How i can export Android code to java library in Android Studio

I'm developing a library for an Android application, I wrote some classes that contains different functions.

I have a problem in the exporting process from Java to Jar. I did the following:

1) From an existing source code, File -> New module -> Java Library

2) Android Studio at this point create a "sub project", with a default class

3) Cut and paste my java code in the library created at point 2

At this point I have some problems/questions:

• Some part of code cannot be resolved like ByteBuffer, JSON...

• Should I import in the JSON - HTTP library?

• I don't understand why ConnectivityManager, NetworkInfo cannot be resolved.

EDIT 1

app gradle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.3"

    defaultConfig {
        applicationId "MY ID"
        minSdkVersion 16
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.3.0'
    compile files('libs/httpcore-4.4.4.jar')
}

Di gradle

apply plugin: 'java'

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
}

Project gradle

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.1.0'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        jcenter()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}