Java "OutOfMemoryError: PermGen space" (Legacy JDK 7) - Fix in CI

By Daniel Zoghalchali·Latchkey

On JDK 7 and earlier, class metadata lived in a fixed-size "permanent generation" (PermGen). OutOfMemoryError: PermGen space means that region filled - too many loaded classes, heavy reflection/proxies, or repeated redeploys leaking classloaders. PermGen was removed in JDK 8 (replaced by Metaspace).

What this error means

On a legacy JDK, a build or app fails with java.lang.OutOfMemoryError: PermGen space, often after loading many frameworks/generated classes or after several hot redeploys in a long-lived process.

Exception in thread "main" java.lang.OutOfMemoryError: PermGen space
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:800)

Common causes

Too many loaded classes for the fixed PermGen

Large frameworks, dynamic proxies, and code generation load enough classes to exceed the default MaxPermSize on JDK 7.

Classloader leak across redeploys

A long-running JVM that reloads applications can leak classloaders, so PermGen grows until it is exhausted.

How to fix it

Raise MaxPermSize on the legacy JDK

As a stopgap on JDK 7, give PermGen more room.

export MAVEN_OPTS="-XX:MaxPermSize=512m -XX:PermSize=256m"
mvn -B verify

Move to a modern JDK (the real fix)

JDK 8+ removed PermGen entirely; class metadata lives in native Metaspace, which grows dynamically.

- uses: actions/setup-java@v4
  with:
    distribution: temurin
    java-version: '21'   # no PermGen; uses Metaspace

How to prevent it

• Run on a supported JDK (8+) where PermGen no longer exists.
• On legacy JVMs, size -XX:MaxPermSize for the framework/class load.
• Fix classloader leaks in long-lived processes rather than just enlarging PermGen.

Frequently asked questions

Related guides

References

• Apache Maven guides
• Gradle user manual
• GitHub Actions documentation