Java新建Maven项目学习Spring注解开发显示：Caused by: java.lang.reflect.InaccessibleObjectException

发生缘由

学习Spring中IOC/DI注解开发

环境

jdk版本：jdk-16.0.2
Idea版本：2021.2
电脑系统：win10

问题及补救

问题描述

新建如下类和接口：

public interface BookDao {
 　　public void save();
}

@Component("bookDao")
public class BookDaoImpl implements BookDao {
    @Override
    public void save() {
        System.out.println("book dao save ...");
    }
}

@Configuration
@ComponentScan("com.linxuan.dao.impl")
public class SpringConfig {
}

public class AppForAnnotation {
    public static void main(String[] args) {
        ApplicationContext ctx = new AnnotationConfigApplicationContext(SpringConfig.class);
        BookDao bookDao = (BookDao) ctx.getBean("bookDao");
        System.out.println(bookDao);
    }
}

运行主方法却发现报错，报错信息如下：

Exception in thread "main" java.lang.IllegalStateException: Cannot load configuration class: com.linxuan.config.SpringConfig
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.enhanceConfigurationClasses(ConfigurationClassPostProcessor.java:410)
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanFactory(ConfigurationClassPostProcessor.java:263)
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:284)
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:130)
    at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:678)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:520)
    at org.springframework.context.annotation.AnnotationConfigApplicationContext.<init>(AnnotationConfigApplicationContext.java:84)
    at com.linxuan.domain.App.main(App.java:12)
Caused by: java.lang.ExceptionInInitializerError
    at org.springframework.cglib.core.KeyFactory$Generator.getProtectionDomain(KeyFactory.java:136)
    at org.springframework.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:206)
    at org.springframework.cglib.core.KeyFactory$Generator.create(KeyFactory.java:149)
    at org.springframework.cglib.core.KeyFactory.create(KeyFactory.java:117)
    at org.springframework.cglib.core.KeyFactory.create(KeyFactory.java:109)
    at org.springframework.cglib.core.KeyFactory.create(KeyFactory.java:105)
    at org.springframework.cglib.proxy.Enhancer.<clinit>(Enhancer.java:71)
    at org.springframework.context.annotation.ConfigurationClassEnhancer.newEnhancer(ConfigurationClassEnhancer.java:119)
    at org.springframework.context.annotation.ConfigurationClassEnhancer.enhance(ConfigurationClassEnhancer.java:107)
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.enhanceConfigurationClasses(ConfigurationClassPostProcessor.java:400)
    ... 7 more
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 @335eadca
    at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:357)
    at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:297)
    at java.base/java.lang.reflect.Method.checkCanSetAccessible(Method.java:199)
    at java.base/java.lang.reflect.Method.setAccessible(Method.java:193)
    at org.springframework.cglib.core.ReflectUtils$1.run(ReflectUtils.java:52)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:312)
    at org.springframework.cglib.core.ReflectUtils.<clinit>(ReflectUtils.java:42)
    ... 17 more

报错信息

解决方案

笔者使用的JDK版本是16，而反射自从JDK8之后就有了限制：JDK 9将类型和资源封装在模块中。
JDK9以上模块不能使用反射去访问非公有的成员/成员方法以及构造方法，除非模块标识为opens去允许反射访问。否则会产生非法反射警告。

解决方法如下：

点击右上角的Select Run/Debug Configuration
点击Edit Configurations...
点击Modify options
点击Add VM options
这时会在Run/Debug Configurations窗口上面多出现一个名为Add VM options的方框。我们只需要在里面键入下面代码即可： --add-opens java.base/java.lang=ALL-UNNAMED
点击Apply，点击OK。右键运行，那么就没有问题了。