Java App Engine Rules for Bazel

Overview

These build rules are used for building Java App Engine application with Bazel. It does not aim at general Java web application support but can be easily modified to handle a standard web application.

Setup

To be able to use the Java App Engine rules, you must make the App Engine SDK available to Bazel. The easiest way to do so is by adding the following to your WORKSPACE file:

load("@bazel_tools//tools/build_rules/appengine:appengine.bzl", "appengine_repositories")

appengine_repositories()

Basic Example

Suppose you have the following directory structure for a simple App Engine application:

[workspace]/
    WORKSPACE
    hello_app/
        BUILD
        java/my/webapp/
            TestServlet.java
        webapp/
            index.html
        webapp/WEB-INF
            web.xml
            appengine-web.xml

Then, to build your webapp, your hello_app/BUILD can look like:

load("@bazel_tools//tools/build_rules/appengine:appengine.bzl", "appengine_war")

java_library(
    name = "mylib",
    srcs = ["java/my/webapp/TestServlet.java"],
    deps = [
        "//external:appengine/java/api",
        "//external:javax/servlet/api",
    ],
)

appengine_war(
    name = "myapp",
    jars = [":mylib"],
    data = glob(["webapp/**"]),
    data_path = "webapp",
)

For simplicity, you can use the java_war rule to build an app from source. Your hello_app/BUILD file would then look like:

load("@bazel_tools//tools/build_rules/appengine:appengine.bzl", "java_war")

java_war(
    name = "myapp",
    srcs = ["java/my/webapp/TestServlet.java"],
    data = glob(["webapp/**"]),
    data_path = "webapp",
    deps = [
        "//external:appengine/java/api",
        "//external:javax/servlet/api",
    ],
)

You can then build the application with bazel build //hello_app:myapp and run in it a development server with bazel run //hello_app:myapp. This will bind a test server on port 8080. If you wish to select another port, simply append the --port=12345 to the command-line.

Another target //hello_app:myapp.deploy allows you to deploy your application to App Engine. It takes an optional argument: the APP_ID. If not specified, it uses the default APP_ID provided in the application. This target needs to be authorized to App Engine. Since Bazel does not connect the standard input, it is easier to run it by:

bazel-bin/hello_app/myapp.deploy APP_ID

After the first launch, subsequent launch will be registered to App Engine so you can just do a normal bazel run //hello_app:myapp.deploy APP_ID to deploy next versions of your application.

appengine_war

appengine_war(name, jars, data, data_path)

java_war

java_war(name, data, data_path, **kwargs)