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fredand44

asked on

How to create a rollback with MySql and Java? (test source valid)

/*
Hello!
I try to find out how to use real transactions with Java and a MySQL database.
With transaction I mean that if a insert or update is done and we got a exception occurs before an other
insert or update is done we will be able to undo the first insert or update (a rollback).

But I do not manage to create a rollback.
What I want to do is to run a rollback when a Exception occurs.

Below is my full test code ready to use, which I thought would do a rollback but it doesn't.

My tables in a database in MySQL looks like:

CREATE TABLE test1
(
id INT NOT NULL AUTO_INCREMENT,
date DATETIME NOT NULL,
PRIMARY KEY(id)
);

CREATE TABLE test2
(
id INT NOT NULL AUTO_INCREMENT,
test1_id INT NOT NULL,
PRIMARY KEY(id),
FOREIGN KEY (test1_id) REFERENCES test1(id)
);

To connect to this database I use a properties file thats looks like:
dbDriver                  com.mysql.jdbc.Driver
dbConnectionString      jdbc:mysql://localhost/my_test_database?user=root&password=my_pass

So if any one could tell me how to create a rollback or tell me if there is a bug please let me know.

Unfortunally I do not use the latest MySQL database, but I use the latest jdbc-driver. And I also use Java 1.4.0.

Best regards
Fredrik

BTW I just got 25 points, sorry!


*/


import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
import java.sql.*;

public class GuestTest2
{
      public static void main(String[] args)
      {
            Connection connection = null;
            PreparedStatement preparedStatement = null;
            ResultSet resultSet = null;

            /*
            This block insert 1 row in table test1 and 1 row in table test2
            If we get a Exception there should be a rollback so all changes is undone.

            To create a exception we can comment the row
            preparedStatement.setInt(1, id.intValue());
            to
            //preparedStatement.setInt(1, id.intValue());
            */
            try
            {
                  Class.forName("com.mysql.jdbc.Driver");
                  connection = DriverManager.getConnection("jdbc:mysql://localhost/internetprogrammering_uppgift6?user=root&password=pass");
                  connection.setAutoCommit(false);
                  preparedStatement = connection.prepareStatement("INSERT INTO test1 (date) VALUES(?)");
                  preparedStatement.setTimestamp(1, new Timestamp(System.currentTimeMillis()) );
                  preparedStatement.execute();

                  preparedStatement = connection.prepareStatement("SELECT MAX(id) FROM test1");
                  preparedStatement.execute();
                  resultSet = preparedStatement.getResultSet();
                  resultSet.next();
                  Integer id = (Integer)resultSet.getObject(1);

                  preparedStatement = connection.prepareStatement("INSERT INTO test2 (test1_id) VALUES(?)");
                  //Comment row below to create a exception
                  preparedStatement.setInt(1, id.intValue());
                  preparedStatement.execute();

                  connection.commit();

                  resultSet.close();
                  preparedStatement.close();
                  connection.close();
            }
            catch(Exception e1)
            {
                  e1.printStackTrace();
                  try
                  {
                        System.out.println("Rollback");
                        connection.rollback();
                        connection.commit();
                  }
                  catch(Exception e2)
                  {
                        e2.printStackTrace();
                  }
            }
            finally
            {
                  try
                  {
                        if(resultSet != null)
                        {
                              resultSet.close();
                        }
                        if(preparedStatement != null)
                        {
                              preparedStatement.close();
                        }
                        if(connection != null)
                        {
                              connection.close();
                        }
                  }
                  catch(Exception e2)
                  {
                        e2.printStackTrace();
                  }
            }


            /*
            This section shows whats in the database after insert with or with out rollbacks.
            */
            try
            {
                  Class.forName("com.mysql.jdbc.Driver");
                  connection = DriverManager.getConnection("jdbc:mysql://localhost/internetprogrammering_uppgift5?user=root&password=snuffa");
                  preparedStatement = connection.prepareStatement("SELECT * FROM test1");
                  preparedStatement.execute();
                  resultSet = preparedStatement.getResultSet();
                  while( resultSet.next() )
                  {
                        StringBuffer stringBuffer = new StringBuffer();
                        stringBuffer.append(resultSet.getString(1));
                        stringBuffer.append(" ");
                        stringBuffer.append(resultSet.getString(2));
                        System.out.println( stringBuffer.toString() );
                  }

                  resultSet.close();
                  preparedStatement.close();
                  connection.close();
            }
            catch(Exception e)
            {
                  e.printStackTrace();
            }
            finally
            {
                  try
                  {
                        if(resultSet != null)
                        {
                              resultSet.close();
                        }
                        if(preparedStatement != null)
                        {
                              preparedStatement.close();
                        }
                        if(connection != null)
                        {
                              connection.close();
                        }
                  }
                  catch(Exception e2)
                  {
                        e2.printStackTrace();
                  }
            }
      }

}
Avatar of DrWarezz
DrWarezz

What do you mean by "it doesn't work"?
Does an error occur when you run it....???

gL,
[r.D]
Avatar of fredand44

ASKER

Hello DrWarezz!

The first insert will always be committed even if I do a rollback. That is what I mean it doesn't work.

Best regards
Fredrik
yep because you commit it before you check for an exception.  check the exception and then only commit. else roll back. you cannot roll back beyond the last commit.
/*
Hello!
The error was the type of DB. At first I did not used InnoDB but after I have created a my.cnf file and restarted the MySQl database with --defaults-extra-file=C:/mysql/data/my.cnf
I could create my tables like:

CREATE TABLE test1
(
id INT NOT NULL AUTO_INCREMENT,
date DATETIME NOT NULL,
PRIMARY KEY(id)
)
TYPE = INNODB;

CREATE TABLE test2
(
id INT NOT NULL AUTO_INCREMENT,
test1_id INT NOT NULL,
PRIMARY KEY(id)
)
TYPE = INNODB;

After that everything worked fine if I got a exception and needed to do a rollback.

Best regards
Fredrik

*/
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modulo

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