How to access Gradle extra properties in src code?

task in build.gradle file -

task automationTest(type: Test) {
    ext.env = rootProject.hasProperty('TS1') ? rootProject['TS2'] : 'TS1'
    println env //printing passed pararmeter successfully
}

now I want to access env in Login class in src/main/java

I know i can access variables from build.gradle to any java class by using system property like systemProperty ‘env’,System.properties[‘env’] ?: ‘dev’ command in build.gradle, from console gradle -Denv=test and then accessing System.getProperty(“env”) from anywhere in src but i want to understand if i create env as ext property or project property then how can i use env from any java class?
Can anyone please help?

Also what should be the ideal way to use variables(System property or project property) in src from Build.gradle?