Most of the Java projects I’ve worked on have used Log4J as the logging framework. We normally change the severity level to ERROR on lo4j.xml before deploying our web application to a production system. But when something goes wrong, you may want to enable debugging for a short time and see the messages, and then turn the level back. There are a couple of ways you can change the severity level on the fly. You can either use a jsp file as explained here or a JMX solution as explained here or here
But we also wanted to take peek at the log data in real time so when we see an error being generated we can change the level back to ERROR and look at server’s log files for debugging. Something like doing a
tail –f logfile.log from the server. In some places, developers are not given SSH access to server, and needs to contact the DBA for any log files. Even if the developer has access to it, SSH access may be limited to internal traffic, and if you want to fix an issue from home, you’re out of luck. A browser based solution would be ideal in these cases. So here we are discussing such a solution, which should be very easy to implement in your own project.
- Place the liveLogger.jar on your WEB-INF/lib folder
- Add the following to your web.xml (before the closing web-app tag)
Monitoring the logs
Once you ran your application, point the browser to, http://<<your server>>/<<your context>>/livelog to get started. I’m assuming that you’ve a valid log4j.properties or log4j.xml file in your classpath. This utility itself uses Log4J for logging with the logger name LiveLogger. Here is a sample screen shot of what you should be seeing on the first page. This is where you can select a logger to change its severity or start streaming log data.
Once you select the logger, you’ll see log data being displayed on the left hand pane as shown below. You can also use this page to change the severity level of your selected logger. Once done, change the level back and stop the monitoring by clicking on Stop button.
How does it work?
Issues with streaming a lot of data to a browser
If there is an influx of messages, then it would severely affect the performance of your application. So I’ve limited the number of messages we can receive on the queue to a 1000.
Making changes to the configuration parameters
At the moment, the only thing that is configurable via web.xml is the maximum number of clients allowed. There are a few other parameters, which I haven’t bothered to get it from web.xml. These are listed here, and I believe all of them are self explanatory.
My Netbeans project files can be downloaded from here, if you want to make any changes and create the jar file. There is also an Ant target “createjar” which generate the jar file. You’ll need to change the location of the jar file though, as it is hard coded at the moment. If you are using any other IDE, create a new project and copy/paste contents of src and web folders to relevent locations.
There is scope for improvement in a number of places.
On the server side, we could use a separate thread to write messages to the client to reduce some of the overheads. But as you already know, creating threads from Servlet is a no-go area. Two JSRs (236 and 237) were created as possible solutions, unfortunately none of them made it to JEE6. While JSR 236 remains inactive, last year JSR237 was withdrawn. There is a commonj project, which can be utilized as a possible solution.
I would appreciate, if you could let me know of any improvements you make to this project.
Files to download
Compiled jar file : liveLogger.jar
Source code (As a Netbeans project) : LiveLoggerV01.zip
********** Please click here for an update script with additional functionalities like multiple header freezing, column freezing and multiple tables ***********
It’s been tested on the following browsers all running on Windows XP.
- Firefox 2.0
- Firefox 3.5
- Google Chrome
The big table
Here is an example of a table we are going to introduce the scrolling functionality. Well, it is not really big, just big enough to test our functionality 🙂
Solution 1: Simple CSS only scrolling without fixing headers
With the help of a bit of CSS, we can implement a simple scroller. Enclose the table element within a div container with an overflow value of auto and a fixed height. Something like
<table …. />
You can see the demo at http://jaimonblog.appspot.com/datascroller/simpleScroller.html
Solution 2: Scrolling with fixed headers using table cloning
You can see a working demo at http://jaimonblog.appspot.com/datascroller/fixedHeaderFullClone.html
Download fxheader1.js and include it in your project as explained on the implementation section
How does it work?
- First we put a scrollable div container around the table element as in our first solution.
- create a div element
- clone the table element using cloneNode(true)
- added the cloned table to this div
- replace the table element with this div
- Create a container on top of the table to place the headers.
- Attach scrollHeader function to the table container div’s onscroll event, so that we can align the heading when the table is scrolled horizontally.
- We then clone the table and place it in the header container. Container height is set, so that only the header row is visible.
- We then set a negative margin top on the original table to hide the actual header.
- Attach fxheader function to window onresize event, so it works when window get resized.
Solution 3: Scrolling with fixed headers using fast table cloning
You can see a working demo at http://jaimonblog.appspot.com/datascroller/fixedHeaderFastClone.html
Download fxheader2.js and include it in your project as explained on the implementation section to get started.
Solution 2 will give you very accurate column widths at the expense of doing a full table cloning. If you have a table with lots of rows, this can take a while. If your rows have elements with unique IDs, you will have to change it on the cloned node to avoid ID collision. Although it will work, it will lead to a sluggish user experience on pages with really large tables.
In solution 3, we are doing a fast clone without any child elements. Then we add the first row to it and set individual column width separately based on the offsetWidth property of each cell. You’ll have to offset cell margin/padding when setting the width. In our example, I deduct 3 from offsetWidth and that works fine for our table in all browsers I’ve tested.
Everything else is similar to solution 2.
Solution 4: Adding scrolling to table generated by ADF Faces 10g with fixed header (With and without pagination support) and automatic height stretching
Although in theory it is similar to solution 3, I had to make a few changes to make it work for a table generated by ADF Faces. The problem is ADF Faces creates three HTML tables for each af:table element. First and third tables are created for pagination support. It doesn’t create an ID for the actual data table itself, so we need to access it as a childNode of the container element. If pagination is there, we need to place this above our fixed header. Since we have the scrolling functionality, I thought the second pagination controls below the data table is not necessary, and I’m removing it from the page.
When cloning table data here, we have to update ID field of each element to avoid ID collision. We also have to set the correct selected index value for pagination selector combo box. Another functionality I’ve implemented here is the ability to auto stretch the table content to fit the page. You should pass in the ID of your last container component to make it work. Please see adjustHeight function in fxheader.js for more details.
As with the second and third solutions, you could add the following line to your JSPX page to get this working.
<afh:script source="fxheader.js" />
<afh:script text="fxheaderInit('testTable','footerContent');" partialTriggers="testTable" />
Where testTable is the ID of your af:table element and footerContent is the ID of your last container component for stretching. Partial Triggers are required here if used with pagination.
You can download a fully functioning JDeveloper project from http://jaimonblog.appspot.com/datascroller/ADF10gScroller.zip
Please note that it is created with JDeveloper version 10.1.3.3. If you are using 11g, then fixed header functionality is already part of it. (Although there are a few issues with it at the time of writing this. One such issue is discussed here http://forums.oracle.com/forums/message.jspa?messageID=4032492#4032492)
As I’m not able to provide a demo link, you can see some screen shots of this solution here,
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