How to Retrieve Request Payload from a POST Request in a Java Servlet

How can I access the request payload from a POST request in my Java servlet?

public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    StringBuilder requestBody = new StringBuilder();
    String line;
    BufferedReader reader = request.getReader();
    while ((line = reader.readLine()) != null) {
        requestBody.append(line);
    }
    String payload = requestBody.toString();
    // Process the payload
}

To access the request payload from a POST request in a Java servlet, use the HttpServletRequest object's getReader() method to read the incoming data. Below are detailed steps to achieve this, including code snippets and explanations.

public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    StringBuilder requestBody = new StringBuilder();
    String line;
    BufferedReader reader = request.getReader();
    while ((line = reader.readLine()) != null) {
        requestBody.append(line);
    }
    String payload = requestBody.toString();
    // Process the payload
    System.out.println(payload); // For debugging purposes
}

Causes

• The request payload might not be properly read if the servlet doesn't handle the data stream correctly.
• Incorrect content type may lead to a misunderstanding of how to parse the data.

Solutions

• Use the getReader() method of HttpServletRequest to obtain an input stream for reading the request body.
• Ensure that your JavaScript library is sending the correct content type in the request header, such as 'application/json' for JSON payloads.

Mistake: Not calling getReader() before trying to access request parameters.

Solution: Ensure that you read the request body before accessing any parameters to avoid getting a blank response.

Mistake: Assuming data is available in request parameters without reading the stream.

Solution: Check the content type and read the payload properly using BufferedReader.