Add instruction to setup code in IntelliJ IDEA

CONTRIBUTING.adoc

@@ -21,7 +21,7 @@ https://eclipse.org/m2e/[M2Eclipse] eclipse plugin for maven support. Other IDEs
 should also work without issue.
 
 === Building from source
-To build the source you will need to install JDK 1.8.
+To build the source you will need to install JDK 11.
 
 ==== Default build
 The project can be built from the root directory using the standard maven command:
@@ -46,6 +46,106 @@ Once imported, you can apply eclipse settings by running:
 
 NOTE: You'll need to close the `spring-javaformat-formatter-eclipse` and `spring-javaformat-formatter-eclipse-runtime` projects following import since they contain rewritten packages that aren't supported by the IDE
 
+=== Importing into IntelliJ IDEA
+
+You can import the code as a maven project into IntelliJ IDEA.
+
+==== Module dependencies
+
+When IntelliJ IDEA parses `pom.xml`, it automatically creates inter-module dependencies if dependent libraries are coming from other modules within the project.
+However, when dependent modules perform repackaging (e.g. `spring-javaformat-formatter-eclipse-runtime` module), the current module cannot resolve all classes by module dependencies because repackaging(shade & binary manipulation) moves around classes.
+Therefore, you need to manually update the dependencies from the module to the produced jars.
+
+Following modules perform repackaging.
+
+* `spring-javaformat-formatter-eclipse`
+* `spring-javaformat-formatter-eclipse-runtime`
+
+Modules that depend on these modules need jar dependencies instead of module dependencies.
+
+===== Setting up jar dependencies
+
+The following steps define jar-based project libraries on IDE and add them to the modules that need jar dependencies.
+
+*Add a jar file-based project library*
+
+* "Project Settings" -> "Libraries"
+* Click "+" sign, then select "Java"
+* Specify the jar file +
+For example, you can specifie the jar file in the target directory(`<PROJECT>/spring-javaformat/spring-javaformat-formatter-eclipse-runtime/target/spring-javaformat-formatter-eclipse-runtime-0.0.28-SNAPSHOT.jar`)
+or one in the local maven repository(`~/.m2/repository/io/spring/javaformat/spring-javaformat-formatter-eclipse-runtime/0.0.28-SNAPSHOT/spring-javaformat-formatter-eclipse-runtime-0.0.28-SNAPSHOT.jar`).
+
+image::src/asciidoc/images/setup-idea-library.png[Setup IntelliJ IDEA library]
+
+*Add library dependencies to modules*
+
+* "Project Settings" -> "Modules"
+* Select a module that depends on repackaging modules
+* Click "+" sign and "2 Library"
+* "Choose Libraries" and select necessary libraries that have added in the previous step
+* Move up the added libraries higher than the module dependencies (or remove the module dependencies)
+
+image::src/asciidoc/images/setup-idea-dependency.png[Setup IntelliJ IDEA Dependencies]
+
+
+=== Setting up IntelliJ IDEA plugin development
+
+==== Download images
+
+To develop the `spring-javaformat-intellij-idea-plugin` module, you need an IntelliJ IDEA application on your local machine.
+
+* Open the `pom.xml` in `spring-javaformat-intellij-idea/spring-javaformat-intellij-idea-runtime`.
+* Check `intellij.binary` and `intellij.source` properties to find out the appropriate IntelliJ IDEA version.
+* Download the binary from the url in `intellij.binary`.  +
+(For OSX, replace the `.tar.gz` to `.dmg` to download the image file.)
+* Install the image to the local machine
+* Download the source files from github specified in `intellij.source` and unzip it.
+
+==== Setup SDK
+
+* Open "Project Structure" - "Platform Settings" - "SDKs"
+* Click "+" sign, "Add Intellij Platform Plugin SDK..."
+* Specify the installed intellij image.  (`/applications/IntelliJ IDEA CE` for OSX)
+* On the right panel, "Sourcepath", Click "+" sign, specify unzipped intellij source directory
+* Specify "Sandbox Home" directory
+
+image::src/asciidoc/images/setup-idea-plugin-sdk.png[Setup IntelliJ IDEA Plugin SDK]
+
+Please see the https://plugins.jetbrains.com/docs/intellij/setting-up-environment.html[IntelliJ IDEA reference] for how to setup a plugin development in details.
+
+==== Convert to Plugin Module
+
+The imported `spring-javaformat-intellij-idea-plugin` module is recognized as a java module.
+This needs to be converted to a plugin module.
+
+* Open `spring-javaformat-intellij-idea-plugin.iml` in `spring-javaformat-intellij-idea/spring-javaformat-intellij-idea-plugin`
+* Change `type="JAVA_MODULE"` to `type="PLUGIN_MODULE"`
++
+[indent=0,xml]
+----
+<module org.jetbrains.idea.maven.project.MavenProjectsManager.isMavenModule="true" type="PLUGIN_MODULE" version="4">
+----
++
+Reference https://stackoverflow.com/questions/18278440/how-to-import-and-run-existing-plugins-from-intellij-community-edition-repo[how to convert existing module to a plugin module]
+
+* Open "Project Structure" - "Modules"
+* Check `spring-javaformat-intellij-idea-plugin` icon turns to a plugin icon
+* "Plugin Deployment" - "Path to META-INF/plugin.xml"
+* Specify `<PROJECT>spring-javaformat/spring-javaformat-intellij-idea/spring-javaformat-intellij-idea-plugin/src/main/resources`
+
+image::src/asciidoc/images/setup-idea-plugin-module.png[Setup IntelliJ IDEA Plugin Module]
+
+
+=== Setting up Gradle plugin development
+
+`spring-javaformat-gradle-plugin` module is a gradle plugin and requires gradle related classes.
+
+To add gradle classes, convert this module to a gradle project.
+
+* On the project pain, right-click `build.gradle` in `spring-javaformat-gradle-plugin` module
+* Select "Import Gradle Project"
+
+
 === Importing into other IDEs
 Maven is well supported by most Java IDEs. Refer to your vendor documentation.
 

README.adoc

@@ -204,6 +204,13 @@ You can use the standard `code` -> `reformat code` action to format the code.
 To install the plugin use the `spring-javaformat-intellij-idea-plugin` jar file.
 You can download the latest version from https://repo.spring.io/release/io/spring/javaformat/spring-javaformat-intellij-idea-plugin/{release-version}[repo.spring.io].
 
+==== Enable the plugin
+The plugin is automatically enabled when one or more of the following conditions match:
+
+* `.springformat` file exists
+* For maven based project, `spring-javaformat-maven-plugin` plugin is defined in `pom.xml`
+* For gradle based project, `io.spring.javaformat` plugin is applied
+
 === About the conventions
 Most of the coding conventions and style comes from the Spring Framework and Spring Boot projects.
 Spring Framework manually formats code, where as Spring Boot uses automatic formatting.