JSF issue with back button

Question

I'm having an issue with the back button, not keeping data in a dynamic dropdown in JSF on a request scoped bean.

I have a form with 2 dropdowns where dropdown2 is dynamic based on what is selected in dropdown1. Below is my code for these dropdowns.

<h:selectOneMenu id="group" label="group" value="#{queryBacking.groupInternalId}">
    <f:ajax event="valueChange" render="membership" />
    <f:selectItems value="#{supportBean.groupInstitutions}" var="group" itemValue="#{group.institutionInternalId}" itemLabel="#{group.institutionName}" />
</h:selectOneMenu>

<h:selectOneMenu id="membership" label="Membership" value="#{queryBacking.institutionInternalId}">
    <f:selectItem itemLabel="Select One" itemValue="0" />
    <f:selectItems value="#{queryBacking.groupMembershipInstitutions}" var="institution" itemValue="#{institution.institutionInternalId}" itemLabel="#{institution.institutionShortName}" />
</h:selectOneMenu>

My code works great except that if you submit the form and then click the back button, dropdown2 does not contain any values. How can fix this issue?

Answer 1

You mean the back button in the browser right?

The browser probably loads the page out of the browser cache. So you need to disable caching with a filter:

public class NoCacheFilter implements Filter {
    private FilterConfig config;

    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {

        HttpServletRequest httpReq = (HttpServletRequest) request;
        HttpServletResponse httpRes = (HttpServletResponse) response;

        if (!httpReq.getRequestURI().startsWith(
                httpReq.getContextPath() + ResourceHandler.RESOURCE_IDENTIFIER)) { 

            httpRes.setHeader("Cache-Control",
                    "no-cache, no-store, must-revalidate"); // HTTP 1.1.
            httpRes.setHeader("Pragma", "no-cache"); // HTTP 1.0.
            httpRes.setDateHeader("Expires", 0); // Proxies.
        }

        chain.doFilter(request, response);
    }

    @Override
    public void destroy() {
        config = null;
    }

    @Override
    public void init(FilterConfig config) throws ServletException {
        this.config = config;
    }
}

And then add this to the web.xml:

<filter>
  <filter-name>NoCacheFilter</filter-name>
  <filter-class>yourpackage.NoCacheFilter</filter-class>
</filter>

<filter-mapping>
  <filter-name>NoCacheFilter</filter-name>
  <url-pattern>/*</url-pattern>
</filter-mapping>

You can specify the pages you want filtered in <url-pattern> </url-pattern>

Answer 2

You can initialize the values for the page in the bean constructor:

TestBean class

@ManagedBean
@ViewScope
public class TestBean {
    private String name;

    public TestBean() {
        //initialize the name attribute

        //recover the value from session
        HttpSession session = (HttpSession)FacesContext.getCurrentInstance()
            .getExternalContext().getSession(false);
        name = session.getAttribute("name");
        if (name == null) {
            name = "Luiggi";
        }
    }

    public String someAction() {
        //save the value in session
        HttpSession session = (HttpSession)FacesContext.getCurrentInstance()
            .getExternalContext().getSession(false);
        session.setAttribute("name", name);
        return "Test";
    }

    //getters and setters...
}

Test.xhtml

<ui:composition
    xmlns="http://www.w3.org/1999/xhtml"
    xmlns:ui="http://java.sun.com/jsf/facelets"
    xmlns:h="http://java.sun.com/jsf/html">
    <h:body>
        <h:outputText value="Hello " />
        <h:outputText value="#{testBean.name}" />
        <h:form>
            <h:outputText value="Write your name: " />
            <h:inputText value="#{testBean.name}" />
            <br />
            <h:commandButton value="Change name" action="#{testBean.someAction}" />
        </h:form>
    </h:body>
</ui:composition>

Adding an example to remove the session attribute before navigating to Text.xhtml

SomeBean class

@ManagedBean
@RequestScope
public class SomeBean {
    public SomeBean() {
    }
    public String gotoTest() {
        //removes an item from session
        HttpSession session = (HttpSession)FacesContext.getCurrentInstance()
            .getExternalContext().getSession(false);
        session.removeAttribute("name");
        return "Test";
    }
}

SomeBean.xhtml

<ui:composition
    xmlns="http://www.w3.org/1999/xhtml"
    xmlns:ui="http://java.sun.com/jsf/facelets"
    xmlns:h="http://java.sun.com/jsf/html">
    <h:body>
        <h:form>
            <!-- Every time you navigate through here, your "name" 
                 session attribute will be removed. When you hit the back
                 button to get Test.xhtml you will see the "name"
                 session attribute that is actually stored. -->
            <h:commandButton value="Go to Test" action="#{someBean.gotoTest}" />
        </h:form>
    </h:body>
</ui:composition>