Custom datastore location on local machine with App Engine

Question

I'm developing App Engine application in Android Studio and testing it on my local machine (with local datastore). It's Java based app. Every time I re-run the server the local datastore is cleared. I've found several solutions for Python developers but it looks like there's no answer for Java.

Android Studio allows only to change:

• WAR Path
• VM Args
• Server Address
• Server Port

I've tried with VM args but these are for Java VM not for the app server obviously. Is there a way to persist local datastore across server restarts? It would be perfect If I could run this configuration directly from Android Studio.

Answer 1

The local datastore gets cleared because it is by default located in the application exploded war directory (which is deleted in its entirety on every build).

Instead of having to running the dev server manually from a terminal, you can actually just add a VM arg to the appengine run configuration to locate the datastore in another location:

-Ddatastore.backing_store="/path/to/datastore/file/location/local_db.bin"

(Solution found on: https://code.google.com/p/android/issues/detail?id=68225)

Answer 2

Like Arjan says, you can use -Ddatastore.backing_store.

If you use Android Studio 1.5, modify build.gradle. On appengine put the paramater jvmFlags. Example:

 appengine {
  downloadSdk = true
  appcfg {
    oauth2 = true
  }
  jvmFlags = ["-Ddatastore.backing_store=\"D:/temp/local_db.bin\""]
}

Answer 3

After several hours of searching I've finally found how to use user defined file as a local storage. Unfortunately it doesn't work directly from Android Studio, servers must be run from the terminal.

Here are arguments for Java's dev-appserver:

Usage: <dev-appserver> [options] <app directory>
Options:
 --help, -h                 Show this help message and exit.
 --sdk_root=DIR             Overrides where the SDK is located.
 --server=SERVER            The server to use to determine the latest
  -s SERVER                   SDK version.
 --address=ADDRESS          The address of the interface on the local machine
  -a ADDRESS                  to bind to (or 0.0.0.0 for all interfaces).
 --port=PORT                The port number to bind to on the local machine.
  -p PORT
 --disable_update_check     Disable the check for newer SDK versions.
 --generated_dir=DIR        Set the directory where generated files are created.
 --default_gcs_bucket=NAME  Set the default Google Cloud Storage bucket name.
 --jvm_flag=FLAG            Pass FLAG as a JVM argument. May be repeated to
                              supply multiple flags.

You have to change generated_dir argument. To run dev server directly from the terminal there's a very nice command:

/usr/lib/jvm/default-java/bin/java -javaagent:$HOME/.gradle/appengine-sdk/appengine-java-sdk-1.9.9/lib/agent/appengine-agent.jar -Xbootclasspath/p:$HOME/.gradle/appengine-sdk/appengine-java-sdk-1.9.9/lib/override/appengine-dev-jdk-overrides.jar -Didea.launcher.port=7533 -Didea.launcher.bin.path=/opt/android-studio/bin -Dfile.encoding=UTF-8 -classpath $HOME/.gradle/appengine-sdk/appengine-java-sdk-1.9.9/lib/appengine-tools-api.jar:/opt/android-studio/lib/idea_rt.jar com.intellij.rt.execution.application.AppMain com.google.appengine.tools.development.DevAppServerMain --address=0.0.0.0 --port=8080 --generated_dir=$HOME/sandbox/ $HOME/app/backend/build/exploded-app

I've changed the generated_dir argument to --generated_dir=$HOME/sandbox/

Please note you've to provide Android Studio path and App Engine SDK version. For my workstation it's /opt/android-studio and appengine-java-sdk-1.9.9 accordingly.