if you are using jsf  so why not make most use of it? Why do you try to use old features of web!!!

instead of using request parameters, you had better to put  a field in your managed bean.
this RequestParameterMap is readonly structure.

consider you have a jsf managed bean as follow:

class MyBean {

    private String myKey;

    //somewhere in your code: myKey = "myValue"

    public String getMyKey(){
           return myKey; 
    }
}

This is a simple example of use these article :

public FileUploadForm() { 
 if(FacesContext.getCurrentInstance().getExternalContext().
 getRequestParameterMap().containsKey("defaultsavepath_name"))
{ 
 this.savePathName=FacesContext.getCurrentInstance().
 getExternalContext().getRequestParameterMap().
 get("defaultsavepath_name").toString();

 FacesContext.getCurrentInstance().getExternalContext().
 getRequestParameterMap().put("defaultsavepath_name",this.savePathName);
}
else
{
 Object tmpDir =
FacesContext.getCurrentInstance().
 getExternalContext().getRequestParameterMap().get("dirName");
 if (tmpDir != null && !tmpDir.toString().equals(""))
 {
 String tmpdirName = tmpDir.toString();
 savePathName = savePathName + "\\" + tmpdirName;
 FacesContext.getCurrentInstance().getExternalContext().
 getRequestParameterMap().
 put("defaultsavepath_name", this.savePathName);
}
...
}

If you have an Exception use this line instead of it :
FacesContext.getCurrentInstance().getExternalContext().getRequest().getSession().setAttribute("myKey") = myValue;

You are going wrong way. ;) JSF doesn't support everything not to let
programmers do invention in their codes ;) Maybe Struts or pure JSP
would be a better choice for them.

please take a look at managed properties

they are the proper way to transfer one object from one managed bean to other in JSF
also if you are using seam with JSF, you can use the seamn injection, outjection and bijection mechanisms.
this makes your code  much more readable and maintainable.