android - Gradle build failed with an Exception

I am quite new to the studio,

I am trying to Run my application

Error is encountered -

What went wrong:

Execution failed for task ':app:dexDebug'.

com.android.ide.common.process.ProcessException: org.gradle.process.internal.ExecException: Process 'command '/Library/Java/JavaVirtualMachines/jdk1.7.0_79.jdk/Contents/Home/bin/java'' finished with non-zero exit value 1

I tried with jdk 1.8 which gave the same error.

So found few answers which said to reduce jdk to 1.7

but the Error still persists

Please Suggest what to do

Gradle :

apply plugin: 'com.android.application'


android {
    compileSdkVersion 21
    buildToolsVersion "22.0.1"
    defaultConfig {
        applicationId "innovapptive.com.mworkorder"
        minSdkVersion 15
        targetSdkVersion 22
        versionCode 1
        versionName "1.0"
    }

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


dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    compile 'com.android.support:appcompat-v7:22.0.0'

}