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	How to extract a subproject

Sometimes, a piece of functionality is developed as part of one project, but grows so much as to warrant becoming its own, separate project.

This tutorial describes how to split part of a Git repository into its own dedicated Git repository, preserving only the history relevant to the subproject being extracted.

Extract the revision history

Use Git's filter-branch feature to extract the Git history of only the subproject:
```
git filter-branch -f --prune-empty --subdirectory-filter <subdir>
```
Where <subdir> is the folder containing the subproject's source code.

Update the Maven build

Assuming you are using Maven to build the subproject:

Add an <scm> section to the pom.xml to reflect the new remote repository's URL (see example):
```
vi pom.xml
git commit -m 'Add SCM location' pom.xml
```
Replace the old <parent> with a new one, such as pom-scijava, pom-imagej or pom-fiji (see example)—or remove the <parent> altogether.
Add a <developers> section to the pom.xml to indicate the project developers (see example). You can also add <contributors> if desired and relevant.
Make sure the project still builds:
```
mvn clean package
```
Add (or adjust) the .gitignore file (see example).

Push the changes

Make sure that all your changes look good:
```
git status
git diff
```
This is good advice in general: check git status and git diff every time before you commit, to prevent making a fool out of yourself.
Commit everything, mentioning the commit of the parent project from which history was rewritten (see example):
```
git add . && git commit -s
```
Create a new repository somewhere for the new project—we recommend GitHub.
Connect your repository with the remote one:
```
git remote set-url origin git@github.com:my-org/my-new-project
```
Where git@github.com:my-org/my-new-project is the remote URL for the new project's dedicated repository.
Push the resultant history to the project's new repository:
```
git push -u origin master
```

Change any online resources

Edit the relevant web page(s) to reflect the new Git repository location
Update any other known links to the project

How to extract a subproject

Contents

Extract the revision history

Update the Maven build

Push the changes

Change any online resources