Gwt Logging into Client UI from Server-side - gwt

Question

I have created GWT app, in which I have a Vertical Panel where I log the details.
Client side logging I'm doing using logger
sample code is:
public static VerticalPanel customLogArea = new VerticalPanel();
public static Logger rootLogger = Logger.getLogger("");
logerPanel.setTitle("Log");
scrollPanel.add(customLogArea);
logerPanel.add(scrollPanel);
if (LogConfiguration.loggingIsEnabled()) {
rootLogger.addHandler(new HasWidgetsLogHandler(customLogArea));
}
And I'm updating my vertical log panel using this code
rootLogger.log(Level.INFO,
"Already Present in Process Workspace\n");
But now my question is , I have to log server side details also into my vertical log panel.
My serverside GreetingServiceImpl code is:
public boolean createDirectory(String fileName)
throws IllegalArgumentException {
Boolean result = false;
try {
rootLogger.log(Level.INFO,
"I want to log this to my UI vertical log Panel");
system.out.println("log this to UI");
File dir = new File("D:/GenomeSamples/" + fileName);
if (!dir.exists()) {
result = dir.mkdir();
}
} catch (Exception e) {
e.printStackTrace();
}
return result;
}
Now I want to log sysoutprt statements to my UI from here. How can I achieve this. Now using rootLogger.log(Level.INFO,
"I want to log this to my UI vertical log Panel"); code it is logging this to eclipse console . But how to log this to my UI in client side.
Please let me know If anything wrong in this question.

Answer 1

If I understood you right, you want to see your server log entries in web interface. And of course, java logger and printStackTrace() won't help you in that: your gwt code is compiled to JavaScript and has nothing to do with console and log files. Besides, your server can't "push" log entries to client - it's up to client to make requests. So if you want to track new log entries and move it to client, you need to poll server for new entries. And yet another problem: you may have many clients polling your servlet and you should keep in mind this multi-threading.
This is how I see probable implementation (it's just concept, may contain some errors and misspellings):
Remote interface:
public interface GreetingService extends RemoteService {
List<String> getLogEntries();
boolean createDirectory(String fileName)throws IllegalArgumentException;
}
Remote Servlet:
public class GreetingServiceImpl extends RemoteServiceServlet implements GreetingService {
public static final String LOG_ENTRIES = "LogEntries";
public List<String> getLogEntries() {
List<String> entries = getEntriesFromSession();
List<String>copy = new ArrayList<String>(entries.size());
copy.addAll(entries);
//prevent loading the same entries twice
entries.clear();
return copy;
}
public boolean createDirectory(String fileName)throws IllegalArgumentException {
Boolean result = false;
try {
log("I want to log this to my UI vertical log Panel");
log("log this to UI");
File dir = new File("D:/GenomeSamples/" + fileName);
if (!dir.exists()) {
result = dir.mkdir();
}
} catch (Exception e) {
log("Exception occurred: " + e.getMessage());
}
return result;
}
private List<String> getEntriesFromSession() {
HttpSession session= getThreadLocalRequest().getSession();
List<String>entries = (List<String>)session.getAttribute(LOG_ENTRIES);
if (entries == null) {
entries = new ArrayList<String>();
session.setAttribute(LOG_ENTRIES,entries);
}
return entries;
}
private void log(String message) {
getEntriesFromSession().add(message);
}
Simple implementation of polling (gwt client-side):
Timer t = new Timer() {
#Override
public void run() {
greetingAsyncService.getLogEntries(new AsyncCallBack<List<String>>() {
void onSuccess(List<String>entries) {
//put entries to your vertical panel
}
void onFailure(Throwable caught){
//handle exceptions
}
});
}
};
// Schedule the timer to run once in second.
t.scheduleRepeating(1000);
greetingAsyncService.createDirectory(fileName, new AsyncCallBack<Void>(){
void onSuccess(List<String>entries) {
//no need to poll anymore
t.cancel();
}
void onFailure(Throwable caught){
//handle exceptions
}
});
}
As you can see, I have used session to keep log entries, because session is client-specific and so different clients will receive different logs. It's up to you to decide what to use - you may create your own Logger class that will track users itself and give appropriate logs to appropriate clients.
And also you may want to save level of your messages (INFO,ERROR etc.) and then display messages in different colors (red for ERROR, for instance). To do so, you need to save not List, but some your custom class.

Answer 2

You'd create a logging servlet that has the same methods as your logging framework to send log messages to your server via RPC.
Here are some sample RPC log methods you can use:
public interface LogService extends RemoteService {
public void logException(String logger, String priority, String message, String error, StackTraceElement[] stackTrace, String nativeStack);
}
public interface LogServiceAsync {
public void logException(String logger, String priority, String message, String error, StackTraceElement[] stackTrace, String nativeStack, AsyncCallback<Void> callback);
}
public class LogServiceImpl extends RemoteServiceServlet implements LogService {
public void logException(String loggerName, String priority, String logMessage, String errorMessage, StackTraceElement[] stackTrace, String nativeStack) {
Logger logger = getLogger(loggerName);
Level level = getLevel(priority);
// Create a Throwable to log
Throwable caught = new Throwable();
if (errorMessage != null && stackTrace != null) {
caught = new Throwable(errorMessage);
caught.setStackTrace(stackTrace);
}
//do stuff with the other passed arguments (optional)
logger.log(level, message, caught);
}
}

Answer 3

Although those implementations are very nice, forget about timers and repeated server queries. We've something better now.
It's possible to push data from server to client using Atmosphere which supports WebSockets.