Refactored JELProviders to enable users to add custom expressions

Author: preet-dev

src/main/java/io/opentelemetry/contrib/generator/core/ResourceModelGenerator.java

@@ -18,7 +18,7 @@
 
 import io.opentelemetry.contrib.generator.core.dto.*;
 import io.opentelemetry.contrib.generator.core.jel.ExpressionProcessor;
-import io.opentelemetry.contrib.generator.core.jel.JELProvider;
+import io.opentelemetry.contrib.generator.core.jel.ResourceExpressionsJELProvider;
 import io.opentelemetry.contrib.generator.core.jel.methods.ResourceModelExpressions;
 import io.opentelemetry.contrib.generator.core.utils.CommonUtils;
 import io.opentelemetry.proto.common.v1.KeyValue;
@@ -47,7 +47,7 @@ public class ResourceModelGenerator {
 
     private final Map<String, ResourceDefinition> allResources; //input resource definitions
     private final String requestID;
-    private static final ExpressionProcessor jelProcessor = JELProvider.getJelProcessor();
+    private static final ExpressionProcessor jelProcessor = ResourceExpressionsJELProvider.getJelProcessor();
     private static Map<String, List<GeneratorResource>> resourceModel; //output resource model
     private Map<String, ResourceType> typeMappings; //stores parent & child types for each resource type
 

src/main/java/io/opentelemetry/contrib/generator/core/jel/JELProvider.java

@@ -0,0 +1,84 @@
+/*
+ * Copyright 2022 AppDynamics Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.opentelemetry.contrib.generator.core.jel;
+
+import io.opentelemetry.contrib.generator.core.exception.GeneratorException;
+
+import java.lang.reflect.Method;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * Provides ELProcessor initialized with all the expression methods supported by the resource model definition YAML.
+ */
+public class ResourceExpressionsJELProvider {
+
+    private static ExpressionProcessor jelProcessor;
+
+    private ResourceExpressionsJELProvider() {}
+
+    public static ExpressionProcessor getJelProcessor() {
+        if (jelProcessor == null) {
+            jelProcessor = new ExpressionProcessor();
+        }
+        var expressionsClass = "io.opentelemetry.contrib.generator.core.jel.methods.ResourceModelExpressions";
+        List<String> methods = Arrays.asList("counter", "UUIDFromStringCounter", "roundRobin", "alphanumericSequenceFromEnv",
+                "alphanumericSequence", "IPv4Sequence", "distribution", "count", "getLong", "getDouble", "getBoolean");
+        addMethods(expressionsClass, methods);
+        var operationsClass = "io.opentelemetry.contrib.generator.core.ResourceModelGenerator";
+        methods = Arrays.asList("copyFromParent", "modifyFromParent");
+        addMethods(operationsClass, methods);
+        return jelProcessor;
+    }
+
+    private static void addMethods(String expressionsClass, List<String> methods) {
+        methods.forEach(method -> addExpression("", "", expressionsClass, method));
+    }
+
+    /**
+     * See <a href="https://jakarta.ee/specifications/platform/9/apidocs/jakarta/el/elprocessor#defineFunction-java.lang.String-java.lang.String-java.lang.String-java.lang.String-">...</a>
+     * Must be called in your code before telemetry generation is started.
+     */
+    public static void addExpression(String prefix, String function, String className, String methodName) {
+        if (jelProcessor == null) {
+            jelProcessor = new ExpressionProcessor();
+        }
+        try {
+            jelProcessor.defineFunction(prefix, function, className, methodName);
+        } catch (ClassNotFoundException e) {
+            throw new GeneratorException("Unable to find " + className + " having expression methods");
+        } catch (NoSuchMethodException e) {
+            throw new GeneratorException("Unknown expression method " + className + "." + methodName +
+                    " provided for class", e);
+        }
+    }
+
+    /**
+     * See <a href="https://jakarta.ee/specifications/platform/9/apidocs/jakarta/el/elprocessor#defineFunction-java.lang.String-java.lang.String-java.lang.reflect.Method-">...</a>
+     * Must be called in your code before telemetry generation is started.
+     */
+    public static void addExpression(String prefix, String function, Method method) {
+        if (jelProcessor == null) {
+            jelProcessor = new ExpressionProcessor();
+        }
+        try {
+            jelProcessor.defineFunction(prefix, function, method);
+        } catch (NoSuchMethodException e) {
+            throw new GeneratorException("Unknown expression method " + method + " provided", e);
+        }
+    }
+}

src/main/java/io/opentelemetry/contrib/generator/core/jel/ResourceExpressionsJELProvider.java

@@ -17,7 +17,7 @@
 package io.opentelemetry.contrib.generator.core.jel.methods;
 
 import io.opentelemetry.contrib.generator.core.jel.ExpressionProcessor;
-import io.opentelemetry.contrib.generator.core.jel.JELProvider;
+import io.opentelemetry.contrib.generator.core.jel.ResourceExpressionsJELProvider;
 import io.opentelemetry.contrib.generator.core.jel.helpers.AlphanumericHelper;
 import io.opentelemetry.contrib.generator.core.jel.helpers.IPHelper;
 import jakarta.el.ELProcessor;
@@ -41,7 +41,7 @@ public class ResourceModelExpressions {
     private static final ConcurrentHashMap<String, Integer> counters = new ConcurrentHashMap<>();
     private static final ConcurrentHashMap<String, Double> doubleCounters = new ConcurrentHashMap<>();
     private static final ConcurrentHashMap<String, String> stringCounters = new ConcurrentHashMap<>();
-    private static final ExpressionProcessor jelProcessor = JELProvider.getJelProcessor();
+    private static final ExpressionProcessor jelProcessor = ResourceExpressionsJELProvider.getJelProcessor();
     public static String expressionsGlobalKey = ""; //Modified by the resource model generator every time a new resource/attribute is being processed
 
     private ResourceModelExpressions() {}