How do you troubleshoot a NoSuchBeanDefinitionException in a Spring application?

The exception means Spring searched the context for a bean of the requested type (or name) and found none, so troubleshooting is really a process of figuring out why the bean never got registered.

• Check that the class actually carries a stereotype annotation (@Component, @Service, etc.) or is registered via an explicit @Bean method - a class with none of these is just a plain object as far as Spring is concerned.
• Verify the class sits inside the component-scanned package tree; a class outside the base package (or an unusually structured multi-module project) is invisible to @ComponentScan unless the base package is widened or the class is explicitly imported.
• Check for a @Conditional, @ConditionalOnProperty, or @Profile guarding the bean that isn't currently satisfied - run with --debug to print the auto-configuration/condition evaluation report and see exactly which conditions passed or failed.
• If the lookup was by name (via @Qualifier or getBean("name")), double-check for a typo against the actual registered bean name, which defaults to the class name with a lowercase first letter, or the @Bean method name.