Responding to my own mail... I found an old Andreas mail to the lis ( http://mail-archives.apache.org/mod_mbox/tapestry-dev/200606.mbox/[EMAIL PROTECTED])
that explained how to do this. I'll sumarize my ideas so that I can check if they are correct and maybe it will result usefull to the next person that wants to do this. The idea is to define a class that implements NullHandler ( http://www.ognl.org/2.6.9/Documentation/javadoc/ognl/NullHandler.html). That class job is to handle null's when an specific class access to property returns null. To make tapestry use your NullHandler you define something like this in your hivemind configuration file: <contribution configuration-id="tapestry.ognl.NullHandlers"> <null-handler class="classThatImplementsNullHandler" object="instance:classToCaptureNulls"/> </contribution> where classToCaptureNulls represents the name of the class who's nulls you want to handle and classThatImplementsNullHandler represents the class that knows how to deal with nulls in classToCaptureNulls. Now that I have this working I would like to know how to use it :D I mean, if I have a long ognl expression like obj1.obj2.obj3.obj4 and access to obj2 in obj1 return null, I would like to show an "obj2 not available" message on screen. Can anyone help me on how to use this service? Thanks! Marcos On 7/26/07, Marcos Chicote <[EMAIL PROTECTED]> wrote:
Hi Andreas! When I emailed to Tapestry's list I was prototyping a project. Now I'm actually developing it and I'm very interested in getting this service working. Did you find some code where you used this feature? Thanks! Marcos On 6/29/07, Marcos Chicote <[EMAIL PROTECTED]> wrote: > > Thanks Andreas. > I have to do some more reading then. > > I you have some code that I can use as an example I would be really > grateful. > > Thanks! > > Marcos > > On 6/29/07, Andreas Andreou <[EMAIL PROTECTED]> wrote: > > > > O/H Marcos Chicote έγραψε: > > > Thanks Andreas. > > > Before mailing to this list, I tried looking at the ognl > > documentation > > > and I > > > found the NullHandler interface but I wasn't sure how it worked with > > > > > Tapestry or if it was possible to do it another way without altering > > the > > > BOs. > > > > > > Correct me if I'm wrong but what I understand is that Tapestry > > already > > > implements a Hivemind service that does the null handling. All I > > have > > > to do > > > is make my BOs implement NullHandler interface. Am I right? > > Hmmm, not really... Tapestry simply provides that point so that your > > have a global > > way of registring handlers - so, making your BOs implement NullHandler > > > > is not enough > > > > Also, i'm not sure if that's the correct approach - seems it polutes > > your BOs > > > > I think I'd create a service that would be able to null-handle your > > specific objects, and > > esp. of all those objects have a common superclass, i'd be able to > > register them all at once. > > > > I'll dig in for some code - it's been a while since i last used this > > > > > > > > Thanks a lot! > > > > > > Marcos > > > > > > On 6/29/07, Andreas Andreou <[EMAIL PROTECTED]> wrote: > > >> > > >> > > >> > > http://tapestry.apache.org/tapestry4.1/tapestry-framework/hivedoc/config/tapestry.ognl.NullHandlers.html > > >> > > >> > > >> the way it works, is that you associate implementations of > > >> > > http://www.ognl.org/2.6.9/Documentation/javadoc/ognl/NullHandler.html > > >> with class types whose methods (or properties) may return null > > >> > > >> O/H Marcos Chicote έγραψε: > > >> > Hi! > > >> > I have a Table component (actually I have TableRows, TableView, > > and > > >> all > > >> > those other components that form a Table) and one of the columns > > in > > >> > TableView is declared like this: columnName: > > object1.object2.property. > > >> > > > >> > As you can see this can throw NullPointerException if either > > >> object1 or > > >> > object2 are null. > > >> > > > >> > To solve this problem, I have to alternatives: > > >> > a) Use a Block component called columnNameColumnValue an inside > > the > > >> > block an > > >> > Insert component with a value asociated with the page's class > > that > > >> > handles > > >> > nulls > > >> > b) Declare the column like: columnName:object1.propertyObject2. > > (that > > >> > it a > > >> > getPropertyObject2 method in object1 class that handles nulls). > > >> > > > >> > Is there a better way to solve this?? I would love something like > > a > > >> > prefix > > >> > that allows me to specify that whenever a NPE is found, a blank > > >> space is > > >> > rendered. Is something like that possible? > > >> > > > >> > I'm ussing Tapestry 4.1.1. > > >> > > > >> > Btw, great work with Tap4.1.2, congratulations! > > >> > > > >> > Thanks! > > >> > > > >> > > >> -- > > >> Andreas Andreou - [EMAIL PROTECTED] - http://andyhot.di.uoa.gr > > >> Tapestry / Tacos developer > > >> Open Source / J2EE Consulting > > >> > > >> > > >> > > --------------------------------------------------------------------- > > >> To unsubscribe, e-mail: [EMAIL PROTECTED] > > >> For additional commands, e-mail: [EMAIL PROTECTED] > > >> > > >> > > > > -- > > Andreas Andreou - [EMAIL PROTECTED] - http://andyhot.di.uoa.gr > > Tapestry / Tacos developer > > Open Source / J2EE Consulting > > > > > > --------------------------------------------------------------------- > > To unsubscribe, e-mail: [EMAIL PROTECTED] > > For additional commands, e-mail: [EMAIL PROTECTED] > > > > >
