Accessing C++ Switches In Java

Introduction

Accessing C++ switches in Java is implemented via a Python script which analyzes the C++ switches file and generates the corresponding Java class, based on a template file. The template file must be specified in the GN target.

Usage

  1. Create a template file (ex. FooSwitches.java.tmpl). Change “Copyright 2020” to be whatever the year is at the time of writing (as you would for any other file).

     // Copyright 2020 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 package org.chromium.foo;

 // Be sure to escape any curly braces in your template by doubling as
 // follows.
 /**
  * Contains command line switches that are specific to the foo project.
  */
 public final class FooSwitches {{

 {NATIVE_STRINGS}

     // Prevents instantiation.
     private FooSwitches() {{}}
 }}

  2. Add a new build target and add it to the srcjar_deps of an android_library target:

    if (is_android) {
  import("//build/config/android/rules.gni")
}

if (is_android) {
  java_cpp_strings("java_switches_srcjar") {
    # External code should depend on ":foo_java" instead.
    visibility = [ ":*" ]
    sources = [
      "//base/android/foo_switches.cc",
    ]
    template = "//base/android/java_templates/FooSwitches.java.tmpl"
  }

  # If there's already an android_library target, you can add
  # java_switches_srcjar to that target's srcjar_deps. Otherwise, the best
  # practice is to create a new android_library just for this target.
  android_library("foo_java") {
    srcjar_deps = [ ":java_switches_srcjar" ]
  }
}

  3. The generated file out/Default/gen/.../org/chromium/foo/FooSwitches.java would contain:

    // Copyright $YEAR The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package org.chromium.foo;

/**
 * Contains command line switches that are specific to the foo project.
 */
public final class FooSwitches {

    // ...snip...

    // This following string constants were inserted by
    //     java_cpp_strings.py
    // From
    //     ../../base/android/foo_switches.cc
    // Into
    //     ../../base/android/java_templates/FooSwitches.java.tmpl

    // Documentation for the C++ switch is copied here.
    public static final String SOME_SWITCH = "some-switch";

    // ...snip...

    // Prevents instantiation.
    private FooSwitches() {}
}

See also

Code