ClassNotFoundException aws runtime_error ai_generated true

java.lang.ClassNotFoundException: com.example.MyHandler : Error loading class from SnapStart snapshot

ID: aws/lambda-snapstart-java-class-not-found

Also available as: JSON · Markdown · 中文
78%Fix Rate
82%Confidence
1Evidence
2023-05-20First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
AWS Lambda Java 11 runtime active — — —
AWS Lambda Java 17 runtime active — — —
SnapStart (2023-04-01) active — — —

Root Cause

The Lambda function's handler class is not in the Java classpath or the SnapStart snapshot was built with a different classpath configuration, causing a mismatch during restoration.

generic

中文

Lambda 函数的处理程序类不在 Java 类路径中，或者 SnapStart 快照是在不同的类路径配置下构建的，导致恢复期间不匹配。

Official Documentation

https://docs.aws.amazon.com/lambda/latest/dg/snapstart.html

Workarounds

  1. 88% success Verify the handler class is in the deployment package: `jar tf my-function.jar | grep MyHandler`. If missing, rebuild with correct classpath. Then update the Lambda handler to the fully qualified class name (e.g., 'com.example.MyHandler::handleRequest'). 
    Verify the handler class is in the deployment package: `jar tf my-function.jar | grep MyHandler`. If missing, rebuild with correct classpath. Then update the Lambda handler to the fully qualified class name (e.g., 'com.example.MyHandler::handleRequest').
  2. 75% success Disable SnapStart and redeploy: `aws lambda update-function-configuration --function-name my-function --snap-start ApplyOn=None`. After confirming the function works, re-enable SnapStart with a fresh snapshot. 
    Disable SnapStart and redeploy: `aws lambda update-function-configuration --function-name my-function --snap-start ApplyOn=None`. After confirming the function works, re-enable SnapStart with a fresh snapshot.
  3. 82% success Use a build tool like Maven Shade Plugin or Gradle Shadow to create a fat JAR that includes all dependencies and the correct handler class, then deploy with SnapStart enabled. 
    Use a build tool like Maven Shade Plugin or Gradle Shadow to create a fat JAR that includes all dependencies and the correct handler class, then deploy with SnapStart enabled.

中文步骤

  1. 验证处理程序类是否在部署包中：`jar tf my-function.jar | grep MyHandler`。如果缺失，使用正确的类路径重新构建。然后将 Lambda 处理程序更新为完全限定的类名（例如 'com.example.MyHandler::handleRequest'）。
  2. 禁用 SnapStart 并重新部署：`aws lambda update-function-configuration --function-name my-function --snap-start ApplyOn=None`。确认函数正常工作后，使用新的快照重新启用 SnapStart。
  3. 使用 Maven Shade Plugin 或 Gradle Shadow 等构建工具创建包含所有依赖项和正确处理程序类的 fat JAR，然后启用 SnapStart 进行部署。

Dead Ends

Common approaches that don't work:

  1. 55% fail

    Rebuilding the deployment package without cleaning the build cache may include stale class files that don't match the SnapStart snapshot.

  2. 70% fail

    Adding the class to the system classpath via environment variables (e.g., CLASSPATH) is ignored by SnapStart because it uses a pre-initialized JVM.

  3. 45% fail

    Assuming it's a runtime dependency issue and adding all JARs to the deployment package, when the real issue is a handler class name typo.