Android Gradle jar generation

I have an Android Project with a working build.gradle file. This is used to build an Android App. Additionally now I'd like to add my server code (plain java) to this project and setup the build.gradle file to run/start the emulator app like normal and also generate a jar file of the server code, which I can deploy onto my server.

I am new to Gradle and Groovy, so I am not sure about how to write the tasks correctly to achive my goal as described above. I'd really apprechiate some help in setting up this build file. I know I'll need the jar and java plugins but can't seem to figure out how to integrate everything into the Android build.

What I have so far in the (working) build file:

apply plugin: 'com.android.application'
apply plugin: 'jacoco'

android {
    compileSdkVersion 29
    buildToolsVersion '29.0.3'
    defaultConfig {
        applicationId "com.example.myapp"
        minSdkVersion 19
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility = 1.8
        targetCompatibility = 1.8
    }
}

task jacocoTestReport(type: JacocoReport, dependsOn: 'testDebugUnitTest') {

    reports {
        xml.enabled = true
        html.enabled = true
    }

    def fileFilter = ['**/R.class', '**/R$*.class', '**/BuildConfig.*', '**/Manifest*.*', '**/*Test*.*', 'android/**/*.*']
    def debugTree = fileTree(dir: "${buildDir}/intermediates/javac/debug", excludes: fileFilter)
    def mainSrc = "${project.projectDir}/src/main/java"

    sourceDirectories = files([mainSrc])
    classDirectories = files([debugTree])
    executionData = files("${buildDir}/jacoco/testDebugUnitTest.exec")
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'androidx.appcompat:appcompat:1.0.2'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.0'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.1'

    // https://mvnrepository.com/artifact/com.esotericsoftware/kryonet
    implementation 'com.esotericsoftware:kryonet:2.22.0-RC1'
}