build.gradle error set targetCompatibility t 1.7

Question

i got this error message saying
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 tried to add targetCompatibility = '1.7'and sourceCompatibility = '1.7' inside the dependencies but it still gave me the same error,, how do i solve this?

(i just added mysql connector to my library and it automatically generated that dependency)

 apply plugin: 'com.android.application'

android {
compileSdkVersion 25
buildToolsVersion "25.0.2"
defaultConfig {
    applicationId "com.example.boneyflesh.connectnapls"
    minSdkVersion 17
    targetSdkVersion 25
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
}
}

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2',   {
    exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:25.1.0'
    testCompile 'junit:junit:4.12'
    compile files('libs/mysql-connector-java-5.1.38-bin.jar')

   }

Answer 1

Solved this by adding this to app.gradle

defaultConfig {
    jackOptions {
        enabled true
    }
}
dexOptions {

}

compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_8
    targetCompatibility JavaVersion.VERSION_1_8
}