intellij-sdk-code-samples/topics/basics/project_structure.md
2023-03-29 11:57:31 +02:00

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<!-- Copyright 2000-2023 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license. -->
# Project Structure
<link-summary>Introduction to project structure and components.</link-summary>
[//]: # (TODO: split into parts accordingly to the table of contents)
This topic considers the concept of projects based on the IntelliJ Platform and related subjects, such as _modules_, _facets_, _libraries_, and _SDK_.
The project structure and Java classes available to manage projects and modules are discussed.
> Internal changes related to a significant redesign of the representation of project models are included in 2020.3 release; please see [blog post](https://blog.jetbrains.com/platform/2020/10/new-implementation-of-project-model-interfaces-in-2020-3/) for details.
> This shouldn't affect any plugins using the IntelliJ API properly and which don't access internal classes.
>
{style="note"}
## Project and Its Components
This section briefly discusses the IDEA project structure, project components, and related terms.
For more information about projects and their components, refer to [Project](https://www.jetbrains.com/help/idea/about-projects.html), [Module](https://www.jetbrains.com/help/idea/creating-and-managing-modules.html), [Library](https://www.jetbrains.com/help/idea/working-with-libraries.html), [Facet](https://www.jetbrains.com/help/idea/adding-support-for-frameworks-and-technologies.html#facets) in the IntelliJ IDEA Web Help.
Use [`ProjectSettingsService`](%gh-ic%/platform/lang-impl/src/com/intellij/openapi/roots/ui/configuration/ProjectSettingsService.java) to open related entries in <control>Project Structure</control> dialog.
### Project
In the IntelliJ Platform, a _project_ encapsulates all of a project's source code, libraries, and build instructions into a single organizational unit.
Everything done using the IntelliJ Platform SDK is done within the context of a project.
A project defines collections referred to as _modules_ and _libraries_.
Depending on the project's logical and functional requirements, you can create a _single-module_ or a _multi-module_ project.
### Module
A _module_ is a discrete unit of functionality that can be run, tested, and debugged independently.
Modules include such things as source code, build scripts, unit tests, deployment descriptors, etc.
In a project, each module can use a specific SDK or inherit the SDK defined at the project level (see the [SDK](#sdk) section below in this document).
A module can depend on other modules of the project.
### Library
A _library_ is an archive of compiled code (such as JAR files) on which modules depend.
The IntelliJ Platform supports three types of libraries:
* **Module Library**: the library classes are visible only in this module, and the library information is recorded in the module's <path>.iml</path> file.
* **Project Library**: the library classes are visible within the project, and the library information is recorded in the project's <path>.ipr</path> file or in <path>.idea/libraries</path>.
* **Global Library**: the library information is recorded in the <path>applicationLibraries.xml</path> file in the <path>~/.IntelliJIdea/config/options</path> directory.
Global libraries are similar to project libraries but are visible for different projects.
For more information about libraries, refer to [Library](https://www.jetbrains.com/help/idea/working-with-libraries.html).
### SDK
Every project uses a Software Development Kit (_SDK_).
For Java projects, SDK is referred to as JDK (Java Development Kit).
The SDK determines which API library is used to build the project.
If a project is multi-module, the project SDK is common for all modules within the project by default.
Optionally, a project can configure an individual SDK for each module.
For more information about SDKs, see [Working with SDKs](https://www.jetbrains.com/help/idea/working-with-sdks.html) in the IntelliJ IDEA Web Help.
### Facet
A _facet_ represents a certain configuration, specific for a particular framework/technology associated with a module.
A module can have multiple facets.
E.g., Spring-specific configuration is stored in a Spring facet.
Facets are documented under [Facet](https://www.jetbrains.com/help/idea/adding-support-for-frameworks-and-technologies.html#facets) and [Language and Framework Specific Guidelines](https://www.jetbrains.com/help/idea/language-and-framework-specific-guidelines.html) in the IntelliJ IDEA Web Help.
## Additional Information
For more information on each of these entities, see:
- [Project](project.md)
- [Module](module.md)
- [SDK](sdk.md)
- [Library](library.md)
- [External system integration](external_system_integration.md) (for projects imported from Gradle or similar build systems)