This directory contains the public API for WebEngine. WebEngine provides both a C++ and Java API. Note that while WebEngine's implementation builds on top of //content, its public API does not expose the Content API.
Note: The WebEngine API is still under development and should not be depended upon directly. It will become available through an Android Jetpack Library.
In general, the Java API is a thin veneer over the C++ API. For the most part, functionality should be added to the C++ side with the Java implementation calling into it. Where the two APIs diverge is for platform specific functionality. For example, the Java API uses Android Fragments, which do not apply to the C++ side.
The public API should follow the Android API guidelines (https://goto.google.com/android-api-guidelines). This results in naming differences between the C++ and Java code. For example, NewTabDelegate in C++ vs NewTabCallback in Java.
One of the design constraints of WebEngine's Java implementation is that we do not want embedders to ship their own copy of “//content”. Instead, the implementation is loaded from the WebView APK (not the Chrome APK, because the WebView APK is available on more devices). This constraint results in the Java implementation consisting of three distinct parts.
Code lives in “//weblayer/public/java”. This is the code used by embedders. The client library contains very little logic, rather it delegates to the Java implementation over AIDL.
This code should not have any dependencies on any other code in the chrome repo.
The embedders can use the API surface defined in the org.chromium.webengine package. It spins up an Android Service running the code in the org.chromium.weblayer package. The Service is responsible for loading the implementation from the WebView APK.
This is best thought of as WebEngine's ABI (for Java).
The client library loads the WebEngine implementation from WebView APK and uses AIDL for the IPC. The aidl interfaces are defined in “//weblayer/browser/java/org/chromium/weblayer_private/interfaces”. AIDL is used to enable the implementation to be loaded using a different ClassLoader than the embedder.
In general, any interface ending with ‘Client’ means the interface is from the implementation side to the client library. An interface without ‘Client’ is from the client to the implementation.
This is often referred to as the ‘implementation’ of the Java API. This is where the bulk of the Java code lives and sits on top of the C++ API. The code for this lives in “//weblayer/browser/java”.