Events in JSF Life Cycle, Value Change Events

Events in JSF Life Cycle

• Web applications often need to respond to user events, such as selecting items from a menu or clicking a button. 
• Exa. you might want to respond to the selection of a country in an address form by changing the locale and reloading the current page to better accommodate your users.
• Typically, you register event handlers with components.
  
• JSF supports four kinds of events:
• Value change events
• fired by editable value holders—such as h:inputText, h:selectOneRadio, and h:selectManyMenu
• Action events
• fired by action sources—for example, h:commandButton and h:commandLink
• Phase events
• fired by the JSF life cycle
• System events (since JSF 2.0)
• NOTE: Keep in mind that all JSF events are executed on the server. 
• Event listeners can affect the JSF life cycle in one of three ways:
• Let the life cycle proceed normally.
• Call the renderResponse method of the FacesContext class to skip the rest of the life cycle up to Render Response.
• Call the responseComplete method of the FacesContext class to skip the rest of the life cycle entirely.

Value Change Events

• Components in a web application often depend on each other. 
  
• Exa. the value of the “State” prompt depends on the “Country” menu’s value.
• Two Ways
• 1. Method binding – In input component, specified a bean’s method directly in the “valueChangeListener” attribute.
• In JSF
  
• In JAVA
  
• 2. ValueChangeListener interface – In input component, add a “f:valueChangeListener” tag inside, and specified an implementation class of ValueChangeListener interface.
• In JSF
  
• In JAVA
  

Action Events:

• Action events are fired by buttons and links.
• When you activate a button or link, the surrounding form is submitted and the JSF implementation subsequently fires action events.
• action listeners vs. actions:
• actions are designed for business logic and participate in navigation handling,
• action listeners typically perform user interface logic and do not participate in navigation handling.
• Two Ways
• 1. Method binding 
• In JSF
  
• 2. ActionListener interface – 
• In JSF