how can I debug a jar at runtime

Question

I m into a quite strange position  from my java-newbie point of view     using Eclipse I wrote a  java program   some  java files with classes into  which essentially  batch  reads a text   csv file   evaluates  its contents  and writes out results into an   out csv text file  To locate the input file it uses a  file chooser   got sample from here  http   docs oracle com javase tutorial uiswing components filechooser html  I debugged all the code and  using the debugger  it works  I ran the code  the main class  which calls all the other in sequence  and it works  while in Eclipse  I exported all the project s contents into a  runnable jar  file    Notice that  file chooser apart  this is mainly a  batch  which reads and writes  nearly no User Interface at all  While into Eclipse I shown some internal results using something like  if debug  System out print  something to print     providing to set  debug  TRUE while debugging and FALSE while in production environment   ALL of the above worked   Now  starting the runnable jar  double-click on the jar file  in Win XP   I can see the file chooser and I can use it but  after choosing the input file    nothing more   having no user interface  I don t know if the file was read  I don t see any generated output file  and I ve even no  console  to list any intermediate debug message  to see if the jar is working  even if I re-export it with the debug variable set to TRUE   Is there a way to  runtime debug  the running jar  like VB s MsgBox  or something other   some kind of  log file  I can  enable  or look into   obviously  as my jar is not writing the result file  I just can t try writing a   log too   I have also to say I just can t install other than Eclipse on my machine  and just been lucky it ran   so no usual developer s tools  utilities and other useful things

User · Answer

You can activate JVM s debugging capability when starting up the java command with a special option   java -agentlib jdwp transport dt socket address 8000 server y suspend y -jar path to some war or jar jar   Starting up jar jar like that on the command line will    put this JVM instance in the role of a server  server y  listening on port 8000  address 8000  write Listening for transport dt socket at address  8000 to stdout and then pause the application  suspend y  until some debugger connects  The debugger acts as the client in this scenario    Common options for selecting a debugger are    Eclipse Debugger  Under Run -  Debug Configurations    -  select Remote Java Application -  click the New launch configuration button  Provide an arbitrary Name for this debug configuration  Connection Type  Standard  Socket Attach  and as Connection Properties the entries Host  localhost  Port  8000  Apply the Changes and click Debug  At the moment the Eclipse Debugger has successfully connected to the JVM  jar jar should begin executing  jdb command-line tool  Start it up with jdb -connect com sun jdi SocketAttach port 8000

User · Answer

Even though it is a runnable jar  you can still run it from a console -- open a terminal window  navigate to the directory containing the jar  and enter  java -jar yourJar jar    It will run in that terminal window  and sysout and syserr output will appear there  including stack traces from uncaught exceptions   Be sure to have your debug set to true when you compile   And good luck     Just thought of something else -- if you re on Win7  it often has permission problems with user applications writing files to specific directories   Make sure the directory to which you are writing your output file is one for which you have permissions   In a future project  if it s big enough  you can use one of the standard logging facilities for  debug  output  then it will be easy ier  to redirect it to a file instead of depending on having a console   But for a smaller job like this  this should be fine

User · Answer

With IntelliJ IDEA you can create a Jar Application runtime configuration  select the JAR  the sources  the JRE to run the Jar with and start debugging  Here is the documentation

User · Answer

http   www eclipsezone com eclipse forums t53459 html  Basically run it with   -Xdebug -Xrunjdwp transport dt socket server y suspend y address 1044   The application  at launch  will wait until you connect from another source

[java] how can I debug a jar at runtime?

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