I am going to use Log4j in my web application and I am new to that. What is the uses of Log4j and how I use it in my application. Thanks in advance.
I think the Log4J home page offers the best overview and rationale behind its use.
With log4j it is possible to enable
logging at runtime without modifying
the application binary. The log4j
package is designed so that these
statements can remain in shipped code
without incurring a heavy performance
cost. Logging behavior can be
controlled by editing a configuration
file, without touching the application
binary.
Logging equips the developer with
detailed context for application
failures. On the other hand, testing
provides quality assurance and
confidence in the application. Logging
and testing should not be confused.
They are complementary. When logging
is wisely used, it can prove to be an
essential tool.
To add to this, with Log4J you can dynamically switch logging on/off. You can change the format dynamically (do you want timestamps ? datestamps ?) and you can change where the logging goes (to the console ? to a file ? to a database ?), all without changing your code.
At its most basic level, you can think of it as a replacement for System.out.println's in your code. Why is it better than System.out.println's? The reasons are numerous.
To begin with, System.out.println outputs to standard output, which typically is a console window. The output from Log4j can go to the console, but it can also go to an email server, a databaseW table, a log file, or various other destinations.
Another great benefit of Log4j is that different levels of logging can be set. The levels are hierarchical and are as follows: TRACE, DEBUG, INFO, WARN, ERROR, and FATAL. If you set a particular log level, messages will get logged for that level and all levels above it, and not for any log levels below that. As an example, if your log level is set to ERROR, you will log messages that are errors and fatals. If your log level is set to INFO, you will log messages that are infos, warns, errors, and fatals. Typically, when you develop on your local machine, it's good to set the log level to DEBUG, and when you deploy a web application, you should set the log level to INFO or higher so that you don't fill up your error logs with debug messages.
Log4j can do other great things. For instance, you can set levels for particular Java classes, so that if a particular class spits out lots of warnings, you can set the log level for that class to ERROR to suppress all the warning messages.
Read more...
The beauty of log4j is in its architecture of appenders and layouts. As mentioned by previous poster, you change the aspect of logging of your application without much hassle, most of the time it's just a matter of simple configuration. One of the usages I would add on my part is centralized logging which can be added to your application without touching its code base. For example - look at this.
Related
Currently I'm trying out ElasticSearch as a logging solution to pump out ETW events to.
I've followed this tutorial (https://learn.microsoft.com/en-us/azure/service-fabric/service-fabric-diagnostic-how-to-use-elasticsearch), and this is working great for my own custom ActorEventSource logs, but I haven't found a way to log the Actor Runtime events (ActorMethodStart, ActorMethodStop... etc) using the "in-process" trace capturing.
1) Is this possible using the in-process trace capturing?
I'm also considering using the "out-of-process" trace capturing, which to me seems like the preferable way of doing things in our situation, as we already have WAD setup which includes all of the Actor Runtime events already. Not to mention the potential performance impact / other side-effects of running the ElasticSearchListener inside of our Actor Services.
2) I'm not quite sure how to implement this.The https://github.com/Azure/azure-diagnostics-tools/tree/master/ES-MultiNode project doesn't seem to include Logstash, so i'm assuming I would need a template such as this one: https://github.com/Azure/azure-diagnostics-tools/tree/master/ELK-Semantic-Logging/ELK/AzureRM/elk-simple-on-ubuntu, otherwise I would need to modify the ES-MultiNode project to install Logstash as well? Just trying to get an idea if I'm going down the right path with regards to this.
If there's any other suggestions in terms of logging, I'd love to hear them!
There are two popular logging frameworks in NodeJS. One is winston and another one is Bunyan. There is another tool called debug.
As far as I understand, they are just doing the same thing which is logging something. debug is a default component of an Express app and it looks quite popular based on the number of downloads in NPM.
Can you suggest when to use debug and other logging framework? I am not asking to compare between different logging frameworks. I just wonder the position of debug.
debug is geared specifically toward interactive debugging. It logs human-readable plaintext and is designed to usually be disabled and then have interesting modules enabled periodically when a developer is actively debugging something. It is also fairly good in both node and browser environments. Its main use seems to be for re-usable libraries as opposed to applications.
winston, bunyan, and bole are geared toward newline-delimited JSON format which is mostly intended to be computer-readable. It's good for applications where your log data is gathered and stored in a central database for later analysis and searching and long-term trending.
So a quick rule of thumb might be debug for re-usable packages published to npm and one of the ndjson-format ones for applications where logs are stored long-term and analyzed later.
I'm trying to evaluate the reasons to use a logging system like Winston in node.js vs just writing my own logging method. It seems like logging libraries don't really offer much.
Some logging systems (like log4j) have logging hierarchies where if you log to a.b.c it logs to a.b and a as well (unless you have other complicated stop-propogation configurations). Is this kind of stuff usually overkill? What situation would you need that for?
I'm considering just writing a logging function that writes logs to a mongo database, which I'll then be able to pretty easily query and search through. Presumably a logging library can do that, but it seems like it would be just as much work to use a library for that as to write it from scratch.
So in short: what are the benefits to using a logging system?
I don't know about log4j, and not too much about Winston; haven't used it for more than 3 minutes.
But here are the few advantages I'd like to see in a logging system:
Error levels
I must be able to specify the log level I'd like to write to. It's good to have some defaults also (warning, error, debug, etc).
Streaming
You are able to do everything you want when something gets logged: Write it to a file, write it to the database, etc. It's up to you.
Customization
I'd like to be able to:
Timestamped messages
Colored messages when writing to process.stdout (super important while developing!)
Possibility of prefixing the message with the level (for files), or with anything else (when launching various loggers within the same process). This is useful for differentiating between various levels/logger instances that write to the same stream.
I am using log4net for logging calls to an API. Many calls. The methods I am calling have multiple megabytes of data for request/response pairs, and it is very hard to read logs that have multiple calls written to the same file, no matter what logging pattern I use. So, I feel the best approach is to log to multiple files.
I am having a hard time figuring out how to get log4net to do this, or if it even supports it.
From the Log4Net FAQ - Can the outputs of multiple client request go to different log files?
Many developers are confronted with the problem of distinguishing the log output originating from the same class but different client requests. They come up with ingenious mechanisms to fan out the log output to different files. In most cases, this is not the right approach.
It is simpler to use a context property or stack (ThreadContext) ... Thereafter, log output will automatically include the context data so that you can distinguish logs from different client requests even if they are output to the same file.
I looked at the documentation on Contexts and Context Properties. It seemed Event Context fit best, but I tried reading docs for other Contexts too. It seems they just allow me to put additional properties that end up in my log files, rather than being a component of a log file name, or allow me to automatically append to different files.
Is there a way to configure appenders to create different files for different context properties or context stack levels, etc?
Edit:
I am using log4net via Castle Windsor Logging facility, and I'm considering switching to NLog to solve this problem.
NLog seems to support this behavior by using the {logger} layout renderer in the File target's fileName property. I can effectively set this property by making a child logger with Windsor's ILogger.CreateChildLogger method, and setting {logger.shortName=True}.
See:
http://nlog-project.org/forum#nabble-td1685989
I'd still prefer to use log4net if possible, since the project I am testing uses it. Maybe my NLog example can give someone inspiration on how this could be done on log4net, and maybe they can help me figure it out :)
This article may be of interest to you: Log4Net: Programmatically specify multiple loggers (with multiple file appenders)
Also if you are only worried about readability there may be log file viewers that can seperate out log entries by thread name.
Another possibility you have is to log the entries in a database including your thread name and these entries are easily filtered using sql.
I'm wondering if anyone has any experience using log4net in a multi-threaded environment like asp.net. We are currently using log4net and I want to make sure we won't run into any issues.
We run log4net (and log4cxx) in highly multi-threaded environments without issue. You will want to be careful how you configure them though.
The issue with log4net that Jeff describes pertains to the use of a certain appender. We stick with simple log file appenders on the whole to reduce the impact of logging on the operation of the code. Writing a line to a file is pretty minimal, kicking off another database transaction is very heavy.