Why Does My Spring Boot 1.5.7 App Hang? Fixing NoSuchMethodError Caused by Jar Conflicts

A Spring Boot project using version 1.5.7 (Spring 4.1.3) suddenly failed to start; the IDE showed the process hanging without any log output. Since no logs were available, the thread stack was inspected using IDEA's built‑in thread dump tool.

Problem Analysis

The stack trace revealed that the main thread was waiting on CountDownLatch.await(). Further inspection of the code showed that the waiting occurs in Spring Boot's safe initialization class, which listens for SpringApplicationEvent events and calls preinitializationComplete.await().

The event object turned out to be a failure event containing the key exception:

NoSuchMethodError: "org.springframework.util.ObjectUtils.unwrapOptional(Ljava/lang/Object;)Ljava/lang/Object;"

Hypothesis

The error indicates a missing method, typically caused by incompatible jar versions. The method exists only in spring‑core 5.x, while the project uses spring‑core 4.1.3. The suspicion was that a recent Maven change introduced a newer spring‑context dependency.

Verification

Checking recent pom.xml commits revealed the addition of:

<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-context</artifactId>
  <version>5.1.6.RELEASE</version>
</dependency>

Because Maven gives direct dependencies higher priority, this 5.1.6 version overrode the boot‑provided 4.1.3 version, causing the method mismatch.

Solution

Removing the explicit spring-context 5.1.6 dependency (or aligning all Spring modules to the same version) resolves the startup hang; the application starts normally and logs are printed.

Takeaway

When logs are absent, thread dumps can pinpoint where a Java application is stuck. NoSuchMethodError usually points to jar version conflicts; reviewing recent Maven changes and ensuring consistent library versions is essential for quick resolution.