是否可以包含Java9（或10）依赖项？因为Kotlin到目前为止只能编译到Java 8。我得到一个java.lang.UnsupportedClassVersionError错误，显然说明我所包含的JAR /依赖项中的一个类已经被更新版本的Java Runtime编译。但是，我无法指定更新的JDK，它能够运行使用旧版本编译的类（Kotlin的东西？）。
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.7.0</version>
<configuration>
<release>9</release>
<source>${maven.compiler.source}</source>
<target>${maven.compiler.target}</target>
<encoding>${project.build.sourceEncoding}</encoding>
</configuration>
<dependencies>
<dependency>
<groupId>org.ow2.asm</groupId>
<artifactId>asm</artifactId>
<version>6.1</version> <!-- Use newer version of ASM -->
</dependency>
</dependencies>
</plugin>
使用属性
<maven.compiler.source>9</maven.compiler.source>
<maven.compiler.target>9</maven.compiler.target>
但现在我收到了错误：
"Error:Kotlin: Unknown JVM target version: 1.9
Supported versions: 1.6, 1.8"
Kotlin版本是1.2.41，到目前为止我总是可以切换到最新版本直到它发布...
可以使用以下XML片段。但是java.lang.UnsupportedClassVersionError的问题仍然存在。
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.5.1</version>
<configuration>
<source>9</source>
<target>9</target>
</configuration>
<executions>
<!-- Replacing default-compile as it is treated specially by maven -->
<execution>
<id>default-compile</id>
<phase>none</phase>
</execution>
<!-- Replacing default-testCompile as it is treated specially by maven -->
<execution>
<id>default-testCompile</id>
<phase>none</phase>
</execution>
<execution>
<id>java-compile</id>
<phase>compile</phase>
<goals> <goal>compile</goal> </goals>
</execution>
<execution>
<id>java-test-compile</id>
<phase>test-compile</phase>
<goals> <goal>testCompile</goal> </goals>
</execution>
</executions>
</plugin>
我正在尝试为我当前的Java9项目构建一个Kotlin模块/ maven包。
Maven-Kotlin插件配置为：
<plugin>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-maven-plugin</artifactId>
<version>${kotlin.version}</version>
<configuration>
<jvmTarget>1.8</jvmTarget>
</configuration>
<executions>
<execution>
<id>compile</id>
<phase>compile</phase>
<goals>
<goal>compile</goal>
</goals>
<configuration>
<sourceDirs>
<source>src/main/java</source>
<source>src/main/kotlin</source>
</sourceDirs>
</configuration>
</execution>
<execution>
<id>test-compile</id>
<phase>test-compile</phase>
<goals>
<goal>test-compile</goal>
</goals>
<configuration>
<sourceDirs>
<source>src/test/java</source>
<source>src/test/kotlin</source>
</sourceDirs>
</configuration>
</execution>
</executions>
</plugin>
我的整个pom.xml：
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>restful-web</groupId>
<artifactId>restful-web</artifactId>
<version>1.0-SNAPSHOT</version>
<properties>
<kotlin.version>1.2.41</kotlin.version>
<kotlin.compiler.jvmTarget>1.8</kotlin.compiler.jvmTarget>
<sirix.version>0.8.9-SNAPSHOT</sirix.version>
<main.verticle>org.sirix.rest.SirixVerticle</main.verticle>
<maven.compiler.source>9</maven.compiler.source>
<maven.compiler.target>9</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>io.vertx</groupId>
<artifactId>vertx-core</artifactId>
<version>3.5.1</version>
</dependency>
<dependency>
<groupId>io.vertx</groupId>
<artifactId>vertx-web</artifactId>
<version>3.5.1</version>
</dependency>
<dependency>
<groupId>io.vertx</groupId>
<artifactId>vertx-lang-kotlin</artifactId>
<version>3.5.1</version>
</dependency>
<dependency>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-stdlib-jdk8</artifactId>
<version>${kotlin.version}</version>
</dependency>
<dependency>
<groupId>com.github.sirixdb.sirix</groupId>
<artifactId>sirix-core</artifactId>
<version>${sirix.version}</version>
</dependency>
<dependency>
<groupId>com.github.sirixdb.sirix</groupId>
<artifactId>sirix-xquery</artifactId>
<version>${sirix.version}</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.5.1</version>
<configuration>
<source>${maven.compiler.source}</source>
<target>${maven.compiler.target}</target>
</configuration>
<executions>
<!-- Replacing default-compile as it is treated specially by maven -->
<execution>
<id>default-compile</id>
<phase>none</phase>
</execution>
<!-- Replacing default-testCompile as it is treated specially by maven -->
<execution>
<id>default-testCompile</id>
<phase>none</phase>
</execution>
<execution>
<id>java-compile</id>
<phase>compile</phase>
<goals> <goal>compile</goal> </goals>
</execution>
<execution>
<id>java-test-compile</id>
<phase>test-compile</phase>
<goals> <goal>testCompile</goal> </goals>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-shade-plugin</artifactId>
<version>2.3</version>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>shade</goal>
</goals>
<configuration>
<transformers>
<transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
<manifestEntries>
<Main-Class>io.vertx.core.Launcher</Main-Class>
<Main-Verticle>${main.verticle}</Main-Verticle>
</manifestEntries>
</transformer>
<transformer implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
<resource>META-INF/services/io.vertx.core.spi.VerticleFactory</resource>
</transformer>
</transformers>
<artifactSet>
</artifactSet>
<outputFile>${project.build.directory}/${project.artifactId}-${project.version}-fat.jar</outputFile>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-maven-plugin</artifactId>
<version>${kotlin.version}</version>
<configuration>
<jvmTarget>1.8</jvmTarget>
</configuration>
<executions>
<execution>
<id>compile</id>
<phase>compile</phase>
<goals>
<goal>compile</goal>
</goals>
<configuration>
<sourceDirs>
<source>src/main/java</source>
<source>src/main/kotlin</source>
</sourceDirs>
</configuration>
</execution>
<execution>
<id>test-compile</id>
<phase>test-compile</phase>
<goals>
<goal>test-compile</goal>
</goals>
<configuration>
<sourceDirs>
<source>src/test/java</source>
<source>src/test/kotlin</source>
</sourceDirs>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
<pluginRepositories>
<pluginRepository>
<id>kotlin-bintray</id>
<name>Kotlin Bintray</name>
<url>http://dl.bintray.com/kotlin/kotlin-dev</url>
<releases>
<enabled>true</enabled>
</releases>
<snapshots>
<enabled>false</enabled>
</snapshots>
</pluginRepository>
</pluginRepositories>
<repositories>
<repository>
<id>sonatype-nexus-snapshots</id>
<name>Sonatype Nexus Snapshots</name>
<url>https://oss.sonatype.org/content/repositories/snapshots</url>
<releases>
<enabled>false</enabled>
</releases>
<snapshots>
<enabled>true</enabled>
</snapshots>
</repository>
</repositories>
</project>
错误消息/堆栈跟踪的相关部分是：
java.lang.UnsupportedClassVersionError: org/sirix/access/conf/DatabaseConfiguration has been compiled by a more recent version of the Java Runtime (class file version 53.0), this version of the Java Runtime only recognizes class file versions up to 52.0
答案 0 :(得分：5)
我怀疑问题出现在Kotlin Maven插件中，该插件直接从-jvm-target / maven.compiler.source属性推断出maven.compiler.target参数值，而没有考虑到Kotlin编译器这一事实仅支持1.6和1.8版。例如，解决方法是将JVM字节码目标版本明确指定为1.8（请注意，1.8目标字节码将在Java 9上运行得很好）：
<plugin>
<artifactId>kotlin-maven-plugin</artifactId>
<groupId>org.jetbrains.kotlin</groupId>
<version>${kotlin.version}</version>
...
<configuration>
<jvmTarget>1.8</jvmTarget>
</configuration>
</plugin>
也就是说，我无法在一个小样本项目中重现您的问题，所以如果您有一分钟，如果您在https://kotl.in/issue报告了问题，我将非常感谢