Servlet Data

The HttpServletRequest gives you information about the request, including the data passed in a query string or form.

String getParameter(String)

We can access form data with the getParameter method.

The form below will submit firstName and lastName to the server.

<form action="info.do" method="POST">
    <label for="firstName">First</label> <input type="text" name="firstName">
    <br >
    <label for="lastName">Last</label> <input type="text" name="lastName">
</form>

The servlet's doPost() method retrieves each parameter's value by calling getParameter(paramName).

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

  String fn = req.getParameter("firstName");
  String ln = req.getParameter("lastName");

  // ...
}

The connection between the form's input and the servlet's call to getParameter is important to note. * The input's name is the key getParameter() can use to access the data value.

Checkbox Data - getParameterValues

HTML checkboxes send data to the servlet in the format key=value1&key=value2.

For example, this input

<h3>Choose your interests</h3>
<div>
  <input type="checkbox" id="coding" name="interest" value="coding">
  <label for="coding">Coding</label>
</div>
<div>
  <input type="checkbox" id="animals" name="interest" value="animals">
  <label for="animals">Animals</label>
</div>
<div>
  <input type="checkbox" id="presidents" name="interest" value="presidents">
  <label for="presidents">Presidents</label>
</div>

can send three values for input name="interest".

interest=coding&interest=animals&interest=presidents

Use String[] getParameterValues(String) to get the values as an array.

String[] interests = req.getParameterValues("interest");

// [coding, animals, presidents]

This method returns null if the parameter does not exist in the request.

String[] nope = req.getParameterValues("interestssss");

// null

Practice Exercise

getParameter and getParameterValues always return String data, so if you need an int, for example, you have to parse each String and handle any exceptions.

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