James.Strachan wrote:
>
> 2008/12/23 cmoulliard <cmoulli...@gmail.com>:
>>
>> Hi,
>>
>> I'm currently working on a small prototype to bind CSV data to POJOs
>> using
>> annotation. Camel through its component file:/// and dataformat will
>> provide
>> me the infrastructure that I need to parse the file content, extract each
>> CSV record and return an array of String for each record found in a file.
>>
>> Remark : A string contains the list of CSV values separated by a comma.
>>
>> In order to bind the CSV values to my POJOs, I have created two
>> annotations
>> :
>>
>> @Retention(RetentionPolicy.RUNTIME)
>> public @interface CSVRecord {
>>
>> String name(); --> root name of the class handling the content of
>> a CSV
>> record
>> String separator(); --> separator used to separate CSV data
>>
>> }
>>
>> @Retention(RetentionPolicy.RUNTIME)
>> public @interface CSVField {
>>
>> int pos(); --> key indicating the position of the CSV data in the
>> CSV
>> record
>> String name(); --> key assigned to the column name of a CSV field
>>
>> }
>>
>> Here is an example of a POJO (= Model) using these annotations :
>>
>> @CSVRecord(separator =",", name = "OrderModel")
>> public class OrderModel {
>>
>> @CSVField(name = "Number", pos = 0)
>> String orderNr;
>>
>> @CSVField(name = "Client Number", pos = 1)
>> String clientNr;
>>
>> @CSVField(name = "ISIN", pos = 2)
>> String ISIN_Code;
>>
>> @CSVField(name = "Name", pos = 3)
>> String Instrument_Name;
>>
>> @CSVField(name = "Quantity", pos = 4)
>> String Quantity;
>>
>> @CSVField(name = "Cur", pos = 5)
>> String Currency;
>
> Minor point - but you could use more defaults in that if you like.
> e.g. default "," if its not specified and maybe default the name to be
> the name of the field if its not specified (maybe even default the
> position?)
>
>>> OK. I will check that.
>
>
>> Here is my question ?
>>
>> Using reflection (or project ASM in an next step), I'm able at the launch
>> of
>> the application to discover all the fields annotated and their
>> parameters.
>> With this information, I'm able to set the field value with the CSV data
>> using the following syntax :
>>
>>
>> String[] result = record.split(csv.retrieveSeparator()); --> to retrieve
>> the
>> separator assigned to my CSVRecord
>> ....
>> field.set(order, result[csvField.pos()]);
>>
>> A CSV record can contain one or several classes like :
>> - Order (with reference to a client, instrument, billing, ...),
>> - Client,
>> - Instrument,
>> - Billing
>> where annotations have been defined for the fields corresponding to what
>> we
>> have in CSV record.
>>
>> Remark : In this first prototype implementation, I will only support
>> mapping
>> 1-1 between objects
>>
>> Questions :
>>
>> 1) What is the best to strategy to recursively find all the annotated
>> fields
>> defined within the different classes ?
>
> Probably keeping a cache of class -> metadata rather like we do with
> the annotation metadata for bean binding (see BeanInfo /
> MethodInfoCache in the org.apache.camel.component.bean package).
>
>>> OK. I will check Camel code.
>
>
>> 2) Should we have to create a kind of java tree objects to store the
>> annotated Fields with existing relation between the different classes (=
>> model) ?
>>
>> ex : RootNode = Order, value = list of annotatedFields, childNode =
>> Client,
>> childNode = Instrument, ...
>>
>> 3) Is there performant java algorythm to read the Java Tree in order to
>> find
>> the annotated field corresponding to a key no matter if the field is
>> defined
>> in the parent node or any its children ?
>
> Not totally sure I follow this last bit. Are you talking about nested
> CSVs? Or is it you flatten a master/detail type record into a single
> row of the csv?
>
>>> Yes except that we only have a relation 1-1 between the parent class and
>>> all these children.
>
> The internals of JPA providers or JAXB could be useful
> maybe (though possibly too complex :).
>
>>> For sure. I hope that in the future a JCP project will be created to
>>> handle binding of non XML data (JAnXB) ;-)
>
> Given the flat nature of a CSV its gonna be hard walking an arbitrary
> object graph and mapping it to a row; but I guess for 1-1
> relationships you could bind nested fields (e.g. fields of Currency in
> your example) as optional columns in the parent object's row. In this
> special case though, just walking the field types (for non-primitive
> types) would do the trick I think? You'd probably only be able to walk
> one or two levels deep - and just keep track of types you've already
> walked maybe?
>
>>> What do you mean by optional columns in the parent object ? Can you
>>> provide me an example James ?
>
> --
> James
> -------
> http://macstrac.blogspot.com/
>
> Open Source Integration
> http://fusesource.com/
>
>
-----
Charles Moulliard
SOA Architect
My Blog : http://cmoulliard.blogspot.com/ http://cmoulliard.blogspot.com/
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