Keywords: Java | Servlet | HTTP 405 | POST | doGet
Abstract: This article explains the common HTTP 405 error in Java Servlets when using the POST method, focusing on the issue caused by unimplemented doGet() method calls, and provides step-by-step solutions with code examples. Content includes problem description, root cause analysis, HttpServlet default behavior, code correction, and supplementary configuration.
Problem Description
When developing a web application with Java Servlets, developers may encounter an HTTP 405 error, displaying "HTTP method POST is not supported by this URL," even though the servlet implements the doPost() method. This often leads to data insertion failures, as in the user's attempt to insert into a MySQL database.
Error Cause Analysis
Based on the provided servlet code, the root cause lies in the doPost() method calling doGet(request, response);. Since the handlingReg class extends HttpServlet but does not override the doGet() method, the default doGet() in HttpServlet throws a 405 error. This reflects the internal handling mechanism of the Servlet engine.
HttpServlet Default Behavior
The HttpServlet class provides default implementations for HTTP methods like GET and POST. If a servlet does not override a method, the default implementation invokes HttpServlet.service(), which checks if the request method is supported; if not, it returns a 405 status code. In the user's code, calling doGet() within doPost() triggers the default doGet() to throw the error.
Solution
To resolve this issue, modify the servlet code by removing the doGet(request, response); call from the doPost() method. This ensures that doPost() only handles POST requests, avoiding the default behavior. If the application needs to handle GET requests, override the doGet() method separately instead of calling it from doPost().
Code Correction Example
Here is a simplified version of the servlet's doPost() method with the erroneous call removed:
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String enteredUsername = request.getParameter("txtregUsername");
String enteredPw = request.getParameter("txtregPassword");
String enteredName = request.getParameter("txtregName");
String enteredEmail = request.getParameter("txtregEmail");
try {
Statement stmnt = con.createStatement();
stmnt.executeUpdate("INSERT INTO regUsers VALUES('" + enteredUsername + "','" + enteredPw + "','" + enteredName + "','" + enteredEmail + "')");
} catch (SQLException ex) {
System.out.println(ex.getMessage());
}
out.println("<html><body>Register Success!</body></html>");
}This modification ensures the servlet handles only POST requests and avoids unnecessary calls to doGet().
Supplementary Configuration Method
As mentioned in Answer 2, one might add <http-method>POST</http-method> in web.xml to explicitly support the POST method. However, this is usually unnecessary if the servlet correctly implements doPost() and avoids code anomalies. This approach is more suitable for complex configuration scenarios, not as the primary solution for this issue.
Conclusion
HTTP 405 errors in Java Servlets often arise from unimplemented or incorrectly called HTTP methods. By ensuring servlets override only necessary methods and avoid invoking default behaviors, developers can effectively mitigate such errors. Additionally, configuration files like web.xml should be used as supplementary measures, not primary dependencies.