Redirecting to the same page results in blank page

Question

I am creating a java servlet web applicaiton where I take user input at index.jsp and shows result at result.jsp page upon POST action. Before submiting the form I validate user input. If any validation error is found than I want to redirect user to the same index.jsp page with the error messages. But the redirect action results in a blank page. Here is what I have done so far -

Servlet class doPost method -

protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    String name = req.getParameter("name");

    //this is just a dto class
    CovidQa covidQa = new CovidQa(name);

    CovidTestValidator validator = new CovidTestValidator();
    boolean hasError = validator.validate(covidQa, req);

    if (hasError) {
        req.getRequestDispatcher("/index.jsp").forward(req, resp);
    }

    req.getRequestDispatcher("/result.jsp").forward(req, resp);
}

Validator's validate method-

public boolean validate(CovidQa covidQa, HttpServletRequest request) {
    boolean hasError = false;

    if (covidQa.getName() == null || covidQa.getName().equals("")) {
        request.setAttribute("nameErr", "Name can not be null");
        hasError = true;
    }

    return hasError;
}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">

    <servlet>
        <servlet-name>Covid-19</servlet-name>
        <servlet-class>CovidTest</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>Covid-19</servlet-name>
        <url-pattern>/Cov</url-pattern>
    </servlet-mapping>

</web-app>

index.jsp -

<form action="Cov" method="post">
    //input fields
    <label>Name</label>
    <input type="text"
           id="name"
           name="name">
    <span>${nameErr}</span>

    <button type="submit">Submit</button>
</form>

1) You're not redirecting at all. You're forwarding. 2) When there's an error, you're forwarding to index.jsp and then to result.jsp. Clearly the system got confused. Shouldn't you logically put the forward to result.jsp in an else block? — BalusC, Jun 17 '20 at 16:25

Erfan Ahmed · Accepted Answer · 2020-06-18T14:30:18.763

req.getRequestDispatcher() doesn't return from the method implicitly. If you don't mention return explicitly, immediate lines also will be executed by the compiler.
As @BalusC commented the system got confused by executing two req.getRequestDispatcher() statement consecutively.

Either you need to return explicitly -

if (hasError) {
    req.getRequestDispatcher("/index.jsp").forward(req, resp);
    return;
}

req.getRequestDispatcher("/result.jsp").forward(req, resp);

Or, put the later one inside else block -

if (hasError) {
    req.getRequestDispatcher("/index.jsp").forward(req, resp);
} else {
    req.getRequestDispatcher("/result.jsp").forward(req, resp);
}

Redirecting to the same page results in blank page

1 Answers1