Java Reference
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test message #1
opening file x.txt
writing test message #2 to file x.txt
closing file x.txt
cannot connect to file-based logger
What happens when logging is moved to another location? For example, move
logging totherootdirectoryandrun TestLogger .YouwillNowobserveanerror
messageabouttheJVMnotfindingthe logging packageandits LoggerFactory
You can solve this problem by specifying -classpath when running the java
tool, or by adding the location of the logging package to the CLASSPATH envir-
onment variable. You'll probably find it more convenient to use the former option, as
demonstrated in the following Windows-specific command line:
java -classpath \;. TestLogger
ward slash as an alternative.) Also, the period represents the current directory. If it is
missing, the JVM complains about not finding the TestLogger classfile.
Tip IfyoudiscoveranerrormessagewheretheJVMreportsthatitcannotfindan
application classfile, try appending a period character to the classpath. Doing so will
probably fix the problem.
Packages and JAR Files
Chapter 1 briefly introduced you to the JDK's jar tool, which is used to archive
classfiles in JAR files, and is also used to extract a JAR file's classfiles. It probably
comes as no surprise that you can store packages in JAR files, which greatly simplify
the distribution of your package-based class libraries.
ToshowyouhoweasyitistostoreapackageinaJARfile,wewillcreatea log-
ger.jar filethatcontainsthe logging package'sfourclassfiles( Logger.class ,
LoggerFactory.class , Console.class , and File.class ). Complete the
following steps to accomplish this task:
1. Makesurethatthecurrentdirectorycontainsthepreviouslycreated logging
directory with its four classfiles.
2. Execute jar cf logger.jar logging\*.class .Youcouldalternat-
ivelyexecute jar cf logger.jar logging/*.class .(The c option
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