1. Software Engineering and Architecture
Dependency Management

2. Henrik Bærbak Christensen
Motivation
Software Reuse
The holy grail in software engineering for decades…
Lot of hard work and research, and relatively little success
Shaw: It is not the functionality, it is the packaging
Until…
The big open source organizations and the companies that does not earn their money from selling software began publishing libraries
Apache, Eclipse, Goggle, Amazon, …
Henrik Bærbak Christensen

3. Henrik Bærbak Christensen
Example
I want to make a ”Hello World” web service ala
Exercise: How much coding would that take given only raw Java language?
Henrik Bærbak Christensen

4. Reusing Web Frameworks
One web framework is ‘Spark’ which allows pretty compact code…
All nice and well…
But…
You need the Spark library
Which depends on a lot of other reusable libraries…
Core dependency: Eclipse Jetty, open source web server
To clean ivy cache: c:\users\(user)\.ivy2
Henrik Bærbak Christensen

5. Henrik Bærbak Christensen
The Dependencies
17 Libraries!
Tedious and error prone to
Fetch all libraries in proper version
Very long classpath in Java
Henrik Bærbak Christensen

6. Henrik Bærbak Christensen
The Solution
Dependency Management
Tool to resolve the transitive closure of dependencies
Locate and download library,
recursively locate and download any dependencies
Resolve conflicts
A version 1 depends on B version 1 and C version 3
B version 1 depends on D version 2
C version 3 depends on D version 3
Tool will eject D version 2 and only provide D version 3
A Dependency Description
Stating which libraries we need
And – repositories of libraries
Maven repository ‘mvnrepository.com’ is a major player!
Henrik Bærbak Christensen

7. Henrik Bærbak Christensen
SWEA Context
Gradle is a modern build management tool and it has already built-in dependency management !!!
Earlier SWEA/dSoftArk used Ant which does not…
And then had to use a plug-in tool, Ivy, to help out
Henrik Bærbak Christensen

8. The Process Goal: I want Spark-java library in my project
Open mvnrepository.com and search for the library ‘sparkjava’
Take care: Apache has a project with the same name 
Henrik Bærbak Christensen

9. Henrik Bærbak Christensen
The Process
Select the project, version, and click the ‘gradle’ pane
Now you can copy the gradle declaration…
Which is the text that goes into your dependency description
Henrik Bærbak Christensen

10. Henrik Bærbak Christensen
The Process
… and paste it into your build.gradle
Henrik Bærbak Christensen

11. Demo
Gradle will: * Check if the .jar is in local cache * If not, download it from mvnrepository * Recurse on any dependencies
* Set the CLASSPATH correctly
Henrik Bærbak Christensen

12. Henrik Bærbak Christensen
JCenter / BinTray
An alternative (which Gradle defaults to) to Maven Repository is JCenter.
Is free to upload to
And, less cumbersome than MvnRepository
MiniDraw is hosted there
Henrik Bærbak Christensen

13. Henrik Bærbak Christensen
DM in SWEA
We will in SWEA only pull dependencies
And you will always be given the build.gradle files
Pushing to a repository is out-of-scope for our course
Security you know
Need to create credentials, secret tokens for pushing, and stuff...
Henrik Bærbak Christensen

14. Henrik Bærbak Christensen
Summary
Declarative approach
State what you need, not how to get it
A DSL (domain specific language) for defining dependencies
A dependency description
Tool (Gradle ) to resolve
Public repositories with numerous libraries
Possible to create own repos’ and publish team/organization specific libraries as well…
Henrik Bærbak Christensen