastException: [B cannot be cast to IVR

How to repeat:
ResultSet rs;		
ivrsql = "select * from ivr";
ps = conn.prepareStatement(ivrsql);
rs = ps.executeQuery();
rs.next();
j = (IVR)rs.getObject("data"); // java.lang.ClassCastException thrown here
rs.close();
ps.close();
conn.close();

---

ivr table:
uuid - char(36)
data - blob ---------> Reading object from this field
updated - timestamp

Suggested fix:
Not qualified to suggest :)

The driver hasn't automatically deserialized objects since 3.1.5, are you using "autoDeserialize=true" in your JDBC URL?

I have not... I wasn't even aware of that fact. Will try adding the suggesting phrase into the url and report back.

I added the suggested phrase to the URL. A different exception is thrown now.

SQLException: Class not found: java.lang.ClassNotFoundException: IVR while reading serialized object
SQLState: null
VendorError: 0

I would expect this to not be thrown as a SQLException. Still makes me think the object is not being read back in by getObject() properly. I'm pretty sure the data is correct on the insert as using the streams method (in and out) everything is fine.

JDBC drivers are expected to throw checked exceptions, namely SQLExceptions, so this is following the API.

The CNFE, is probably due to the JDBC driver being in a different class loader than the class in question? All the JDBC driver is doing is creating a binary input stream and pulling that through an ObjectInputStream.

I figured getObject/setObject were wrappers... Still not quite sure why when I use the byte stream process for deserialization my class is deserialized properly. Are there any other tests I can do and attach to this report?

There was something else I was reading when doing serialization, it was recommended for maximum portability to provide a SQLType INT when calling PreparedStatement.setObject(int parameter, Object obj, int SQLType).

Anthony,

Can you attach a complete java test case, which first serializes and then de-serializes the object from BLOB field in IVR table?
Thanks.

Java test case - serialize with setObject() and byte stream comparison

Attachment: 59977-serializer-testcase.zip (application/zip, text), 1.45 KiB.

Ok I just uploaded a zip file containing to .java src files that will do the testcase. I have zero experience with JUnit so this was my only recourse (I'm a hobbyist programmer :P)

IVR table schema:

mysql> desc ivr;
+---------+-----------+------+-----+-------------------+-------+
| Field             | Type                  | Null       | Key     | Default                                | Extra       |
+---------+-----------+------+-----+-------------------+-------+
| uuid              | char(36)           | NO         | PRI      | NULL                                   |                  |
| data              | blob                  | YES        |             | NULL                                   |                  |
| updated       | timestamp       | NO         |             | CURRENT_TIMESTAMP     |                  |
+---------+-----------+------+-----+-------------------+-------+
3 rows in set (0.00 sec)

Hi Anthony,

Thank you for the test case.
I tried running it in my environment and here is the output I initially received:

IVR@59a34
Yup!
[B@1cef4f7

The first time object de-serialized correctly through the ByteArrayInputStream class. Then de-serializing it from rs.getObject() gives just the byte array.

Next, I enabled autoDeserialize=true and here is the output:

IVR@21e554
Yup!
IVR@b30913

As you see, both times the object was de-serialized into IVR. I did not get any exceptions when enabling automatic deserialization. Probably you should try never version of Connector/J, which is 5.1.15.
Thanks.

Bogdan,

Confirmed. I upgraded to 5.1.15 and I am able to successfully deserialize objects. Looks like whatever it was was fixed in the new minor release. Thanks!