Скачать или смотреть Resolving java.lang.VerifyError in OSGi Applications

Learn how to tackle the `java.lang.VerifyError` issue in OSGi applications running on Tomcat. We break down the causes and provide a step-by-step solution to ensure stability in your Java applications.
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This video is based on the question https://stackoverflow.com/q/65353739/ asked by the user 'G.Vitelli' ( https://stackoverflow.com/u/8757350/ ) and on the answer https://stackoverflow.com/a/65824126/ provided by the user 'G.Vitelli' ( https://stackoverflow.com/u/8757350/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

If you’re developing or maintaining Java applications, especially those running on Tomcat with OSGi, you may encounter java.lang.VerifyError: Bad type on operand stack. This error can be puzzling and may disrupt your application’s functionality. Below, we’ll explore the origins of this issue and provide practical debugging steps to resolve it.

Understanding the Problem

The core of the problem arises from classloading quirks in OSGi environments. Often, applications consist of multiple OSGi bundles that may inadvertently load different versions of the same class. In our scenario, we faced an inconsistency with javax.servlet classes, leading to runtime errors that seemed unpredictable.

Symptoms of the Issue

Intermittent failure: The application sometimes starts up without issues and at other times throws the java.lang.VerifyError.

Dependency Conflicts: You may be pulling different versions of javax.servlet, causing the bytecode mismatch.

Diagnosing the Error

Classloading Logs: These logs are your best friend. They help you identify which versions of classes are being resolved during runtime. Use logs to track the loading of javax.servlet.

Identify Conflicts: Look for dependency chains that might lead to the same class being loaded in different versions. For example:

If Class A (V1.0) is used by Class C, while Class B uses Class A (V1.1), calling methods that rely on older versions will throw a java.lang.VerifyError.

Solution Steps

Step 1: Review the Imports

Examine your bundle imports to ensure you're pulling the correct versions of libraries.

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If your bundle imports javax.servlet, and another dependency does too, it may lead to version clashes. In our resolution, we identified that our bundle shouldn't be importing this package since the OSGI service already does.

Step 2: Avoid Duplicated Dependencies

This is crucial. Ensure that your OSGi bundles do not import the same libraries multiple times. Remove unnecessary imports from your custom bundles that lead to ambiguities.

Step 3: Blocking Unwanted Runtime Bundles

To effectively eliminate the conflict, you can create a dummy file to prevent the creation of conflicting javax.servlet bundles. This process can block the erroneous bundle creation at runtime.

Create a file:

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Place this file in your plugin folder. This file will block the deployment of any additional javax.servlet.http versions created dynamically.

Step 4: Cleanup and Test

After applying these changes, clear your Tomcat cache and restart your application. Verify the classloading log again to ensure only the desired version of javax.servlet is being loaded.

Conclusion

The java.lang.VerifyError doesn't have a single solution, as it stems from deeply rooted issues in classloading and dependency management. By carefully analyzing your imports, recognizing potential conflicts, and proactively blocking unwanted classes, you can stabilize your application and prevent similar future issues.

If you’ve encountered this problem, I hope this guide assists you in resolving it effectively!