What can f metadata f viewParam and f viewAction be used for

Question

Can anyone clarify how we can use in general, or a in real world example, this snippet?

<f:metadata>
    <f:viewParam id="id" value="#{bean.id}" />
    <f:viewAction action="#{bean.init}" />
</f:metadata>

This question is related to jsf jsf-2 viewparams viewaction

User · Answer

Send params from View to an other View  from Sender View to Receiver View use viewParam and includeViewParams true In Sender  Declare params to be sent  We can send String  Object      Sender xhtml  lt f metadata gt         lt f viewParam name  quot ID quot  value  quot   senderMB  strID  quot    gt   lt  f metadata gt    We   re going send param ID  it will be included with    includeViewParams true    in return String of click button event Click button fire senderMB clickBtnDetail dto  with dto from senderMB  arrData  Sender xhtml  lt p dataTable rowIndexVar  quot index quot  id  quot dataTale quot value  quot   senderMB  arrData  quot  var  quot dto quot  gt         lt p commandButton action  quot   senderMB clickBtnDetail dto   quot  value  quot    quot         ajax  quot false quot   gt   lt  p dataTable gt   In senderMB clickBtnDetail dto  we assign  strID with argument we got from button event  dto   here this is Sender DTO and assign to senderMB  strID Sender MB java     public String clickBtnDetail sender DTO sender dto            this  strID   sender dto getStrID            return  quot Receiver faces-redirect true amp includeViewParams true quot          The link when clicked will become http   localhost 8080 my project view Receiver xhtml  ID 12345  In Recever  Get viewParam Receiver xhtml In Receiver we declare f viewParam to get param from get request  receive   the name of param of receiver must be the same with sender  page   Receiver xhtml  lt f metadata gt  lt f viewParam name  quot ID quot  value  quot   receiver MB  strID  quot   gt  lt  f metadata gt   It will get param ID from sender View and assign to receiver MB  strID  Use viewParam In Receiver  we want to use this param in sql query before the page render  so that we use preRenderView event  We are not going to use constructor because constructor will be invoked before viewParam is received So that we add  Receiver xhtml  lt f event listener  quot   receiver MB preRenderView  quot  type  quot preRenderView quot    gt   into f metadata tag Receiver xhtml  lt f metadata gt   lt f viewParam name  quot ID quot  value  quot   receiver MB  strID  quot    gt   lt f event listener  quot   receiver MB preRenderView  quot              type  quot preRenderView quot    gt   lt  f metadata gt   Now we want to use this param in our read database method  it is available to use Receiver MB java public void preRenderView ComponentSystemEvent event  throws Exception           if  FacesContext getCurrentInstance   isPostback                  return                    readFromDatabase          private void readFromDatabase       use  strID to read and set property

User · Answer

Process GET parameters The  lt f viewParam gt  manages the setting  conversion and validation of GET parameters  It s like the  lt h inputText gt   but then for GET parameters  The following example  lt f metadata gt       lt f viewParam name  quot id quot  value  quot   bean id  quot    gt   lt  f metadata gt   does basically the following   Get the request parameter value by name id  Convert and validate it if necessary  you can use required  validator and converter attributes and nest a  lt f converter gt  and  lt f validator gt  in it like as with  lt h inputText gt   If conversion and validation succeeds  then set it as a bean property represented by   bean id  value  or if the value attribute is absent  then set it as request attribtue on name id so that it s available by   id  in the view   So when you open the page as foo xhtml id 10 then the parameter value 10 get set in the bean this way  right before the view is rendered  As to validation  the following example sets the param to required  quot true quot  and allows only values between 10 and 20  Any validation failure will result in a message being displayed   lt f metadata gt       lt f viewParam id  quot id quot  name  quot id quot  value  quot   bean id  quot  required  quot true quot  gt           lt f validateLongRange minimum  quot 10 quot  maximum  quot 20 quot    gt       lt  f viewParam gt   lt  f metadata gt   lt h message for  quot id quot    gt    Performing business action on GET parameters You can use the  lt f viewAction gt  for this   lt f metadata gt       lt f viewParam id  quot id quot  name  quot id quot  value  quot   bean id  quot  required  quot true quot  gt           lt f validateLongRange minimum  quot 10 quot  maximum  quot 20 quot    gt       lt  f viewParam gt       lt f viewAction action  quot   bean onload  quot    gt   lt  f metadata gt   lt h message for  quot id quot    gt   with public void onload                   The  lt f viewAction gt  is however new since JSF 2 2  the  lt f viewParam gt  already exists since JSF 2 0   If you can t upgrade  then your best bet is using  lt f event gt  instead   lt f event type  quot preRenderView quot  listener  quot   bean onload  quot    gt   This is however invoked on every request  You need to explicitly check if the request isn t a postback  public void onload         if   FacesContext getCurrentInstance   isPostback                              When you would like to skip  quot Conversion Validation failed quot  cases as well  then do as follows  public void onload         FacesContext facesContext   FacesContext getCurrentInstance        if   facesContext isPostback    amp  amp   facesContext isValidationFailed                              Using  lt f event gt  this way is in essence a workaround hack  that s exactly why the  lt f viewAction gt  was introduced in JSF 2 2   Pass view parameters to next view You can  quot pass-through quot  the view parameters in navigation links by setting includeViewParams attribute to true or by adding includeViewParams true request parameter   lt h link outcome  quot next quot  includeViewParams  quot true quot  gt   lt  -- Or -- gt   lt h link outcome  quot next includeViewParams true quot  gt   which generates with the above  lt f metadata gt  example basically the following link  lt a href  quot next xhtml id 10 quot  gt   with the original parameter value  This approach only requires that next xhtml has also a  lt f viewParam gt  on the very same parameter  otherwise it won t be passed through   Use GET forms in JSF The  lt f viewParam gt  can also be used in combination with  quot plain HTML quot  GET forms   lt f metadata gt       lt f viewParam id  quot query quot  name  quot query quot  value  quot   bean query  quot    gt       lt f viewAction action  quot   bean search  quot    gt   lt  f metadata gt       lt form gt       lt label for  quot query quot  gt Query lt  label gt       lt input type  quot text quot  name  quot query quot  value  quot   empty bean query   param query   bean query  quot    gt       lt input type  quot submit quot  value  quot Search quot    gt       lt h message for  quot query quot    gt   lt  form gt       lt h dataTable value  quot   bean results  quot  var  quot result quot  rendered  quot   not empty bean results  quot  gt            lt  h dataTable gt   With basically this  RequestScoped bean  private String query  private List lt Result gt  results   public void search         results   service search query      Note that the  lt h message gt  is for the  lt f viewParam gt   not the plain HTML  lt input type  quot text quot  gt   Also note that the input value displays   param query  when   bean query  is empty  because the submitted value would otherwise not show up at all when there s a validation or conversion error  Please note that this construct is invalid for JSF input components  it is doing that  quot under the covers quot  already    See also   ViewParam vs  ManagedProperty value    quot   param id  quot   Communication in JSF 2 0 - Processing GET request parameters

[jsf] What can <f:metadata>, <f:viewParam> and <f:viewAction> be used for?

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