Introduce SPI Loading for Log4j ContextFieldSuppliers

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

@@ -0,0 +1,18 @@
+package com.sap.hcp.cf.logging.common.serialization;
+
+import java.util.ArrayList;
+import java.util.ServiceLoader;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class ContextFieldSupplierServiceLoader<T> {
+
+    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();
+        return Stream.concat(original, spiSuppliers).sorted().collect(Collectors.toCollection(ArrayList::new));
+    }
+
+}

cf-java-logging-support-log4j2/src/main/java/com/sap/hcp/cf/log4j2/converter/api/Log4jContextFieldSupplier.java

@@ -6,4 +6,9 @@
 @FunctionalInterface
 public interface Log4jContextFieldSupplier extends EventContextFieldSupplier<LogEvent> {
 
+    // These are constants for the order. The default is 0. To retain the original order, negative values were chosen.
+    int BASE_FIELDS = -100;
+    int CONTEXT_FIELDS = -90;
+    int REQUEST_FIELDS = -80;
+
 }

cf-java-logging-support-log4j2/src/main/java/com/sap/hcp/cf/log4j2/layout/ContextFieldSupplierElement.java

@@ -6,9 +6,9 @@
 import org.apache.logging.log4j.core.config.plugins.PluginBuilderFactory;
 
 @Plugin(name = "contextFieldSupplier", category = Node.CATEGORY, printObject = true)
-public class ContextFieldSupplierElement {
+public class ContextFieldSupplierElement implements ElementSupplier {
 
-    private String supplierClass;
+    private final String supplierClass;
 
     public ContextFieldSupplierElement(Builder builder) {
         this.supplierClass = builder.clazz;
@@ -19,6 +19,7 @@ public static Builder newBuilder() {
         return new Builder();
     }
 
+    @Override
     public String getSupplierClass() {
         return supplierClass;
     }

cf-java-logging-support-log4j2/src/main/java/com/sap/hcp/cf/log4j2/layout/ElementSupplier.java

@@ -0,0 +1,5 @@
+package com.sap.hcp.cf.log4j2.layout;
+
+public interface ElementSupplier {
+    String getSupplierClass();
+}

cf-java-logging-support-log4j2/src/main/java/com/sap/hcp/cf/log4j2/layout/JsonPatternLayout.java

@@ -1,21 +1,18 @@
 package com.sap.hcp.cf.log4j2.layout;
 
-import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.jr.ob.JSON;
 import com.fasterxml.jackson.jr.ob.JSONComposer;
 import com.fasterxml.jackson.jr.ob.comp.ArrayComposer;
 import com.fasterxml.jackson.jr.ob.comp.ComposerBase;
 import com.fasterxml.jackson.jr.ob.comp.ObjectComposer;
 import com.sap.hcp.cf.log4j2.converter.api.Log4jContextFieldSupplier;
-import com.sap.hcp.cf.log4j2.layout.supppliers.BaseFieldSupplier;
-import com.sap.hcp.cf.log4j2.layout.supppliers.EventContextFieldSupplier;
 import com.sap.hcp.cf.log4j2.layout.supppliers.LogEventUtilities;
-import com.sap.hcp.cf.log4j2.layout.supppliers.RequestRecordFieldSupplier;
 import com.sap.hcp.cf.logging.common.Fields;
 import com.sap.hcp.cf.logging.common.converter.LineWriter;
 import com.sap.hcp.cf.logging.common.converter.StacktraceLines;
 import com.sap.hcp.cf.logging.common.serialization.ContextFieldConverter;
 import com.sap.hcp.cf.logging.common.serialization.ContextFieldSupplier;
+import com.sap.hcp.cf.logging.common.serialization.ContextFieldSupplierServiceLoader;
 import com.sap.hcp.cf.logging.common.serialization.JsonSerializationException;
 import org.apache.logging.log4j.core.LogEvent;
 import org.apache.logging.log4j.core.StringLayout;
@@ -28,10 +25,9 @@
 import java.io.OutputStream;
 import java.io.PrintWriter;
 import java.nio.charset.Charset;
-import java.util.ArrayList;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
+import java.util.*;
+import java.util.function.Function;
+import java.util.stream.Stream;
 
 /**
  * A {@link StringLayout} implementation that encodes an {@link LogEvent} as a JSON object.
@@ -56,48 +52,62 @@ public final class JsonPatternLayout extends AbstractStringLayout {
 
     private static final String NEWLINE = "\n";
     private final ContextFieldConverter contextFieldConverter;
-    private List<Log4jContextFieldSupplier> log4jContextFieldSuppliers = new ArrayList<>();
-    private List<ContextFieldSupplier> contextFieldSuppliers = new ArrayList<>();
-    private int maxStacktraceSize;
+    private final List<Log4jContextFieldSupplier> log4jContextFieldSuppliers;
+    private final List<ContextFieldSupplier> contextFieldSuppliers;
+    private final int maxStacktraceSize;
 
-    private boolean sendDefaultValues;
+    private final boolean sendDefaultValues;
 
-    private JSON json;
+    private final JSON json;
 
-    protected JsonPatternLayout(Charset charset, boolean sendDefaultValues, int maxStacktraceSize,
-                                String jsonBuilderClass, CustomFieldElement[] customFieldMdcKeys,
-                                Log4jContextFieldSupplierElement[] log4jContextFieldSupplierElements,
-                                ContextFieldSupplierElement[] contextFieldSupplierElements) {
+    private JsonPatternLayout(Charset charset, boolean sendDefaultValues, int maxStacktraceSize,
+                              String jsonBuilderClass, CustomFieldElement[] customFieldMdcKeys,
+                              Log4jContextFieldSupplierElement[] log4jContextFieldSupplierElements,
+                              ContextFieldSupplierElement[] contextFieldSupplierElements) {
         super(charset);
         this.sendDefaultValues = sendDefaultValues;
         this.maxStacktraceSize = maxStacktraceSize > 0 ? maxStacktraceSize : 55 * 1024;
         this.contextFieldConverter = contextFieldConverter(sendDefaultValues, customFieldMdcKeys);
         this.json = createJson(jsonBuilderClass);
-        this.log4jContextFieldSuppliers.add(new BaseFieldSupplier());
-        this.log4jContextFieldSuppliers.add(new EventContextFieldSupplier());
-        this.log4jContextFieldSuppliers.add(new RequestRecordFieldSupplier());
-        if (log4jContextFieldSupplierElements != null) {
-            for (Log4jContextFieldSupplierElement current: log4jContextFieldSupplierElements) {
-                try {
-                    Log4jContextFieldSupplier instance =
-                            createInstance(current.getSupplierClass(), Log4jContextFieldSupplier.class);
-                    log4jContextFieldSuppliers.add(instance);
-                } catch (ReflectiveOperationException cause) {
-                    LOGGER.warn("Cannot register Log4jContextFieldSupplier.", cause);
-                }
-            }
+        this.log4jContextFieldSuppliers =
+                getContextFieldSuppliers(log4jContextFieldSupplierElements, Log4jContextFieldSupplier.class);
+        this.contextFieldSuppliers = getContextFieldSuppliers(contextFieldSupplierElements, ContextFieldSupplier.class);
+    }
+
+    private static <E extends ElementSupplier, S extends ContextFieldSupplier> List<S> getContextFieldSuppliers(
+            E[] elements, Class<S> supplierClass) {
+        Stream<S> configSuppliers = loadContextFieldSuppliersFromConfig(elements, createInstance(supplierClass));
+        return ContextFieldSupplierServiceLoader.addFieldSuppliers(configSuppliers, supplierClass);
+    }
+
+    private static <E extends ElementSupplier, S extends ContextFieldSupplier> Stream<S> loadContextFieldSuppliersFromConfig(
+            E[] elements, Function<E, S> mapper) {
+        if (elements == null || elements.length == 0) {
+            return Stream.empty();
         }
-        if (contextFieldSupplierElements != null) {
-            for (ContextFieldSupplierElement current: contextFieldSupplierElements) {
-                try {
-                    ContextFieldSupplier instance =
-                            createInstance(current.getSupplierClass(), ContextFieldSupplier.class);
-                    contextFieldSuppliers.add(instance);
-                } catch (ReflectiveOperationException cause) {
-                    LOGGER.warn("Cannot register ContextFieldSupplier.", cause);
-                }
+        return Stream.of(elements).map(mapper).filter(Objects::nonNull);
+    }
+
+    private static <T extends ElementSupplier, R extends ContextFieldSupplier> Function<T, R> createInstance(
+            Class<R> clazz) {
+        return e -> {
+            try {
+                return createInstance(e.getSupplierClass(), clazz);
+            } catch (ReflectiveOperationException cause) {
+                LOGGER.warn("Cannot register ContextFieldSupplier <" + clazz.getSimpleName() + ">.", cause);
+                return null;
             }
-        }
+        };
+    }
+
+    // for testing
+    List<ContextFieldSupplier> getContextFieldSuppliers() {
+        return contextFieldSuppliers;
+    }
+
+    // for testing
+    List<Log4jContextFieldSupplier> getLog4jContextFieldSuppliers() {
+        return log4jContextFieldSuppliers;
     }
 
     @PluginFactory
@@ -169,8 +179,7 @@ public String toSerializable(LogEvent event) {
         }
     }
 
-    private <P extends ComposerBase> void addMarkers(ObjectComposer<P> oc, LogEvent event)
-            throws IOException, JsonProcessingException {
+    private <P extends ComposerBase> void addMarkers(ObjectComposer<P> oc, LogEvent event) throws IOException {
         if (sendDefaultValues || event.getMarker() != null) {
             ArrayComposer<ObjectComposer<P>> ac = oc.startArrayField(Fields.CATEGORIES);
             addMarker(ac, event.getMarker());
@@ -198,8 +207,7 @@ private Map<String, Object> collectContextFields(LogEvent event) {
         return contextFields;
     }
 
-    private <P extends ComposerBase> void addStacktrace(ObjectComposer<P> oc, LogEvent event)
-            throws IOException, JsonProcessingException {
+    private <P extends ComposerBase> void addStacktrace(ObjectComposer<P> oc, LogEvent event) throws IOException {
         if (event.getThrown() != null) {
             LineWriter lw = new LineWriter();
             event.getThrown().printStackTrace(new PrintWriter(lw));

cf-java-logging-support-log4j2/src/main/java/com/sap/hcp/cf/log4j2/layout/Log4jContextFieldSupplierElement.java

@@ -6,9 +6,9 @@
 import org.apache.logging.log4j.core.config.plugins.PluginBuilderFactory;
 
 @Plugin(name = "log4jContextFieldSupplier", category = Node.CATEGORY, printObject = true)
-public class Log4jContextFieldSupplierElement {
+public class Log4jContextFieldSupplierElement implements ElementSupplier {
 
-    private String supplierClass;
+    private final String supplierClass;
 
     public Log4jContextFieldSupplierElement(Builder builder) {
         this.supplierClass = builder.clazz;
@@ -19,6 +19,7 @@ public static Builder newBuilder() {
         return new Builder();
     }
 
+    @Override
     public String getSupplierClass() {
         return supplierClass;
     }

cf-java-logging-support-log4j2/src/main/java/com/sap/hcp/cf/log4j2/layout/supppliers/BaseFieldSupplier.java

@@ -12,6 +12,11 @@
 
 public class BaseFieldSupplier implements Log4jContextFieldSupplier {
 
+    @Override
+    public int order() {
+        return Log4jContextFieldSupplier.BASE_FIELDS;
+    }
+
     @Override
     public Map<String, Object> map(LogEvent event) {
         Map<String, Object> fields = new HashMap<>(6);

cf-java-logging-support-log4j2/src/main/java/com/sap/hcp/cf/log4j2/layout/supppliers/EventContextFieldSupplier.java

@@ -9,6 +9,11 @@
 public class EventContextFieldSupplier extends AbstractContextFieldSupplier<LogEvent>
         implements Log4jContextFieldSupplier {
 
+    @Override
+    public int order() {
+        return Log4jContextFieldSupplier.CONTEXT_FIELDS;
+    }
+
     @Override
     protected Map<String, String> getContextMap(LogEvent event) {
         return event.getContextData().toMap();

cf-java-logging-support-log4j2/src/main/java/com/sap/hcp/cf/log4j2/layout/supppliers/RequestRecordFieldSupplier.java

@@ -7,6 +7,11 @@
 public class RequestRecordFieldSupplier extends AbstractRequestRecordFieldSupplier<LogEvent>
         implements Log4jContextFieldSupplier {
 
+    @Override
+    public int order() {
+        return Log4jContextFieldSupplier.REQUEST_FIELDS;
+    }
+
     @Override
     protected boolean isRequestLog(LogEvent event) {
         return LogEventUtilities.isRequestLog(event);

cf-java-logging-support-log4j2/src/main/resources/META-INF/services/com.sap.hcp.cf.log4j2.converter.api.Log4jContextFieldSupplier

@@ -0,0 +1,3 @@
+com.sap.hcp.cf.log4j2.layout.supppliers.BaseFieldSupplier
+com.sap.hcp.cf.log4j2.layout.supppliers.EventContextFieldSupplier
+com.sap.hcp.cf.log4j2.layout.supppliers.RequestRecordFieldSupplier

cf-java-logging-support-log4j2/src/test/java/com/sap/hcp/cf/log4j2/layout/JsonPatternLayoutTest.java

@@ -0,0 +1,80 @@
+package com.sap.hcp.cf.log4j2.layout;
+
+import com.sap.hcp.cf.log4j2.converter.api.Log4jContextFieldSupplier;
+import com.sap.hcp.cf.log4j2.layout.supppliers.BaseFieldSupplier;
+import com.sap.hcp.cf.log4j2.layout.supppliers.EventContextFieldSupplier;
+import com.sap.hcp.cf.log4j2.layout.supppliers.RequestRecordFieldSupplier;
+import com.sap.hcp.cf.logging.common.serialization.ContextFieldSupplier;
+import org.apache.logging.log4j.core.LogEvent;
+import org.junit.jupiter.api.Test;
+
+import java.nio.charset.StandardCharsets;
+import java.util.Collections;
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class JsonPatternLayoutTest {
+
+    private final JsonPatternLayout LAYOUT =
+            JsonPatternLayout.createLayout(StandardCharsets.UTF_8, false, 10, null, new CustomFieldElement[0],
+                                           new Log4jContextFieldSupplierElement[] {
+                                                   Log4jContextFieldSupplierElement.newBuilder().setClazz(
+                                                           SampleLog4jContextFieldSupplier.class.getName()).build() },
+                                           new ContextFieldSupplierElement[] { ContextFieldSupplierElement.newBuilder()
+                                                                                                          .setClazz(
+                                                                                                                  SampleContextFieldSupplier.class.getName()).build() },
+                                           null);
+
+    @Test
+    void loadsContextFieldSuppliers() {
+        assertThat(LAYOUT.getContextFieldSuppliers()).map(Object::getClass).map(Class::getName)
+                                                     .containsExactly(SampleContextFieldSupplier.class.getName(),
+                                                                      SpiContextFieldSupplier.class.getName());
+    }
+
+    @Test
+    void getLog4jContextFieldSuppliers() {
+        assertThat(LAYOUT.getLog4jContextFieldSuppliers()).map(Object::getClass).map(Class::getName)
+                                                          .containsExactly(BaseFieldSupplier.class.getName(),
+                                                                           EventContextFieldSupplier.class.getName(),
+                                                                           RequestRecordFieldSupplier.class.getName(),
+                                                                           SampleLog4jContextFieldSupplier.class.getName(),
+                                                                           SpiLog4jContextFieldSupplier.class.getName());
+    }
+
+    static class SampleContextFieldSupplier implements ContextFieldSupplier {
+        @Override
+        public Map<String, Object> get() {
+            return Collections.emptyMap();
+        }
+    }
+
+    public static class SpiContextFieldSupplier implements ContextFieldSupplier {
+
+        public SpiContextFieldSupplier() {
+        }
+
+        @Override
+        public Map<String, Object> get() {
+            return Collections.emptyMap();
+        }
+
+    }
+
+    static class SampleLog4jContextFieldSupplier implements Log4jContextFieldSupplier {
+
+        @Override
+        public Map<String, Object> map(LogEvent event) {
+            return Collections.emptyMap();
+        }
+    }
+
+    public static class SpiLog4jContextFieldSupplier implements Log4jContextFieldSupplier {
+
+        @Override
+        public Map<String, Object> map(LogEvent event) {
+            return Collections.emptyMap();
+        }
+    }
+}

cf-java-logging-support-log4j2/src/test/resources/META-INF/services/com.sap.hcp.cf.log4j2.converter.api.Log4jContextFieldSupplier

@@ -0,0 +1 @@
+com.sap.hcp.cf.log4j2.layout.JsonPatternLayoutTest$SpiLog4jContextFieldSupplier

cf-java-logging-support-log4j2/src/test/resources/META-INF/services/com.sap.hcp.cf.logging.common.serialization.ContextFieldSupplier

@@ -0,0 +1 @@
+com.sap.hcp.cf.log4j2.layout.JsonPatternLayoutTest$SpiContextFieldSupplier

cf-java-logging-support-logback/src/main/java/com/sap/hcp/cf/logback/converter/api/LogbackContextFieldSupplier.java

@@ -6,6 +6,7 @@
 @FunctionalInterface
 public interface LogbackContextFieldSupplier extends EventContextFieldSupplier<ILoggingEvent> {
 
+    // These are constants for the order. The default is 0. To retain the original order, negative values were chosen.
     int BASE_FIELDS = -100;
     int CONTEXT_FIELDS = -90;
     int REQUEST_FIELDS = -80;