If "java -jar" is run from a command line,
is there a way to set local dos variable from java program so that
after java is exited, it can still be present in the same session?
example
(cmd)
c:\java package.Class
/*then in program you do something like
'System.setVariable("name","value");'
*/
// java exited
echo %name%
value
No. Processes cannot modify their parents' environment.
The best thing you can do is cheat a little and do either of the following:
Let the Java program write out a batch file in some known location and call it afterwards to set variables. Since batch files run in the current cmd process they can alter environment variables there.
Let the program output name/value pairs or complete set commands, catch the output and set the variables yourself afterwards. Goes wrong as soon as you want or have other output, I guess.
It's possible to set environment variables, according to question 2121795. However, I've never tried these methods so can't verify if they work.
If they do work, remember that setting an environment variable will not take effect in the current session (you'd need to restart the cmd window).
Also interesting is this question which has answers explaining how to use the Preferences API to modify the registry. I guess you should be able to modify environment variables via this route (didn't check thorougly).
Related
Summary: Id like to alter the way .hprofs are named when automatically created to incorporate machine's hostname + process PID
Long version: According to documentation (https://docs.oracle.com/javase/8/docs/technotes/guides/troubleshoot/clopts001.html) you can pass an option to the VM to create heapdumps under certain conditions (HeapDumpOnOutOfMemoryError), and can further customize this behavior by specifying a different path for the resulting .hprof file. You can change the name/path. What I would like to know is if its possible to make this option (HeapDumpPath) incorporate the hostname+PID to have uniquely named .hprofs (to be saved in a centralized location, but thats another scope). Could it be done? Can HeapDumpPath accept a parameter to get the hostname?
It doesn't look like there are options to inject values into the path. Depending on your shell you should be able to at least insert the hostname. The PID may not be possible since it is created after the process starts. You may be able to use a different variable like the application name though. In bash it would look something like this:
java -XX:+HeapDumpOnOutOfMemoryError -mn256m -mx512m ConsumeHeap -XX:HeapDumpPath=/disk2/dumps/$(hostname)/${APPLICATION_NAME}
Managed to do it just by using the Windows Environment Variable COMPUTERNAME in the wrapper.conf file for that particular Java VM. The full line is:
wrapper.java.additional.32=-XX:HeapDumpPath=./%COMPUTERNAME%.hprof
I have a console program written in Java that should respond to single key presses, but the user does not press enter.
I'm making pong.. so need the up and down keys to move the bat thing.
Alternative approaches welcome! (apart from making a GUI instead)
-- Edit:
I'm only going to run my program on UNIX systems (OSX and Linux), so I think I can put the terminal into "raw" mode with this: stty raw
When I type that into the console before running the program it works! But I need Java to do it automatically, so I tried this:
Runtime.getRuntime().exec("stty raw");
and it does nothing... probably because the JVM is just running it as a separate process and not as a process within this terminal.
I think you can't without native code and JNI. Take a look at Java Curses library:
http://sourceforge.net/projects/javacurses/
I want to hide arguments (password paraphrase) from a running java process (can be seen from command line).
For example, when i type jps -m on cmd, it shows me all the java processes along with their arguments:
Output after running jps -m: 6120 someproject.jar -password
where 6210 is pid.
I need that password to run java process. The problem is if my machine is compromised, someone could read password and can do further damage.
One solution could be storing password in a file locally. But still someone can get it if machine is compromised.
Any ideas how i proceed ?
Thanks in advance.
update1: The password is hashed but still i want it to hide.
The way you would handle this in (for example) a C program would be to write over the argument list supplied to the main(...) entry point method. For more information read this:
https://unix.stackexchange.com/questions/8223/can-other-users-view-the-arguments-passed-to-a-command
Unfortunately, the "overwrite" approach is not available to a Java application. From pure Java, it is simply not possible. Even with native code library, it would be difficult to find where in memory the (native) argument vector is stored.
(And besides, there is a small time window in which the arguments are exposed ... before the application erases them.)
So your best bet is to pass the secret information another way. For example, pass the secret info via an environment variable, via a temporary file with access restrictions, or via standard input.
I have a simple java program which is just a single piece of code that reads from a database and modifies the contents of the database based on certain conditions. Now, what I want is that this program should start automatically at the startup and silently run in the background unless someone kills it from the task manager.
I have never done something like this before and don't know exactly how to go about it. Can someone help me out as to how this can be done?
Thank you..
Follow the these steps to do the job :(Assuming you are using windows and jre is installed )
First compile your java program and place the class file at one location.
Now create a bat file and place java LOCATION TO THAT CLASS FILE/MyProgram in that.
Put your bat file in start up programs
Restart the system, you will get your program running in back ground..!
Hope this will help you.
There are two problems here
How to add this program to the startup
Windows - Run Java application at Windows startup
Linux - Linux start-up script for java application
Run the program as a daemon (background process)
Simplest way to do is using a while loop and sleep for required time interval in the while loop. Then perform the database
operation.
Also for windows, you can check this JSL
http://www.roeschter.com/
Thanks.
first create you jar bash and then add it to you crontab task list.
I am in the process of writing a cross platform Swing based application in which I want to utilize a file association which has been registered with the OS.
So iv got to the point where I can click on a file and my app loads, but what I need to know is how I can get my application to know where the file is that launched it and then query the contents.
Is there something further I have to do with the file association registration? Or can Java do this for me?
I'm not positive, but I'd expect that the name of the file you're processing by file click will end up in the arguments to your main() method. Have you tried/checked that?
If this is on Windows (you didn't specify):
In the registry wherever you specified your application path for the file type registered to it, add to "%1". This is a special parameter Windows will fill in with the path of the file that was clicked. So your registry entry would look something like c:\path\to\app.exe "%1"
One way to do this is to have the file association run your Java app via a script or batch file, and have the batch file pass the pathname of the file as a command line argument, environment variable or Java property.
Extensions can be linked to applications, you can setup the registry keys during installation. Which keys you need is documented here:
http://support.microsoft.com/?scid=kb%3Ben-us%3B185453&x=6&y=11
From java you can't access the windows registry in a direct way.
Using Runtime you could do something like that
http://www.rgagnon.com/javadetails/java-0480.html
There're two commands on Windows that can help, assoc and ftype, so that you needn't do the dirty laundry to manipulate registry. Invoke the commands using, say, java.lang.Process. http://www.rgagnon.com/javadetails/java-0592.html