Java Examples in a Nutshell, 3rd Edition

Another Simple Servlet

You may recall Example 11-18, an error handler utility class that displays Java exceptions to the user in a dialog box and allows them to be reported to a server through a URL. The servlet shown in Example 20-2 is the server-side portion of that example: it handles an HTTP POST request from the ErrorHandler class, deserializes the exception, and returns a response. (The response claims that the exception has been recorded, when in fact it is simply discarded. Saving the exception to a database is left as an exercise; we’ll see an example later in the chapter of a servlet that does communicate with a database.)

The code for this example is simple. It demonstrates the use of ServletRequest.getInputStream( ) to read the body of an HTTP POST request and the use of HttpServletResponse.sendError( ) to send an HTTP error.

Example 20-2. ErrorHandlerServlet.java

package je3.servlet; import java.io.*; import javax.servlet.*; import javax.servlet.http.*; import java.sql.*; /** * This servlet is the server-side companion to the * ErrorHandler.reportThrowable( ) utility method developed elsewhere in this * this book; it responds to the HTTP POST request initiated by that method. **/ public class ErrorHandlerServlet extends HttpServlet { // This servlet only supports HTTP POST requests public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException { ObjectInputStream in = new ObjectInputStream(request.getInputStream( )); try { Throwable throwable ...