Android studio(2.1.1 April 28-2016) Strange Error converting bytecode to dex. Dex cannot parse version 52 byte code

Question

I'm trying to build my project and get this strange error (cause all worked perfectly in previous AS versions)

Error:Error converting bytecode to dex:
Cause: Dex cannot parse version 52 byte code.
This is caused by library dependencies that have been compiled using Java 8 or above.
If you are using the 'java' gradle plugin in a library submodule add 
targetCompatibility = '1.7'
sourceCompatibility = '1.7'
to that submodule's build.gradle file.

I understand that the problem is that (as the error tells me) some of my dependencies was compiled with java ver.8 but how I know which one of them?

Here is my build.gradle

apply plugin: 'com.android.application'
apply plugin: 'com.neenbedankt.android-apt'

android {

    compileSdkVersion 23
    buildToolsVersion "23.0.3"

    defaultConfig {
        applicationId "com.android.app.mysuperapp"
        minSdkVersion 15
        targetSdkVersion 21
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    sourceSets {
        androidTest {
            setRoot('src/test')
        }
    }
}

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    sourceCompatibility = 1.7
    targetCompatibility = 1.7

    //<!-- TestFrameWork
    testCompile 'org.robolectric:robolectric:3.1-rc1'
    androidTestCompile 'junit:junit:4.12'
    //
    compile 'com.android.support:appcompat-v7:23.4.0'
    compile 'com.google.code.gson:gson:2.6.2'
    compile 'me.dm7.barcodescanner:zxing:1.8.4'
    //----Materal design libs
    compile 'com.github.rey5137:material:1.2.2'
    compile 'com.github.navasmdc:MaterialDesign:1.5@aar'
    compile 'com.rengwuxian.materialedittext:library:2.1.4'
    compile('com.github.ganfra:material-spinner:1.1.0') {
        exclude group: 'com.nineoldandroids', module: 'library'
        exclude group: 'com.android.support', module: 'appcompat-v7'
    }
    //<--
    compile 'se.emilsjolander:stickylistheaders:2.7.0'
    compile('com.thoughtworks.xstream:xstream:1.4.8') {
        exclude group: 'xmlpull', module: 'xmlpull'
    }
    //----LogBack&SLF4J
    compile 'org.slf4j:slf4j-api:1.7.21'
    compile 'com.github.tony19:logback-android-core:1.1.1-5'
    compile('com.github.tony19:logback-android-classic:1.1.1-5') {
        // workaround issue #73
        exclude group: 'com.google.android', module: 'android'
    }
    compile 'com.jakewharton:butterknife:8.0.1'
    apt 'com.jakewharton:butterknife-compiler:8.0.1'
}

I've googled alredy similar questions on SO (like this one or this) but adding this lines to build gradle

dependencies {

sourceCompatibility = 1.7
targetCompatibility = 1.7
}

didn't solve my problem. I am pretty stuck and I need someone help. Thanks in advance.

Answer 1

Your problem is compile('com.thoughtworks.xstream:xstream:1.4.8') that depends on Java 8

Version 1.4.7 doesn't depend on Java8, so if you can live with 1.4.7 the fix is quite simple.