When Starting XRebel, an Exception is Thrown: A Comprehensive Guide to Troubleshooting the Issue

Introduction

XRebel is a powerful tool for profiling and debugging Java applications. However, when starting XRebel with certain versions of Spring Boot and Tomcat, you may encounter an exception that prevents the application from launching. This article will guide you through the troubleshooting process, providing clear and direct instructions to resolve the issue.

The Problem: When Starting XRebel, an Exception is Thrown

If you’re using version 3.2.6 of Spring Boot and version 10.1.24 of Tomcat-embed-core, you may encounter the following exception when starting XRebel:

java.lang.IllegalStateException: Failed to introspect Class [org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory] from ClassLoader [sun.misc.Launcher$AppClassLoader@18b4aac2]
    at org.zeroturnaround.jrebel.agent.main.ReloadingClassHelper.getPackageAnnotations(ReloadingClassHelper.java:104)
    at org.zeroturnaround.jrebel.agent.main.ReloadingClassHelper.getAnnotations(ReloadingClassHelper.java:74)
    at org.zeroturnaround.jrebel.agent.main.ReloadingClassHelper.getAnnotation(ReloadingClassHelper.java:64)
    at org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory.getWebServer(TomcatServletWebServerFactory.java:172)
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.createWebServer(ServletWebServerApplicationContext.java:180)
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:153)
    ...
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 @18b4aac2
    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.checkCanAccessException(Method.java:102)
    at java.base/java.lang.reflect.Method.invoke(Method.java:556)
    at org.zeroturnaround.jrebel.agent.main.ReloadingClassHelper.getPackageAnnotations(ReloadingClassHelper.java:94)
    ...

Causes of the Exception

The exception is caused by the incompatibility between XRebel and the Java 11 module system. XRebel uses Java Reflection to introspect and instrument Java classes, but Java 11 introduced stricter access controls that prevent XRebel from accessing certain classes.

Java 11 Module System

In Java 11, the module system was introduced to improve the security and scalability of Java applications. The module system provides better isolation between modules, but it also introduces stricter access controls that can cause issues with reflective access.

XRebel and Reflection

XRebel uses Java Reflection to instrument and introspect Java classes. This requires XRebel to access private and protected members of the classes, which is no longer allowed by the Java 11 module system.

Solutions to the Exception

There are two solutions to the exception: adding the `–add-opens` JVM argument and using the XRebel agent configuration file.

Solution 1: Add the –add-opens JVM Argument

One solution is to add the `–add-opens` JVM argument to allow XRebel to access the required classes. You can do this by adding the following configuration to your `application.properties` file:

spring:
  jmx:
    enabled: false
  main:
    allow-bean-definition-overriding: true
  boot:
    admin:
      jmx:
        enabled: false
  java:
    arguments: [--add-opens, java.base/java.lang=ALL-UNNAMED]

This configuration adds the `–add-opens` JVM argument, which allows XRebel to access the `java.lang` package.

Solution 2: Use the XRebel Agent Configuration File

The second solution is to use the XRebel agent configuration file to specify the classes that XRebel needs to access. You can create a `jrebel.config` file with the following content:

[
  {
    "class": "java.lang.ClassLoader",
    "methods": ["defineClass"]
  }
]

This configuration file specifies that XRebel needs to access the `defineClass` method of the `java.lang.ClassLoader` class.

Additional Configuration

In addition to the above solutions, you may need to add additional configuration to your Spring Boot application. This includes disabling JMX and allowing bean definition overriding.

Disable JMX

JMX can cause issues with XRebel, so it’s recommended to disable it in your Spring Boot application. You can do this by adding the following configuration to your `application.properties` file:

spring:
  jmx:
    enabled: false
  boot:
    admin:
      jmx:
        enabled: false

Allow Bean Definition Overriding

XRebel requires bean definition overriding to work correctly. You can enable this by adding the following configuration to your `application.properties` file:

spring:
  main:
    allow-bean-definition-overriding: true

Conclusion

In conclusion, the exception thrown when starting XRebel with version 3.2.6 of Spring Boot and version 10.1.24 of Tomcat-embed-core is caused by the incompatibility between XRebel and the Java 11 module system. The two solutions to the exception are adding the `–add-opens` JVM argument and using the XRebel agent configuration file. Additionally, you may need to add additional configuration to your Spring Boot application, including disabling JMX and allowing bean definition overriding.

FAQs

Q: What is XRebel?

XRebel is a powerful tool for profiling and debugging Java applications. It provides a detailed overview of the application’s performance, including CPU usage, memory allocation, and database queries.

Q: What is the Java 11 module system?

The Java 11 module system provides better isolation between modules, improving the security and scalability of Java applications. However, it also introduces stricter access controls that can cause issues with reflective access.

Q: How do I disable JMX in my Spring Boot application?

You can disable JMX in your Spring Boot application by adding the following configuration to your `application.properties` file:

spring:
  jmx:
    enabled: false
  boot:
    admin:
      jmx:
        enabled: false

Q: How do I allow bean definition overriding in my Spring Boot application?

You can allow bean definition overriding in your Spring Boot application by adding the following configuration to your `application.properties` file:

spring:
  main:
    allow-bean-definition-overriding: true

Version	Description
3.2.6	Spring Boot version
10.1.24	Tomcat-embed-core version
Java 11	Java version with module system

1. Spring Boot JMX Documentation
2. Java 11 ClassLoader Documentation
3. XRebel Configuration Documentation

Note: This article is for informational purposes only and is not affiliated with XRebel or Spring Boot.

Frequently Asked Question

If you’re experiencing issues with XRebel throwing exceptions when starting, don’t worry, we’ve got you covered! Below are some frequently asked questions that might help you troubleshoot the problem.