Return attribute key template

semconv/src/main/java/io/opentelemetry/semconv/AttributeKeyTemplate.java

@@ -0,0 +1,120 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.semconv;
+
+import io.opentelemetry.api.common.AttributeKey;
+import io.opentelemetry.api.common.AttributeType;
+import java.util.List;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+import java.util.function.Function;
+
+/**
+ * This class provides a handle for creating and caching dynamic / template-type attributes of the
+ * form <b>&lt;prefix&gt;.&lt;key&gt;</b>. The &lt;prefix&gt; is fixed for a template instance while
+ * {@link AttributeKey}s can be created and are cached for different values of the &lt;key&gt; part.
+ *
+ * <p>An example template-type attribute is the set of attributes for HTTP headers:
+ * <b>http.request.header.&lt;key&gt;</b>
+ *
+ * @param <T> The type of the nested {@link AttributeKey}s.
+ */
+public final class AttributeKeyTemplate<T> {
+
+  private final String prefix;
+  private final Function<String, AttributeKey<T>> keyBuilder;
+  private final ConcurrentMap<String, AttributeKey<T>> keysCache = new ConcurrentHashMap<>(1);
+
+  private AttributeKeyTemplate(String prefix, Function<String, AttributeKey<T>> keyBuilder) {
+    this.prefix = prefix;
+    this.keyBuilder = keyBuilder;
+  }
+
+  /**
+   * Create an {@link AttributeKeyTemplate} with type {@link AttributeType#STRING} and the given
+   * {@code prefix}.
+   */
+  public static AttributeKeyTemplate<String> stringKeyTemplate(String prefix) {
+    return new AttributeKeyTemplate<>(prefix, AttributeKey::stringKey);
+  }
+
+  /**
+   * Create an {@link AttributeKeyTemplate} with type {@link AttributeType#STRING_ARRAY} and the
+   * given {@code prefix}.
+   */
+  public static AttributeKeyTemplate<List<String>> stringArrayKeyTemplate(String prefix) {
+    return new AttributeKeyTemplate<>(prefix, AttributeKey::stringArrayKey);
+  }
+
+  /**
+   * Create an {@link AttributeKeyTemplate} with type {@link AttributeType#BOOLEAN} and the given
+   * {@code prefix}.
+   */
+  public static AttributeKeyTemplate<Boolean> booleanKeyTemplate(String prefix) {
+    return new AttributeKeyTemplate<>(prefix, AttributeKey::booleanKey);
+  }
+
+  /**
+   * Create an {@link AttributeKeyTemplate} with type {@link AttributeType#BOOLEAN_ARRAY} and the
+   * given {@code prefix}.
+   */
+  public static AttributeKeyTemplate<List<Boolean>> booleanArrayKeyTemplate(String prefix) {
+    return new AttributeKeyTemplate<>(prefix, AttributeKey::booleanArrayKey);
+  }
+
+  /**
+   * Create an {@link AttributeKeyTemplate} with type {@link AttributeType#LONG} and the given
+   * {@code prefix}.
+   */
+  public static AttributeKeyTemplate<Long> longKeyTemplate(String prefix) {
+    return new AttributeKeyTemplate<>(prefix, AttributeKey::longKey);
+  }
+
+  /**
+   * Create an {@link AttributeKeyTemplate} with type {@link AttributeType#LONG_ARRAY} and the given
+   * {@code prefix}.
+   */
+  public static AttributeKeyTemplate<List<Long>> longArrayKeyTemplate(String prefix) {
+    return new AttributeKeyTemplate<>(prefix, AttributeKey::longArrayKey);
+  }
+
+  /**
+   * Create an {@link AttributeKeyTemplate} with type {@link AttributeType#DOUBLE} and the given
+   * {@code prefix}.
+   */
+  public static AttributeKeyTemplate<Double> doubleKeyTemplate(String prefix) {
+    return new AttributeKeyTemplate<>(prefix, AttributeKey::doubleKey);
+  }
+
+  /**
+   * Create an {@link AttributeKeyTemplate} with type {@link AttributeType#DOUBLE_ARRAY} and the
+   * given {@code prefix}.
+   */
+  public static AttributeKeyTemplate<List<Double>> doubleArrayKeyTemplate(String prefix) {
+    return new AttributeKeyTemplate<>(prefix, AttributeKey::doubleArrayKey);
+  }
+
+  private AttributeKey<T> createAttributeKey(String keyName) {
+    String key = prefix + "." + keyName;
+    return keyBuilder.apply(key);
+  }
+
+  /**
+   * Returns an {@link AttributeKey} object for the given attribute key whereby the key is the
+   * variable part of the full attribute name in a template-typed attribute, for example
+   * <b>http.request.header.&lt;key&gt;</b>.
+   *
+   * <p>{@link AttributeKey} objets are being created and cached on the first invocation of this
+   * method for a certain key. Subsequent invocations of this method with the same key return the
+   * cached object.
+   *
+   * @param key The variable part of the template-typed attribute name.
+   * @return An {@link AttributeKey} object for the given key.
+   */
+  public AttributeKey<T> getAttributeKey(String key) {
+    return keysCache.computeIfAbsent(key, this::createAttributeKey);
+  }
+}