Heroku部署Java 13应用遇UnsupportedClassVersionError问题求助

Let's break down what's going wrong here and fix it step by step:

1. Fix your system.properties file #

Your current system.properties has an invalid configuration for java.runtime.version — this property should only specify the Java version number, not include runtime flags or your main class. Update it to:

java.runtime.version=13

The --enable-preview flag can't be set here; we need to add it to the JVM arguments used to start your app instead.

2. Add --enable-preview to your appassembler-maven-plugin configuration #

You're using the appassembler-maven-plugin to generate your startup script, but right now it's not including the preview features flag in the JVM arguments. Modify the <program> section of the plugin to add <jvmArguments>:

<plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>appassembler-maven-plugin</artifactId>
    <version>2.1.0</version>
    <configuration>
        <assembleDirectory>target</assembleDirectory>
        <programs>
            <program>
                <mainClass>Main</mainClass>
                <name>teemitze-anna-bot</name>
                <!-- Add this line to enable preview features at runtime -->
                <jvmArguments>--enable-preview</jvmArguments>
            </program>
        </programs>
    </configuration>
    <executions>
        <execution>
            <phase>package</phase>
            <goals>
                <goal>assemble</goal>
            </goals>
        </execution>
    </executions>
</plugin>

This ensures the generated startup script passes the --enable-preview flag to the JVM when launching your app.

3. Confirm your Maven compiler plugin setup is correct #

Your existing maven-compiler-plugin configuration is already correct — it includes <compilerArgs>--enable-preview</compilerArgs> which enables preview features during compilation. This matches your class file version (57.65535, which is Java 13 with preview features), so no changes needed here.

4. Re-deploy your app #

After making these changes:

• Run mvn clean package locally to generate the updated startup script
• Push your code to Heroku or re-deploy the updated package

Your app should now start successfully with preview features enabled.

内容的提问来源于stack exchange，提问作者Teemitze