How to programmatically read the date when my Android apk was built?

Question

Is it possible to programmatically read the date when my Android apk was built? I could not find anything in the PackageInfo class.

I want to expire beta versions of my app and the easiest way would be to read out such a date and expire it after a fixed period of days, so I don't have to update the code for that every time I build and deploy a beta version.

Answer 1

12/2/22 Note: This is a newer way to put the timestamp into the BuildConfig.java than I suggested previously, but I am keeping the legacy instructions at the bottom for anyone who might want it. The instructions are for the relatively new build.gradle.kts format.

First, update build.gradle to include:

android {
    buildFeatures {
        buildConfig = true
    }
}

The above is needed as the buildConfigField feature may have been disabled by default, starting with Android Studio Flamingo Canary 9. See here for more about that.

Next, add to the top of build.gradle.kts:

 import com.android.build.api.variant.BuildConfigField

and outside of the android { ... } part of build.config.kts add this:

androidComponents {
    onVariants {
       it.buildConfigFields.put(
            "BUILD_TIME", BuildConfigField(
                "String", "\"" + System.currentTimeMillis().toString() + "\"", "build timestamp"
            )
        )
    }
}

As with the previous instructions, the build timestamp is accessed in Kotlin like this:

private val buildDate = Date(BuildConfig.BUILD_TIME.toLong())
Log.i("MyProgram", "This .apk was built on ${buildDate.toString()}");

That's it. Keep reading if you've got an older versions of Android Studio/Gradle and want the older more Java-oriented instructions.

Note 6/1/2020: Android Studio 4.1 Canary 10 w/Gradle >= 6.5 has updated instructions. If you are seeing an "Unsupported BuildConfig type : java.util.Date error, scroll down for the fix.

[Older Instructions]

In build.gradle, each of your build types should have a buildConfigField. (This is a simplified version of the configuration- you're likely to have other stuff in here, but I wanted to show where you put it):

android {
    signingConfigs {
        buildTypes {
            debug {
                buildConfigField "java.util.Date", "BUILD_TIME", "new java.util.Date(" + System.currentTimeMillis() + "L)"
            }
            release { 
                buildConfigField "java.util.Date", "BUILD_TIME", "new java.util.Date(" + System.currentTimeMillis() + "L)"
            }
        }
    }
}    

(Note that "BuildConfigField" is the newer version of "BuildConfigLine" as of the 0.8.0 build system.)

The next time gradle does assembleRelease or assembleDebug, it should generate:

./build/source/buildConfig/releaseORdebug/com/your/project/BuildConfig.java

Next, inside that BuildConfig file, you should see something has been auto-generated like:

public final class BuildConfig {
    public static final java.util.Date BUILD_TIME = new java.util.Date(1395794838381L);
}

So, to access the build date within your app....

Date buildDate = BuildConfig.BUILD_TIME;
Log.i("MyProgram", "This .apk was built on " + buildDate.toString());

(You can format the date however you like using a SimpleDateFormat.)

Update 6/1/2020 -- In Android Studio 4.1 Canary 10 w/Gradle 6.5, the above solution results in an "Unsupported BuildConfig type : java.util.Date" error. A slight variation to the above should be used instead:

android {
    signingConfigs {
        buildTypes {
            debug {
                buildConfigField("String", "BUILD_TIME", System.currentTimeMillis().toString())
            }
            release { 
                buildConfigField("String", "BUILD_TIME", System.currentTimeMillis().toString())
            }
        }
    }
} 

Update 7/30/2020 After gradle 6.6-rc4, you need to include the enclosing quotes for the time by changing to this line:

        buildConfigField("String", "BUILD_TIME", "\"" + System.currentTimeMillis().toString() + "\"")

Inside the BuildConfig file, you should see something has now been auto-generated like:

public final class BuildConfig {
      public static final String BUILD_TIME = "1590735284503";
}

So now, to access the build date within your app....

private Date buildDate = new Date(Long.parseLong(BuildConfig.BUILD_TIME));
Log.i("MyProgram", "This .apk was built on " + buildDate.toString());

As before, you can format the date however you like using a SimpleDateFormat.

Hope this is helpful.