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There are some cases where files need to be bundled with the JDK in order to expose functionality in the runtime JVM. For example, the inclusion of unlimited strength Java Cryptography Extensions (JCE) is often added to a JDK in order to utilize stronger cryptographic libraries. To handle such cases, Heroku will copy files designated by the app in a
.jdk-overlay folder into the JDK’s directory structure.
If you have questions about Java on Heroku, consider discussing them in the Java on Heroku forums.
To include additional files in the JVM, follow these instructions:
Specify a JDK Version
system.properties file if one does not already exist, specify the version, and commit it to git. Versions 1.6, 1.7, and 1.8 are supported.
$ echo "java.runtime.version=1.7" > system.properties $ git add system.properties $ git commit -m "JDK 7"
In your application’s root directory, create a
$ mkdir .jdk-overlay $ ls -la total 24 drwxr-xr-x 9 user staff 306 Oct 16 14:43 . drwxr-xr-x 202 user staff 6868 Oct 16 14:40 .. drwxr-xr-x 13 user staff 442 Oct 16 15:06 .git drwxr-xr-x 3 user staff 102 Oct 16 14:43 .jdk-overlay -rw-r--r-- 1 user staff 45 Oct 16 14:40 Procfile -rw-r--r-- 1 user staff 1860 Oct 16 14:40 pom.xml drwxr-xr-x 3 user staff 102 Oct 16 14:40 src -rw-r--r-- 1 user staff 25 Oct 16 14:40 system.properties
Add Custom Files
Copy any custom files into the
.jdk-overlay file. The files will be copied to their equivalent directory in the JDK. For example, to define a custom security policy, the
java.policy file could be placed in the
.jdk-overlay/jre/lib/security/ directory of your app’s repository.
Commit the Custom Files
$ git add .jdk-overlay $ git commit -m "Custom JDK Files"
Deploy to Heroku
$ git push heroku master ...
Verify the Copy
The copies can be verified by starting a bash session on Heroku and checking the JDK directory. The JDK directory is located in
For example, to verify Java Cryptography Extensions were copied correctly, the
$HOME/.jdk/jre/lib/security/ directory can be checked.
$ heroku run bash Running `bash` attached to terminal... up, run.1 ~ $ ls -lah .jdk/jre/lib/security/ total 196K drwxrwxr-x 2 u47919 47919 4.0K Jun 4 17:57 . drwxrwxr-x 11 u47919 47919 4.0K Jun 4 17:57 .. -rw-rw-r-- 1 u47919 47919 2.5K Oct 16 21:44 US_export_policy.jar -rw-r--r-- 1 u47919 47919 159K Jun 4 17:48 cacerts -rw-r--r-- 1 u47919 47919 2.2K Jun 4 17:48 java.policy -rw-r--r-- 1 u47919 47919 9.8K Jun 4 17:48 java.security -rw-rw-r-- 1 u47919 47919 2.5K Oct 16 21:44 local_policy.jar
This method can be used for Java extensions when necessary. Though a dependency management tool, such as Maven, should be the preferred mechanism for introducing dependencies.