从start.spring.io下载的Maven Java项目在IntelliJ中运行报错求助

Hey there, let's work through this issue you're facing—running a Spring Boot 2.0.0 project (with Web, JPA, Vaadin dependencies) on Java 9 in IntelliJ has been throwing errors, and you've had similar issues with start.spring.io projects before. Here are the most likely fixes:

1. Fix Version Compatibility Gaps #

Spring Boot 2.0.0 has experimental, limited support for Java 9—it was primarily built for Java 8. This mismatch often causes module system (JPMS) conflicts or missing compatibility layers.

• Option 1: Downgrade your Java SDK to 8. This is the most reliable fix since Spring Boot 2.0.x is fully optimized for Java 8.
• Option 2: Upgrade your Spring Boot version to 2.1.x or later. These releases have much better Java 9 support and resolve many of the early compatibility bugs.

2. Resolve Vaadin-Java 9 Compatibility #

Older Vaadin versions paired with Spring Boot 2.0.0 might not handle Java 9's module system correctly.

• Check your pom.xml for the Vaadin version—upgrade it to a release that explicitly supports Java 9 (Vaadin 10+ should work, but verify the compatibility matrix with your Spring Boot version).
• If you're using the Spring Boot Vaadin starter, make sure the starter version aligns with both your Spring Boot and Vaadin versions to avoid dependency conflicts.

3. Correct IntelliJ's Project Configuration #

IntelliJ sometimes misconfigures Java 9 projects, especially with older Spring Boot versions:

• Open Project Structure (Ctrl+Alt+Shift+S on Windows/Linux, Cmd+; on Mac):
  • Confirm the Project SDK is set to Java 9.
  • Set the Language Level for your module to 9 (or "9 - Modules, private methods, etc.").
• Try switching your project dependencies from Module Path to Class Path: Right-click your project → Open Module Settings → Libraries → Select each library → Change from "Module Path" to "Class Path". This bypasses JPMS module issues that early Spring Boot versions don't handle well.

4. Fix Maven Compiler Configuration #

Your pom.xml might not be set up to compile for Java 9, leading to runtime mismatches:
Add or update the maven-compiler-plugin in your build plugins section:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.8.1</version>
            <configuration>
                <source>9</source>
                <target>9</target>
                <!-- Optional: Add this if you hit JPA-related module access issues -->
                <compilerArgs>
                    <arg>--add-modules java.xml.bind</arg>
                </compilerArgs>
            </configuration>
        </plugin>
    </plugins>
</build>

The --add-modules java.xml.bind flag fixes common JPA errors since Java 9 moved JAXB to optional modules.

5. Clean Corrupted Maven Dependencies #

If you've had issues with other start.spring.io projects before, your local Maven repository might have corrupted or incomplete dependencies:

• Delete the relevant folders from your local Maven repo (usually ~/.m2/repository/org/springframework and ~/.m2/repository/com/vaadin).
• Run mvn clean install in your project root to re-download fresh, uncorrupted dependencies.

Give these steps a shot—if you still hit errors, sharing the exact stack trace from IntelliJ would help pinpoint the exact issue faster!

内容的提问来源于stack exchange，提问作者Glement