Use Apex class to redirect page

Use Apex class to do this action: When open page 'RedirectPage', move to 'TargetPage' directly.

RedirectPage is name of Visualforce page
Code:

<apex:page controller="RedirectCtrl" action="{!doRedirect}">
    Redirect to TargetPage directly...
</apex:page>

RedirectCtrl is name of Apex class that use to control 'RedirectPage'
Code:

public class RedirectCtrl {
   // create redirect function
   public PageReference doRedirect() {
        // set target page
        PageReference pageRef = Page.TargetPage;
        // set a parameter to url, format 'site.com?PARAME_TYPE=PARAME_TYPE_STR'
        pageref.getParameters().put('PARAME_TYPE','PARAME_TYPE_STR');
        // do page redirect
        pageRef.setRedirect(true);
       // begin to redirect
        return pageRef;
    }
}

TargetPage is name of Visualforce page that 'RedirectPage' will redirect to.
Code:

<apex:page>
    This is target page of redirect action.
</apex:page>

That is all.