Two ways for Android Studio to add jar or aar dependencies

It is assumed here that both jar and aar are placed in the libs directory of the module.

method one

In the dependencies of build.gradle in the module directory, add

implementation fileTree(include: ['*.jar', '*.aar'], dir: 'libs')

This method is simple and rude, but does not allow jars (or aars) of different compilation types of the same module to appear at the same time.
For example, if libs has both test-release.aar and test-debug.aar, they are all packaged from the same module , but only the compilation types are different. If they exist at the same time, they will not compile.
Full version

apply plugin: 'com.android.application'

android {
   ...
}

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

Method 2

Add in the module's build.gradle first

repositories {
    flatDir {
        dirs 'libs'
    }
}

Same level as dependencies
and then add in dependencies

implementation(name:'xxx', ext:'aar')
// 或
implementation(name:'xxx', ext:'jar')

full version

apply plugin: 'com.android.application'

android {
    ...
}

repositories {
    flatDir {
        dirs 'libs'
    }
}

dependencies {
    implementation(name:'xxx-debug', ext:'aar')
    //或
    implementation(name:'xxx-debug', ext:'jar')
}