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I'm genericly using collections
but I would like to kow the type (meta data ..... name ....) of the individual items in the collection.
Is there a passive way( not changing any data) to find out the
the class characteristics of the individual items.
for example genericly getting the record type of a resultset after a query .
equivalent with class.getComponentType() for an array
thanls in advance
All type information for generic containers (or other generic classes) has gone during runtime, i.e. the generics mechanism is a compile time issue; the collections themselves simply manipulate Objects.
You could try to get the class from any object in a collection; would that work for you? Why do you want that information?
kind regards,
Jos
why:
I want to be able to dynicaly react, and prepare output formatting
ex: in JSF Component depending on the table content change my format
the table content itself is not known by the caller, and depending on the type of selection
the table to present can contain recordset made in selection or any entity objecrt from an other origin (specified in a List, Array(solved), or general collection
at the time of interpretation the different objects could be even empty ...
accessing the meta data is handled by reflection.
get the class from an object ?
that could be possible, but is not preferable
Is there realy no solution ?
If those classes don't know how they should be formatted and you (your target class) doesn't know their format all you can do is associate a format with the name of the classes. Get the name of the class, retrieve the format (if it exists) and format that particular object. Maybe a Properties object can handle it where the keys are the fully qualified class names and the associated values are the format Strings?Quote:
Originally Posted by dreuzel
kind regards,
Jos
this would never work, far to much overhead.
the formatting information exists it's called meta data
except tht java seems not to pass it ....
per object one can detect
isArray (simple to get at the individual classes ....)
isIntanceOf itterable/ collection
is a specific class
..
all Entity classes have getter /setters ....
getter have return specifications
any class is composed of getter specs that are complex => handle later
recursive
as the getter setter points to txt, integer/float/numeric ......
for the few basic types I've written het handler
..... so no more problem and if needed I can add
specific handlers .. as needed
all handlers Know of the field names , field names are translated using text resources in different titles ...... they color in Columns or rows....
except I need to find the information in an as strctured way as possible
example object -> class = list/array/enum...... -> handle the sub class ... by preference do not access the OBject any more
since going from Object-> class----> object is not very structured ....
the thing is based on verry few handlers to implement IN and output
txt string
txt area (edit HTML)
numerical(integer/float/....) javascript corrects for errors
bit/byte
(object selecter) selector but results in the object instead of a value
...
future extensions
a phone number
a bitmap
passing the formatting information an other time (explicit/ proprierty) makes all obsolete ....
since at run time using reflextion I can get at all info including the annotations ....
the only restriction is collections ... I need to know what the content class is
thanks for answering ,
is there no solution to get there using collections ?
as a record example
Maybe if you focussed a little.
It could just be me, but some of that seemed a little like word-salad.
Are you implying you want to be able to take any Object in Java and, based on the underlying accesible attributes it possesses in its real Class, decide how to format the screen to display it?
Forget about arrays and all that...is that paragraph there correct?
somehow we are misunderstanding one another.
Maybe it's to late on the day
but as I get any object , and find out its class , i get to know a lot about that object .....
as I standardize on objects as I/O structures defined using getter's and setters .... I'm fully compatible with seam, Hibernate , JSF....
implicitely i've a world of objects (comming from messages/ db/ bussiness structures .... defined by a getter- setter interface ....
I do not realy consider other objects but these (defined above)
I can easily handle those objects individualy :
and as I want to present (I/O) them i feed them to JSF
using some proprierty JSF components ....
Using reflection on the getter - setters i decide what to do
prior to setting up my page ..... This works fine
I've added some annotations to the getter//setters usable in (JSF/hibernate/seam..... that assist me in fields I'm intersted in seeing
and not want to display, including a taborder....)
now the second part:
depending on the application i use lists/hashmap's...collections ...array's of the above mentioned objects
ex: select * from invoices ...... all what happens ; i get a list of objects in clasical terms called a recordset . Feeding these the list/hashmap,collection/ array to my component I can now make list of
presenting multiple records /objects this is classicaly called a table
Since I'm able to present individual records .... it is easy to present
lists of objects .....
Instead of feeeding the object to JSF I feed the list as a whole
this is detected by my component ( value="#{invoiceDBlist}" )
and the component finds the Class of the individual items .... and presents then in a table
My problem with Collections is that I can not do the getClass() without
handling the Object (as opposed to remaining in the Class (more generic )
area. the difference is important since Noone would know what the getter setter really ... it could execute some code (so is realy active)
i do not want my collection scan to be active on the data, just active on the meta data.
I know I'm living here in an object world but this is what Java is all about isn't it ???
OK. I see now.
Because the type stuff of a Collection is lost at compile time then you don't know, without there being at least one object in the collection, what the collection was originally a collection of.
Does that sound correct?