Improve code and document of sentinel-datasource-etcd module

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

sentinel-extension/sentinel-datasource-etcd/README.md

@@ -1,8 +1,10 @@
 # Sentinel DataSource Etcd
 
-Sentinel DataSource Etcd provides integration with Etcd so that Etcd
+Sentinel DataSource Etcd provides integration with etcd so that etcd
 can be the dynamic rule data source of Sentinel. The data source uses push model (watcher).
 
+> **NOTE**: This module requires JDK 1.8 or later.
+
 To use Sentinel DataSource Etcd, you should add the following dependency:
 
 ```xml
@@ -12,29 +14,26 @@ To use Sentinel DataSource Etcd, you should add the following dependency:
     <version>x.y.z</version>
 </dependency>
 ```
-Configure Etcd Connect Properties By Config File (for example sentinel.properties)
+
+We could configure Etcd connection configuration by config file (for example `sentinel.properties`):
 
 ```
-csp.sentinel.etcd.end.points=http://ip1:port1,http://ip2:port2
+csp.sentinel.etcd.endpoints=http://ip1:port1,http://ip2:port2
 csp.sentinel.etcd.user=your_user
 csp.sentinel.etcd.password=your_password
 csp.sentinel.etcd.charset=your_charset
-csp.sentinel.etcd.auth.enable=true //if ture open user/password or ssl check
-csp.sentinel.etcd.authority=authority //ssl
+csp.sentinel.etcd.auth.enable=true # if ture, then open user/password or ssl check
+csp.sentinel.etcd.authority=authority # ssl
 ```
-or JVM args(Add -D prefix)
 
+Or we could configure via JVM -D args or via `SentinelConfig.setConfig(key, value)`.
 
-Then you can create an `EtcdDataSource` and register to rule managers.
-For instance:
+Then we can create an `EtcdDataSource` and register to rule managers. For instance:
 
 ```java
-  //`rule_key` is the rule config key
-  ReadableDataSource<String, List<FlowRule>> flowRuleEtcdDataSource = new EtcdDataSource<>(rule_key, (rule) -> JSON.parseArray(rule, FlowRule.class));
-  FlowRuleManager.register2Property(flowRuleEtcdDataSource.getProperty());
+// `rule_key` is the rule config key
+ReadableDataSource<String, List<FlowRule>> flowRuleEtcdDataSource = new EtcdDataSource<>(rule_key, (rule) -> JSON.parseArray(rule, FlowRule.class));
+FlowRuleManager.register2Property(flowRuleEtcdDataSource.getProperty());
 ```
 
-> Note: It needs to update JDK version to JDK8
-
-
 We've also provided an example: [sentinel-demo-etcd-datasource](https://github.com/alibaba/Sentinel/tree/master/sentinel-demo/sentinel-demo-etcd-datasource)

sentinel-extension/sentinel-datasource-etcd/src/main/java/com/alibaba/csp/sentinel/datasource/etcd/EtcdConfig.java

@@ -19,15 +19,14 @@ import com.alibaba.csp.sentinel.config.SentinelConfig;
 import com.alibaba.csp.sentinel.util.StringUtil;
 
 /**
- * Configure Etcd Connect Properties
+ * Etcd connection configuration.
  *
  * @author lianglin
  * @since 1.7.0
  */
 public final class EtcdConfig {
 
-
-    public final static String END_POINTS = "csp.sentinel.etcd.end.points";
+    public final static String END_POINTS = "csp.sentinel.etcd.endpoints";
     public final static String USER = "csp.sentinel.etcd.user";
     public final static String PASSWORD = "csp.sentinel.etcd.password";
     public final static String CHARSET = "csp.sentinel.etcd.charset";
@@ -36,7 +35,6 @@ public final class EtcdConfig {
 
     private final static String ENABLED = "true";
 
-
     public static String getEndPoints() {
         return SentinelConfig.getConfig(END_POINTS);
     }
@@ -50,25 +48,21 @@ public final class EtcdConfig {
     }
 
     public static String getCharset() {
-        String etcdCharSet = SentinelConfig.getConfig(CHARSET);
-        if (StringUtil.isNotBlank(etcdCharSet)) {
-            return etcdCharSet;
+        String etcdCharset = SentinelConfig.getConfig(CHARSET);
+        if (StringUtil.isNotBlank(etcdCharset)) {
+            return etcdCharset;
         }
         return SentinelConfig.charset();
     }
 
     public static boolean isAuthEnable() {
-        if (ENABLED.equalsIgnoreCase(SentinelConfig.getConfig(AUTH_ENABLE))) {
-            return true;
-        }
-        return false;
+        return ENABLED.equalsIgnoreCase(SentinelConfig.getConfig(AUTH_ENABLE));
     }
 
     public static String getAuthority() {
         return SentinelConfig.getConfig(AUTHORITY);
     }
 
-    private EtcdConfig() {
-    };
+    private EtcdConfig() {}
 
 }

sentinel-extension/sentinel-datasource-etcd/src/main/java/com/alibaba/csp/sentinel/datasource/etcd/EtcdDataSource.java

@@ -18,6 +18,7 @@ package com.alibaba.csp.sentinel.datasource.etcd;
 import com.alibaba.csp.sentinel.datasource.AbstractDataSource;
 import com.alibaba.csp.sentinel.datasource.Converter;
 import com.alibaba.csp.sentinel.log.RecordLog;
+
 import io.etcd.jetcd.ByteSequence;
 import io.etcd.jetcd.Client;
 import io.etcd.jetcd.KeyValue;
@@ -38,48 +39,46 @@ import java.util.concurrent.CompletableFuture;
  */
 public class EtcdDataSource<T> extends AbstractDataSource<String, T> {
 
-
-    private Client client;
+    private final Client client;
     private Watch.Watcher watcher;
 
-    private String key;
+    private final String key;
     private Charset charset = Charset.forName(EtcdConfig.getCharset());
 
     /**
-     * Create Etcd Data Source, Retrieve Connect Config Properties from ${@link EtcdConfig}
+     * Create an etcd data-source. The connection configuration will be retrieved from {@link EtcdConfig}.
      *
-     * @param key    Config key
-     * @param parser Value Parser
+     * @param key    config key
+     * @param parser data parser
      */
     public EtcdDataSource(String key, Converter<String, T> parser) {
         super(parser);
         if (!EtcdConfig.isAuthEnable()) {
             this.client = Client.builder()
-                    .endpoints(EtcdConfig.getEndPoints().split(",")).build();
+                .endpoints(EtcdConfig.getEndPoints().split(",")).build();
         } else {
             this.client = Client.builder()
-                    .endpoints(EtcdConfig.getEndPoints().split(","))
-                    .user(ByteSequence.from(EtcdConfig.getUser(), charset))
-                    .password(ByteSequence.from(EtcdConfig.getPassword(), charset))
-                    .authority(EtcdConfig.getAuthority())
-                    .build();
+                .endpoints(EtcdConfig.getEndPoints().split(","))
+                .user(ByteSequence.from(EtcdConfig.getUser(), charset))
+                .password(ByteSequence.from(EtcdConfig.getPassword(), charset))
+                .authority(EtcdConfig.getAuthority())
+                .build();
         }
         this.key = key;
         loadInitialConfig();
         initWatcher();
-
     }
 
-
     private void loadInitialConfig() {
         try {
             T newValue = loadConfig();
             if (newValue == null) {
-                RecordLog.warn("[EtcdDataSource] WARN: initial application is null, you may have to check your data source");
+                RecordLog.warn(
+                    "[EtcdDataSource] Initial configuration is null, you may have to check your data source");
             }
             getProperty().updateValue(newValue);
         } catch (Exception ex) {
-            RecordLog.warn("[EtcdDataSource] Error when loading initial application", ex);
+            RecordLog.warn("[EtcdDataSource] Error when loading initial configuration", ex);
         }
     }
 
@@ -92,17 +91,16 @@ public class EtcdDataSource<T> extends AbstractDataSource<String, T> {
                         T newValue = loadConfig();
                         getProperty().updateValue(newValue);
                     } catch (Exception e) {
-                        RecordLog.warn("[EtcdDataSource] update rule config error: ", e);
+                        RecordLog.warn("[EtcdDataSource] Failed to update config", e);
                     }
                 } else if (eventType == WatchEvent.EventType.DELETE) {
+                    RecordLog.info("[EtcdDataSource] Cleaning config for key <{0}>", key);
                     getProperty().updateValue(null);
-                    RecordLog.info("[EtcdDataSource] clean rule config of {0}", key);
                 }
             }
         });
     }
 
-
     @Override
     public String readSource() throws Exception {
         CompletableFuture<GetResponse> responseFuture = client.getKVClient().get(ByteSequence.from(key, charset));
@@ -116,7 +114,7 @@ public class EtcdDataSource<T> extends AbstractDataSource<String, T> {
             try {
                 watcher.close();
             } catch (Exception ex) {
-                RecordLog.info("[EtcdDataSource] close watcher error", ex);
+                RecordLog.info("[EtcdDataSource] Failed to close watcher", ex);
             }
         }
         if (client != null) {