java.util.zip.ZipException: duplicate entry

Make sure you have the latest build toolds and sdk from the SDK manager. I have converted those jars to Gradle dependencies.

build.gradle:

// Top-level build file where you can add configuration options common to all sub-projects/modules.
buildscript {
    repositories {
        jcenter()
        maven { url 'https://oss.sonatype.org/content/repositories/ksoap2-android-releases/' } // <-- added for ksoap
    }

    dependencies {
        classpath 'com.android.tools.build:gradle:1.1.3' // <-- updated
    }
}

allprojects {
    repositories {
        jcenter()
        maven { url 'https://oss.sonatype.org/content/repositories/ksoap2-android-releases/' } // <-- added for ksoap
    }
}

app/build.gradle:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 22
    buildToolsVersion "22.0.1" // <-- updated

    defaultConfig {
        applicationId "com.appname.android"
        minSdkVersion 8
        targetSdkVersion 22  // <-- updated
        // multiDexEnabled true  // <-- you do not need this
    }

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

dependencies {
    compile 'com.android.support:support-v4:22.1.1'
    compile 'com.google.code.ksoap2-android:ksoap2-android:3.4.0'
    // compile files('libs/ksoap2-android-assembly-3.1.0-jar-with-dependencies.jar') // <-- avoid using jars
    compile 'com.google.zxing:core:3.2.0'
    // provided files('libs/zxing-core.jar') // <-- avoid using jars
}