Sunday, April 12, 2009

User home dirs ("user.dir") on the Google App Engine/J

A Java application running on the Google App Engine is only allowed to read files stored inside the user's home dir. The path to this directory is stored in the read-only system property "user.dir" (System.getProperties().get("user.dir")).

Trying to read files outside of your home dir will raise the following exception: access denied ( ... read)
The path of the "user.dir" on Google App Engine/J follows the following structure:
The version-id appears to be a version identifier followed by a dot (".") and then an 18 digit random number.

A new home directory is created each time you deploy your app using " update".

Combining the fact that you're allowed to read your own home dir with the fact that a new deployment gives rise to a new home dir gives you the following method to get the exact date and time of your last deployment:
Date deployTime = new Date(new File((String) System.getProperties().get("user.dir")).lastModified());


  1. Hello,
    Is that mean that the only solution to save textual data is the JDO Or JPA of google app engine??

  2. Yours posted perspective user home dirs ("user.dir") on the Google App Engine/J which give users a lot of knowledge.
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