Duplicate class in protobuf lite and protobuf java

Question

I'm using grpc with protobuf lite in android implementation. but protobuf lite doesn't have google time stamp, and my protos has import "google/protobuf/timestamp.proto". so i added implementation 'com.google.protobuf:protobuf-java:3.7.1' to gradle that contains google time stamp. but after that code compilaition has errors. such as :Duplicate class com.google.protobuf.AbstractMessageLite found in modules protobuf-java-3.7.1.jar (com.google.protobuf:protobuf-java:3.7.1) and protobuf-lite-3.0.1.jar (com.google.protobuf:protobuf-lite:3.0.1). any idea to fix this would be appreciated.

apply plugin: 'com.android.application'
apply plugin: 'com.google.protobuf'

android {
    compileSdkVersion 28
    buildToolsVersion "29.0.0"
    defaultConfig {
        minSdkVersion 21
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        debug {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }

    sourceSets {
        main {
            proto {
                srcDir 'src/main'
            }
            java {
                srcDir 'src/main'
            }
        }
    }
}

protobuf {
    protoc { artifact = 'com.google.protobuf:protoc:3.7.1' }
    plugins {
        javalite { artifact = "com.google.protobuf:protoc-gen-javalite:3.0.0" }
        grpc {
            artifact = 'io.grpc:protoc-gen-grpc-java:1.20.0' // CURRENT_GRPC_VERSION
        }
    }

    generateProtoTasks {
        all().each { task ->
            task.plugins {
                javalite {}
                grpc { // Options added to --grpc_out
                    option 'lite'
                }
            }
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'androidx.appcompat:appcompat:1.0.2'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    implementation 'androidx.legacy:legacy-support-v4:1.0.0'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test:runner:1.2.0'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
    implementation 'com.google.android.material:material:1.0.0'

    // You need to build grpc-java to obtain these libraries below.
    implementation 'io.grpc:grpc-okhttp:1.20.0'
    implementation 'io.grpc:grpc-protobuf-lite:1.22.1'
    implementation 'io.grpc:grpc-stub:1.20.0'
    implementation 'javax.annotation:javax.annotation-api:1.3.2'
    implementation 'com.google.protobuf:protobuf-java:3.7.1'
}

given error is:

Duplicate class com.google.protobuf.AbstractMessageLite found in modules      protobuf-java-3.7.1.jar (com.google.protobuf:protobuf-java:3.7.1) and protobuf-lite-3.0.1.jar (com.google.protobuf:protobuf-lite:3.0.1)
Duplicate class com.google.protobuf.AbstractMessageLite$Builder found in modules protobuf-java-3.7.1.jar (com.google.protobuf:protobuf-java:3.7.1) and protobuf-lite-3.0.1.jar (com.google.protobuf:protobuf-lite:3.0.1)
Duplicate class com.google.protobuf.AbstractMessageLite$Builder$LimitedInputStream found in modules protobuf-java-3.7.1.jar (com.google.protobuf:protobuf-java:3.7.1) and protobuf-lite-3.0.1.jar (com.google.protobuf:protobuf-lite:3.0.1)
Duplicate class com.google.protobuf.AbstractParser found in modules protobuf-java-3.7.1.jar (com.google.protobuf:protobuf-java:3.7.1) and protobuf-lite-3.0.1.jar (com.google.protobuf:protobuf-lite:3.0.1)
Duplicate class com.google.protobuf.AbstractProtobufList found in modules protobuf-java-3.7.1.jar (com.google.protobuf:protobuf-java:3.7.1) and protobuf-lite-3.0.1.jar (com.google.protobuf:protobuf-lite:3.0.1)
Duplicate class com.google.protobuf.BooleanArrayList found in modules protobuf-java-3.7.1.jar (com.google.protobuf:protobuf-java:3.7.1) and protobuf-lite-3.0.1.jar (com.google.protobuf:protobuf-lite:3.0.1)
Duplicate class com.google.protobuf.ByteBufferWriter found in modules protobuf-java-3.7.1.jar (com.google.protobuf:protobuf-java:3.7.1) and protobuf-lite-3.0.1.jar (com.google.protobuf:protobuf-lite:3.0.1)
Duplicate class com.google.protobuf.ByteOutput found in modules protobuf-java-3.7.1.jar (com.google.protobuf:protobuf-java:3.7.1) and protobuf-lite-3.0.1.jar (com.google.protobuf:protobuf-lite:3.0.1)
Duplicate class com.google.protobuf.ByteString found in modules protobuf-java-3.7.1.jar (com.google.protobuf:protobuf-java:3.7.1) and protobuf-lite-3.0.1.jar (com.google.protobuf:protobuf-lite:3.0.1)
Duplicate class com.google.protobuf.ByteString$1 found in modules protobuf-java-3.7.1.jar (com.google.protobuf:protobuf-java:3.7.1) and protobuf-lite-3.0.1.jar (com.google.protobuf:protobuf-lite:3.0.1)

Answer 1

The missing classes is a known issue. Full proto and lite proto can't be mixed; they use different generated code. Do not depend on protobuf-java as an implementation dependency, but as a protobuf dependency which will cause gradle-protobuf-plugin to generate code for the .protos.

dependencies {
  ...
  protobuf 'com.google.protobuf:protobuf-java:3.7.1'
}

Note that this solution only really works for an application. If you are a library, it is dangerous because users of your library may then see multiple copied of the generated code for the well-known protos.