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Use java to set and get environment variable ?

Posted on 2002-06-21
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How do I use java to set and get environment variable ?
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Question by:j_script
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8 Comments
 

Expert Comment

by:javaXpert
ID: 7100325
Use JNI to call a native function that will handle the call to the host-specific API. On Win32, the two following functions are responsible for getting and setting environment variables:

DWORD GetEnvironmentVariable(
  LPCTSTR lpName,  // environment variable name
  LPTSTR lpBuffer, // buffer for variable value
  DWORD nSize      // size of buffer
);

BOOL SetEnvironmentVariable(
  LPCTSTR lpName,  // environment variable name
  LPCTSTR lpValue  // new value for variable
);

Please note that when using GetEnvironmentVariable, the length of the desired environment variable length is limited to the the size of the allocated buffer. It is always a good idea to enlarge the buffer if the allocated one does not suffice. More information about these functions can be found on MSDN.
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Author Comment

by:j_script
ID: 7100889
Can I use pure java to get/set the environment variable ?
I cannot use JNI.
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Expert Comment

by:javaXpert
ID: 7100915
No. Accessing and modifing environment variables cannot be done in Pure Java, though you can avoid using JNI. Anyway, why can't you use JNI?
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Accepted Solution

by:
fi76631 earned 400 total points
ID: 7101156
Reading an environment variable is relatively simple:

String envVar = System.getProperty("PROPERTY_NAME");

However, I am guessing that you are more interested in setting rather than getting.

In short, its not possible if you run on NT, it is possible on UNIX.

The reason that its not possible on NT is that each process runs in its own process space and has no access to the process space that created it.

Therefore, if you COULD set the environment variable only YOUR process would be able to see it. No other processes would be aware of it or its value.

If all you want to do is change it in the context of the currently running process, then you could use:

String cmd = "set myEnvVar=\"Hello World\"";
Runtime.getRuntime().exec(cmd);

If you explain 'why' you need to do this in more detail, maybe I can provide you with an alternative solution.
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LVL 92

Expert Comment

by:objects
ID: 7101185
You can get them by passing the value via the command line.
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LVL 1

Expert Comment

by:mraible
ID: 7103531
I set a "dateFormat" property in a StartupServlet in my web application with:

System.setProperty("dateFormat", "MM/dd/yyyy");

For simplicity - I've replaced my variables with the string values you see above.

This property is then available for all my servlets/classes used throughout the lifecycle of my web application using:

System.getProperty("dateFormat");

HTH,

Matt
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LVL 9

Expert Comment

by:doronb
ID: 7103553
Hi,


I suppose it might be silly of me to ask, but why not read/write these properties to a properties file which all your Servlets can access?


Doron :o
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LVL 5

Expert Comment

by:Netminder
ID: 8581058
Force-accepted.

Netminder
EE Admin
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