🐛 fix: align supply/finalize with CF buildpack patterns

- add hooks import to supply/cli so Dynatrace BeforeCompile fires in supply phase
- make WriteConfigYml failure fatal (Error + return err) instead of silent warning
- add WriteEnvFile(JAVA_HOME) for multi-buildpack env propagation
- add AddBinDependencyLink(java) so java binary is on PATH for subsequent buildpacks
- add LinkDirectoryInDepDir(lib) so JRE native libs are on LD_LIBRARY_PATH
- fix bin/finalize PROFILE_DIR=${5:-} to avoid nounset crash without 5th arg
- propagate JRE finalization errors instead of swallowing as warning

Author: ramonskie

bin/finalize

@@ -5,7 +5,7 @@ BUILD_DIR=$1
 CACHE_DIR=$2
 DEPS_DIR=$3
 DEPS_IDX=$4
-PROFILE_DIR=$5
+PROFILE_DIR=${5:-}
 
 export BUILDPACK_DIR=$(dirname $(readlink -f ${BASH_SOURCE%/*}))
 source "$BUILDPACK_DIR/scripts/install_go.sh"

src/java/finalize/finalize.go

@@ -151,8 +151,7 @@ func (f *Finalizer) finalizeJRE() error {
 	f.Log.BeginStep("Finalizing JRE: %s", f.JREName)
 
 	if err := f.JRE.Finalize(); err != nil {
-		f.Log.Warning("Failed to finalize JRE: %s (continuing)", err.Error())
-		// Don't fail the build if JRE finalization fails
+		return fmt.Errorf("failed to finalize JRE %s: %w", f.JREName, err)
 	}
 
 	f.Log.Info("JRE finalization complete")

src/java/jres/openjdk.go

@@ -74,6 +74,29 @@ func (o *OpenJDKJRE) Supply() error {
 		o.ctx.Log.Debug("Created profile.d script: java.sh")
 	}
 
+	// Write JAVA_HOME to the deps env dir so subsequent buildpacks can use it.
+	// This is the multi-buildpack pattern used by go-buildpack (WriteEnvFile for GOROOT)
+	// and dotnet-core-buildpack.
+	if err := o.ctx.Stager.WriteEnvFile("JAVA_HOME", javaHome); err != nil {
+		o.ctx.Log.Warning("Could not write JAVA_HOME env file: %s", err.Error())
+	}
+
+	// Symlink the java binary into the shared bin directory so it is on PATH
+	// for subsequent buildpacks — mirrors go-buildpack's AddBinDependencyLink for "go".
+	javaBin := filepath.Join(javaHome, "bin", "java")
+	if err := o.ctx.Stager.AddBinDependencyLink(javaBin, "java"); err != nil {
+		o.ctx.Log.Warning("Could not add java bin dependency link: %s", err.Error())
+	}
+
+	// Link the JRE lib directory into the deps dir so native libraries (.so files)
+	// are included on LD_LIBRARY_PATH — mirrors dotnet-core-buildpack's LinkDirectoryInDepDir.
+	libDir := filepath.Join(javaHome, "lib")
+	if _, err := os.Stat(libDir); err == nil {
+		if err := o.ctx.Stager.LinkDirectoryInDepDir(libDir, "lib"); err != nil {
+			o.ctx.Log.Warning("Could not link JRE lib directory: %s", err.Error())
+		}
+	}
+
 	// Determine Java major version
 	javaMajorVersion, err := common.DetermineJavaVersion(javaHome)
 	if err != nil {

src/java/supply/cli/main.go

@@ -6,6 +6,7 @@ import (
 	"path/filepath"
 	"time"
 
+	_ "github.com/cloudfoundry/java-buildpack/src/java/hooks" // Register hooks (Dynatrace)
 	"github.com/cloudfoundry/java-buildpack/src/java/supply"
 	"github.com/cloudfoundry/libbuildpack"
 )

src/java/supply/supply.go

@@ -77,7 +77,8 @@ func Run(s *Supplier) error {
 		"jre_version": jre.Version(),
 		"java_home":   jre.JavaHome(),
 	}); err != nil {
-		s.Log.Warning("Could not write config: %s", err.Error())
+		s.Log.Error("Could not write config: %s", err.Error())
+		return err
 	}
 
 	return nil