GradleでSpring Bootをビルドしたときのjarファイル

Spring Boot 2.5からGradleでビルドすると *.jar と *-plain.jar の２つが生成されるようになったので、これらについてのメモ。

Demo

Spring InitializrからGradle Projectを選択してプロジェクトを作成する。（ArtifactなどのProject Metadataはデフォルトのまま）

% tree .
.
├── HELP.md
├── build.gradle
├── gradle
│   └── wrapper
│       ├── gradle-wrapper.jar
│       └── gradle-wrapper.properties
├── gradlew
├── gradlew.bat
├── settings.gradle
└── src
    ├── main
    │   ├── java
    │   │   └── com
    │   │       └── example
    │   │           └── demo
    │   │               └── DemoApplication.java
    │   └── resources
    │       └── application.properties
    └── test
        └── java
            └── com
                └── example
                    └── demo
                        └── DemoApplicationTests.java

14 directories, 10 files

build.gradle

plugins {
    id 'org.springframework.boot' version '2.6.3'
    id 'io.spring.dependency-management' version '1.0.11.RELEASE'
    id 'java'
}

group = 'com.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '11'

repositories {
    mavenCentral()
}

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter'
    testImplementation 'org.springframework.boot:spring-boot-starter-test'
}

tasks.named('test') {
    useJUnitPlatform()
}

このプロジェクトをビルドすると、2つのjarファイルができる。

• demo-0.0.1-SNAPSHOT.jar
• demo-0.0.1-SNAPSHOT-plain.jar

demo-0.0.1-SNAPSHOT.jar

bootJarタスクによって生成されるSpring Boot fat jarで、全てのモジュールのdependenciesを含んでいるため、java -jar demo-0.0.1-SNAPSHOT.jar で実行できる。

% jar tf build/libs/demo-0.0.1-SNAPSHOT.jar
META-INF/
META-INF/MANIFEST.MF
org/
org/springframework/
org/springframework/boot/
org/springframework/boot/loader/
org/springframework/boot/loader/ClassPathIndexFile.class
org/springframework/boot/loader/ExecutableArchiveLauncher.class
org/springframework/boot/loader/JarLauncher.class
org/springframework/boot/loader/LaunchedURLClassLoader$DefinePackageCallType.class
org/springframework/boot/loader/LaunchedURLClassLoader$UseFastConnectionExceptionsEnumeration.class
org/springframework/boot/loader/LaunchedURLClassLoader.class
org/springframework/boot/loader/Launcher.class
org/springframework/boot/loader/MainMethodRunner.class
org/springframework/boot/loader/PropertiesLauncher$1.class
org/springframework/boot/loader/PropertiesLauncher$ArchiveEntryFilter.class
org/springframework/boot/loader/PropertiesLauncher$ClassPathArchives.class
org/springframework/boot/loader/PropertiesLauncher$PrefixMatchingArchiveFilter.class
org/springframework/boot/loader/PropertiesLauncher.class
org/springframework/boot/loader/WarLauncher.class
org/springframework/boot/loader/archive/
org/springframework/boot/loader/archive/Archive$Entry.class
org/springframework/boot/loader/archive/Archive$EntryFilter.class
org/springframework/boot/loader/archive/Archive.class
org/springframework/boot/loader/archive/ExplodedArchive$AbstractIterator.class
org/springframework/boot/loader/archive/ExplodedArchive$ArchiveIterator.class
org/springframework/boot/loader/archive/ExplodedArchive$EntryIterator.class
org/springframework/boot/loader/archive/ExplodedArchive$FileEntry.class
org/springframework/boot/loader/archive/ExplodedArchive$SimpleJarFileArchive.class
org/springframework/boot/loader/archive/ExplodedArchive.class
org/springframework/boot/loader/archive/JarFileArchive$AbstractIterator.class
org/springframework/boot/loader/archive/JarFileArchive$EntryIterator.class
org/springframework/boot/loader/archive/JarFileArchive$JarFileEntry.class
org/springframework/boot/loader/archive/JarFileArchive$NestedArchiveIterator.class
org/springframework/boot/loader/archive/JarFileArchive.class
org/springframework/boot/loader/data/
org/springframework/boot/loader/data/RandomAccessData.class
org/springframework/boot/loader/data/RandomAccessDataFile$1.class
org/springframework/boot/loader/data/RandomAccessDataFile$DataInputStream.class
org/springframework/boot/loader/data/RandomAccessDataFile$FileAccess.class
org/springframework/boot/loader/data/RandomAccessDataFile.class
org/springframework/boot/loader/jar/
org/springframework/boot/loader/jar/AbstractJarFile$JarFileType.class
org/springframework/boot/loader/jar/AbstractJarFile.class
org/springframework/boot/loader/jar/AsciiBytes.class
org/springframework/boot/loader/jar/Bytes.class
org/springframework/boot/loader/jar/CentralDirectoryEndRecord$1.class
org/springframework/boot/loader/jar/CentralDirectoryEndRecord$Zip64End.class
org/springframework/boot/loader/jar/CentralDirectoryEndRecord$Zip64Locator.class
org/springframework/boot/loader/jar/CentralDirectoryEndRecord.class
org/springframework/boot/loader/jar/CentralDirectoryFileHeader.class
org/springframework/boot/loader/jar/CentralDirectoryParser.class
org/springframework/boot/loader/jar/CentralDirectoryVisitor.class
org/springframework/boot/loader/jar/FileHeader.class
org/springframework/boot/loader/jar/Handler.class
org/springframework/boot/loader/jar/JarEntry.class
org/springframework/boot/loader/jar/JarEntryCertification.class
org/springframework/boot/loader/jar/JarEntryFilter.class
org/springframework/boot/loader/jar/JarFile$1.class
org/springframework/boot/loader/jar/JarFile$JarEntryEnumeration.class
org/springframework/boot/loader/jar/JarFile.class
org/springframework/boot/loader/jar/JarFileEntries$1.class
org/springframework/boot/loader/jar/JarFileEntries$EntryIterator.class
org/springframework/boot/loader/jar/JarFileEntries$Offsets.class
org/springframework/boot/loader/jar/JarFileEntries$Zip64Offsets.class
org/springframework/boot/loader/jar/JarFileEntries$ZipOffsets.class
org/springframework/boot/loader/jar/JarFileEntries.class
org/springframework/boot/loader/jar/JarFileWrapper.class
org/springframework/boot/loader/jar/JarURLConnection$1.class
org/springframework/boot/loader/jar/JarURLConnection$JarEntryName.class
org/springframework/boot/loader/jar/JarURLConnection.class
org/springframework/boot/loader/jar/StringSequence.class
org/springframework/boot/loader/jar/ZipInflaterInputStream.class
org/springframework/boot/loader/jarmode/
org/springframework/boot/loader/jarmode/JarMode.class
org/springframework/boot/loader/jarmode/JarModeLauncher.class
org/springframework/boot/loader/jarmode/TestJarMode.class
org/springframework/boot/loader/util/
org/springframework/boot/loader/util/SystemPropertyUtils.class
BOOT-INF/
BOOT-INF/classes/
BOOT-INF/classes/com/
BOOT-INF/classes/com/example/
BOOT-INF/classes/com/example/demo/
BOOT-INF/classes/com/example/demo/DemoApplication.class
BOOT-INF/classes/application.properties
BOOT-INF/lib/
BOOT-INF/lib/spring-boot-autoconfigure-2.6.3.jar
BOOT-INF/lib/spring-boot-2.6.3.jar
BOOT-INF/lib/jakarta.annotation-api-1.3.5.jar
BOOT-INF/lib/spring-context-5.3.15.jar
BOOT-INF/lib/spring-aop-5.3.15.jar
BOOT-INF/lib/spring-beans-5.3.15.jar
BOOT-INF/lib/spring-expression-5.3.15.jar
BOOT-INF/lib/spring-core-5.3.15.jar
BOOT-INF/lib/snakeyaml-1.29.jar
BOOT-INF/lib/logback-classic-1.2.10.jar
BOOT-INF/lib/log4j-to-slf4j-2.17.1.jar
BOOT-INF/lib/jul-to-slf4j-1.7.33.jar
BOOT-INF/lib/spring-jcl-5.3.15.jar
BOOT-INF/lib/logback-core-1.2.10.jar
BOOT-INF/lib/slf4j-api-1.7.33.jar
BOOT-INF/lib/log4j-api-2.17.1.jar
BOOT-INF/lib/spring-boot-jarmode-layertools-2.6.3.jar
BOOT-INF/classpath.idx
BOOT-INF/layers.idx

demo-0.0.1-SNAPSHOT-plain.jar

jarタスクによって生成されるplain jarファイルで、このモジュールのclassとresourceのみを含んでいる。

% jar tf build/libs/demo-0.0.1-SNAPSHOT-plain.jar
META-INF/
META-INF/MANIFEST.MF
com/
com/example/
com/example/demo/
com/example/demo/DemoApplication.class
application.properties

plain jarを生成したくない場合は、build.gradleにこの設定を追加する。

jar {
    enabled = false
}

参考

• https://stackoverflow.com/questions/67935064/difference-between-spring-boot-2-5-0-generated-jar-and-plain-jar
• https://docs.spring.io/spring-boot/docs/2.6.3/gradle-plugin/reference/htmlsingle/#packaging-executable.and-plain-archives