Java New Added 9 September 2026

Spring Boot: IllegalStateException: Failed to load ApplicationContext

A test could not build its context, and the message that matters is further down the caused by chain rather than on the first line. The usual reasons are a bean the test slice does not scan, a property that only exists in the production profile, and a mock that was removed while the test still injects it.

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

# Read the real cause, which is normally the last "Caused by"
mvn -Dtest=OrderServiceTest test | sed -n '/Caused by/,$p'

// A slice loads part of the context, so collaborators must be mocked
@WebMvcTest(OrderController.class)
class OrderControllerTest {
    @MockitoBean OrderService service;   // @MockBean before Spring Boot 3.4
}

# Tests need their own properties, not the production ones
# src/test/resources/application.properties
spring.datasource.url=jdbc:h2:mem:test;DB_CLOSE_DELAY=-1

// Turn on the failure analysis report for a fuller explanation
@SpringBootTest(properties = "debug=true")

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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