Program type already present: okhttp3.Call$Factory

Question

I have a very simple Android project that refuses to build in Android Studio and just gives me this cryptic error message:

Program type already present: okhttp3.Call$Factory
Message{kind=ERROR, text=Program type already present: okhttp3.Call$Factory, sources=[Unknown source file], tool name=Optional.of(D8)}

Here are my dependencies:

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation 'com.android.support:appcompat-v7:27.1.0'
    implementation 'com.android.support.constraint:constraint-layout:1.0.2'
    implementation 'net.openid:appauth:0.7.0'
    implementation 'com.squareup.okhttp3:okhttp:3.10.0'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.1'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
    implementation files('libs/easywsdl/ksoap2-android-assembly-3.6.2-jar-with-dependencies.jar')
    implementation files('libs/easywsdl/ExKsoap2-1.0.2.0.jar')
}

How can I troubleshoot that?

Answer 1

One of your .jar should already contain okHttp3, and this is probably why there is an issue with implementation 'com.squareup.okhttp3:okhttp:3.10.0'.

If you remove this dependency, you should not get the error.

You can print a tree of all the dependencies used with gradlew app:dependencies (where app is the name of the module used for your application, and usually the default name when you create a new android app project)