用servlet关闭数据库连接的问题

Question

I am trying to run my app with tomcat an the first time that I am debugging/running the app its work fine. but when I am trying to run on second time I am getting error "XJ040".

      "Failed to start database 'C:\Documents and Settings\vitaly87\.netbeans-     derby\articals' with class loader WebappClassLoader
         context: /WebApplication1
     delegate: false
        repositories:

I thinks the problem because something wrong with closing the connections.Because when I stop my server the problem goes away until the second run.

here the code:

      private Connection connect = null;
//private Statement  stmt = null;
private PreparedStatement preparedStatement = null;
private ResultSet resultSet = null;
     public  ArrayList<story> stories=new ArrayList<story>();
            void getStories(String  version) throws SQLException{

       try{

         Class.forName("org.apache.derby.jdbc.EmbeddedDriver");

          }catch(ClassNotFoundException e){
              System.out.println(e);
          }
            connect = DriverManager.getConnection( "jdbc:derby:C:\\Documents and Settings\\vitaly87\\.netbeans-derby\\articals", "admin", "admin");
         // statement = connect.createStatement();
              int  ArticlesId= Integer.parseInt(version);
          preparedStatement = connect.prepareStatement("SELECT * FROM admin.articles  where    id>"+ArticlesId+"");
              resultSet = preparedStatement.executeQuery();
          while (resultSet.next()) {
    stories.add(new      story(resultSet.getString("title"),resultSet.getString("date"),resultSet.getString("text")));
}
            close();
            }
            //close connection
private void close() {
    try {
        if (resultSet != null) {
            resultSet.close();
        }



        if (connect != null) {
            connect.close();
        }
    } catch (Exception e) {

    }

thanks for helping

Answer 1

Best always close connections in a finally

connect = DriverManager.getConnection(...)

try
{
    // use connection
}
finally
{
    try
    {
        connect.close()
    }
    catch (SQLException e)
    {
        // log e
    }
}

In your code the connection will not be closed if you have an exception for example in parseInt(version) or exequteQuery()

also in your case I don't think closing of result set is necessary because you are closing the connection anyway.

try {
    if (resultSet != null) {
        resultSet.close();
    }

    if (connect != null) {
        connect.close();
    }
} catch (Exception e) {

}

is problematic because 1. if resultSet.close() throws an exception the connection is never closed and 2. you won't see any exceptions thrown in this method. I'd recommend to at least log the catched exceptions.