The error message you're seeing, (Caused by: java.lang.reflect.InaccessibleObjectException: Unable to make field private final java.util.Comparator java.util.TreeMap.comparator accessible: module java.base does not "opens java.util" to unnamed module @6d4a82") or java.lang.reflect.InaccessibleObjectException, is related to module system changes introduced in Java 9 and later versions. It occurs when you try to access a field, method, or class that is not accessible due to module restrictions. In this case, it appears that you're trying to access the private final java.util.Comparator field of a java.util.TreeMap, which is not accessible because the java.base module does not open java.util to unnamed modules.
How to fix this error? Solution
To fix this error, you have a few options:
1. Use Reflection with --add-opens Flag (Temporary Solution)
You can use the --add-opens flag when running your Java application to temporarily open the package containing the inaccessible class. This flag is used to open a package in a module to other modules, including unnamed modules.
For example:
$ java --add-opens java.base/java.util=ALL-UNNAMED yourMainClass
Replace yourMainClass with the name of your main class. However, note that this is a temporary workaround and may not be recommended for production code, as it bypasses module encapsulation.
2. Update Your Code to Avoid Reflection (Preferred Solution)
A better approach is to modify your code to avoid using reflection to access private fields, methods, or classes whenever possible. If you have control over the code that's causing the issue, consider refactoring it to use public or package-private APIs instead of accessing private members through reflection. This approach is more robust and follows best practices.
3. Check for Java 9+ Compatible Libraries
If you are using third-party libraries that are not compatible with Java 9+ module system changes, you may want to check if there are updated versions of those libraries that are compatible. Many libraries have been updated to support Java 9 and later versions.
4. Migrate to Modules (if applicable)
If your application is large and complex, and you're encountering module-related issues frequently, consider migrating your codebase to the Java module system. Modularizing your code can help you better control dependencies and encapsulation, reducing the likelihood of such issues.
Full error message
Here is the full error message one of my reader was getting when it encountered this error while working on Java Java based Spring MVC application in NetBeans IDE
Caused by: java.lang.reflect.InaccessibleObjectException: Unable to make field private final java.util.Comparator java.util.TreeMap.comparator accessible: module java.base does not "opens java.util" to unnamed module @8d3a14
at java.lang.reflect.AccessibleObject.checkCanSetAccessible (AccessibleObject.java:354)
at java.lang.reflect.AccessibleObject.checkCanSetAccessible (AccessibleObject.java:297)
at java.lang.reflect.Field.checkCanSetAccessible (Field.java:178)
at java.lang.reflect.Field.setAccessible (Field.java:172)
at com.thoughtworks.xstream.converters.collections.TreeMapConverter.<clinit> (TreeMapConverter.java:59)
at com.thoughtworks.xstream.XStream.setupConverters (XStream.java:679)
at com.thoughtworks.xstream.XStream.<init> (XStream.java:456)
at com.thoughtworks.xstream.XStream.<init> (XStream.java:381)
at com.thoughtworks.xstream.XStream.<init> (XStream.java:356)
at org.apache.maven.plugin.war.util.WebappStructureSerializer.<clinit> (WebappStructureSerializer.java:47)
at org.apache.maven.plugin.war.AbstractWarMojo.<init> (AbstractWarMojo.java:324)
at org.apache.maven.plugin.war.WarMojo.<init> (WarMojo.java:53)
at jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0 (Native Method)
at jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance (NativeConstructorAccessorImpl.java:77)
at jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance (DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstanceWithCaller (Constructor.java:499)
at java.lang.reflect.Constructor.newInstance (Constructor.java:480)
at com.google.inject.internal.DefaultConstructionProxyFactory$ReflectiveProxy.newInstance (DefaultConstructionProxyFactory.java:126)
at com.google.inject.internal.ConstructorInjector.provision (ConstructorInjector.java:114)
at com.google.inject.internal.ConstructorInjector.access$000 (ConstructorInjector.java:32)
at com.google.inject.internal.ConstructorInjector$1.call (ConstructorInjector.java:98)
at com.google.inject.internal.ProvisionListenerStackCallback$Provision.provision (ProvisionListenerStackCallback.java:112)
at com.google.inject.internal.ProvisionListenerStackCallback$Provision.provision (ProvisionListenerStackCallback.java:127)
at com.google.inject.internal.ProvisionListenerStackCallback.provision (ProvisionListenerStackCallback.java:66)
at com.google.inject.internal.ConstructorInjector.construct (ConstructorInjector.java:93)
at com.google.inject.internal.ConstructorBindingImpl$Factory.get (ConstructorBindingImpl.java:306)
at com.google.inject.internal.InjectorImpl$1.get (InjectorImpl.java:1050)
at com.google.inject.internal.InjectorImpl.getInstance (InjectorImpl.java:1086)
at org.eclipse.sisu.space.AbstractDeferredClass.get (AbstractDeferredClass.java:48)
at com.google.inject.internal.ProviderInternalFactory.provision (ProviderInternalFactory.java:85)
at com.google.inject.internal.InternalFactoryToInitializableAdapter.provision (InternalFactoryToInitializableAdapter.java:57)
at com.google.inject.internal.ProviderInternalFactory$1.call (ProviderInternalFactory.java:66)
at com.google.inject.internal.ProvisionListenerStackCallback$Provision.provision (ProvisionListenerStackCallback.java:112)
at com.google.inject.internal.ProvisionListenerStackCallback$Provision.provision (ProvisionListenerStackCallback.java:127)
at com.google.inject.internal.ProvisionListenerStackCallback.provision (ProvisionListenerStackCallback.java:66)
at com.google.inject.internal.ProviderInternalFactory.circularGet (ProviderInternalFactory.java:61)
at com.google.inject.internal.InternalFactoryToInitializableAdapter.get (InternalFactoryToInitializableAdapter.java:47)
at com.google.inject.internal.InjectorImpl$1.get (InjectorImpl.java:1050)
at org.eclipse.sisu.inject.Guice4$1.get (Guice4.java:162)
at org.eclipse.sisu.inject.LazyBeanEntry.getValue (LazyBeanEntry.java:81)
at org.eclipse.sisu.plexus.LazyPlexusBean.getValue (LazyPlexusBean.java:51)
at org.codehaus.plexus.DefaultPlexusContainer.lookup (DefaultPlexusContainer.java:263)
at org.codehaus.plexus.DefaultPlexusContainer.lookup (DefaultPlexusContainer.java:255)
at org.apache.maven.plugin.internal.DefaultMavenPluginManager.getConfiguredMojo (DefaultMavenPluginManager.java:520)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:124)
at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute2 (MojoExecutor.java:370)
at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute (MojoExecutor.java:351)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:215)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:171)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:163)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:298)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
at org.apache.maven.cli.MavenCli.execute (MavenCli.java:960)
at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:293)
at org.apache.maven.cli.MavenCli.main (MavenCli.java:196)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:77)
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke (Method.java:568)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
You can see that the root cause of this error is module related restriction which comes when reflection is used to access a field.
That's all about how to fix "java.lang.reflect.InaccessibleObjectException: module java.base does not "opens java.util" to unnamed module" error in Java. Remember that using the --add-opens flag is a workaround and should be used cautiously. It's better to update your code and dependencies to be compatible with the Java module system whenever possible to ensure long-term stability and maintainability.
Thank you, I was stuck due to this error your solution helped me to move further.
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