The Java Servlet specification does not include handling a PATCH request. That means that class javax.servlet.http.HttpServlet does not have a doPatch() method, unlike doGet, doPost, doPut etc.

That does not mean that a Java Servlet can not handle PATCH requests. It is quite simple to make it do that.

The trick is overriding the service(request,response) method – and have it respond to PATCH requests (in a special way) and to all other requests in the normal way. Or to do it one step more elegantly:

create an abstract class – MyServlet for example – that extends from HttpServlet, override servce() and add an abstract doPatch() method – that is not supposed to be ever invoked but only be overridden

package nl.amis.patch.view;
 
import java.io.IOException;
 
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
public abstract class MyServlet extends HttpServlet {
 
    public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        if (request.getMethod().equalsIgnoreCase("PATCH")){
           doPatch(request, response);
        } else {
            super.service(request, response);
        }
    }
     
    public abstract void doPatch(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException;
 
}

any servlet (class) that should handle PATCH requests should extend from this class [MyServlet] and implement the doPatch() method

package nl.amis.patch.view;
 
import java.io.IOException;
import java.io.PrintWriter;
 
import javax.servlet.*;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
 
@WebServlet(name = "TheServlet", urlPatterns = { "/theservlet" })
public class TheServlet extends MyServlet {
    private static final String CONTENT_TYPE = "text/html; charset=windows-1252";
 
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
    }
 
    public void doPatch(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType(CONTENT_TYPE);
        PrintWriter out = response.getWriter();
        out.println("<html>");
        out.println("<head><title>TheServlet</title></head>");
        out.println("<body>");
        out.println("<p>The Servlet has received a PATCH request and will do something meaningful with it! This is the reply.</p>");
        out.println("</body></html>");
        out.close();
    }
}

Here is the result of sending a PATCH request from Postman to the Servlet:

Handle HTTP PATCH request with Java Servlet

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Lucas Jellema

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Lucas Jellema