Environment variable to control java io tmpdir

Question

I ve used the TMP environment variable to control things like where gcc writes it s temporary files  but I can t seem to find an equivalent for java s createTempFile API   Does such an environment variable exist

User · Answer

Use       java -XshowSettings Property settings      java home    home nisar javadev javasuncom jdk1 7 0 17 jre     java io tmpdir    tmp

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According to the java io File Java Docs     The default temporary-file directory is specified by the system property java io tmpdir  On UNIX systems the default value of this property is typically   tmp  or   var tmp   on Microsoft Windows systems it is typically  c  temp   A different value may be given to this system property when the Java virtual machine is invoked  but programmatic changes to this property are not guaranteed to have any effect upon the the temporary directory used by this method    To specify the java io tmpdir System property  you can invoke the JVM as follows   java -Djava io tmpdir  path to tmpdir   By default this value should come from the TMP environment variable on Windows systems

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we can change the default tomcat file upload location  as we have to set the environment variable like   CATALINA TEMPDIR   YOUR FILE UPLOAD LOCATION  this location will change the path here  java -Djava io tmpdir  path to tmpdir

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You could set your  JAVA OPTIONS environmental variable  For example in bash this would do the trick     export  JAVA OPTIONS -Djava io tmpdir  new tmp dir   I put that into my bash login script and it seems to do the trick

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Hmmm -- since this is handled by the JVM  I delved into the OpenJDK VM source code a little bit  thinking that maybe what s done by OpenJDK mimics what s done by Java 6 and prior   It isn t reassuring that there s a way to do this other than on Windows   On Windows  OpenJDK s get temp directory   function makes a Win32 API call to GetTempPath    this is how on Windows  Java reflects the value of the TMP environment variable   On Linux and Solaris  the same get temp directory   functions return a static value of  tmp    I don t know if the actual JDK6 follows these exact conventions  but by the behavior on each of the listed platforms  it seems like they do

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To be clear about what is going on here    The recommended way to set the temporary directory location is to set the System property called  java io tmpdir   e g  by giving the option -Djava io tmpdir  mytempdir to the java command   The property can also be changed from within a program by calling System setProperty  java io tmpdir     mytempdir      modulo sandbox security issues  If you don t explicitly set the  java io tmpdir  property on startup  the JVM initializes it to a platform specific default value   For Windows  the default is obtained by a call to a Win32 API method   For Linux   Solaris the default is apparently hard-wired   For other JVMs it could be something else    Empirically  the  TMP  environment variable works on Windows  with current JVMs   but not on other platforms   If you care about portability you should explicitly set the system property

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Use below command on UNIX terminal     java -XshowSettings   This will display all java properties and system settings  In this look for java io tmpdir value

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It isn t an environment variable  but still gives you control over the temp dir     -Djava io tmpdir   ex    java -Djava io tmpdir  mytempdir

User · Answer

If you look in the source code of the JDK  you can see that for unix systems the property is read at compile time from the paths h or hard coded  For windows the function GetTempPathW from win32 returns the tmpdir name  For posix systems you might expect the standard TMPDIR to work  but that is not the case  You can confirm that TMPDIR is not used by running TMPDIR  mytmp java -XshowSettings

[java] Environment variable to control java.io.tmpdir?

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