In gradle, how to use a variable for a plugin version?

As of Gradle 5.6, you can declare your plugin versions in the gradle.properties file, and reference these properties in plugins block.

For example, the gradle.properties file：

springBootVersion=2.2.0.RELEASE

the plugins block in build.gradle:

plugins {
    id "org.springframework.boot" version "${springBootVersion}"
}

See: https://github.com/gradle/gradle/issues/1697#issuecomment-506910915.

See also:

1. https://docs.gradle.org/5.6/release-notes.html#central-management-of-plugin-versions-with-settings-script
2. https://docs.gradle.org/5.6/userguide/plugins.html#sec:plugin_management