User defined class available in CLASSPATH when starting H2 Database Server at command line

Question

I am starting the H2 Server Tool from Command Line as:

java -cp h2*.jar org.h2.tools.Server

And I am trying to use a user defined class like the Function one shown in the User-Defined Functions and Stored Procedures section.

I have made several attempts with my user function:

• compiling it to a Function.class file
• compiling it to a acme/Function.class file
• packaging it in a acme.jar file
• packaging it in a h2acme.jar file

And tried several ways of including it to the classpath, with no luck.
For example:

[user@host h2]$ java -cp ./h2*.jar:./acme.jar org.h2.tools.Server -tcp -web
Error: Could not find or load main class org.h2.tools.Server

I have read this related issue and followed the indications there.
But it does not seem to work.

Answer 1

The only way I was able to make this work is by updating h2*.jar file with my user defined class:

[user@host h2]$ jar uf h2-1.4.197.jar acme/Function.class 
[user@host h2]$ jar tvf h2-1.4.197.jar | grep acme
   421 Wed Sep 26 12:17:16 EEST 2018 acme/Function.class

And then from the H2 Shell:

[user@host h2]$ java -cp h2*.jar org.h2.tools.Shell -user sa -password sa -url jdbc:h2:tcp://localhost/~/mydb
Welcome to H2 Shell 1.4.197 (2018-03-18)
...
sql> CREATE ALIAS IS_PRIME FOR "acme.Function.isPrime";
(Update count: 0, 9 ms)
sql> CALL IS_PRIME(5);
PUBLIC.IS_PRIME(5)
TRUE
(1 row, 31 ms)

Though I did want to keep my user defined functions in a separated jar.
If anyone knows how to do it, it would be appreciated.

Answer 2

I got H2 server to use my Java & Kotlin functions in a user defined function. There are several steps that must be done correctly for it to work.

First, is to build the jar with your functions (I had both a Java and Kotlin functions). After several error messages from H2, when it tried to compile and run my functions, I realized that including my project's standard jar was not enough. I had to include all its dependencies. Luckily, Gradle and Maven can make this kind of fat jar. I used the maven-assembly-plugin to make mine.

Second, I told H2 where to find the H2 jar and my fat jar in my local Maven repo.

H2_JAR=/Users/me/.m2/repository/com/h2database/h2/1.4.200/h2-1.4.200.jar
MY_JAR=/Users/me/.m2/repository/my/foo/app/1.0-SNAPSHOT/myfooapp-1.0-SNAPSHOT-jar-with-dependencies.jar

java -cp "$H2_JAR:$MY_JAR" org.h2.tools.Server -tcpPort 27777 -tcp

FYI: If you want H2 to call a Kotlin function, then the Kotlin standard lib must be in the fat jar. (The maven-assembly-plugin will include it.). Also, your Kotlin function will need to be in a companion object . I also added the @JvmStatic annotation to that Kotlin function.