Java – redirect from jsf

I am working on application with jsp, jstl and jsf for my college project, thats being said, I am as well very new to jsf.

Everything is going great so far. However, I seems to have a problem figuring out how to do redirect from managed bean to page with dinamyc parameters.
For example article.jsp?article_id=2

Can somebody tell me how it is done ?

I been trying to use somethinng like

FacesContext.getCurrentInstance().getExternalContext().dispatch("faces/article.jsp2?article_id=" + articleId);

But get error:

javax.servlet.ServletException: #{postComment.postClick}: javax.faces.FacesException: javax.servlet.ServletException: javax.faces.component.UIViewRoot cannot be cast to com.sun.faces.application.StateManagerImpl$TreeNode
    javax.faces.webapp.FacesServlet.service(FacesServlet.java:256)

I been trying to use

response.sendRedirect("faces/article.jsp2?article_id=" + articleId);
            return;

But again getting an error.

javax.servlet.ServletException: Cannot forward after response has been committed
    javax.faces.webapp.FacesServlet.service(FacesServlet.java:256)

Can somebody please tell me how do i redirect from managed java bean when working with jsf ?

Bellow is my code (maybe something wrong with that and thats why redirect not working).

HttpServletRequest request = (HttpServletRequest) FacesContext.getCurrentInstance().getExternalContext().getRequest();
        HttpServletResponse response = (HttpServletResponse) FacesContext.getCurrentInstance().getExternalContext().getResponse();

        String articleId = request.getSession().getAttribute("article_id").toString();
        //String articleId  = request.getParameter("article_id");
        String authorName = request.getSession().getAttribute("user_name").toString();

        java.util.Calendar calendar = java.util.Calendar.getInstance();
        String commentDate = String.valueOf(calendar.get(java.util.Calendar.DAY_OF_MONTH)) + ".";
        commentDate += String.valueOf(calendar.get(java.util.Calendar.MONTH)) + ".";
        commentDate += String.valueOf(calendar.get(java.util.Calendar.YEAR));

         ArrayList error = new ArrayList();

        if(commentName.contains("<"))
        {
            error.add("Comment name contains illegal characters");
        }

        if(commentBody.isEmpty() && commentBody.contains("<script"))
        {
            error.add("Your message body contains illegal characters");
        }

        if(error.size() > 0)
        {
            request.getSession().setAttribute("error", error);
            error.clear();
            FacesContext.getCurrentInstance().getExternalContext().dispatch("article.jsp2?article_id=" + articleId);
        }
        else
        {
            Comment comment = new Comment();
            comment.setCommentAuthor(authorName);
            comment.setCommentBody(commentBody);
            comment.setCommentDate(commentDate);
            comment.setCommentName(commentName);
            comment.setArticleId(articleId);

            DisplayArticleIO addComment = new DisplayArticleIO();
            addComment.postComment(comment);
//            FacesContext.getCurrentInstance().getExternalContext().dispatch("faces/article.jsp2?article_id=" + articleId);
            response.sendRedirect("faces/article.jsp2?article_id=" + articleId);
            return;
        }

Thank you in advance.