ho fatto una modifica

cerca.jsp
codice:
<%
            Utente u = new Utente();
            String op = request.getParameter("op");
            String ruolo = (String) session.getAttribute("ruolo");
            String prenota = "";

            System.out.println("op sono qui: "+op);
            //System.exit(0);
            int c=u.getNum();
            Libro lib[] = new Libro[c];
            
            if(op.equals("ricerca")){
            lib = (Libro[]) request.getAttribute("libro");
            
            }
            if (op.equals("prenota")) {
                prenota = (String) request.getAttribute("prenotazione");
            }
%>
adesso ho un errore
codice:
java.lang.ArrayIndexOutOfBoundsException: 0
        at org.apache.jsp.cerca_jsp._jspService(cerca_jsp.java from :118)
        at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:111)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
        at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:403)
        at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:492)
        at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:378)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
        at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1534)
        at org.apache.catalina.core.ApplicationDispatcher.doInvoke(ApplicationDispatcher.java:787)
        at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:649)
        at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:604)
        at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:534)
        at org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:1015)
        at org.apache.jsp.cerca_005flibri_jsp._jspService(cerca_005flibri_jsp.java from :161)
        at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:111)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
        at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:403)
        at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:492)
        at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:378)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
        at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1534)
        at org.apache.catalina.core.ApplicationDispatcher.doInvoke(ApplicationDispatcher.java:787)
        at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:649)
        at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:483)
        at org.apache.catalina.core.ApplicationDispatcher.doDispatch(ApplicationDispatcher.java:454)
        at org.apache.catalina.core.ApplicationDispatcher.dispatch(ApplicationDispatcher.java:350)
        at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:300)
        at Java.Controller.processRequest(Controller.java:156)
        at Java.Controller.doGet(Controller.java:208)