Android build error : Error:Execution failed for task ':app:transformClassesAndResourcesWithProguardForRelease'

Question

I am new in using proguard and when I am building the api after creating signed api, I am getting these warnings and exceptions. I don't know how to solve it.

Here's the Error Log :

Warning:okio.DeflaterSink: can't find referenced class org.codehaus.mojo.animal_sniffer.IgnoreJRERequirement
Warning:okio.Okio: can't find referenced class java.nio.file.Files
Warning:okio.Okio: can't find referenced class java.nio.file.Path
Warning:okio.Okio: can't find referenced class java.nio.file.OpenOption
Warning:okio.Okio: can't find referenced class java.nio.file.Path
Warning:okio.Okio: can't find referenced class java.nio.file.OpenOption
Warning:okio.Okio: can't find referenced class org.codehaus.mojo.animal_sniffer.IgnoreJRERequirement
Warning:okio.Okio: can't find referenced class java.nio.file.Path
Warning:okio.Okio: can't find referenced class java.nio.file.OpenOption
Warning:okio.Okio: can't find referenced class java.nio.file.Path
Warning:okio.Okio: can't find referenced class java.nio.file.OpenOption
Warning:okio.Okio: can't find referenced class org.codehaus.mojo.animal_sniffer.IgnoreJRERequirement
Warning:retrofit2.Platform$Java8: can't find referenced class java.lang.invoke.MethodHandles$Lookup
Warning:retrofit2.Platform$Java8: can't find referenced class java.lang.invoke.MethodHandle
Warning:retrofit2.Platform$Java8: can't find referenced class java.lang.invoke.MethodHandles
Warning:retrofit2.Platform$Java8: can't find referenced class java.lang.invoke.MethodHandle
Warning:retrofit2.Platform$Java8: can't find referenced class java.lang.invoke.MethodHandles$Lookup
Warning:retrofit2.Platform$Java8: can't find referenced class org.codehaus.mojo.animal_sniffer.IgnoreJRERequirement
Warning:rx.internal.util.unsafe.BaseLinkedQueueConsumerNodeRef: can't find referenced class sun.misc.Unsafe
Warning:rx.internal.util.unsafe.BaseLinkedQueueProducerNodeRef: can't find referenced class sun.misc.Unsafe
Warning:rx.internal.util.unsafe.ConcurrentCircularArrayQueue: can't find referenced class sun.misc.Unsafe
Warning:rx.internal.util.unsafe.ConcurrentSequencedCircularArrayQueue: can't find referenced class sun.misc.Unsafe
Warning:rx.internal.util.unsafe.MpmcArrayQueueConsumerField: can't find referenced class sun.misc.Unsafe
Warning:rx.internal.util.unsafe.MpmcArrayQueueProducerField: can't find referenced class sun.misc.Unsafe
Warning:rx.internal.util.unsafe.MpscLinkedQueue: can't find referenced class sun.misc.Unsafe
Warning:rx.internal.util.unsafe.SpmcArrayQueueConsumerField: can't find referenced class sun.misc.Unsafe
Warning:rx.internal.util.unsafe.SpmcArrayQueueProducerField: can't find referenced class sun.misc.Unsafe
Warning:rx.internal.util.unsafe.SpscArrayQueue: can't find referenced class sun.misc.Unsafe
Warning:rx.internal.util.unsafe.SpscUnboundedArrayQueue: can't find referenced class sun.misc.Unsafe
Warning:rx.internal.util.unsafe.UnsafeAccess: can't find referenced class sun.misc.Unsafe
Warning:there were 66 unresolved references to classes or interfaces.
Warning:Exception while processing task java.io.IOException: Please correct the above warnings first.
Error:Execution failed for task ':app:transformClassesAndResourcesWithProguardForRelease'.
> Job failed, see logs for details

and my gradle looks like this:

android {
    compileSdkVersion 25
    buildToolsVersion "25.0.2"
    defaultConfig {

        minSdkVersion 18
        targetSdkVersion 25
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        packagingOptions {
            exclude 'LICENSE.txt'
        }
        lintOptions {
            abortOnError false
        }
        useLibrary 'org.apache.http.legacy'
        multiDexEnabled true
    }
    buildTypes {
        release {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    testOptions {
        unitTests.returnDefaultValues = true
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:25.3.1'
    compile 'com.android.support.constraint:constraint-layout:1.0.2'
    testCompile 'junit:junit:4.12'

    compile 'com.squareup.retrofit2:converter-scalars:2.1.0'

    compile 'com.android.support:support-annotations:25.3.1'

    compile 'com.squareup.retrofit2:retrofit:2.0.1'
    compile "com.squareup.retrofit2:adapter-rxjava:2.1.0"


    compile 'com.google.code.gson:gson:2.6.1'
    compile 'com.squareup.retrofit2:converter-gson:2.1.0'

    compile 'io.reactivex:rxandroid:1.2.1'
    compile 'io.reactivex:rxjava:1.1.6'


}

I don't know how to solve the error. I want to use proguard to reduce the size. Any help would be appreciated.

Answer 1

You need to add those lines to your proguard-rules.pro file:

# exclusions for Okio
-dontwarn okio.**

# exclusions for Retrofit
-dontnote retrofit2.Platform
-dontwarn retrofit2.Platform$Java8
-keepattributes Signature
-keepattributes Exceptions

# exclusions for RxJava
-keepclassmembers class rx.internal.util.unsafe.*ArrayQueue*Field* {
    long producerIndex;
    long consumerIndex;
}
-keepclassmembers class rx.internal.util.unsafe.BaseLinkedQueueProducerNodeRef {
    rx.internal.util.atomic.LinkedQueueNode producerNode;
}
-keepclassmembers class rx.internal.util.unsafe.BaseLinkedQueueConsumerNodeRef {
    rx.internal.util.atomic.LinkedQueueNode consumerNode;
}
-dontwarn sun.misc.Unsafe

Dont' forget to load the correct file during the release build

release {
    minifyEnabled true
    proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}