Overriding The Spring DispatcherServlet For Developer Feedback

The Spring DispatcherServlet can be easily overriden to output all of the key communication coming from the browser to the server.

The Importance Of Having Good Developer Feedback

Having good developer feedback in your web application is critical to efficient development and debugging. Overriding the Spring DispatcherServlet allows you to show the following to the developer in the web application console, or in logs. Of course, the feedback isn't limited to these items only but these are the most important. Ideally you will want to program this to only be enabled in a development environment and turned off in production.

The URL/URI being called. This helps the developer determine which controller method is being called.
The time the call is being made, just to help the developer sort out which calls are part of the same request.
The parameters being sent from the browser, both name and value.
The view being returned.

Good feedback like this can save developers hours of guessing what was sent from the browser, and trying to figure out which controller method was called, and what view was rendered. If the developer does have to fire up the debugger, then they will know exactly where to put their breakpoint.

Specifying The Overriden DispatcherServlet in web.xml

Spring's main entry point in a web application is the DispatcherServlet. Therefore, to use your own version you simply replace Spring's implementation with your implementation that extends the Spring version. The reference is located in web.xml in your web application in the "/web-inf" folder. An example of this configuration is shown below.

The Spring documentation is located here Spring MVC Documentation

Example web.xml entry

        
        <servlet>
            <servlet-name>spring</servlet-name>
            <servlet-class>com.utopiasoftware.springOverride.BDDispatcherServlet</servlet-class>            
            <load-on-startup>2</load-on-startup>
        </servlet>

Overriding The DispatcherServlet

Make sure that the Spring MVC jar files are in your java build path. Below is a working example code for the Dispatcher override. More information can be found at An Intro to the Spring DispatcherServlet. Notice that ultimately the super class version of the same method is also called.

Java Code Of A Class Overriding The DispatcherServlet To Provide Developer Feedback

        
        package com.utopiasoftware.springOverride;

        import java.util.Date;
        import java.util.Enumeration;
        
        import javax.servlet.http.HttpServletRequest;
        import javax.servlet.http.HttpServletResponse;
        
        import org.springframework.web.servlet.ModelAndView;
        
        
        public class BDDispatcherServlet extends org.springframework.web.servlet.DispatcherServlet {
                       
            /**
             * displayParameters method.
             * @param request HttpServletRequest
             * @param feedBack StringBuffer
             * @return StringBuffer
             */
            private StringBuffer displayParameters(final HttpServletRequest request, final StringBuffer feedBack) {
                Enumeration<String> parameterNamesEnumeration = request.getParameterNames();
                
                StringBuffer parametersInfo = new StringBuffer();
                                
                while (parameterNamesEnumeration.hasMoreElements()) {
                    String name = (String) parameterNamesEnumeration.nextElement();
                    String[] values = request.getParameterValues(name);
                    String nameUppercase = name.toUpperCase();
                    if (nameUppercase.indexOf("PASSWORD")== -1) {
                        if( values == null ){
                            feedBack.append("\r\n >>>>>>>>> The parameter :" + name + " was not found in request parameters ");
                        }else{
                            for( int x = 0; x < values.length; x++ ){
                                String paramArrayIndex = "";
                                if (values.length>1) {
                                    paramArrayIndex = "["+x+"]";
                                }
                                parametersInfo.append(" .... \tName = " + name + "; Value = '" +  values[ x ] + "'\r\n");
                            }
                        }
                    }
                }                
                                        
                if (parametersInfo.toString().length() > 1) {
                    feedBack.append("\r\n Parameters:");
                    feedBack.append("\r\n"+parametersInfo.toString());
                } else {
                    feedBack.append("\r\n .... \tNONE");
                }
                
                return feedBack;        
            }
            
            /**
             * render Outputs information for debugging during development.
             *  @param mv ModelAndView
             *  @param request HttpServletRequest
             *  @param response HttpServletResponse
             *  @throws Exception Exception
             */
            @Override
            protected void render(final ModelAndView mv, final HttpServletRequest request,final HttpServletResponse response) throws Exception {
                
                    StringBuffer feedBack = new StringBuffer();
                    
                    feedBack.append("..\r\n\r\n\r\n");
                    
                    feedBack.append("\r\n ==================== START REQUEST =====================");         
                    
                    // ****** DISPLAY URI ******************************************************
                    feedBack.append("\r\n");
                    
                    feedBack.append("\r\n URI = "+request.getRequestURI());
                    feedBack.append("\r\n");
                    
                    feedBack.append(" "+new Date()+"\r\n");
            
                    // ****** DISPLAY PARAMETERS ******************************************************         
                    feedBack = displayParameters(request,feedBack);
                    
                    // ****** DISPLAY JSP ******************************************************
                    feedBack.append("\r\n");
                    
                    feedBack.append("\r\n View = "+mv.getViewName());
                    
                    feedBack.append("\r\n ");
                    
                    feedBack.append("\r\n ======================= END REQUEST ===================\r\n");            
                            
                    System.out.println(feedBack);
                
                // call the original
                super.render(mv, request, response);
            }
            
            
        
        }