Gradleでjavadoc.jarを生成したい

Question

実現したいこと

javadoc.jarを生成したい

問題

gradle build実行時にエラー: この文字(0x84)は、エンコーディングwindows-31jにマップできませんが発生します。
task javadocJarを削除すれば問題なくgradle buildが実行されますが、
javadoc.jarを生成したいので、削除するわけにはいきません。

該当のソースコード・ログ

buildscript {
  ext {
    jackson = '2.9.9'
    slf4j = '1.7.28'
    lombok = '1.18.8'
    assertj = '3.13.2'
    junit = '5.5.1'
  }
}

def defaultEncoding = 'UTF-8'

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'idea'

sourceCompatibility = JavaVersion.VERSION_11
targetCompatibility = JavaVersion.VERSION_11

repositories {
  mavenCentral()
}

wrapper {
  gradleVersion = '5.6'
}

tasks.withType(JavaCompile) {
  options.encoding = defaultEncoding
}

task sourcesJar(type: Jar, dependsOn: classes) {
  archiveClassifier.set('sources')
  from sourceSets.main.allSource
}

task javadocJar(type: Jar, dependsOn: javadoc) {
  archiveClassifier.set('javadoc')
  from javadoc.destinationDir
}

artifacts {
  archives sourcesJar
  archives javadocJar
}

test {
  useJUnitPlatform {
    includeEngines 'junit-jupiter'
  }
}

task javadoc(type: Javadoc, overwrite: true) {
  source = sourceSets.main.allJava
  options.links('https://docs.oracle.com/javase/jp/11/docs/api/')
  options.memberLevel = JavadocMemberLevel.PRIVATE
  destinationDir = new File("$projectDir" + '/docs')
  options.charSet = defaultEncoding
  options.encoding = defaultEncoding
}

dependencies {
  implementation "com.fasterxml.jackson.core:jackson-databind:${jackson}"
  implementation "com.fasterxml.jackson.datatype:jackson-datatype-jsr310:${jackson}"
  implementation "org.slf4j:slf4j-simple:${slf4j}"
  annotationProcessor "org.projectlombok:lombok:${lombok}"
  compileOnly "org.projectlombok:lombok:${lombok}"
  testAnnotationProcessor "org.projectlombok:lombok:${lombok}"
  testImplementation "org.projectlombok:lombok:${lombok}"
  testImplementation "org.assertj:assertj-core:${assertj}"
  testImplementation "org.junit.jupiter:junit-jupiter-api:${junit}"
  testRuntimeOnly "org.junit.jupiter:junit-jupiter-engine:${junit}"
}

エラー詳細。

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':javadoc'.
> Javadoc generation failed. Generated Javadoc options file (useful for troubleshooting): 'C:\develop\project\example\build\tmp\javadoc\javadoc.options'

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 2s
4 actionable tasks: 1 executed, 3 up-to-date

トレースログ（文字数制限のため一部省略）

org.gradle.api.tasks.TaskExecutionException: Execution failed for task ':javadoc'.
        at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter$3.accept(ExecuteActionsTaskExecuter.java:166)
        at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter$3.accept(ExecuteActionsTaskExecuter.java:163)
        at org.gradle.internal.Try$Failure.ifSuccessfulOrElse(Try.java:191)
        at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:156)
Caused by: org.gradle.api.GradleException: Javadoc generation failed. Generated Javadoc options file (useful for troubleshooting): 'C:\develop\project\example\build\tmp\javadoc\javadoc.options'
        at org.gradle.api.tasks.javadoc.internal.JavadocGenerator.execute(JavadocGenerator.java:58)
        at org.gradle.api.tasks.javadoc.internal.JavadocGenerator.execute(JavadocGenerator.java:31)
        at org.gradle.api.tasks.javadoc.Javadoc.executeExternalJavadoc(Javadoc.java:158)
        at org.gradle.api.tasks.javadoc.Javadoc.generate(Javadoc.java:146)
        ... 34 more
Caused by: org.gradle.process.internal.ExecException: Process 'command 'C:\develop\java\jdk-11.0.2\bin\javadoc.exe'' finished with non-zero exit value 1
        at org.gradle.process.internal.DefaultExecHandle$ExecResultImpl.assertNormalExitValue(DefaultExecHandle.java:409)
        at org.gradle.process.internal.DefaultExecAction.execute(DefaultExecAction.java:38)
        at org.gradle.api.tasks.javadoc.internal.JavadocGenerator.execute(JavadocGenerator.java:53)
        ... 94 more

Answer 1

build.gradleでエンコーディングを指定することを諦めました。
環境変数にJAVA_TOOL_OPTIONS: -Dfile.encoding=UTF8を追加し対応しました。