Often, it can be very helpful to
look at edtFTPj/Free's extensive logging output if any
problems are experienced communicating with FTP servers. edtFTPj/Free
has a powerful logging API modelled on the popular log4j library
– in fact full integration with log4j is supported.
All commands sent to the FTP server
and subsequent replies are logged, and can be made
available on the console or directed to a log file. Much other useful
information is also logged.
Statements within edtFTPj/Free are
logged at different levels, ranging from least verbose (FATAL), to most
verbose (DEBUG). Intermediate levels are ERROR, WARN,and
INFO. An overall level can be set for the library, and all statements up to and
including that level will be outputted.
For example, if the overall level
is set to INFO
then FATAL,ERROR,WARNand INFOlog statements will be outputted, but DEBUG
will not be.
There are also two additional
levels that can be conveniently used - OFF which means no
logging will occur, and ALL which means all log statements will be
outputted, no matter what
level they are. TheALL
level is actually an additional level which is used for extremely
output - so when the level is set to ALL more log statements may be
outputted than at DEBUG.
Logging levels are encapsulated in the Level
class. For example, the WARN level is represented by
By default, the log level is
switched to OFF, so that no logging will appear.
The log level can be changed in two ways. Firstly, it can be changed
explicitly by calling the setLevel
method on the Logger
class. For example:
Using edtFTPj/Free's logging in your
own application is very similar to using log4j. A logger is created,
and its methods used to write logging information. Rather than use the
Level class, the Logger class has convenience methods for logging at
each level. An example is shown below:
Logger log =
log.info("Connecting to server " +
to a file
As noted, all logging by default
goes to standard output. A FileAppender
must be added if logging is to go to a file (and this will disable
logging to standard out). An example is shown below:
Now all logging output will go to
the FileAppender's file, and no logging will go to standard output.
Multiple FileAppenders can be added. If the StandardOutputAppender
is added to the Logger as well, logging will be directed to the file
and to standard output.
Full integration with log4j is possible. A System property, edtftp.log.log4j,
is used to indicate that log4j integration should be attempted. It must
be set to “true”. Also, the log4j jar file must be
available in the CLASSPATH. Once this is done all logging calls are
directed via log4j, using reflection, and the standard log4j settings are used. More details on
log4j can be found at the log4j site listed in the references.