Java
Because the application is multithreaded and the error is occuring at high load-times, I realized that the application is not thread safe and that is probably the cause. So I looked into my classes and entities and realized that one class is not thread-safe because it has two attributes that were not accessed and edited in a thread safe way. The solution in java was to use Atomic classes for example AtomicInteger and to change the value using methods of this class. This way we make the class thread safe and NullPointerException is solved.
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I implemented a custom WebSocketAppender for log4j. Log messages were escaped using String.escapeHtml4, newlines were replaced with <br>.
Depending on the log level, messages where printed in bold (WARNING) or in red (ERROR or FATAL).
Events that were considered a problem that needs the user's attention were explicitly stored in a collection, and written to the websocket at the end when the program was done.
The answer is: it depends.
It depends on the programming language you are using and partially on the database you are using.
Most of the databases are services running on a web service. We can communicate with them using a special protocol, while we know the address and the port of the server where it runs. There are also databases stored in files, where we specify the target file.
Most of the programming lanugages and frameworks provide a "Connector" for databases, which allows us to communicate with the database. Of course you need to check if your programming language has a driver for the database type you want to connect to. Some frameworks or programming languaes also offer a higher level control structures called object-relational mapping, where the user can easily read or write some objects defined in the project.
There are many different possibilities to answer this question. We will go top down beginning with the browser.
Most of the browsers support the html input tag of type "email" and most of them would automatically warn the user about a wrong format of the address. However there are many standards of email address pattern. Furthermore the user might disable the browser validation, so we should not rely on this.
The second station is the javascript of the browser. Probably the easiest way to validate the email address is to use a regular expression an match the input against this expression. However the user may disable the javascript or send a request in other way than browser. Therefore it's absolutely necessary to validate the email address on the server side. This might be done by a regular expression, but some more sophisticated systems would check the MX record of the domain given in the email address, to be sure it might be a real address of a real mail server.
Use automated UI Test, which is possible with the Selenium library and a browser driver. The browser driver allows us to run actions in a browser while writing code. The Selenium library is an interface to connect many browsers with the same code base. So now we are able to code a simple test, where a robot is automatically clicking through the website and trying out the login functionality. This technique may also apply to test other important and high priority UI features.
Nested tables? Do you actually mean TreeTables? PrimeFaces is throwing out so many new widgets every 6 months, some old features are just not being improved anymore. Check out their new wisget set in showcases. Also, what is maybe not always the best solution, but often helps, is to develop your own custom widget. It is actually easy to do, and will give you the best understanding of how certain components function. I work with JSF for almost 8 years already, I am a senior dev, and I still manage to find enormous amount of bugs within their framework. Some of them I also reported, which were later turned into features in the new versions.
When explaining the highly technical problem such as this, one really must specify all the integrating parts, including the versions of each and every libraries in use. This seems to me as one of those problems that are so simple, that overthinking prevents you from solving it. Have you perhaps tried reaching out to .NET community online (you must know stackoverflow)? But before posting there, read this https://stackoverflow.com/help/how-to-ask :). If that doesn't help, I have some friends who are .NET gurus and will be more then wiling to help :)
Also, I must denote, days and days of such agony were my usual weekly routine when I started working as a junior dev.
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integrate a Google Map into a Website using JSF
If you are implementing a Website using JSF and Java, and you want to add a Google Maps, there can be different solutions.
You can use one of the PrimeFaces components. There is a nice little component called GMap: http://www.primefaces.org/showcase/ui/gmapHome.jsf
However it is doesn’t offer every function we are used to have with a Google Map.
A better possibility is to use gmap4jsf. To add a Google Mao into your JSF Page you need to add the gmaps4jsf tab library.
Here is a simple Example of who you can use it:
<%@ taglib uri="http://code.google.com/p/gmaps4jsf/" prefix="m" %>
The Example in the attachment uses the latitude and longitude to present a marker on a specific point on the Google Map. The picture in the attachment presents the resulting outcome.
Further examples can be found using the following link:
http://www.mashups4jsf.com/gmaps4jsf-examples/home.jsf
The gmpas4jsf provides JSF tags that make it easy to create a map using latitude and longitude or an address. You can add a marker to the map or an information text. Also some nice additional function like a zoom in and out or switching between map types can be used.
You can read an overview about the functionalities of gmaps4jsf using the following link: http://code.google.com/p/gmaps4jsf/
To calculate your coordinates you can use the Java API for Google geocoder v3
An overview about the functionality and also information about the Maven Repository can be found under the following link: http://code.google.com/p/geocoder-java/
The geocoder is an easy possibility if you want to search for a specifiy city or route that you want to presents in your Google Map.
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Kill running process in a Unix-based console with the example of the Java Web Server Grizzly
1. Step: We need to find the proper running process in the background, for that we will use the command...
ps aux
... which lists all running processes which mostly is too long of a list:
jurgen 39191 0.0 0.8 904472 69368 ?? S 2:19PM 0:11.78 /Applications/Google Chrome
jurgen 39043 0.0 0.2 2524472 13976 ?? Ss 9:51AM 0:02.62 com.apple.security.pboxd
jurgen 38473 0.0 0.0 2467260 432 ?? Ss Tue03PM 0:00.20 com.apple.XType.FontHelper
...
So we filter out only the process that we are looking for, by using the command 'grep' and using the console pipe '|' to concatenate the commands
ps aux | grep java
Result:
jurgen 39543 0.1 1.9 4845420 163316 s008 S+ 5:49PM 0:07.18 /Library/Java/JavaVirtu... exec:java
jurgen 39573 0.0 0.0 2432768 460 s007 S+ 6:08PM 0:00.00 grep java
Now this returns us the proper process but also the 'grep' process itself which we were just running in our pipe, to filter this, we concatenate yet another 'grep -v grep':
ps aux | grep java | grep -v grep
... and we only get the process we need
jurgen 39543 0.1 1.9 4845420 163316 s008 S+ 5:49PM 0:07.18 /Library/Java/JavaVirtu... exec:java
Now that we have identified our process with its process number 39543 (second column in our process), we can terminate it with the 'kill -9'* command, as follows:
kill -9 39543
* If your wondering: The -9 parameter tells the kill-Command to send a SIGKILL signal to our process
In conclusion the following - more generic code - needs to be executed:
ps aux | grep [server_process_name] | grep -v grep
kill -9 [identified_process_id]
Stop Java process
Steps:
1. After login to the server where the process was running, we look for the Java process to be stopped (since the application is in Java, this should be visible in the process list). The "ps aux" command searches through all running processes and the "grep" command filters based on a key word:
ps aux |grep java
2. In order to be sure that our process is still active, we can look also for the specific name of the application:
ps aux |grep java|grep [application_name]
3.a. In case there are no other Java processes on the server (as it can be verified from the results of the first command), the easiest would be to kill all the Java processes:
killall -9 java
3.b. In case there are several Java processes running on the server, then from the results of the first command we can identify the process ID of our Java application. This process ID can then used for stopping the process:
kill -9 [process_ID]
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