Question

How can validate a jsp page through java class ( servlet ) and depending on the result to go forward or to go back with error message?

Thanks in advance.

Answer 1

• POST a form from jsp to setvlet
• in doPost() of servlet, receive the data
• perform the validation on the received data

If it validates correctly conditionally forward the request to success page or in case of validation fail set the error message in request attribute and forward request again to the FORM page

For example

// Prepare messages.
Map<String, String> messages = new HashMap<String, String>();
request.setAttribute("messages", messages);

// Get and validate name.
String name = request.getParameter("name");
if (name == null || name.trim().isEmpty()) {
    messages.put("name", "Please enter name");
} else if (!name.matches("\\p{Alnum}+")) {
    messages.put("name", "Please enter alphanumeric characters only");
}

// Get and validate age.
String age = request.getParameter("age");
if (age == null || age.trim().isEmpty()) {
    messages.put("age", "Please enter age");
} else if (!age.matches("\\d+")) {
    messages.put("age", "Please enter digits only");
}

// No validation errors? Do the business job!
if (messages.isEmpty()) {
    messages.put("success", String.format("Hello, your name is %s and your age is %s!", name, age));
}

request.getRequestDispatcher("/WEB-INF/hello.jsp").forward(request, response);

See detailed information