解决java.lang.ClassFormatError：模块java.base未开放java.lang至未命名模块

异常信息 #

org.springframework.cglib.core.CodeGenerationException: java.lang.reflect.InaccessibleObjectException-->Unable to make protected final java.lang.Class java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain) throws java.lang.ClassFormatError accessible: module java.base does not "opens java.lang" to unnamed module @1ed4004b
    at org.springframework.cglib.core.ReflectUtils.defineClass(ReflectUtils.java:547) ~[spring-core-6.1.3.jar:6.1.3]
    at org.springframework.cglib.core.AbstractClassGenerator.generate(AbstractClassGenerator.java:371) ~[spring-core-6.1.3.jar:6.1.3]
    at org.springframework.cglib.proxy.Enhancer.generate(Enhancer.java:575) ~[spring-core-6.1.3.jar:6.1.3]
    at org.springframework.cglib.core.AbstractClassGenerator$ClassLoaderData.lambda$new$1(AbstractClassGenerator.java:107) ~[spring-core-6.1.3.jar:6.1.3]
    at org.springframework.cglib.core.internal.LoadingCache.lambda$createEntry$1(LoadingCache.java:52) ~[spring-core-6.1.3.jar:6.1.3]
    at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) ~[na:na]
    at org.springframework.cglib.core.internal.LoadingCache.createEntry(LoadingCache.java:57) ~[spring-core-6.1.3.jar:6.1.3]
    at org.springframework.cglib.core.internal.LoadingCache.get(LoadingCache.java:34) ~[spring-core-6.1.3.jar:6.1.3]
    at org.springframework.cglib.core.AbstractClassGenerator$ClassLoaderData.get(AbstractClassGenerator.java:130) ~[spring-core-6.1.3.jar:6.1.3]
    at org.springframework.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:317) ~[spring-core-6.1.3.jar:6.1.3]
    at org.springframework.cglib.proxy.Enhancer.createHelper(Enhancer.java:562) ~[spring-core-6.1.3.jar:6.1.3]
    at org.springframework.cglib.proxy.Enhancer.createClass(Enhancer.java:407) ~[spring-core-6.1.3.jar:6.1.3]
    at org.springframework.context.annotation.ConfigurationClassEnhancer.createClass(ConfigurationClassEnhancer.java:138) ~[spring-context-6.1.3.jar:6.1.3]
    at org.springframework.context.annotation.ConfigurationClassEnhancer.enhance(ConfigurationClassEnhancer.java:109) ~[spring-context-6.1.3.jar:6.1.3]
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.enhanceConfigurationClasses(ConfigurationClassPostProcessor.java:533) ~[spring-context-6.1.3.jar:6.1.3]
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanFactory(ConfigurationClassPostProcessor.java:310) ~[spring-context-6.1.3.jar:6.1.3]
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:363) ~[spring-context-6.1.3.jar:6.1.3]
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:153) ~[spring-context-6.1.3.jar:6.1.3]
    at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:788) ~[spring-context-6.1.3.jar:6.1.3]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:606) ~[spring-context-6.1.3.jar:6.1.3]
    at spring.boot@3.2.2/org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:146) ~[spring-boot-3.2.2.jar:na]
    at spring.boot@3.2.2/org.springframework.boot.SpringApplication.refresh(SpringApplication.java:754) ~[spring-boot-3.2.2.jar:na]
    at spring.boot@3.2.2/org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:456) ~[spring-boot-3.2.2.jar:na]
    at spring.boot@3.2.2/org.springframework.boot.SpringApplication.run(SpringApplication.java:334) ~[spring-boot-3.2.2.jar:na]
    at spring.boot@3.2.2/org.springframework.boot.SpringApplication.run(SpringApplication.java:1354) ~[spring-boot-3.2.2.jar:na]
    at spring.boot@3.2.2/org.springframework.boot.SpringApplication.run(SpringApplication.java:1343) ~[spring-boot-3.2.2.jar:na]


Caused by: java.lang.reflect.InaccessibleObjectException: Unable to make protected final java.lang.Class java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain) throws java.lang.ClassFormatError accessible: module java.base does not "opens java.lang" to unnamed module @1ed4004b
    at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:354) ~[na:na]
    at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:297) ~[na:na]
    at java.base/java.lang.reflect.Method.checkCanSetAccessible(Method.java:199) ~[na:na]
    at java.base/java.lang.reflect.Method.setAccessible(Method.java:193) ~[na:na]
    at org.springframework.cglib.core.ReflectUtils.defineClass(ReflectUtils.java:505) ~[spring-core-6.1.3.jar:6.1.3]
    ... 26 common frames omitted

问题背景 #

运行Spring Boot 3.2.2 + Java 17项目时抛出上述异常，删除module-info.java后异常消失，但调整该文件的依赖声明无法解决问题。

当前module-info.java内容 #

module a {
    requires java.sql;
    requires spring.boot.autoconfigure;
    requires spring.boot;
    requires io.swagger.v3.oas.annotations;
    requires spring.web;
    requires org.slf4j;
    requires org.apache.commons.lang3;
    requires jakarta.validation;
    //exports...
    opens a;
}

当前pom.xml内容 #

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.2.2</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <artifactId>a</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>a</name>
    <properties>
        <java.version>17</java.version>
        <springdoc.version>2.3.0</springdoc.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springdoc</groupId>
            <artifactId>springdoc-openapi-starter-webmvc-ui</artifactId>
            <version>${springdoc.version}</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.eclipse.jetty</groupId>
            <artifactId>jetty-util-ajax</artifactId>
            <version>9.4.46.v20220331</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

解决思路 #

1. 添加JVM反射权限参数 #

CGLib在模块模式下需要访问java.base模块的内部API，添加以下JVM启动参数：

--add-opens java.base/java.lang=ALL-UNNAMED
--add-opens java.base/java.lang.reflect=ALL-UNNAMED

该参数允许未命名模块（如Spring部分依赖）访问java.base的指定包，解决反射权限问题。

2. 补全模块声明的依赖 #

当前module-info.java缺少Spring核心模块的声明，补充后让模块系统正确解析依赖：

requires spring.context;
requires spring.core;

3. 排查并解决CGLib依赖冲突 #

通过Maven依赖树检查是否存在旧版CGLib：

mvn dependency:tree | grep cglib

若发现冲突，在spring-boot-starter-web中排除旧版，确保使用Spring自带的适配JPMS的版本：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <groupId>cglib</groupId>
            <artifactId>cglib</artifactId>
        </exclusion>
    </exclusions>
</dependency>

4. 升级不兼容的第三方依赖 #

jetty-util-ajax 9.4.x未适配JPMS，升级到支持模块的版本：

<dependency>
    <groupId>org.eclipse.jetty</groupId>
    <artifactId>jetty-util-ajax</artifactId>
    <version>11.0.15</version>
</dependency>

5. 配置Spring Boot Maven插件的模块支持 #

显式指定模块名称和主类，避免打包时的模块识别问题：

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <configuration>
        <mainClass>a.YourApplicationMainClass</mainClass>
        <moduleName>a</moduleName>
    </configuration>
</plugin>

替换a.YourApplicationMainClass为你的主类全限定名。

内容的提问来源于stack exchange，提问作者Vincent Gates