Speed up docker re-builds using mvn dependency:go-offline (#19078)

* go offline

* dup

Author: ReallyLiri

Dockerfile

@@ -10,14 +10,23 @@ COPY ./LICENSE ${GEN_DIR}
 # Required to compile openapi-generator
 COPY ./google_checkstyle.xml ${GEN_DIR}
 
+# All poms are copied, then we go offline, to allow for better caching of code changes without fetching all dependencies each time
+COPY ./modules/openapi-generator-gradle-plugin/pom.xml ${GEN_DIR}/modules/openapi-generator-gradle-plugin/
+COPY ./modules/openapi-generator-maven-plugin/pom.xml ${GEN_DIR}/modules/openapi-generator-maven-plugin/
+COPY ./modules/openapi-generator-online/pom.xml ${GEN_DIR}/modules/openapi-generator-online/
+COPY ./modules/openapi-generator-cli/pom.xml ${GEN_DIR}/modules/openapi-generator-cli/
+COPY ./modules/openapi-generator-core/pom.xml ${GEN_DIR}/modules/openapi-generator-core/
+COPY ./modules/openapi-generator/pom.xml ${GEN_DIR}/modules/openapi-generator/
+COPY ./pom.xml ${GEN_DIR}
+RUN mvn dependency:go-offline
+
 # Modules are copied individually here to allow for caching of docker layers between major.minor versions
 COPY ./modules/openapi-generator-gradle-plugin ${GEN_DIR}/modules/openapi-generator-gradle-plugin
 COPY ./modules/openapi-generator-maven-plugin ${GEN_DIR}/modules/openapi-generator-maven-plugin
 COPY ./modules/openapi-generator-online ${GEN_DIR}/modules/openapi-generator-online
 COPY ./modules/openapi-generator-cli ${GEN_DIR}/modules/openapi-generator-cli
 COPY ./modules/openapi-generator-core ${GEN_DIR}/modules/openapi-generator-core
 COPY ./modules/openapi-generator ${GEN_DIR}/modules/openapi-generator
-COPY ./pom.xml ${GEN_DIR}
 
 # Pre-compile openapi-generator-cli
 RUN mvn -B -am -pl "modules/openapi-generator-cli" package