构建取决于Android Project Gradle的Java库

Question

I have an Android project that defines various datatypes that are serialized via Protocol Buffers. I would like to have a separate Java project that is able to deserialize these data types on the server.

My project is structured as follows:

Android Library
  - Data
      - TypeA 
      - TypeB
      - ...

Java Server
  - Parser (depends on .Data)

In this example, all classes in the package Data handle marshaling themselves.

When trying to build the Java Server, it successfully compiles the Android project, but ultimately fails with Gradle saying it cannot find the referenced packages.

Note, that I can successfully build the Java Server with cross project dependencies if I only pull in other Java libraries, leading me to believe this is a Java -> Android dependency problem rather than a Gradle configuration issue.

On possible solution I have considered is to pull out all of these data types from the Android project and place them in a separate Java library. The trouble with this however is that some of these classes merely provide a means of converting Android specific classes ( SensorEvent, Location, etc ) into a type that can be used with ProtoBuf. One solution I've been considering would look like this:

Data Types
  - TypeA
  - TypeB
  - ...

Android Library
  - Data
    - AndroidTypeA (Class with Android Specific constructor that can be cast to the parent type)
    - AndroidTypeB
    - ...

Java Server
  - Parser ( Depends on the Data Types module )  

While this would indeed solve my issue, it hardly seems like the best solution.

Is there any way to accomplish this through Gradle alone?

---

For reference here are abbreviated versions of my build.gradle files.

Android Library:

apply plugin: 'com.android.library'

android {
    compileSdkVersion 21
    buildToolsVersion "21.0.2"

    defaultConfig {
        applicationId "com.foo.bar.androidlib"
        ...
    }
    buildTypes {
        release {
            runProguard false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    ...
    compile 'com.google.protobuf:protobuf-java:2.6.1'
}

Java Server:

apply plugin: 'java'


dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.google.protobuf:protobuf-java:2.6.1'
    compile project(':androidlib')
}

Edit:

Specifically Gradle gives the following error:

error: package com.foo.bar.androidlib does not exist

Answer 1

In Gradle, you can't have a Java library that depends on an Android library. This is because the Android plugin in Gradle isn't based on the Java plugin and isn't compatible with it, so Java doesn't understand its sourcesets and can't otherwise play nice with it.

I don't think you can solve this problem purely through Gradle configuration, and even if you could, it would probably make your build wickedly complex and fragile. Your best bet is to have your Java stuff rely only on Java stuff, isolating out the common protobuf dependencies there, and have the Android side depend on Java. You outlined an approach with Android versions of some of the classes; that may work, but I don't know enough details about what you're doing to comment on it in detail.