How to redirect user when certain condition is met

问题:

I used to just use Tomcat and JSP pages which I can execute query, then assign query result into the array or object then pass that data onto client side via response.

request.setAttribute("errorMessage", "this is error!!");
request.getRequestDispatcher("report.jsp").forward(request, response);

In client jsp code, I could do something like:

${errorMessage}

Then the "this is error!!" message would show up.

I want to do the same thing with REST JAX-RS GlassFish v3.

    @Path("schedule/test")
    @POST
    @Consumes("application/x-www-form-urlencoded")
    @Produces("application/vnd.ms-excel")
    public Object tmpTest(String content) {
        try {

            //just my method to execute query and get result
            Vector out = (Vector)QueryManager.executeQuery;

            //if query result is empty, I want user to redirect to report.jsp page
            if(out.isEmpty()) {
                request.setAttribute("errorMessage", "This is error!!");
                request.getRequestDispatcher("report.jsp").forward(request, response);
                return null;
            }
        ....continue code......
   }

This results in mysterious exception I've never seen.

java.lang.ClassCastException: $Proxy109 cannot be cast to org.apache.catalina.core.ApplicationHttpRequest
            at org.apache.catalina.core.ApplicationHttpRequest.getRequestFacade(ApplicationHttpRequest.java:1001)
            at org.apache.catalina.core.ApplicationDispatcher.doDispatch(ApplicationDispatcher.java:472)
            at org.apache.catalina.core.ApplicationDispatcher.dispatch(ApplicationDispatcher.java:379)
            at org.apache.catalina.core.ApplicationDispatcher.dispatch(ApplicationDispatcher.java:336)
            at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:314)

So how can I redirect a user to report.jsp and also pass message like "This is error" ?

The client jsp expects the error msg variable to have a value:

<b>${errorMessage}</b>

回答1:

That's not RESTful. You need to throw a WebApplicationException with a specific status code so that the client understands what exactly went wrong. E.g. when it's actually the server's mistake:

throw new WebApplicationException(Response.Status.INTERNAL_SERVER_ERROR);

Or when it was after all client's mistake:

throw new WebApplicationException(Response.Status.BAD_REQUEST);

See also HTTP status code definitions for an overview.

---

The ClassCastException which you're facing is by the way occurring because the dispatched request is actually not an instance of the servletcontainer-provided implementation (in this particular case, the one of Tomcat or a Tomcat-fork). After all, you shouldn't be doing it this way. You're developing a REST webservice, not a JSP/Servlet website. It are two distinct worlds.

回答2:

As mentioned before, you should try WebApplicationException.

I believe you this would give you your desired answer:
Try this:

        if(out.isEmpty()) {
             java.net.URI location = new java.net.URI("report.jsp");
             throw new WebApplicationException(Response.seeOther(location).build());
         }