What causes "No classes files were found - did you compile your project?" in GoogleContainerTools/jib?

Run the compile step first (gradle jib depends on classes normally; if invoking tasks directly, run gradle classes jib:build or just gradle jib)

GoogleContainerTools/jib · warning

No classes files were found - did you compile your project?

Error message

No classes files were found - did you compile your project?

What it means

GradleProjectProperties logs this warning when the Gradle plugin builds a container in 'explode' (classes) mode and none of the project's classes output directories exist or contain anything, so the image would have an empty classes layer. It is almost always a sign that the project was not compiled before running Jib.

Source

Thrown at jib-gradle-plugin/src/main/java/com/google/cloud/tools/jib/gradle/GradleProjectProperties.java:266

                  .collect(Collectors.toList()))
          .addProjectDependencies(
              projectDependencies.getFiles().stream()
                  .map(File::toPath)
                  .collect(Collectors.toList()));

      switch (containerizingMode) {
        case EXPLODED:
          // Adds resource files
          if (Files.exists(resourcesOutputDirectory)) {
            javaContainerBuilder.addResources(resourcesOutputDirectory);
          }

          // Adds class files
          for (File classesOutputDirectory : classesOutputDirectories) {
            javaContainerBuilder.addClasses(classesOutputDirectory.toPath());
          }
          if (classesOutputDirectories.isEmpty()) {
            log(LogEvent.warn("No classes files were found - did you compile your project?"));
          }
          break;

        case PACKAGED:
          // Add a JAR
          Jar jarTask = (Jar) project.getTasks().findByName("jar");
          Path jarPath = jarTask.getArchiveFile().get().getAsFile().toPath();
          log(LogEvent.debug("Using JAR: " + jarPath));
          javaContainerBuilder.addToClasspath(jarPath);
          break;

        default:
          throw new IllegalStateException("unknown containerizing mode: " + containerizingMode);
      }

      return javaContainerBuilder.toContainerBuilder();

    } catch (IOException ex) {

View on GitHub (pinned to fb949e2676)

Solutions

Run the compile step first (gradle jib depends on classes normally; if invoking tasks directly, run gradle classes jib:build or just gradle jib)
Verify the project actually has sources under src/main/java; an empty project legitimately produces this warning
Check custom sourceSets/output configuration so classesOutputDirectories points at real directories (e.g. build/classes/java/main)
If packaging a fat JAR instead, switch the packaging mode to PACKAGED

Example fix

// before
./gradlew jib   # may skip compile in odd setups
// after: ensure classes are built
./gradlew classes jib

Defensive patterns

Strategy: validation

Validate before calling

// fail the pipeline if classes output is empty before jib
if [ -z "$(find build/classes -name '*.class' 2>/dev/null)" ]; then
  echo "No compiled classes — run gradle classes first"; exit 1
fi

Try / catch

tasks.named("jib") {
  // jib already depends on classes; if invoking programmatically:
  dependsOn("classes")
}

Prevention

Always invoke jib tasks through Gradle so the classes dependency runs
Verify the project has sources and sourceSets are not customized away
Check build/classes/java/main exists in CI logs before pushing images

When it happens

Trigger: createJibContainerBuilder on a Gradle project where javaContainerBuilderToContainerBuilder walks classesOutputDirectories and the list is empty — i.e. the classes task produced no output directories (e.g. jib task run before compileJava, or an empty/no-source project).

Common situations: Running jibBuildImage with --offline or in CI before running the compile step; a project with no Java/Kotlin sources; misconfigured sourceSets so classes land elsewhere; Gradle build cache/task wiring issues leaving build/classes empty.

Understand the failure class

Background: EmptyResultError / "no results found": when an API or scraper succeeds but returns zero rows — this error's family across 9 libraries.

Related errors

AI-assisted analysis of GoogleContainerTools/jib@fb949e2676 (2026-09-06). Data as JSON: /api/errors/28e34de0acdfbbb7. Report an issue: GitHub.