On 01/07/2012 20:26, Peter wrote:
Hi guys,
Basically, as the title says, I would like to store a shared object in a MySQL
database
and retrieve it at a later time. So I wrote a simple shared class Test:
public class Test implements Serializable {
private int statusId;
public Test() {
}
public Test(int statusId) {
this.statusId = statusId;
}
}
Now I have an rpc that stores an instance of the Test class into a
single-column table
(the MySQL type is BLOB). This is the rpc implementation:
public void storeTest(Test test) {
try {
Class.forName("com.mysql.jdbc.Driver");
Connection conn =
DriverManager.getConnection(MySQLConnection.DB_URL,
MySQLConnection.DB_USER, MySQLConnection.DB_PWD);
PreparedStatement statement = conn.prepareStatement("insert into
test_table
(test_object) values (?)");
statement.setObject(1, test);
statement.executeUpdate();
} catch (SQLException e) {
} catch (ClassNotFoundException e) {
}
}
For retrieval, I have another rpc as follows (server side code again):
public Test getTest() {
Test t = new Test();
try {
Class.forName("com.mysql.jdbc.Driver");
Connection conn =
DriverManager.getConnection(MySQLConnection.DB_URL,
MySQLConnection.DB_USER, MySQLConnection.DB_PWD);
PreparedStatement statement = conn.prepareStatement("select
test_object from
test_table");
ResultSet resultSet = statement.executeQuery();
resultSet.next();
t = (Test) resultSet.getObject(1);
} catch (SQLException e) {
} catch (ClassNotFoundException e) {
}
return t;
}
The storeTest(Test test) method runs fine (at least I think it does) - no
errors are
returned and the record is inserted into the MySQL table. However, the method
getTest()
fails during the conversion *t = (Test) resultSet.getObject(1)*. Now I've done
some
digging and apparently the object returned by resultSet.getObject(1) is an
instance of a
class called *[B*, which seems to be a JNI byte array which can't be converted
into Test.
It is unclear to me why this happens. I would expect that the BLOB column
contains all the
necessary info to rebuild the Test object. I'm pretty sure I'm missing something
fundamental here, but can't quite figure it out.
I have no experience with storing object data in a blob of a SQL base. Maybe it acts like
serialization (I see you made your class serializable).
The first Google hit I got uses a slightly different, more indirect method:
http://www.easywayserver.com/blog/how-to-serializable-object-in-java-2/
The second hit explains why your method doesn't work, and why ObjectInputStream is
necessary: http://hans.liss.pp.se/node/700
--
Philippe Lhoste
-- (near) Paris -- France
-- http://Phi.Lho.free.fr
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