Current answer

With Android Gradle Plugin 7.1 it is now very simple to do this without needing any complicated scripts. AGP now also handles creating source and javadocs jar.

You don’t need any separate scripts, just write everything into your build.gradle file of your module:

plugins {
    ...
    id 'maven-publish'
}
android {
    ...
    publishing {
        singleVariant("release") {
            // if you don't want sources/javadoc, remove these lines
            withSourcesJar()
            withJavadocJar()
        }
    }
}
afterEvaluate {
    publishing {
        publications {
            release(MavenPublication) {
                from components.release
                groupId 'com.example'
                artifactId 'mylibrary'
                version = android.defaultConfig.versionName // or manually '1.0'
            }
        }
    }
}

See also: https://developer.android.google.cn/studio/build/maven-publish-plugin

---

Old answer

Updated 3.3.2020:

Since release of Android Studio 3.6 the support for building AAR (or even APK and AAB) is implemented in Android Gradle plugin 3.6.0 (and newer).

We don’t need to handle the XML dependencies and stuff ourselves anymore.

Here is my updated Gist for Android Studio 3.6.0: https://gist.github.com/Robyer/a6578e60127418b380ca133a1291f017

Code from gist:

apply plugin: 'maven-publish'

task androidJavadocs(type: Javadoc) {
    source = android.sourceSets.main.java.srcDirs
    classpath += project.files(android.getBootClasspath().join(File.pathSeparator))
    android.libraryVariants.all { variant ->
        if (variant.name == 'release') {
            owner.classpath += variant.javaCompileProvider.get().classpath
        }
    }
    exclude '**/R.html', '**/R.*.html', '**/index.html'
}

task androidJavadocsJar(type: Jar, dependsOn: androidJavadocs) {
    archiveClassifier.set('javadoc')
    from androidJavadocs.destinationDir
}

task androidSourcesJar(type: Jar) {
    archiveClassifier.set('sources')
    from android.sourceSets.main.java.srcDirs
}

// Because the components are created only during the afterEvaluate phase, you must
// configure your publications using the afterEvaluate() lifecycle method.
afterEvaluate {
    publishing {
        publications {
            // Creates a Maven publication called "release".
            release(MavenPublication) {
                // Applies the component for the release build variant.
                from components.release

                // Adds javadocs and sources as separate jars.
                artifact androidJavadocsJar
                artifact androidSourcesJar

                // You can customize attributes of the publication here or in module's build.gradle file (if you save this as script and include it build.gradle file, then you can just replicate this whole block there only with changed fields).
                //groupId = 'com.example'
                //artifactId = 'custom-artifact'
                version = android.defaultConfig.versionName // or just '1.0'
            }
        }
    }
}

---

Old answer:

Here is my improved solution, based on other answers.

Gist: https://gist.github.com/Robyer/a6578e60127418b380ca133a1291f017

Changes from other answers:

• Changed classifier – it must be "sources" (not "source")
• Handles dependencies

  • Supports also @aar and transitive: false. In that case we set exclusion in POM to ignore all transitive dependencies of this dependency.

  • Supports also custom exclude rules on dependencies, e.g.:

      compile('com.example:something:1.0', {
          exclude group: 'com.exclude.this', module: 'some-module'
      })
    

• Doesn’t need to specify artifact path manually.

Changelog:

• 27.3.2018 – Added support for api / implementation dependencies in new Gradle
• 23.11.2018 – Renamed bundleRelease to bundleReleaseAar as it was changed in new Gradle (see this answer)
• 23.11.2018 – Changed getAllDependencies to getDependencies to fix duplicated resulting entries (as mentioned in comments on my Gist).
• 23.04.2019 – Wrapped in project.afterEvaluate{...} to fix it for new Gradle.

---

apply plugin: 'maven-publish'

task androidJavadocs(type: Javadoc) {
    source = android.sourceSets.main.java.srcDirs
    classpath += project.files(android.getBootClasspath().join(File.pathSeparator))
    android.libraryVariants.all { variant ->
        if (variant.name == 'release') {
            owner.classpath += variant.javaCompile.classpath
        }
    }
    exclude '**/R.html', '**/R.*.html', '**/index.html'
}

task androidJavadocsJar(type: Jar, dependsOn: androidJavadocs) {
    classifier="javadoc"
    from androidJavadocs.destinationDir
}

task androidSourcesJar(type: Jar) {
    classifier="sources"
    from android.sourceSets.main.java.srcDirs
}

project.afterEvaluate {
    publishing {
        publications {
            maven(MavenPublication) {
                //groupId 'cz.example'
                //artifactId 'custom-artifact'
                //version = android.defaultConfig.versionName
    
                artifact bundleReleaseAar
                artifact androidJavadocsJar
                artifact androidSourcesJar
    
                pom.withXml {
                    final dependenciesNode = asNode().appendNode('dependencies')
    
                    ext.addDependency = { Dependency dep, String scope ->
                        if (dep.group == null || dep.version == null || dep.name == null || dep.name == "unspecified")
                            return // ignore invalid dependencies
    
                        final dependencyNode = dependenciesNode.appendNode('dependency')
                        dependencyNode.appendNode('groupId', dep.group)
                        dependencyNode.appendNode('artifactId', dep.name)
                        dependencyNode.appendNode('version', dep.version)
                        dependencyNode.appendNode('scope', scope)
    
                        if (!dep.transitive) {
                            // If this dependency is transitive, we should force exclude all its dependencies them from the POM
                            final exclusionNode = dependencyNode.appendNode('exclusions').appendNode('exclusion')
                            exclusionNode.appendNode('groupId', '*')
                            exclusionNode.appendNode('artifactId', '*')
                        } else if (!dep.properties.excludeRules.empty) {
                            // Otherwise add specified exclude rules
                            final exclusionNode = dependencyNode.appendNode('exclusions').appendNode('exclusion')
                            dep.properties.excludeRules.each { ExcludeRule rule ->
                                exclusionNode.appendNode('groupId', rule.group ?: '*')
                                exclusionNode.appendNode('artifactId', rule.module ?: '*')
                            }
                        }
                    }
    
                    // List all "compile" dependencies (for old Gradle)
                    configurations.compile.getDependencies().each { dep -> addDependency(dep, "compile") }
                    // List all "api" dependencies (for new Gradle) as "compile" dependencies
                    configurations.api.getDependencies().each { dep -> addDependency(dep, "compile") }
                    // List all "implementation" dependencies (for new Gradle) as "runtime" dependencies
                    configurations.implementation.getDependencies().each { dep -> addDependency(dep, "runtime") }
                }
            }
        }
    }
}