http://blog.csdn.net/hgd250/article/details/3614976

下面是在log4j官方的API中寫的，足以能解釋logger與category的區別。。。

public class Categoryextends java.lang.Objectimplements AppenderAttachable

This class has been deprecated and replaced by theLogger subclass. It will be kept around to preserve backward compatibility until mid 2003.

Logger is a subclass of Category, i.e. it extends Category. In other words, a loggeris a category. Thus, all operations that can be performed on a category can be performed on a logger. Internally, whenever log4j is asked to produce a Category object, it will instead produce a Logger object. Log4j 1.2 willnever produce Category objects but only Logger instances. In order to preserve backward compatibility, methods that previously accepted category objects still continue to accept category objects.

For example, the following are all legal and will work as expected.

???// Deprecated form:Category cat = Category.getInstance("foo.bar")// Preferred form for retrieving loggers:Logger logger = Logger.getLogger("foo.bar")

The first form is deprecated and should be avoided.

There is absolutely no need for new client code to use or refer to theCategory class. Whenever possible, please avoid referring to it or using it.

See the short manual for an introduction on this class.

See the document entitled preparing for log4j 1.3 for a more detailed discussion.

Author:

Ceki Gülcü, Anders Kristensen

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http://topic.csdn.net/u/20070421/11/ce65977d-a698-4d65-a229-6ac44f26a40d.html

配置根Logger，其語法為：0

　　log4j.rootLogger ? = ? [ ? level ? ] ? , ? appenderName, ? appenderName, ? …

　　其中，level ? 是日志記錄的優先級，分為OFF、FATAL、ERROR、WARN、INFO、DEBUG、ALL或者自定義的級別。Log4j建議只使用四個級別，優先級從高到低分別是ERROR、WARN、INFO、DEBUG。通過在這里定義的級別，您可以控制到應用程序中相應級別的日志信息的開關。比如在這里定義了INFO級別，則應用程序中所有DEBUG級別的日志信息將不被打印出來。 ? appenderName就是指定日志信息輸出到哪個地方?？赏瑫r指定多個輸出目的地。
log4j.rootCategory=DEBUG, ? stdout，R

就是說我要顯示所有優先權等於和高于Debug的信息。
在log4j.properties文件里把 "log4j.rootCategory=DEBUG,stdout,R "改寫成 "log4j.rootCategory=OFF, ? stdout,R "，這樣所有的log信息都不會顯示了；解決了本文開始提出的問題。
在log4j.properties文件里把 "log4j.rootCategory=DEBUG,stdout,R "改寫成 "log4j.rootCategory=INFO, ? stdout,R "，這樣只顯示INFO, ? WARN, ? ERROR的log信息，而DEBUG信息不會被顯示；

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