Add example of creating interop between Realm Kotlin and a Java project.

.github/workflows/android.yml

@@ -19,6 +19,15 @@ jobs:
         java-version: '17'
         distribution: 'adopt'
 
+    - name: Building Java-Kotlin-Maven Interop Sample
+      working-directory: ./JavaKotlinMavenInterop
+      run: |
+        chmod +x gradlew
+        ./gradlew :kotlin-lib:publishToMavenLocal
+        ./gradlew :java-app-gradle:run
+        cd java-app-maven
+        mvn compile exec:java
+
     - name: JVM Console
       working-directory: ./JVMConsole
       run: |
@@ -54,3 +63,4 @@ jobs:
       run: |
         chmod +x gradlew
         ./gradlew assemble  
+

.gitignore

@@ -1,4 +1,3 @@
-
 # Created by https://www.gitignore.io/api/c,git,c++,java,cmake,xcode,kotlin,android,intellij,visualstudiocode
 # Edit at https://www.gitignore.io/?templates=c,git,c++,java,cmake,xcode,kotlin,android,intellij,visualstudiocode
 
@@ -257,7 +256,6 @@ fabric.properties
 .mtj.tmp/
 
 # Package Files #
-*.jar
 *.war
 *.nar
 *.ear
@@ -327,3 +325,6 @@ DerivedData/
 **/xcshareddata/WorkspaceSettings.xcsettings
 
 # End of https://www.gitignore.io/api/c,git,c++,java,cmake,xcode,kotlin,android,intellij,visualstudiocode
+
+# Custom 
+JavaKotlinMavenInterop/java-app-maven/target

JavaKotlinMavenInterop/README.md

@@ -0,0 +1,97 @@
+# Java-Kotlin-Maven Interop Sample
+
+This sample shows how a Java project using either Gradle or Maven can use Realm Kotlin.
+
+This can be a problem for multiple reasons:
+
+- The main app is written in Java and do not want to introduce Kotlin code directly into 
+  that codebase.
+
+- The main app is using Maven as a build system, which is incompatible with Kotlin 
+  Multiplatform as it only supports Gradle.
+
+In order to work around this we introduce a seperate Gradle Module containing the Realm code,
+and then that module will expose an interface that is consumable from Java. This module will
+then be publish to either MavenLocal or some other Nexus as this will allow the Java app to
+find it regardless of it using Gradle or Maven.
+
+In this sample project we call the abstraction `RealmRepository` which expose a CRUD like 
+interface, but it should be modified to fit the context of the project.
+
+
+## Requirements
+
+- JDK 11
+- The project can be opened in IntelliJ, which will support both Gradle and Maven in the same project, making it possible
+  to edit all modules from there.
+
+## How to Run
+
+1. Deploy the Kotlin library to Maven Local using:
+
+   ```
+   >./gradlew :kotlin-lib:publishToMavenLocal
+
+   ```
+
+2. Run the Java App using Gradle:
+
+   ```
+   >./gradlew :java-app-gradle:run
+
+   ```
+
+3. Run the Java App using Maven:
+
+   ```
+   > cd java-app-maven
+   > mvn compile exec:java
+
+   ```
+
+
+## Publish The Kotlin library
+
+The Kotlin library contains a skeleton setup for deploying both to MavenLocal as well as a custom Nexus. You deply to 
+each by using:
+
+```shell
+# Publish to Maven Local
+> ./gradlew :kotlin-lib:publishToMavenLocal
+
+# Publish to a custom nexus
+> ./gradlew :kotlin-lib:publishAllPublicationsToCustomNexusRepository
+```
+
+Note, you need to setup credentials and URLs for the custom nexus inside the the [build.gradle.kts](kotlin-lib/build.gradkle.kts) file.
+The artifacts are not signed, and this will need to be added if required by the Nexus. 
+
+
+## Consume from Maven
+
+Once deployed, the Kotlin library can be consumed like any other Maven artifact:
+
+```xml
+<project>
+	<!-- ... -->
+    <dependencies>
+        <dependency>
+            <groupId>com.mongodb.devicesync</groupId>
+            <artifactId>kotlin-lib</artifactId>
+            <version>1.0-SNAPSHOT</version>
+        </dependency>
+    </dependencies>
+	<!-- ... -->
+</project>
+```
+
+or Gradle:
+
+```gradle
+dependencies {
+    implementation("com.mongodb.devicesync:kotlin-lib:1.0-SNAPSHOT")
+}
+```
+
+
+

JavaKotlinMavenInterop/build.gradle.kts

@@ -0,0 +1,5 @@
+plugins {
+    kotlin("jvm") version "1.9.21" apply false
+    id("io.realm.kotlin") version "1.13.0" apply false
+}
+rootProject.extra["realmVersion"] = "1.13.0"

JavaKotlinMavenInterop/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,5 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.5-all.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

JavaKotlinMavenInterop/gradlew

@@ -0,0 +1,240 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/master/subprojects/plugins/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+APP_HOME=$( cd "${APP_HOME:-./}" && pwd -P ) || exit
+
+APP_NAME="Gradle"
+APP_BASE_NAME=${0##*/}
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+# Collect all arguments for the java command;
+#   * $DEFAULT_JVM_OPTS, $JAVA_OPTS, and $GRADLE_OPTS can contain fragments of
+#     shell script including quotes and variable substitutions, so put them in
+#     double quotes to make sure that they get re-expanded; and
+#   * put everything else in single quotes, so that it's not re-expanded.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        org.gradle.wrapper.GradleWrapperMain \
+        "$@"
+
+# Stop when "xargs" is not available.
+if ! command -v xargs >/dev/null 2>&1
+then
+    die "xargs is not available"
+fi
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"