Question

Where is the proper ‘place’ in JSF to put initialisation snippet that follows, in order to get it executed just one time when the server starts?

1.  ExternalContext extContext = FacesContext.getCurrentInstance().getExternalContext();
2.  HttpSession sesion = (HttpSession)extContext.getSession(true); 
3.  String parA = extContext.getInitParameter("parA");
4.  String parB = someCalculations(parA);       
5.  sesion.setAttribute("parB", parB);

Basically I want to read a parameter parA from web.xml context-param section, do some transformations, and include it in session (as new parB parameter).

PostConstructApplicationEvent and eager=true techniques doesn’t works because session is null at this point (line 4).
ServletContextListener technique doesn’t works because FacesContext isn’t available.

Thanks!

Answer 1

There are no sessions at application start time; this requirement is impossible to meet.

I interpret your requirements as:

• perform an expensive application-scope calculation
• inject this application-scope result into other scopes

The JSF way to do this is via managed beans. Here is an application-scope bean to perform the one-time transformation of the context parameter:

package foo;

import javax.faces.bean.ApplicationScoped;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.ManagedProperty;

@ManagedBean
@ApplicationScoped
public class SomeCalculationsBean {
  @ManagedProperty("#{initParam.paraA}")
  private String paraA;

  private String someCalculation;

  public String getParaA() {
    return paraA;
  }

  public void setParaA(String paraA) {
    this.paraA = paraA;
    this.someCalculation = //do some transformation
  }

  public String getSomeCalculation() {
    return someCalculation;
  }
}

This value can then be injected into other scopes as you need it:

package foo;

import javax.faces.bean.ManagedBean;
import javax.faces.bean.ManagedProperty;
import javax.faces.bean.SessionScoped;

@ManagedBean
@SessionScoped
public class SomeSessionBean {
  @ManagedProperty("#{someCalculationsBean.someCalculation}")
  private String paraB;

  public String getParaB() {
    return paraB;
  }

  public void setParaB(String paraB) {
    this.paraB = paraB;
  }
}

Code untested. This implementation assumes JSF annotation support but you can do the same thing with faces-config.xml bean configuration.