Java New Added 10 September 2026

Spring Boot: required a bean of type 'X' that could not be found

Component scanning starts at the package of the class annotated with @SpringBootApplication and covers only that package and below. A bean in a sibling package, or one whose @Component annotation is missing, is never registered, which is why the same class works in a test that declares it explicitly.

Quick fix

Read the commands before running them. Anything that restarts a service, deletes data or changes permissions should be tried on a non-production system first.

Quick fix

# What did Spring actually consider? The condition report explains each choice
java -jar app.jar --debug
# or: mvn spring-boot:run -Dspring-boot.run.arguments=--debug

// The application class must sit above every package you expect to be scanned
// com.example.app.Application  scans com.example.app.**

// Stereotype annotation missing is the other half of the cases
@Repository
public class JdbcOrderRepo implements OrderRepo { }

// Bean defined in another module or package
@SpringBootApplication(scanBasePackages = {"com.example.app", "com.example.shared"})

// Conditional beans: a bean behind @Profile or @ConditionalOnProperty is absent
// until that profile or property is active
SPRING_PROFILES_ACTIVE=prod java -jar app.jar

// Optional collaborators should say so
public OrderService(ObjectProvider<Auditor> auditor) { }

How to diagnose Java errors

Java errors concentrate at the class loading boundary (ClassNotFoundException, NoClassDefFoundError, UnsupportedClassVersionError) and around resource pools under load. Class loading errors are almost always classpath or version problems rather than missing code. UnsupportedClassVersionError in particular is a pure bytecode-version mismatch and tells you exactly which JDK compiled the class.

If the quick fix above does not resolve it, work through these steps. They apply to this whole class of error, not just to this one message, which is usually what saves the time.

Print the actual runtime version with java -version and compare it against your build target. Major bytecode version 65 is Java 21, 61 is Java 17, 52 is Java 8.
Inspect the resolved dependency tree (mvn dependency:tree, gradle dependencies) to find duplicate or conflicting versions of the same library.
For pool exhaustion, log pool metrics (HikariCP exposes active, idle and pending counts). Exhaustion means connections are not being returned, which is a try-with-resources problem.
Enable -verbose:class temporarily to see which jar a class is loaded from when two versions are on the classpath.
Capture a heap dump on OOM with -XX:+HeapDumpOnOutOfMemoryError and analyse it rather than raising -Xmx blindly.

Tools worth reaching for

mvn dependency:tree
jcmd / jstack / jmap
-verbose:class
Eclipse MAT
JFR (Java Flight Recorder)

Authoritative references

Primary documentation for this error, worth reading before applying any fix in production.

docs.spring.io

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