Dependencies and Repositories

Declaring a dependency

Add a library by its GAV coordinates. Maven downloads it – and everything it needs – automatically:

<dependency>
  <groupId>com.google.code.gson</groupId>
  <artifactId>gson</artifactId>
  <version>2.11.0</version>
</dependency>

The same dependency in Gradle is one line:

implementation 'com.google.code.gson:gson:2.11.0'

Where dependencies come from

Build tools resolve dependencies in stages. They first check a local cache on your machine (~/.m2 for Maven, ~/.gradle for Gradle); anything missing is downloaded once from a remote repository, chiefly Maven Central, and then reused.

Transitive dependencies

You declare only your direct dependencies; the tool pulls in everything they depend on – the transitive graph. Gson may need nothing, but a web framework can pull in dozens of JARs from your one declaration. Inspect the full tree when versions clash:

mvn dependency:tree
gradle dependencies

Scopes

A scope limits where a dependency is available, keeping the final artifact lean:

• compile / implementation – available everywhere (the default).
• test / testImplementation – only when compiling and running tests (e.g. JUnit).
• provided / compileOnly – needed to compile but supplied at runtime by the server (e.g. the Servlet API in a WAR).
• runtime – needed only at runtime, not to compile (e.g. a JDBC driver).

Key points

• Declare dependencies by GAV; the tool downloads them automatically.
• Resolution checks a local cache first, then a remote repo like Maven Central.
• Transitive dependencies come in through your direct ones – inspect the tree on conflicts.
• Scopes (test, provided/compileOnly, runtime) control where a dependency applies.