Problem

Spring boot application (behind corporate proxy) using Apache HTTPClient could not access the internet even with http_proxy and https_proxy configured

Solution

Use HTTPClient's HttpClientBuilder.create().useSystemProperties() to apply system properties such as proxy configuration

Test

Once Spring Boot application is ran (i.e. ./gradlew bootRun or java -jar app.jar), the POC application will invoke two HTTP requests to the defined URL, one without useSystemProperties and one using the said solution.