[ISSUE 4254] Every utility class should be annotated with @UtilityClass as we are using lombok

docs/plugins/core-engines-configuration.md

@@ -0,0 +1,135 @@
+# EventMesh Core Engines Configuration Guide
+
+EventMesh provides powerful core engines (`Filter`, `Transformer`, `Router`) to dynamically process messages. These engines are configured via **MetaStorage** (Governance Center, e.g., Nacos, Etcd), supporting on-demand loading and hot-reloading.
+
+## 0. Core Concepts
+
+Before configuration, it is important to understand the specific role of each engine in the message flow:
+
+*   **Filter (The Gatekeeper)**: Decides **"Whether to pass"**.
+    *   It inspects the message (CloudEvent) attributes. If the message matches the rules, it passes; otherwise, it is dropped.
+    *   *Use Case*: Block debug logs from production traffic; Only subscribe to specific event types.
+
+*   **Transformer (The Translator)**: Decides **"What it looks like"**.
+    *   It modifies the message content (Payload or Metadata) according to templates or scripts.
+    *   *Use Case*: Convert XML to JSON; Mask sensitive data (PII); Adapt legacy protocols to new standards.
+
+*   **Router (The Dispatcher)**: Decides **"Where to go"**.
+    *   It dynamically changes the destination (Topic) of the message.
+    *   *Use Case*: Route traffic to a Canary/Gray release topic; Route high-priority orders to a dedicated queue.
+
+---
+
+## 1. Overview
+
+The configuration is not in local property files but distributed via the MetaStorage. EventMesh listens to specific **Keys** based on client Groups.
+
+- **Data Source**: Configured via `eventMesh.metaStorage.plugin.type`.
+- **Loading Mechanism**: Lazy loading & Hot-reloading.
+- **Key Format**: `{EnginePrefix}-{GroupName}`.
+- **Value Format**: JSON Array.
+
+| Engine | Prefix | Scope | Description |
+| :--- | :--- | :--- | :--- |
+| **Router** | `router-` | Pub Only | Routes messages to different topics. |
+| **Filter** | `filter-` | Pub & Sub | Filters messages based on CloudEvent attributes. |
+| **Transformer** | `transformer-` | Pub & Sub | Transforms message content (Payload/Header). |
+
+---
+
+## 2. Router (Routing)
+
+**Scope**: Publish Only (Upstream)  
+**Key**: `router-{producerGroup}`
+
+Decides the target storage topic for a message sent by a producer.
+
+### Configuration Example (JSON)
+
+```json
+[
+  {
+    "topic": "original-topic",
+    "routerConfig": {
+      "targetTopic": "redirect-topic",
+      "expression": "data.type == 'urgent'"
+    }
+  }
+]
+```
+
+*   **topic**: The original topic the producer sends to.
+*   **targetTopic**: The actual topic to write to Storage.
+*   **expression**: Condition to trigger routing (e.g., SpEL).
+
+---
+
+## 3. Filter (Filtering)
+
+**Scope**: Both Publish (Upstream) & Subscribe (Downstream)
+
+### A. Publish Side (Upstream)
+**Key**: `filter-{producerGroup}`  
+**Effect**: Intercepts messages **before** they are sent to Storage.
+
+### B. Subscribe Side (Downstream)
+**Key**: `filter-{consumerGroup}`  
+**Effect**: Intercepts messages **before** they are pushed to the Consumer.
+
+### Configuration Example (JSON)
+
+```json
+[
+  {
+    "topic": "test-topic",
+    "filterPattern": {
+      "source": ["app-a", "app-b"],
+      "type": [{"prefix": "com.example"}]
+    }
+  }
+]
+```
+
+*   **filterPattern**: Rules matching CloudEvent attributes. If a message doesn't match, it is dropped.
+
+---
+
+## 4. Transformer (Transformation)
+
+**Scope**: Both Publish (Upstream) & Subscribe (Downstream)
+
+### A. Publish Side (Upstream)
+**Key**: `transformer-{producerGroup}`  
+**Effect**: Modifies message content **before** sending to Storage.
+
+### B. Subscribe Side (Downstream)
+**Key**: `transformer-{consumerGroup}`  
+**Effect**: Modifies message content **before** pushing to the Consumer.
+
+### Configuration Example (JSON)
+
+```json
+[
+  {
+    "topic": "raw-topic",
+    "transformerConfig": {
+      "transformerType": "template",
+      "template": "{\"id\": \"${id}\", \"new_content\": \"${data.content}\"}"
+    }
+  }
+]
+```
+
+*   **transformerType**: e.g., `original`, `template`.
+*   **template**: The transformation template definition.
+
+---
+
+## 5. Verification
+
+1.  **Publish Config**: Add the JSON config to your Governance Center (e.g., Nacos) with the Data ID `router-MyGroup`.
+2.  **Send Message**: Use EventMesh SDK to send a message from `MyGroup`.
+3.  **Observe**:
+    *   For **Router**: Check if the message appears in the `targetTopic` in your MQ.
+    *   For **Filter**: Check if blocked messages are skipped.
+    *   For **Transformer**: Check if the message body in MQ (for Pub) or Consumer (for Sub) is modified.

eventmesh-admin-server/src/main/java/org/apache/eventmesh/admin/server/web/utils/Base64Utils.java

@@ -25,31 +25,31 @@
 import java.io.InputStream;
 import java.io.OutputStream;
 
-public class Base64Utils {
-    private static final int CACHE_SIZE = 1024;
+import lombok.experimental.UtilityClass;
 
-    public Base64Utils() {
-    }
+@UtilityClass
+public class Base64Utils {
+    private final int CACHE_SIZE = 1024;
 
-    public static byte[] decode(String base64) throws Exception {
+    public byte[] decode(String base64) throws Exception {
         return Base64.decode(base64.toCharArray());
     }
 
-    public static String encode(byte[] bytes) throws Exception {
+    public String encode(byte[] bytes) throws Exception {
         return new String(Base64.encode(bytes));
     }
 
-    public static String encodeFile(String filePath) throws Exception {
+    public String encodeFile(String filePath) throws Exception {
         byte[] bytes = fileToByte(filePath);
         return encode(bytes);
     }
 
-    public static void decodeToFile(String filePath, String base64) throws Exception {
+    public void decodeToFile(String filePath, String base64) throws Exception {
         byte[] bytes = decode(base64);
         byteArrayToFile(bytes, filePath);
     }
 
-    public static byte[] fileToByte(String filePath) throws Exception {
+    public byte[] fileToByte(String filePath) throws Exception {
         byte[] data = new byte[0];
         File file = new File(filePath);
         if (file.exists()) {
@@ -71,7 +71,7 @@ public static byte[] fileToByte(String filePath) throws Exception {
         return data;
     }
 
-    public static void byteArrayToFile(byte[] bytes, String filePath) throws Exception {
+    public void byteArrayToFile(byte[] bytes, String filePath) throws Exception {
         InputStream in = new ByteArrayInputStream(bytes);
         File destFile = new File(filePath);
         if (!destFile.getParentFile().exists()) {

eventmesh-admin-server/src/main/java/org/apache/eventmesh/admin/server/web/utils/EncryptUtil.java

@@ -22,11 +22,12 @@
 import java.io.FileReader;
 import java.io.IOException;
 
+import lombok.experimental.UtilityClass;
+
+@UtilityClass
 public class EncryptUtil {
-    public EncryptUtil() {
-    }
 
-    private static byte[] hexStringToBytes(String hexString) {
+    private byte[] hexStringToBytes(String hexString) {
         if (hexString != null && !hexString.equals("")) {
             hexString = hexString.toUpperCase();
             int length = hexString.length() / 2;
@@ -44,7 +45,7 @@ private static byte[] hexStringToBytes(String hexString) {
         }
     }
 
-    public static String byteToHexString(byte[] b) {
+    public String byteToHexString(byte[] b) {
         String a = "";
 
         for (int i = 0; i < b.length; ++i) {
@@ -59,11 +60,11 @@ public static String byteToHexString(byte[] b) {
         return a;
     }
 
-    private static byte charToByte(char c) {
+    private byte charToByte(char c) {
         return (byte) "0123456789ABCDEF".indexOf(c);
     }
 
-    private static String readFileContent(String filePath) {
+    private String readFileContent(String filePath) {
         File file = new File(filePath);
         BufferedReader reader = null;
         StringBuffer key = new StringBuffer();
@@ -100,7 +101,7 @@ private static String readFileContent(String filePath) {
         return key.toString();
     }
 
-    public static String decrypt(String sysPubKeyFile, String appPrivKeyFile, String encStr) throws Exception {
+    public String decrypt(String sysPubKeyFile, String appPrivKeyFile, String encStr) throws Exception {
         String pubKeyBase64 = readFileContent(sysPubKeyFile);
         String privKeyBase64 = readFileContent(appPrivKeyFile);
         byte[] encBin = hexStringToBytes(encStr);
@@ -109,7 +110,7 @@ public static String decrypt(String sysPubKeyFile, String appPrivKeyFile, String
         return new String(privDecBin);
     }
 
-    public static String decrypt(ParamType pubKeyType, String sysPubKey, ParamType privKeyType, String appPrivKey, ParamType passwdType,
+    public String decrypt(ParamType pubKeyType, String sysPubKey, ParamType privKeyType, String appPrivKey, ParamType passwdType,
                                  String passwd) throws Exception {
         String pubKeyBase64 = pubKeyType == ParamType.FILE ? readFileContent(sysPubKey) : sysPubKey;
         String privKeyBase64 = privKeyType == ParamType.FILE ? readFileContent(appPrivKey) : appPrivKey;
@@ -120,15 +121,15 @@ public static String decrypt(ParamType pubKeyType, String sysPubKey, ParamType p
         return new String(privDecBin);
     }
 
-    public static String encrypt(String appPubKeyFile, String sysPrivKeyFile, String passwd) throws Exception {
+    public String encrypt(String appPubKeyFile, String sysPrivKeyFile, String passwd) throws Exception {
         String pubKeyBase64 = readFileContent(appPubKeyFile);
         String privKeyBase64 = readFileContent(sysPrivKeyFile);
         byte[] pubEncBin = RSAUtils.encryptByPublicKeyBlock(passwd.getBytes(), pubKeyBase64);
         byte[] privEncBin = RSAUtils.encryptByPrivateKeyBlock(pubEncBin, privKeyBase64);
         return byteToHexString(privEncBin);
     }
 
-    public static String encrypt(ParamType pubKeyType, String appPubKey, ParamType privKeyType, String sysPrivKey, String passwd) throws Exception {
+    public String encrypt(ParamType pubKeyType, String appPubKey, ParamType privKeyType, String sysPrivKey, String passwd) throws Exception {
         String pubKeyBase64 = pubKeyType == ParamType.FILE ? readFileContent(appPubKey) : appPubKey;
         String privKeyBase64 = privKeyType == ParamType.FILE ? readFileContent(sysPrivKey) : sysPrivKey;
         byte[] pubEncBin = RSAUtils.encryptByPublicKeyBlock(passwd.getBytes(), pubKeyBase64);

eventmesh-admin-server/src/main/java/org/apache/eventmesh/admin/server/web/utils/JdbcUtils.java

@@ -19,9 +19,12 @@
 
 import com.alibaba.druid.pool.DruidDataSource;
 
+import lombok.experimental.UtilityClass;
+
+@UtilityClass
 public class JdbcUtils {
 
-    public static DruidDataSource createDruidDataSource(String url, String userName, String passWord) {
+    public DruidDataSource createDruidDataSource(String url, String userName, String passWord) {
         DruidDataSource dataSource = new DruidDataSource();
         dataSource.setUrl(url);
         dataSource.setUsername(userName);