Interfacing with Database on Server
Frederic Bregier
fredbregier at free.fr
Sat Oct 24 16:55:37 EDT 2009
Hi,
Yes, you get it perfectly!
Additionaly, it ensures that at most one thread is running at a time for the
same channel (for the ordered one of course).
Cheers,
Frederic
vimana wrote:
>
> Thank you!! This definately helped me out!
> One last thing. I just want to make sure I understand what the execution
> handler is doing:
> So when a request comes in from the client, the execution handler receives
> it and fires off the business logic handler in a new thread. From there
> the business logic handler can do all its lengthy calculations and not
> worry about blocking the execution handler which is responsible for
> handling the i/o requests.
>
> Let me know if that's correct.
>
> Once again thanks for clarifying!
>
>
> Frederic Bregier wrote:
>>
>> Hi,
>>
>> For 1) The execution handler is included in the pipeline at construction
>> (from a factory for instance) and you don't have to take care of it. Its
>> goal is "just" to enable a new thread pool to execute the next handlers
>> such that those handlers do not run in the IO thread. And as you do
>> external request (like SGBD) which could take long time, then you have
>> the good idea to include this execution handler.
>> So on your question, just include it in the pipeline at construction then
>> forget it.
>>
>> 2) For the initialization of the connection pool, I would suggest to do
>> it before creating the server bootstrap and to pass this connection pool
>> as a fix argument to your ChannelPipelineFactory such that any new
>> pipeline will create the business handler with this pool as argument like
>> :
>>
>> public class YourPipelinbeFactory implements ChannelPipelineFactory {
>> private YourPool yourPool;
>> private OrderedMemoryAwareThreadPoolExecutor yourExec;
>> public YourPipelineFactory(YourPool yourPool) {
>> this.yourPool = yourPool;
>> yourExec = new OrderedMemoryAwareThreadPoolExecutor(...);
>> }
>> /**
>> * Returns a newly created {@link ChannelPipeline}.
>> */
>> ChannelPipeline getPipeline() throws Exception;
>> ChannelPipeline pipeline = Channels.pipeline();
>> pipeline.addLast("codec", new YourCodec());
>> pipeline.addLast("Exec", yourExec);
>> pipeline.addLast("handler", new YourBusinessHandler(yourPool));
>> return pipeline;
>> }
>>
>> then in the YourBusinessHandler, you can use the pool to request a new
>> connection from the pool.
>>
>> 3) No you don't have to make the Handler create a runnable objet. Just
>> extends SimpleChannelHandler for instance should be enough. As the
>> Executor handler is before the business handler, you already have the
>> thread support.
>>
>> So in your businessHandler, you could do something like :
>>
>> public class YourBusinessHandler extends SimpleChannelHandler {
>> private YourPool yourPool;
>> public YourBusinessHandler(YourPool yourPool) {
>> this.yourPool = yourPool
>> }
>> public void messageReceived(ChannelHandlerContext ctx,
>> MessageEvent e) {
>> // get the message from e
>> xxx
>> // determine if a request has to be done
>> // if so, get a connection from the pool
>> // then execute the request
>> // determine if a response is needed
>> // if so
>> ctx.getChannel.write(response);
>> // determine if the connection should be closed or not (generaly, the
>> client close the connection
>> // but it depends on the logic of the protocol)
>> }
>>
>> }
>>
>> In fact, you are almost there if I get your point... ;-)
>>
>> HTH,
>> Frederic
>>
>>
>> vimana wrote:
>>>
>>> Hi,
>>>
>>> Thanks for your response. It certainly cleared a number of questions.
>>> I'm still a bit unsure of the following:
>>> 1. How does the execution handler interact with the process mentioned
>>> below?
>>> I'm guessing I would need to execute the query using the execution
>>> handler? If so, would I need to pass the query to the execution handler
>>> using the sendupstream? I'm still confused on how to make use of the
>>> execution handler. I've looked at the API and I'm still very confused on
>>> this.
>>>
>>> 2. Where do I create and initialize my connection pool?
>>>
>>> 3. Do I need to create a runnable object in my Business Logic Handler
>>> class?
>>>
>>> At the moment I'm using my business logic handler to receive the message
>>> -> check if the message is to write to a database (no response to send
>>> to client), or to retrieve data from the database (response sent back to
>>> client as xml). At this point, I was thinking of generating the sql
>>> query and passing the query string downstream to the DB Handler. The DB
>>> Handler would retrieve a connection from the connection pool and execute
>>> the query and the result (if any) would be passed back to the Business
>>> Logic Handler. The business logic handler will forward it back to the
>>> client using write(Object) which would invoke the encoder codec. But in
>>> this process, at which point does the execution handler get invoked? And
>>> is there a particular method which I must call upon to invoke the
>>> execution handler from within the DB Handler or Business Logic Handler?
>>>
>>> Thanks!
>>>
>>>
>>>
>>> Frederic Bregier wrote:
>>>>
>>>> Hi,
>>>>
>>>> I would suggest something in your pipeline like in that order :
>>>>
>>>> - handlers for codec (your protocol on how to receive or answer
>>>> information)
>>>> - handler for execution handler (OrderedMemoryAwareThreadPoolExecutor)
>>>> - handler for business
>>>>
>>>> In your business, you could make all of your business code, including
>>>> the request from the DB pool.
>>>> Then you know what and when you need to answer to the client.
>>>>
>>>> Another option is as you wrote:
>>>> - handlers for codec (your protocol on how to receive or answer
>>>> information)
>>>> - handler for execution handler (OrderedMemoryAwareThreadPoolExecutor)
>>>> - handler for business
>>>> - handler for DB connection and queries
>>>>
>>>> Then your business just pass the request (if any) to the Db Connection
>>>> and Queries handler (using downstream).
>>>> The Db Conn & Query handler if needed to answer just write the answer
>>>> (in the form you need for instance as an Object) using upstream.
>>>> Then the business get the upstream and decide or not to forward it to
>>>> the client...
>>>>
>>>> But my guess is that only one handler is easier but it greatly depends
>>>> on your dev and logic...
>>>>
>>>> HTH,
>>>> Frederic
>>>>
>>>>
>>>> vimana wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> I'm having difficulty understanding how to interface with a DB (MySQL)
>>>>> on the Server.
>>>>> From what I've gathered, I'll need to create a connection pool (which
>>>>> I've done using Apache DBCP), add an execution handler to my pipeline
>>>>> (I used the OrderedMemoryAwareThreadPoolExecutor) and my business
>>>>> logic handler checks if the request from the client is to save
>>>>> something to the db or retrieve something from the db. I then would
>>>>> want the business logic handler to pass this request to the execution
>>>>> handler which will grab a connection from the connection pool and run
>>>>> the query. If the query was to return a result to the client then the
>>>>> execution handler would write the result back to the client. I'm not
>>>>> sure if this is the correct way to go about it and if it is how do I
>>>>> pass the request from the logic handler to execution handler
>>>>> (sendupstream?). And How does the execution handler receive the
>>>>> message ? Do i attach a runnable object to the context object
>>>>> associated with the channel in the business logic handler,
>>>>> sendupstream and then in the handleupstream in Executionhandler get
>>>>> the attachment and do a .execute((Runnble)ctx.getAttachment())?
>>>>>
>>>>> It would help a lot if I can get a high level overview of the correct
>>>>> way to interact with the database.
>>>>>
>>>>> Thanks!
>>>>>
>>>>
>>>>
>>>
>>>
>>
>>
>
>
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