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Clarification on JDBC assignments

 
whippersnapper
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Got two questions on the JDBC assignments.
  • Sharing connections. Is it OK to getConnection() each time a servlet needs a connection, or should we try to get a connection up front and pool or share it somehow?
  • Videos.java. As I see it, you could write this assignment with or without the Videos class. (Well, it would be a modified version.) Is there a preferred way?


  • [ February 25, 2002: Message edited by: Michael Matola ]
     
    Chicken Farmer ()
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    Personally, I have each servlet get a connection if needed, and then close it out when done. I would think having a shared connection that is passed around would be viable, though I'm not sure if there are pro's and con's to having a single connection being used like that. I figure if you open the connection only when you need it, you're reducing resources *shrugs*.

    I didn't use a Video.java file, just printed the results as I went, instead of building a separate object and then retrieving the info. Probably could go either way (hope that is what you are referring to).
    Hope that helps
    Jason
     
    Sheriff
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    Got two questions on the JDBC assignments.
    1. Sharing connections. Is it OK to getConnection() each time a servlet needs a connection ...


    Yes

    2. Videos.java. As I see it, you could write this assignment with or without the Videos class. (Well, it would be a modified version.) Is there a preferred way?

    The JDBC assignments should look very similar to the Servlets-4 assignments. The main difference is that you store the Videos in a database rather than in an ArrayList.

    Does that answer your question?
     
    Michael Matola
    whippersnapper
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    MdQ: Does that answer your question?
    Depends on whether the capital "V" in your preceding sentence was intentional...
    Here's (what I believe to be) a (slightly) less cryptic version of my question: should I modify Video.java so that a given Video object knows how to write itself out to a database and read itself in from a database? Or is there really no need to create actual Video objects at all -- just have the servlets do the selecting and inserting?
    I think what I'm hearing from you and Jason is that there's no need to create individual Video objects. Was just looking for confirmation of that.
     
    Michael Matola
    whippersnapper
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    Originally posted by jason adam:
    I would think having a shared connection that is passed around would be viable, though I'm not sure if there are pro's and con's to having a single connection being used like that. I figure if you open the connection only when you need it, you're reducing resources *shrugs*.


    Don't know how it is with JDBC, but in general I understand that database connections are fairly expensive to establish. So it's not uncommon to reuse them when it's cheaper to have one open all the time (even if it sits idle) than to constantly open and close new ones.
    When I tried to code JDBC-2 with a shared connection though, I was able to reduce the amount of boilerplate database connection code, but ended up increasing the amount of exception-handling code as a consequence. So it looks like a tradeoff there too.


    I didn't use a Video.java file, just printed the results as I went, instead of building a separate object and then retrieving the info. Probably could go either way (hope that is what you are referring to).


    Yep. That's exactly what I was referring to. I had in mind not just the printing part, but also writing to and reading from the database.
    [ February 26, 2002: Message edited by: Michael Matola ]
     
    Ranch Hand
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    While learning JDBC last fall I had several assingments that made me create Servlets to manage database connection pools. This builds a lot of flexibility into a system so as it grows it can manage database hits efficiently.
    J2EE containers like WebLogic and WebSphere have the functionality built in. You configure the connection parameters for a database and enter the number of connections to be pooled. That's pretty cool!
     
    Marilyn de Queiroz
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    Originally posted by Michael Matola:
    should I modify Video.java so that a given Video object knows how to write itself out to a database and read itself in from a database?


    No. You should not modify Video.java.

    Or is there really no need to create actual Video objects at all -- just have the servlets do the selecting and inserting?

    right.

    I think what I'm hearing from you and Jason is that there's no need to create individual Video objects. Was just looking for confirmation of that.

    confirmed.
     
    Trailboss
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    Marilyn asked me to drop a note in here about "pooling".
    True pooling is something well beyond the scope of these assignments. To learn more about it, I suggest you bring it up in the JDBC forum.
    I suggest that you open a new connection each time you need one. If you don't have "true" pooling available, I think this is the best route. The reason is twofold:
    a) Sometimes after a lot of use, a connection "goes stupid". That's why true pooling refreshes connections periodically.
    b) Leaving a connection open while it is not being used is generally considered a bad idea. Many databases permit only a limited number of connections. And as your apps grow, you may have multiple apps accessing the same database at the same time.
    Opening a connection is a slow process and the best solution to all things is pooling - but again, let's not worry about that just yet
     
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