Overview

This is a Gradle plugin to allow easily performing Java code generation for Apache Avro. It supports JSON schema declaration files, JSON protocol declaration files, and Avro IDL files.

Compatibility

NOTE: Pre-1.0 versions used a different publishing process/namespace. It is strongly recommended to upgrade to a newer version. Further details can be found in the change log.

• Currently tested against Java 8-15
  • Java 15 support requires Gradle 6.7 or higher (as per Gradle's release notes)
  • Java 14 support requires Gradle 6.3 or higher (as per Gradle's release notes)
  • Java 13 support requires Gradle 6.0 or higher
  • Java 11 support requires Gradle 5.1 or higher (versions lower than 5.1 are no longer supported)
  • Though not supported yet, tests are also run against early-access builds of Java 16 to provide early notification of potential incompatibilities
• Currently built against Gradle 6.7.1
  • Currently tested against Gradle 5.1-5.6.4 and 6.0-6.7.1
• Currently built against Avro 1.10.1
  • Currently tested against Avro 1.10.0-1.10.1
• Support for Kotlin
  • Currently tested against Kotlin plugin versions 1.3.20-1.3.72 and 1.4.0-1.4.20 using the latest compatible version of Gradle
  • Currently tested against Kotlin plugin versions 1.2.20-1.2.71 and 1.3.0-1.3.11 using Gradle 5.1
  • Kotlin plugin versions starting with 1.4.0 require Gradle 5.3+
  • Kotlin plugin versions prior to 1.2.30 do not support Java 10+
  • Version of the Kotlin plugin prior to 1.2.20 are unlikely to work
• Support for Gradle Kotlin DSL

Usage

Add the following to your build files. Substitute the desired version based on CHANGES.md.

settings.gradle:

pluginManagement {
    repositories {
        gradlePluginPortal()
        mavenCentral()
    }
}

build.gradle:

plugins {
    id "com.github.davidmc24.gradle.plugin.avro" version "VERSION"
}

Additionally, ensure that you have a compile dependency on Avro, such as:

repositories {
    mavenCentral()
}
dependencies {
    compile "org.apache.avro:avro:1.10.1"
}

If you now run gradle build, Java classes will be compiled from Avro files in src/main/avro. Actually, it will attempt to process an "avro" directory in every SourceSet (main, test, etc.)

Configuration

There are a number of configuration options supported in the avro block.

createSetters

Valid values: true (default), false; supports equivalent String values

Set to false to not create setter methods in the generated classes.

Example:

avro {
    createSetters = false
}

createOptionalGetters

Valid values: false (default), true; supports equivalent String values

Set to true to create additional getter methods that return their fields wrapped in an Optional. For a field with name abc and type string, this setting will create a method Optional<java.lang.String> getOptionalAbc().

Example:

avro {
    createOptionalGetters = false
}

gettersReturnOptional

Valid values: false (default), true; supports equivalent String values

Set to true to cause getter methods to return Optional wrappers of the underlying type. Where createOptionalGetters generates an additional method, this one replaces the existing getter.

Example:

avro {
    gettersReturnOptional = false
}

optionalGettersForNullableFieldsOnly

Valid values: false (default), true; supports equivalent String values

Set to true in conjuction with gettersReturnOptional to true to return Optional wrappers of the underlying type. Where gettersReturnOptional alone changes all getters to return Optional, this one only returns Optional for nullable (null union) field definitions. Setting this to true without setting gettersReturnOptional to true will result in this flag having no effect.

Example:

avro {
    gettersReturnOptional = true
    optionalGettersForNullableFieldsOnly = true
}

fieldVisibility

Valid values: any FieldVisibility or equivalent String name (matched case-insensitively); default "PUBLIC_DEPRECATED" (default)

By default, the fields in generated Java files will have public visibility and be annotated with @Deprecated. Set to "PRIVATE" to restrict visibility of the fields, or "PUBLIC" to remove the @Deprecated annotations.

Example:

avro {
    fieldVisibility = "PRIVATE"
}

outputCharacterEncoding

Valid values: any Charset or equivalent String name

Controls the character encoding of generated Java files. If using the plugin's conventions (i.e., not just the base plugin), the associated JavaCompile task's encoding will be used automatically. Otherwise, it will use the value configured in the avro block, defaulting to "UTF-8".

Examples:

// Option 1: configure compilation task (avro plugin will automatically match)
tasks.withType(JavaCompile).configureEach {
    options.encoding = 'UTF-8'
}
// Option 2: just configure avro plugin
avro {
    outputCharacterEncoding = "UTF-8"
}

stringType

Valid values: any StringType or equivalent String name (matched case-insensitively); default "String" (default)

By default, the generated Java files will use java.lang.String to represent string types. Alternatively, you can set it to "Utf8" to use org.apache.avro.util.Utf8 or "charSequence" to use java.lang.CharSequence.

avro {
    stringType = "CharSequence"
}

templateDirectory

By default, files will be generated using Avro's default templates. If desired, you can override the template set used by either setting this property or the "org.apache.avro.specific.templates" System property.

avro {
    templateDirectory = "/path/to/velocity/templates"
}

enableDecimalLogicalType

Valid values: true (default), false; supports equivalent String values

By default, generated Java files will use java.math.BigDecimal for representing fixed or bytes fields annotated with "logicalType": "decimal". Set to false to use java.nio.ByteBuffer in generated classes.

Example:

avro {
    enableDecimalLogicalType = false
}

IntelliJ Integration

The plugin attempts to make IntelliJ play more smoothly with generated sources when using Gradle-generated project files. However, there are still some rough edges. It will work best if you first run gradle build, and after that run gradle idea. If you do it in the other order, IntelliJ may not properly exclude some directories within your build directory.

Alternate Usage

If the defaults used by the plugin don't work for you, you can still use the tasks by themselves. In this case, use the com.github.davidmc24.gradle.plugin.avro-base plugin instead, and create tasks of type GenerateAvroJavaTask and/or GenerateAvroProtocolTask.

Here's a short example of what this might look like:

import com.github.davidmc24.gradle.plugin.avro.GenerateAvroJavaTask

apply plugin: "java"
apply plugin: "com.github.davidmc24.gradle.plugin.avro-base"

dependencies {
    implementation "org.apache.avro:avro:1.10.1"
}

def generateAvro = tasks.register("generateAvro", GenerateAvroJavaTask) {
    source("src/avro")
    outputDir = file("dest/avro")
}

tasks.named("compileJava").configure {
    source(generateAvro)
}

File Processing

When using this plugin, it is recommended to define each record/enum/fixed type in its own file rather than using inline type definitions. This approach allows defining any type of schema structure, and eliminates the potential for conflicting definitions of a type between multiple files. The plugin will automatically recognize the dependency and compile the files in the correct order. For example, instead of Cat.avsc:

{
    "name": "Cat",
    "namespace": "example",
    "type": "record",
    "fields" : [
        {
            "name": "breed",
            "type": {
                "name": "Breed",
                "type": "enum",
                "symbols" : [
                    "ABYSSINIAN", "AMERICAN_SHORTHAIR", "BIRMAN", "MAINE_COON", "ORIENTAL", "PERSIAN", "RAGDOLL", "SIAMESE", "SPHYNX"
                ]
            }
        }
    ]
}

use Breed.avsc:

{
    "name": "Breed",
    "namespace": "example",
    "type": "enum",
    "symbols" : ["ABYSSINIAN", "AMERICAN_SHORTHAIR", "BIRMAN", "MAINE_COON", "ORIENTAL", "PERSIAN", "RAGDOLL", "SIAMESE", "SPHYNX"]
}

and Cat.avsc:

{
    "name": "Cat",
    "namespace": "example",
    "type": "record",
    "fields" : [
        {"name": "breed", "type": "Breed"}
    ]
}

There may be cases where the schema files contain inline type definitions and it is undesirable to modify them. In this case, the plugin will automatically recognize any duplicate type definitions and check if they match. If any conflicts are identified, it will cause a build failure.

Kotlin Support

The Java classes generated from your Avro files should be automatically accessible in the classpath to Kotlin classes in the same sourceset, and transitively to any sourcesets that depend on that sourceset. This is accomplished by this plugin detecting that the Kotlin plugin has been applied, and informing the Kotlin compilation tasks of the presence of the generated sources directories for cross-compilation.

This support does not support producing the Avro generated classes as Kotlin classes, as that functionality is not currently provided by the upstream Avro library.

Kotlin DSL Support

Special notes relevant to using this plugin via the Gradle Kotlin DSL:

• Apply the plugin declaratively using the plugins {} block. Otherwise, various features may not work as intended. See Configuring Plugins in the Gradle Kotlin DSL for more details.
• Configuration in the avro {} block must be applied differently than in the Groovy DSL. See the example below for details.

Example Kotlin DSL Setup:

In gradle.build.kts add:

plugins {
    // Find latest release here: https://github.com/davidmc24/gradle-avro-plugin/releases
    id("com.github.davidmc24.gradle.plugin.avro") version "VERSION"
}

And then in your settings.gradle.kts add:

pluginManagement {
    repositories {
        gradlePluginPortal()
        mavenCentral()
    }
}

The syntax for configuring the extension looks like this:

avro {
    isCreateSetters.set(true)
    isCreateOptionalGetters.set(false)
    isGettersReturnOptional.set(false)
    isOptionalGettersForNullableFieldsOnly(false)
    fieldVisibility.set("PUBLIC_DEPRECATED")
    outputCharacterEncoding.set("UTF-8")
    stringType.set("String")
    templateDirectory.set(null as String?)
    isEnableDecimalLogicalType.set(true)
}

Resolving schema dependencies

If desired, you can generate JSON schema with dependencies resolved.

Example build:

import com.github.davidmc24.gradle.plugin.avro.ResolveAvroDependenciesTask

apply plugin: "com.github.davidmc24.gradle.plugin.avro-base"

tasks.register("resolveAvroDependencies", ResolveAvroDependenciesTask) {
    source file("src/avro/normalized")
    outputDir = file("build/avro/resolved")
}

Generating schema files from protocol/IDL

If desired, you can generate JSON schema files. To do this, apply the plugin (either avro or avro-base), and define custom tasks as needed for the schema generation. From JSON protocol files, all that's needed is the GenerateAvroSchemaTask. From IDL files, first use GenerateAvroProtocolTask to convert the IDL files to JSON protocol files, then use GenerateAvroSchemaTask.

Example using base plugin with support for both IDL and JSON protocol files in src/main/avro:

import com.github.davidmc24.gradle.plugin.avro.GenerateAvroProtocolTask
import com.github.davidmc24.gradle.plugin.avro.GenerateAvroSchemaTask

apply plugin: "com.github.davidmc24.gradle.plugin.avro-base"

def generateProtocol = tasks.register("generateProtocol", GenerateAvroProtocolTask) {
    source file("src/main/avro")
    include("**/*.avdl")
    outputDir = file("build/generated-avro-main-avpr")
}

tasks.register("generateSchema", GenerateAvroSchemaTask) {
    dependsOn generateProtocol
    source file("src/main/avro")
    source file("build/generated-avro-main-avpr")
    include("**/*.avpr")
    outputDir = file("build/generated-main-avro-avsc")
}