Improve resilience of service loader

Avoid crashing if registered service cannot be loaded. This may lead to missing fields
in the log output. But it will not keep an application from starting because of a wrongly
registered class on the classpath.

Signed-off-by: Karsten Schnitter <k.schnitter@sap.com>

Author: KarstenSchnitter

cf-java-logging-support-core/src/main/java/com/sap/hcp/cf/logging/common/serialization/ContextFieldSupplierServiceLoader.java

@@ -1,18 +1,40 @@
 package com.sap.hcp.cf.logging.common.serialization;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import java.util.ArrayList;
+import java.util.ServiceConfigurationError;
 import java.util.ServiceLoader;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 public class ContextFieldSupplierServiceLoader<T> {
 
+    private static Logger logger() {
+        return LoggerFactory.getLogger(ContextFieldSupplierServiceLoader.class);
+    }
+
     private ContextFieldSupplierServiceLoader() {
     }
 
     public static <T extends ContextFieldSupplier> ArrayList<T> addFieldSuppliers(Stream<T> original, Class<T> clazz) {
-        Stream<T> spiSuppliers = ServiceLoader.load(clazz).stream().map(ServiceLoader.Provider::get).sorted();
+        Stream<T> spiSuppliers = loadSafely(clazz);
         return Stream.concat(original, spiSuppliers).sorted().collect(Collectors.toCollection(ArrayList::new));
     }
 
+    private static <T extends ContextFieldSupplier> Stream<T> loadSafely(Class<T> clazz) {
+        ArrayList<T> result = new ArrayList<>();
+        var iterator = ServiceLoader.load(clazz).iterator();
+        while (true) {
+            try {
+                if (!iterator.hasNext()) break;
+                result.add(iterator.next());
+            } catch (ServiceConfigurationError e) {
+                logger().warn("Skipping invalid SPI provider for {}: {}", clazz.getName(), e.getMessage());
+            }
+        }
+        return result.stream();
+    }
+
 }

cf-java-logging-support-core/src/test/java/com/sap/hcp/cf/logging/common/serialization/ContextFieldSupplierServiceLoaderTest.java

@@ -0,0 +1,39 @@
+package com.sap.hcp.cf.logging.common.serialization;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Map;
+import java.util.stream.Stream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatCode;
+
+class ContextFieldSupplierServiceLoaderTest {
+
+    public static class ValidSupplier implements ContextFieldSupplier {
+        @Override
+        public Map<String, Object> get() {
+            return Collections.emptyMap();
+        }
+    }
+
+    @Test
+    void doesNotThrowWhenSpiProviderIsInvalid() {
+        assertThatCode(() -> ContextFieldSupplierServiceLoader.addFieldSuppliers(Stream.empty(),
+                                                                                 ContextFieldSupplier.class))
+                .doesNotThrowAnyException();
+    }
+
+    @Test
+    void skipsInvalidSpiProviderAndKeepsValidOnes() {
+        ValidSupplier valid = new ValidSupplier();
+
+        ArrayList<ContextFieldSupplier> result = ContextFieldSupplierServiceLoader.addFieldSuppliers(
+                Stream.of(valid), ContextFieldSupplier.class);
+
+        assertThat(result).contains(valid);
+    }
+
+}

cf-java-logging-support-core/src/test/resources/META-INF/services/com.sap.hcp.cf.logging.common.serialization.ContextFieldSupplier

@@ -0,0 +1,2 @@
+# Intentionally invalid entry (does not implement ContextFieldSupplier) to trigger a ServiceConfigurationError for testing.
+com.sap.hcp.cf.logging.common.helper.StacktraceGenerator