How do you diagnose a missing or ambiguous Spring bean?

Traces the injection point, candidate type, registration path, conditions, profiles, generics, qualifiers, and package boundaries.

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TL;DR

For a missing bean, I read the root exception and identify the required type, injection point, and configuration class being created. Then I verify that the intended implementation is registered through scanning, a @Bean method, an import, or auto-configuration, and that its profile or conditions match. For multiple candidates, I list the type matches and decide whether one should be primary, semantically qualified, or injected as a collection. I do not add @Component blindly.

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Evidence-driven resolution of no-candidate and multiple-candidate failures without random annotations.

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Core answer
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Overview
Start from the exact injection point and explain which candidate should exist and why the container did or did not select it.
For a missing bean, I read the root exception and identify the required type, injection point, and configuration class being created. Then I verify that the intended implementation is registered through scanning, a @Bean method, an import, or auto-configuration, and that its profile or conditions match. For multiple candidates, I list the type matches and decide whether one should be primary, semantically qualified, or injected as a collection. I do not add @Component blindly.
Checkpoint
Stronger answer
Optional upgrade with examples, trade-offs, and sharper phrasing.
Common causes include the implementation sitting outside the scan root, a test loading only a slice, a missing classpath dependency, an inactive profile, or an auto-configuration backing off because another bean exists. Generic types and factory-method return types can affect candidate matching. A qualifier narrows type candidates; it should describe meaning rather than depend accidentally on a generated bean name. The condition report is essential when Boot made the registration decision.

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Use these to catch weak phrasing, shallow reasoning, and risky claims.

Common mistakesCandidateCommon mistakesMistakes that weaken the answer or signal shallow understanding.Open details

Details

Adding @Component without finding the intended registration path.
Using global @Primary to silence every ambiguity.
Ignoring the condition report for an auto-configured bean.

How do you diagnose a missing or ambiguous Spring bean?

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