protobuf-gradle-plugin

Datetime:2016-08-23 03:11:10          Topic: Java  Gradle           Share

Starting from version 0.7.6 , the plugin requires Gradle 2.12 and later. Please check your Gradle version if you see the following error:

Error:Unable to load class 'org.gradle.api.internal.file.collections.DefaultDirectoryFileTreeFactory'.

Protobuf Plugin for Gradle

The Gradle plugin that compiles Protocol Buffer (aka. Protobuf) definition files ( *.proto ) in your project. There are two pieces of its job:

  1. It assembles the Protobuf Compiler ( protoc ) command line and use it to generate Java source files out of your proto files.
  2. It adds the generated Java source files to the input of the corresponding Java compilation unit ( sourceSet in a Java project; variant in an Android project), so that they can be compiled along with your Java sources.

For more information about the Protobuf Compiler, please refer to Google Developers Site .

Latest Version

The latest version is 0.7.7 . It requires at least Gradle 2.12 and Java 7 . It is available on Maven Central. To add dependency to it:

buildscript {
  repositories {
    mavenCentral()
  }
  dependencies {
    classpath 'com.google.protobuf:protobuf-gradle-plugin:0.7.7'
  }
}

Latest changes are included in the SNAPSHOT artifact:

buildscript {
  repositories {
    maven {
       url 'https://oss.sonatype.org/content/repositories/snapshots/'
    }
  }
  dependencies {
    classpath 'com.google.protobuf:protobuf-gradle-plugin:0.7.8-SNAPSHOT'
  }
}

However, the availability and freshness of the SNAPSHOT artifact are not guaranteed. You can instead download the source and build it with ./gradlew install , then:

buildscript {
  repositories {
    mavenLocal()
  }
  dependencies {
    classpath 'com.google.protobuf:protobuf-gradle-plugin:0.7.8-SNAPSHOT'
  }
}

Usage

Adding the plugin to your project

This plugin must work with either the Java plugin or the Android plugin.

Using the apply method

The Java plugin or the Android plugin must be applied before the Protobuf plugin:

apply plugin: 'java'
apply plugin: 'com.google.protobuf'
apply plugin: 'com.android.application'  // or 'com.android.library'
apply plugin: 'com.google.protobuf'

Using the Gradle plugin DSL

The order of the plugins doesn't matter:

plugins {
  id "com.google.protobuf" version "0.7.7"
  id "java"
}

Configuring Protobuf compilation

The Protobuf plugin assumes Protobuf files ( *.proto ) are organized in the same way as Java source files, in sourceSets . The Protobuf files of a sourceSet (or variant in an Android project) are compiled in a single protoc run, and the generated files are added to the input of the Java compilation run of that sourceSet (or variant ).

Cutomizing source directories

The plugin adds a new sources block named proto alongside java to every sourceSet. By default, it includes all *.proto files under src/$sourceSetName/proto . You can customize it in the same way as you would customize the java sources.

For Java projects, use the top-level sourceSet :

sourceSets {
  main {
    proto {
      // In addition to the default 'src/main/proto'
      srcDir 'src/main/protobuf'
      srcDir 'src/main/protocolbuffers'
      // In addition to the default '**/*.proto' (use with caution).
      // Using an extension other than 'proto' is NOT recommended,
      // because when proto files are published along with class files, we can
      // only tell the type of a file from its extension.
      include '**/*.protodevel'
    }
    java {
      ...
    }
  }
  test {
    proto {
      // In addition to the default 'src/test/proto'
      srcDir 'src/test/protocolbuffers'
    }
  }
}

For Android projects, use android.sourceSets :

android {
  sourceSets {
    main {
      proto {
        ...
      }
      java {
        ...
      }
    }
  }
}

Customizing Protobuf compilation

The plugin adds a protobuf block to the project. It provides all the configuration knobs.

Locate external executables

By default the plugin will search for the protoc executable in the system search path. We recommend you to take the advantage of pre-compiled protoc that we have published on Maven Central:

protobuf {
  ...
  // Configure the protoc executable
  protoc {
    // Download from repositories
    artifact = 'com.google.protobuf:protoc:3.0.0-alpha-3'
  }
  ...
}

You may also specify a local path.

protobuf {
  ...
  protoc {
    path = '/usr/local/bin/protoc'
  }
  ...
}

Mulitple assignments are allowed in the protoc block. The last one wins.

You may also run protoc with codegen plugins. You need to define all the codegen plugins you will use in the plugins block, by specifying the downloadable artifact or a local path, in the same syntax as in the protoc block above. This will not apply the plugins. You need to configure the tasks in the generateProtoTasks block introduced below to apply the plugins defined here.

protobuf {
  ...
  // Configure the codegen plugins
  plugins {
    // Define a plugin with name 'grpc'
    grpc {
      artifact = 'io.grpc:protoc-gen-grpc-java:0.1.0-SNAPSHOT'
      // or
      path = 'tools/protoc-gen-grpc-java'
    }
    xrpc {
      path = 'tools/protoc-gen-xrpc'
    }
    // Any other plugins
    ...
  }
  ...
}

Customize code generation tasks

The Protobuf plugin generates a task for each protoc run, which is for a sourceSet in a Java project, or a variant in an Android project. The task has configuration interfaces that allow you to control the type of outputs, the codegen plugins to use, and parameters.

You must configure these tasks in the generateProtoTasks block, which provides you helper functions to conveniently access tasks that are tied to a certain build element, and also ensures you configuration will be picked up correctly by the plugin.

DONOTs:

  • DO NOT assume the names of the tasks, as they may change.
  • DO NOT configure the tasks outside of the generateProtoTasks block, because there are subtle timing constraints on when the tasks should be configured.
protobuf {
  ...
  generateProtoTasks {
    // all() returns the collection of all protoc tasks
    all().each { task ->
      // Here you can configure the task
    }

    // In addition to all(), you may get the task collection by various
    // criteria:

    // (Java only) returns tasks for a sourceSet
    ofSourceSet('main')
    // (Android only) returns tasks for a flavor
    ofFlavor('demo')
    // (Android only) returns tasks for a buildType
    ofBuildType('release')
    // (Android only) returns tasks for a variant
    ofVariant('demoRelease')
    // (Android only) returns non-androidTest tasks
    ofNonTest()
    // (Android only) return androidTest tasks
    ofTest()
  }
}

Here is how to control protoc built-in outputs in a closure passed to builtins , which configures a NamedDomainObjectContainer .

{ task ->
  // Configure built-in outputs. Each block generates a
  // '--<name>_out' flag to the protoc command line.
  task.builtins {
    // In Java projects, the "java" output is added automatically.
    // You only need it if you want it in an Android project or want to add
    // options.
    // DO NOT omit the braces if you want this builtin to be added.
    java { }
    // In Android projects, the "javanano" output is added automatically.
    // You only need it if you want it in an Java project or want to add
    // options.
    javanano {
      // Options added to --javanano_out
      option 'java_multiple_files=true'
      option 'ignore_services=true'
    }
    // Any other builtins
    ...
  }
}

If you want to remove the built-in output that is automatically added, use remove method of NamedDomainObjectContainer . For example, to generate javanano instead of java in a Java project:

{ task ->
  task.builtins {
    remove java
    javanano { }
  }
}

Here is how you apply codegen plugins that have been defined in the protobuf.plugins block introduced above.

{ task ->
  // Configure codegen plugins. Each block generates two flags
  // to the protoc command line:
  //  - '--plugin=protoc-gen-<name>:<plugin-path>', and
  //  - '--<name>_out=<output-dir>
  // <name> must have been defined in the protobuf.plugins block
  task.plugins {
    // Use the "grpc" plugin in this task.
    grpc {
      // Options added to --grpc_out
      option 'nano=true'
    }
    // Use the "xrpc" plugin, with no options (braces cannot be omitted)
    xrpc { }
    // Any other plugins
  }
}

The task also provides following options:

{ task ->
  // If true, will generate a descriptor_set.desc file under
  // $generatedFilesBaseDir/$sourceSet. Default is false.
  // See --descriptor_set_out in protoc documentation about what it is.
  task.generateDescriptorSet = true

  // Allows to override the default for the descriptor set location
  task.descriptorSetOptions.path =
    "${projectDir}/build/descriptors/{$task.sourceSet.name}.dsc"

  // If true, the descriptor set will contain line number information
  // and comments. Default is false.
  task.descriptorSetOptions.includeSourceInfo = true

  // If true, the descriptor set will contain all transitive imports and
  // is therefore self-contained. Default is false.
  task.descriptorSetOptions.includeImports = true
}

Change where the generated files are

By default generated Java files are under $generatedFilesBaseDir/$sourceSet/$builtinPluginName , where $generatedFilesBaseDir is $buildDir/generated/source/proto by default, and is configurable. E.g.,

protobuf {
  ...
  generatedFilesBaseDir = "$projectDir/src/generated"
}

The subdirectory name, which is by default $builtinPluginName , can also be changed by setting the outputSubDir property in the builtins or plugins block of a task configuration within generateProtoTasks block (see previous section). E.g.,

{ task ->
  task.plugins {
    grpc {
      // Write the generated files under
      // "$generatedFilesBaseDir/$sourceSet/grpcjava"
      outputSubDir = 'grpcjava'
    }
  }
}

Protos in dependencies

If a Java project contains proto files, they will be packaged in the jar files along with the compiled classes. If a compile configuration has a dependency on a project or library jar that contains proto files, they will be added to the --proto_path flag of the protoc command line, so that they can be imported in the proto files of the dependent project. The imported proto files will not be compiled since they have already been compiled in their own projects. Example:

dependencies {
  compile project(':someProjectWithProtos')
  testCompile files("lib/some-testlib-with-protos.jar")
}

If there is a project, package or published artifact that contains just protos files, whose compiled classes are absent, and you want to use these proto files in your project and compile them, you can add it to protobuf dependencies. Example:

dependencies {
  protobuf files('lib/protos.tar.gz')
  testProtobuf 'com.example:published-protos:1.0.0'
}

Pre-compiled protoc artifacts

This Maven Central directory lists pre-compiled protoc artifacts that can be used by this plugin.

Tips for IDEs

IntelliJ IDEA

If IntelliJ complains that the generated classes are not found, you can include the following block in you build.gradle to ask IntelliJ to include the generated Java directories as source folders.

idea {
    module {
        sourceDirs += file("${protobuf.generatedFilesBaseDir}/main/java");
        // If you have additional sourceSets and/or codegen plugins, add all of them
        sourceDirs += file("${protobuf.generatedFilesBaseDir}/main/grpc");
    }
}

Testing the plugin

testProject* are testing projects that uses this plugin to compile .proto files. They also serve as usage examples. Because the tests include an Android project, you need to install Android SDK Tools .

After you made any change to the plugin, be sure to run these tests.

$ ./gradlew install && ./gradlew clean test && ./gradlew test

The tests use the plugin installed in Maven local repo, so you must install it before testing it. We cannot make the tests depend the plugin project directly, because the test projects apply the plugin at evaluation time. At evaluation time the plugin project has not been compiled yet. The second test run is to make sure incremental build works.





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