Add Custom Error Handler in Vaadin 7.6

I took a small break from ADF for a month and helped a customer build their web app using Vaadin 7.6.
They had a very strick requirement on handling "unhandled exception". So I implemented something very similar to what I did for ADF last year :), but in Vaadin style.

In a nutshell :
1. Lets catch the unhandled exception.
2. Generate an unique ID for this incident and generate seaparate log file.
3. Log it with detailed stacktrace and thread dumps and other useful details(username, time etc.)
4. Save it in a specific directory.
5. Redirect the user to an Error page with the incident ID, so that user can report back to the admin people.

First of all, we need 2 classes. One singleton which does the creating incident id and logging, another session scoped bean to store the incident id which we will show the user in the Error page.

Singleton class : CustomExceptionHandler

    private static CustomExceptionHandler instance = null;

    protected CustomExceptionHandler() {

    }

    public static CustomExceptionHandler getInstance() {
        if (instance == null) {
            instance = new CustomExceptionHandler();
        }
        return instance;
    }
   
    private static final ThreadLocal<IncidentContext[]> incidentContext = new ThreadLocal<IncidentContext[]>() {

        @Override
        protected IncidentContext[] initialValue() {

            return new IncidentContext[1];
        }
    };
  
    public void writeException(Throwable t) {

        IncidentContext context = incidentContext.get()[0];
        if (context == null) {
            context = new IncidentContext("No additional context");
        }

        StringBuilder incident = new StringBuilder();

        Calendar calendar = Calendar.getInstance();

        String incidentID = String.format("%s-%2$tY%2$tm%2$td_%2$tH%2$tM%2$tS", context.identification , calendar);
        String incidentFile = String.format("incident-%s.log", incidentID);

        incident.append("--------------------------------------------------------\n");
        incident.append(format(" Filename    : %s\n", incidentFile));
        incident.append(format(" User         : %s\n", VaadinSession.getCurrent().getSession().getAttribute("userName")));
        incident.append(format(" Date        : %1$tB %1$te, %1$tY\n", calendar));
        incident.append(format(" Time        : %1$tl:%1$tM:%1$tS %1$tp\n", calendar));
        incident.append("---------------------------------------------------------------\n\n");
        incident.append(format(" Unexpected error context: %s\n\n %s\n", context.text, ExceptionUtils.getFullStackTrace(t)));

        incident.append("-----------------------------------------------\n\n");
        incident.append(format(" ** THREAD DUMP:\n\n%s\n", dumpThreads()));
        incident.append("-------------------------------------------------\n");
        incident.append("[END]\n");
      
        ExceptionWriter.getCurrentInstance().setExceptionID(incidentID);
      
        String filePath = ExceptionWriter.getCurrentInstance().getFilePath();
        File f = new File(filePath, incidentFile);

        boolean traceWritten = false;
        try {
            FileOutputStream fos = new FileOutputStream(f);
            fos.write(incident.toString().getBytes());
            fos.flush();
            traceWritten = true;
        } catch (FileNotFoundException e) {     
            logger.error("The original exception was :" + incident.toString(), e);
         } catch (IOException e) {
            logger.error("The original exception was :" + incident.toString(), e);
        }
    }
    private String dumpThreads() {

        ThreadMXBean bean = ManagementFactory.getThreadMXBean();
        ThreadInfo[] infos = bean.dumpAllThreads(true, true);

        StringBuilder stack = new StringBuilder();

        for (ThreadInfo info : infos) {
            stack.append(info.toString());
        }

        return stack.toString();
    }
  
    private final static class IncidentContext {

        public static long incidentCount = 1L;

        public final String identification;
        public final String text;

        IncidentContext(Long id, String txt) {

            identification = id.toString();
            text = txt;
        }

        IncidentContext(String txt) {

            identification = String.format("#%d", incidentCount++);
            text = txt;
        }
    }

Session Scoped Bean : ExceptionWriter

    private String filePath;
    private String exceptionID;
  
    public static ExceptionWriter getCurrentInstance() {

        return (ExceptionWriter) VaadinSession.getCurrent().getSession().getAttribute("ExceptionWriter");
    }

    public String getFilePath() {
      
        filePath = getDirectory();     
      
        return filePath;
    }
   
    // Reads the folder to write the log file from web.xml context-param.
   // default folder : D://incident
    private String getDirectory() {
      
        try {
            Context env = (Context)new InitialContext().lookup("java:comp/env");
            String directoryName = (String)env.lookup("incidentFilePath");
            File theDir = new File(directoryName);
            if(theDir.exists() &&theDir.isDirectory()) {
                return directoryName;
            }
        } catch (NamingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return "D://incident";
    }

    public void setExceptionID(String exceptionID) {
        this.exceptionID = exceptionID;
    }

    public String getExceptionID() {
        return exceptionID;
    }

This session  scope bean, needs to be set in the session, I initialized it in my custom VaadinServlet. 
Also, this bean reads a context param from web.xml, the folder path to put the log file. 

<env-entry>
    <env-entry-name>incidentFilePath</env-entry-name>
    <env-entry-type>java.lang.String</env-entry-type>
    <env-entry-value>/domains/vaadin_domain/incidents</env-entry-value>
 </env-entry>  

Now we need to invoke this Exception handler from somewhere :)
Vaadin provides an excellent place for this, "setErrorHandler()" in UI class.
But we also need to redirect the user to the Error page. I created a custom layout for this, with same header and footer content as the normal web app, and with 2 custom div locations

<div location="errorContent"></div>
<div location="homepagelink"></div>


Now in your custom UI class : call the below method from init()

private void setErrorHandler() {
      
        UI.getCurrent().setErrorHandler(new DefaultErrorHandler() {
            @Override
            public void error(com.vaadin.server.ErrorEvent event) {
                // Find the final cause
                CustomExceptionHandler .getInstance().writeException(event.getThrowable());
                ExceptionWriter exceptionWriter = ExceptionWriter.getCurrentInstance();
                String cause = "The server is unable to respond at this time. Thank you for your patience.<br>"
                        + "An unexpected error occurred, please contact System Administrator with the following number :"
                        +  exceptionWriter.getExceptionID();
              
                // Display the error message in a custom fashion
                CustomLayout content = new CustomLayout("ErrorPage");
                VerticalLayout container = new VerticalLayout();
                container.addComponent(new Label(cause, ContentMode.HTML));
                content.addComponent(container, "errorContent");
                // add link to home page
                // add link to home page
                Button toHomePage = new Button("Back to Home page");
                toHomePage.setStyleName("link");
                toHomePage.addClickListener(new Button.ClickListener() {
                    public void buttonClick(Button.ClickEvent event) {
                        Page.getCurrent().reload();
                    }
                });
                content.addComponent(toHomePage, "homepagelink");
                setContent(content);      

                // Do the default error handling (optional)
                doDefault(event);
              }
        });
    }

Please note, I dont have @PreserveOnRefresh, so when I do a reload() from the above method it automatically calls init() again and continue the web app normally.

So, when everything is up and running you see something like this :
(it's in Dutch, but you get it :) ).

 

Notice the number at the end of the second line. Lets check the file then :

 

And the content will look like :

 

Different technologies involved in this :

Vaadin 7.6
Weblogic Server 10.3.6
Java 1.6

Happy coding.