Escaping User Input

Escaping User Input

September 11, 2021

example java server servlets post libraries

This example uses an the Apache Commons Text library to escape user input. Learn more in the java server libraries tutorial.

index.html contains an HTML form:

<!DOCTYPE html>
    <h1>Enter some input:</h1>
    <form action="/user-input-escaped/form" method="POST">
      <input type="text" name="data" value="<h1>oh no</h1>">
      <input type="submit" value="Submit">
</html> handles the POST request by escaping the user’s content and outputting it in the response:

package io.happycoding.servlets;

import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import org.apache.commons.text.StringEscapeUtils;

public class FormServlet extends HttpServlet {

  public void doPost(HttpServletRequest request, HttpServletResponse response)
      throws IOException {

    String userInput = request.getParameter("data");
    String escapedUserInput = StringEscapeUtils.escapeHtml4(userInput);

    response.getWriter().println("You entered: " + escapedUserInput);

input form

Because the servlet escapes the data, the HTML is rendered as text in the output:

html output

See the server libraries tutorial and the sanitizing user input tutorial for more information.

Sanitizing User Input Examples


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