How to add external libraries to Android Project in Android Studio?

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Introduction
The ways to use external libraries
Way 1 - Copy external library to libs folder
Way 2 - Using the module library
Way 3 - Using remote library

1- Introduction

This document is based on:

Android Studio 3.6.1

2- The ways to use external libraries

You are developing an Android app on Android Studio, sometimes you want to use an external library for your project, such as a jar file.

Common langs is an java library with open source code which is provided by the Apache, it has utility methods for working with String, numbers, concurrency ...

Download: commons-lang3-3.10.jar

Suppose that you want to use this library for your Android project. And using one of its utility methods to test whether a String is a number or not.

import org.apache.commons.lang3.StringUtils;
 
public class CheckNumeric {
 
   public void test() {
       String text1 = "0123a4";
       String text2 = "01234";
        
       boolean result1 = StringUtils.isNumeric(text1);
       boolean result2 = StringUtils.isNumeric(text2);
 
       System.out.println(text1 + " is a numeric? " + result1);
       System.out.println(text2 + " is a numeric? " + result2);
 
   }
 
}

In this document I will guide you 3 ways to use the external library:

Add your jar files to libs folder of the project and declare it as a library to use.
Create a Android module and copy your jar file to this module, and then declare your project using the newly created module.
Declare and use a remote library.

3- Way 1 - Copy external library to libs folder

Create a project named AddLibsDemo:

OK, your project has been created.

Change to Project tab:

Copy jar file to libs folder:

Right click jar files, select "Add as Library..":

Turn back to "Android" Tab, you can see that your library has been already declared in build.grade (Module: app)

OK, now your library is being already used.

4- Way 2 - Using the module library

Suppose you have a AddLibsDemo2 project, you want to use common-lang3-3.4.jar library for this project.

Create a Android Module:

Point to the location of the library.

Module library has been created:

Next, you need to declare the dependency of the main project into the newly created module.

File/Project Structure

Add module dependencies:

You can check your module which has been declared in build.grade (Module: app).

5- Way 3 - Using remote library

Android Studio can use the library on a network, it is located in some repository on the Internet. Suppose you have AddLibDemo3 project, and you need to add the remote library to your project.