Log4j pattern layout docs warns that generating caller class information is costly and should be used only when performance is not a concern. I want to have the class name in logs for easy analysis and also doesn't want to have an impact in performance. Having stated that I have two options,
Store class name using getClass().getName() in every class and use that string in logging
String class = getClass().getName();
...
...
logger.debug(class + "log message");
Hardcode the class name and give it in log
String class = "com.foo.myclass";
...
...
logger.debug(class + "log message");
Which would give better performance or is there any other way to log fully qualified class name and method name without affecting performance. Thanks in Advance!
Note: I am using log4j 1.2.16
Generating the caller class name is costly but if you're following the typical Log4J design pattern of one Logger per class with the Logger name being the same as the class name
private static final Logger LOG = Logger.getLogger(ThisClassName.class);
then it may be sufficient to simply use %c instead of %C in your layout pattern. This uses the logger name (which is a property of the logger itself) rather than inspecting the call stack, and does not involve the overhead incurred with patterns like %C or %L.
If you really do need the runtime class of the caller rather than the static name of the class that textually encloses a particular logging call, then you could use a per-instance logger rather than (or as well as) the per-class one
private final Logger instLog = Logger.getLogger(this.getClass());
and now the logger name will be the runtime type of this, i.e. if B extends A and we call a method on an instance of B then the logger name will be B, even for methods that are actually defined by the superclass A.
A usual pattern for loging with log4j is the following
public class Foo {
private static final Logger LOG = Logger.getLogger(Foo.class);
someMethod(){
...
if(LOG.isDebugEnabled()){
LOG.debug("log message");
}
}
}
The classname is the logger name so it will (by default) appears in the log message.
Most importantly regarding performance: there is a guard preventing the overhead of the computation of the log message when the log level is not enabled.
Related
I have seen log and logger as follows,
public static final Log logger = LogFactory.getLog(this.class)
logger.debug something
private final Log log = LogFactory.getLog(this.class)
log.debug(something)
Are there any difference between log and logger?
Note: They are both from apache.commons.
The fundamental difference is not in the names "log" and "logger" (they are different names for a variable of the same type and initialized in the same way, but in this:
public static final Log logger;
private final Log log;
Being "final", which both are, they cannot be modified once initialized. However, "private" means that the variable is only accessible within the class. "public" means that it is accessible to all classes that imported or are within the package. When an object is "static", like logger, there is one value for the entire program; when it is not, like log, it is instantiated with each instance of the object.
I understand that java.lang.SecurityManager is used to check and constrain class access or file access based on a specific scenario.
I need to identify the caller for Log4J Helper class which needs to return the Logger instance based on Class which calls the Helper class.
There are two ways to do this.
Using Threads
public static Logger getLogger() {
final Throwable thread = new Throwable();
final StackTraceElement callerMethod = thread .getStackTrace()[1];
final Logger logger = Logger.getLogger(callerMethod .getClassName());
return logger;
}
This is a performance bottleneck since it involves get the current stacktrace for each call to getLogger
Second Approach
Logging helper to extend java.lang.SecurityManager in which case i can use
getClassContext()[2].getName();
to get the absolute class name for instantiating the Logger.
The LoggingHelper extending the SecurityManager doesn't seem to be a good design principle considering its usage.
Would there any be any reason i can extend SecurityManager to a Logging Utility or is there a better approach?
Note : The application will be running in app server instance.
If you're using Java EE 6 you could use CDI to inject your logger.
public class LoggerProducer {
#Produces
public Log createLogger(final InjectionPoint injectionPoint) {
final String name = injectionPoint.getMember().getDeclaringClass().getName();
return Logger.getLogger(name);
}
}
I've extended the Log4J Logger class and created a custom Logger class that decides whether to to log or not.
My pattern layout has the %F and %M parameters to show the class name and method name from where the log was executed.
The problem is that instead of showing the exception caller class and method name it show my custom logger's class and method name!
What do I need to do to shows the correct information?
You need to provide your class as the fully qualified class name for the forcedLog() method.
private static final String FQCN = MyCustomLogger.class.getName();
...
public void info(Object message) {
if(repository.isDisabled(Level.INFO_INT))
return;
if(Level.INFO.isGreaterOrEqual(this.getEffectiveLevel()))
forcedLog(FQCN, Level.INFO, message, null);
}
....
I'm not sure what you're attempting to filter out, but it might be better to use a filter rather than extend the logger.
I have recently inherited some Java code and need to integrate it into a project that I am working on. My project is a service agent that processes and transforms XML messages. While looking through the new code, I discovered the following logging class:
import org.apache.log4j.BasicConfigurator;
import org.apache.log4j.Level;
import org.apache.log4j.Logger;
public class MyLogger {
private static MyLogger instance = null;
protected final static Logger log = Logger.getLogger(MyLogger.class);
private MyLogger() {
super();
}
public static MyLogger getInstance(){
if(instance == null){
instance = new MyLogger();
BasicConfigurator.configure();
log.setLevel(Level.ALL);
}
return instance;
}
public void info(String myclass, String msg) {
log.info("[" + myclass + "] " + msg);
}
public void error(String myclass, String msg, Exception ce) {
log.error("[" + myclass + "] " + msg, ce);
}
public void warning(String myclass, String msg) {
log.warn("[" + myclass + "] " + msg);
}
}
This class basically wraps log4j with (another) singleton. All of the logging in the classes that I need to integrate look something like this:
public class MyClass {
private final static MyLogger log = MyLogger.getInstance();
private final static String myclass = MyClass.class.getName();
...
log.info(myclass, "Information message...");
}
I do not see any obvious benefit to using an extra class for logging, thus I am considering refactoring this code to remove the MyLogger class and log in the following fashion:
import org.apache.log4j.Logger;
public class MyClass {
private static Logger log = Logger.getLogger(MyClass.class);
...
log.info("Information Message...");
}
This would make the logging mechanism consistent across the project. Before I do this, I would like to know if there are any benefits to wrapping Log4j with a singleton class that I may be missing. Thanks!
EDIT: Thanks everyone for the helpful answers - I pickup up several new insights from each. Accepted Nathan Hughes' answer for pointing out lost functionality by leaving the class intact - I had been assuming that the biggest downside to leaving the singleton alone was simply code bloat. I will trash the class.
Get rid of it. Using this monstrosity means all logging that goes through it will be listed with the same logger (MyLogger) and method (which is why the arguments to its methods include the class of the thing being logged). That means not only do you have to add any class, method, and line number information to each logger call, but you can't do any filtering on log levels for different packages the way you could using the typical log4j approach with classes as loggers.
This thing is a piece of junk and you are better off without it.
The only benefit that I could see is that it would be easy to swap out the log4j implementation with another logging implementation, or get the logging to do something much more customised such as log to one of your own databases.
That said, I would still refactor the code to use log4j directly. Or, more likely in my case, to use SLF4J.
One thing your inherited code does that log4j does is make thing non-thread safe. Since there is no locking in getInstance() you can potentially hand out more than one instance and break the singleton intentions of the code.
You also lose the ability to set logging levels for each class depending on what you are doing.
The only flaw I can tell is, because of this declaration:
protected final static Logger log = Logger.getLogger(MyLogger.class);
The logger is, essentially, hooked to object MyLogger and all logging information/errors/warnings, etc. will be "linked" to MyLogger. You have no idea which object added the logging information, none whatsoever.
The only advantage I see with this Singleton, is:
Single instantation: You never have to worry of declaring a static final Logger implementation all the time.
You don't have to worry what type of Logger you are using. One can change the type of Logger only in this Singleton class. Any further changes to logging is done only in the Singleton.
I have seen this in my company as well, but I don't suggest that type of setup. Rather use SLF4J or the Java Logging Framework.
I have a class in which I see the following things:
this.logger.severe("");
this.logger.warning("");
this.logger.info("");
I do not understand several things:
How can we use a method that was not defined earlier? I mean, there are no "logger" methods defined in the class. I thought that these methods could be defined because the considered class is an extension of another class in which the "logger" is defined. But in the definition of the class there no "extends" statement (only "implements").
I can understand things like that: "objectName.methodName". But what is that "objectName.something1.something2"? "something1.something2" is name of a method? Can method names contain dots?
What exactly these "logger.*" do? I think they save information about the execution of the code. They kind of write report about what happened during the execution. But where I can find this information?
ADDED:
In the beginning of the file I have: import java.util.logging.Logger;
And then in the class I have: private Logger logger = Logger.getLogger("a.b.c.d");
So, logger is an object of the class Logger (but I do not understand why they could not instantiate the class in a usual way using "new Logger()). I also do not understand what exactly logger.severe("") do.
The logger doesn't make anything special. It's all just Java code.
public class SomeClass {
private Logger logger = LogFactory.getLogger(SomeClass.class);
public void doSomething() {
this.logger.debug("foo");
}
}
The this.logger just points to the instance variable named logger of the current instance (this). The this. prefix is by the way superflous in this example. One could also just do logger.debug("foo") here.
If it is not declared in the SomeClass itself, then it's likely been declared in the extending class. Check the class which is declared in extends.
As to your objectName.something1.something2 doubt, have you already looked how System.out.println() works? The System.out returns a PrintStream object which in turn has a println() method. Thus, if objectName.something returns a fullworthy Object with methods, then you can just continue chaining method calls.
Basically,
objectName.something1.something2;
can be translated as
SomeObject someObject = objectName.something1;
someObject.something2;
But if you don't need someObject anywhere else in the code, then it can just be shortened as in your example.
Update: as per your update:
So, logger is an object of the class Logger (but I do not understand why they could not instantiate the class in a usual way using "new Logger()). I also do not understand what exactly logger.severe("") do.
Just read the javadoc of the class in question what it all does. As to why it can't be instantiated, it's because of the factory pattern.
Update 2: as per the another confusion:
I do not understand why they use "this". I mean, if I use just field name, will it not be, by default, the field of this object? I there any difference between "this.x" and "x"?
This way you can be more explicit about which one you'd like to access. If the method contains for example an argument or a local variable with the name logger, then this.logger would still refer to the instance variable.
public class SomeClass {
private Logger logger = LogFactory.getLogger(SomeClass.class);
public void doSomething(Logger logger) {
this.logger.debug("foo"); // Refers to the instance variable.
logger.debug("foo"); // Refers to the method argument.
}
public void doSomethingElse() {
Logger logger = LogFactory.getLogger(SomeClass.class);
this.logger.debug("foo"); // Refers to the instance variable.
logger.debug("foo"); // Refers to the method local variable.
}
}
The logger usually refers to the usage of a class in log4j.
The logger is a member object whose function e.g. severe is called.
The logger usually logs into a file (this can be configured through log4j.xml or some other config file or during the program start).
Edit: Changed the log4j link.
The 'logger' will be another object, not a method. This logger class will have methods defined on it like public void severe(String message)
'something1' will be an object contained by 'objectName'. For example, Car.Engine.Cylinder.Fire(), it's considered bad practise to use a method to fire a car's cylinders like this, and you should do something more like Car.StartEngine() (see the law of demeter for more info)
The logger will keep a record of what's happened in your program, so if there's a crash or a bug later on, you can see what happened. Whether this is recorded to a text file, or to a database somewhere, will be down to the implementation of your logger.
logger is not a method but a class variable which seems to be an object that exposes the methods "severe", "warning" and "info".
Check your class for something like "someClass logger = new someClass();"
The java.util.Logger class is the main access point to the Java logging API. Here is how you create a logger:
Logger logger = Logger.getLogger("myLogger");
The string passed as parameter to the getLogger() factory method is the name of the Logger to create. You can choose the name freely, but the name implies where the Logger is located in the Logger hierarchy. Every . (dot) in the name is interpreted as a branch in the hierarchy.