Optimize template/matrix variable merging in spring-webmvc

dd-java-agent/instrumentation/spring/spring-webmvc/spring-webmvc-3.1/src/main/java/datadog/trace/instrumentation/springweb/MergedMapView.java

@@ -0,0 +1,120 @@
+package datadog.trace.instrumentation.springweb;
+
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * A read-only Map view that lazily merges two maps. When both maps contain the same key, the values
+ * are combined into a {@link PairList}. The actual merge is deferred until the first operation that
+ * requires it (e.g. entrySet, size), avoiding unnecessary HashMap copies when the map is never
+ * iterated.
+ */
+public final class MergedMapView implements Map<String, Object> {
+
+  private final Map<String, Object> primary;
+  private final Map<String, Object> secondary;
+  private Map<String, Object> merged;
+
+  public MergedMapView(Map<String, Object> primary, Map<String, Object> secondary) {
+    this.primary = primary;
+    this.secondary = secondary;
+  }
+
+  private Map<String, Object> merged() {
+    if (merged == null) {
+      merged = new HashMap<>(primary);
+      for (Map.Entry<String, Object> e : secondary.entrySet()) {
+        String key = e.getKey();
+        Object curValue = merged.get(key);
+        if (curValue != null) {
+          merged.put(key, new PairList(curValue, e.getValue()));
+        } else {
+          merged.put(key, e.getValue());
+        }
+      }
+    }
+    return merged;
+  }
+
+  @Override
+  public Object get(Object key) {
+    Object v1 = primary.get(key);
+    Object v2 = secondary.get(key);
+    if (v1 != null && v2 != null) {
+      return new PairList(v1, v2);
+    }
+    return v1 != null ? v1 : v2;
+  }
+
+  @Override
+  public boolean containsKey(Object key) {
+    return primary.containsKey(key) || secondary.containsKey(key);
+  }
+
+  @Override
+  public int size() {
+    return merged().size();
+  }
+
+  @Override
+  public boolean isEmpty() {
+    return primary.isEmpty() && secondary.isEmpty();
+  }
+
+  @Override
+  public boolean containsValue(Object value) {
+    return merged().containsValue(value);
+  }
+
+  @Override
+  public Object put(String key, Object value) {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public Object remove(Object key) {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public void putAll(Map<? extends String, ?> m) {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public void clear() {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public Set<String> keySet() {
+    return merged().keySet();
+  }
+
+  @Override
+  public Collection<Object> values() {
+    return merged().values();
+  }
+
+  @Override
+  public Set<Entry<String, Object>> entrySet() {
+    return merged().entrySet();
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    return merged().equals(o);
+  }
+
+  @Override
+  public int hashCode() {
+    return merged().hashCode();
+  }
+
+  @Override
+  public String toString() {
+    return merged().toString();
+  }
+}

dd-java-agent/instrumentation/spring/spring-webmvc/spring-webmvc-3.1/src/main/java/datadog/trace/instrumentation/springweb/TemplateAndMatrixVariablesInstrumentation.java

@@ -25,7 +25,6 @@
 import datadog.trace.api.iast.propagation.PropagationModule;
 import datadog.trace.bootstrap.instrumentation.api.AgentSpan;
 import datadog.trace.bootstrap.instrumentation.api.AgentTracer;
-import java.util.HashMap;
 import java.util.Map;
 import java.util.Set;
 import java.util.function.BiFunction;
@@ -82,7 +81,7 @@ public void methodAdvice(MethodTransformer transformer) {
   @Override
   public String[] helperClassNames() {
     return new String[] {
-      packageName + ".PairList",
+      packageName + ".PairList", packageName + ".MergedMapView",
     };
   }
 
@@ -136,23 +135,15 @@ public static void after(
 
           // merge the uri template and matrix variables
           Map<String, Object> map = null;
-          if (templateVars instanceof Map) {
+          if (templateVars instanceof Map && !((Map<?, ?>) templateVars).isEmpty()) {
             map = (Map<String, Object>) templateVars;
           }
-          if (matrixVars instanceof Map) {
+          if (matrixVars instanceof Map && !((Map<?, ?>) matrixVars).isEmpty()) {
+            Map<String, Object> matrixMap = (Map<String, Object>) matrixVars;
             if (map != null) {
-              map = new HashMap<>(map);
-              for (Map.Entry<String, Object> e : ((Map<String, Object>) matrixVars).entrySet()) {
-                String key = e.getKey();
-                Object curValue = map.get(key);
-                if (curValue != null) {
-                  map.put(key, new PairList(curValue, e.getValue()));
-                } else {
-                  map.put(key, e.getValue());
-                }
-              }
+              map = new MergedMapView(map, matrixMap);
             } else {
-              map = (Map<String, Object>) matrixVars;
+              map = matrixMap;
             }
           }
 

dd-java-agent/instrumentation/spring/spring-webmvc/spring-webmvc-6.0/src/main/java/datadog/trace/instrumentation/springweb6/TemplateAndMatrixVariablesInstrumentation.java

@@ -64,7 +64,7 @@ public void methodAdvice(MethodTransformer transformer) {
   @Override
   public String[] helperClassNames() {
     return new String[] {
-      packageName + ".PairList",
+      packageName + ".PairList", packageName + ".MergedMapView",
     };
   }
 

dd-java-agent/instrumentation/spring/spring-webmvc/spring-webmvc-6.0/src/main/java17/datadog/trace/instrumentation/springweb6/HandleMatchAdvice.java

@@ -16,7 +16,6 @@
 import datadog.trace.bootstrap.instrumentation.api.AgentSpan;
 import datadog.trace.bootstrap.instrumentation.api.AgentTracer;
 import jakarta.servlet.http.HttpServletRequest;
-import java.util.HashMap;
 import java.util.Map;
 import java.util.function.BiFunction;
 import net.bytebuddy.asm.Advice;
@@ -66,23 +65,15 @@ public static void after(
 
         // merge the uri template and matrix variables
         Map<String, Object> map = null;
-        if (templateVars instanceof Map) {
+        if (templateVars instanceof Map && !((Map<?, ?>) templateVars).isEmpty()) {
           map = (Map<String, Object>) templateVars;
         }
-        if (matrixVars instanceof Map) {
+        if (matrixVars instanceof Map && !((Map<?, ?>) matrixVars).isEmpty()) {
+          Map<String, Object> matrixMap = (Map<String, Object>) matrixVars;
           if (map != null) {
-            map = new HashMap<>(map);
-            for (Map.Entry<String, Object> e : ((Map<String, Object>) matrixVars).entrySet()) {
-              String key = e.getKey();
-              Object curValue = map.get(key);
-              if (curValue != null) {
-                map.put(key, new PairList(curValue, e.getValue()));
-              } else {
-                map.put(key, e.getValue());
-              }
-            }
+            map = new MergedMapView(map, matrixMap);
           } else {
-            map = (Map<String, Object>) matrixVars;
+            map = matrixMap;
           }
         }
 

dd-java-agent/instrumentation/spring/spring-webmvc/spring-webmvc-6.0/src/main/java17/datadog/trace/instrumentation/springweb6/MergedMapView.java

@@ -0,0 +1,120 @@
+package datadog.trace.instrumentation.springweb6;
+
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * A read-only Map view that lazily merges two maps. When both maps contain the same key, the values
+ * are combined into a {@link PairList}. The actual merge is deferred until the first operation that
+ * requires it (e.g. entrySet, size), avoiding unnecessary HashMap copies when the map is never
+ * iterated.
+ */
+public final class MergedMapView implements Map<String, Object> {
+
+  private final Map<String, Object> primary;
+  private final Map<String, Object> secondary;
+  private Map<String, Object> merged;
+
+  public MergedMapView(Map<String, Object> primary, Map<String, Object> secondary) {
+    this.primary = primary;
+    this.secondary = secondary;
+  }
+
+  private Map<String, Object> merged() {
+    if (merged == null) {
+      merged = new HashMap<>(primary);
+      for (Map.Entry<String, Object> e : secondary.entrySet()) {
+        String key = e.getKey();
+        Object curValue = merged.get(key);
+        if (curValue != null) {
+          merged.put(key, new PairList(curValue, e.getValue()));
+        } else {
+          merged.put(key, e.getValue());
+        }
+      }
+    }
+    return merged;
+  }
+
+  @Override
+  public Object get(Object key) {
+    Object v1 = primary.get(key);
+    Object v2 = secondary.get(key);
+    if (v1 != null && v2 != null) {
+      return new PairList(v1, v2);
+    }
+    return v1 != null ? v1 : v2;
+  }
+
+  @Override
+  public boolean containsKey(Object key) {
+    return primary.containsKey(key) || secondary.containsKey(key);
+  }
+
+  @Override
+  public int size() {
+    return merged().size();
+  }
+
+  @Override
+  public boolean isEmpty() {
+    return primary.isEmpty() && secondary.isEmpty();
+  }
+
+  @Override
+  public boolean containsValue(Object value) {
+    return merged().containsValue(value);
+  }
+
+  @Override
+  public Object put(String key, Object value) {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public Object remove(Object key) {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public void putAll(Map<? extends String, ?> m) {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public void clear() {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public Set<String> keySet() {
+    return merged().keySet();
+  }
+
+  @Override
+  public Collection<Object> values() {
+    return merged().values();
+  }
+
+  @Override
+  public Set<Entry<String, Object>> entrySet() {
+    return merged().entrySet();
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    return merged().equals(o);
+  }
+
+  @Override
+  public int hashCode() {
+    return merged().hashCode();
+  }
+
+  @Override
+  public String toString() {
+    return merged().toString();
+  }
+}