Refactor Sentinel data source hierarchy

- Spilt DataSource into two types: ReadableDataSource and WritableDataSource
- The AbstractDataSource now is read-only
- Refactor the file data source for writable implementation
- Rename: ConfigParser -> Converter (represents both encoder `T -> S` and decoder `S -> T`)
- Some other refinement

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

sentinel-extension/sentinel-datasource-apollo/src/main/java/com/alibaba/csp/sentinel/datasource/apollo/ApolloDataSource.java

@@ -1,9 +1,9 @@
 package com.alibaba.csp.sentinel.datasource.apollo;
 
 import com.alibaba.csp.sentinel.datasource.AbstractDataSource;
-import com.alibaba.csp.sentinel.datasource.ConfigParser;
-import com.alibaba.csp.sentinel.datasource.DataSource;
+import com.alibaba.csp.sentinel.datasource.Converter;
 import com.alibaba.csp.sentinel.log.RecordLog;
+
 import com.ctrip.framework.apollo.Config;
 import com.ctrip.framework.apollo.ConfigChangeListener;
 import com.ctrip.framework.apollo.ConfigService;
@@ -14,81 +14,84 @@
 import com.google.common.collect.Sets;
 
 /**
- * A {@link DataSource} with <a href="http://github.com/ctripcorp/apollo">Apollo</a> as its configuration source.
+ * A read-only {@code DataSource} with <a href="http://github.com/ctripcorp/apollo">Apollo</a> as its configuration
+ * source.
  * <br />
  * When the rule is changed in Apollo, it will take effect in real time.
  *
  * @author Jason Song
  */
 public class ApolloDataSource<T> extends AbstractDataSource<String, T> {
 
-  private final Config config;
-  private final String flowRulesKey;
-  private final String defaultFlowRuleValue;
-
-  /**
-   * Constructs the Apollo data source
-   *
-   * @param namespaceName        the namespace name in Apollo, should not be null or empty
-   * @param flowRulesKey         the flow rules key in the namespace, should not be null or empty
-   * @param defaultFlowRuleValue the default flow rules value when the flow rules key is not found or any error occurred
-   * @param parser               the parser to transform string configuration to actual flow rules
-   */
-  public ApolloDataSource(String namespaceName, String flowRulesKey, String defaultFlowRuleValue,
-      ConfigParser<String, T> parser) {
-    super(parser);
+    private final Config config;
+    private final String flowRulesKey;
+    private final String defaultFlowRuleValue;
 
-    Preconditions.checkArgument(!Strings.isNullOrEmpty(namespaceName), "Namespace name could not be null or empty");
-    Preconditions.checkArgument(!Strings.isNullOrEmpty(flowRulesKey), "FlowRuleKey could not be null or empty!");
+    /**
+     * Constructs the Apollo data source
+     *
+     * @param namespaceName        the namespace name in Apollo, should not be null or empty
+     * @param flowRulesKey         the flow rules key in the namespace, should not be null or empty
+     * @param defaultFlowRuleValue the default flow rules value when the flow rules key is not found or any error
+     *                             occurred
+     * @param parser               the parser to transform string configuration to actual flow rules
+     */
+    public ApolloDataSource(String namespaceName, String flowRulesKey, String defaultFlowRuleValue,
+                            Converter<String, T> parser) {
+        super(parser);
 
-    this.flowRulesKey = flowRulesKey;
-    this.defaultFlowRuleValue = defaultFlowRuleValue;
+        Preconditions.checkArgument(!Strings.isNullOrEmpty(namespaceName), "Namespace name could not be null or empty");
+        Preconditions.checkArgument(!Strings.isNullOrEmpty(flowRulesKey), "FlowRuleKey could not be null or empty!");
 
-    this.config = ConfigService.getConfig(namespaceName);
+        this.flowRulesKey = flowRulesKey;
+        this.defaultFlowRuleValue = defaultFlowRuleValue;
 
-    initialize();
+        this.config = ConfigService.getConfig(namespaceName);
 
-    RecordLog.info(String.format("Initialized rule for namespace: %s, flow rules key: %s", namespaceName, flowRulesKey));
-  }
+        initialize();
 
-  private void initialize() {
-    initializeConfigChangeListener();
-    loadAndUpdateRules();
-  }
+        RecordLog.info(String.format("Initialized rule for namespace: %s, flow rules key: %s",
+            namespaceName, flowRulesKey));
+    }
 
-  private void loadAndUpdateRules() {
-    try {
-      T newValue = loadConfig();
-      if (newValue == null) {
-        RecordLog.warn("[ApolloDataSource] WARN: rule config is null, you may have to check your data source");
-      }
-      getProperty().updateValue(newValue);
-    } catch (Throwable ex) {
-      RecordLog.warn("[ApolloDataSource] Error when loading rule config", ex);
+    private void initialize() {
+        initializeConfigChangeListener();
+        loadAndUpdateRules();
     }
-  }
 
-  private void initializeConfigChangeListener() {
-    config.addChangeListener(new ConfigChangeListener() {
-      @Override
-      public void onChange(ConfigChangeEvent changeEvent) {
-        ConfigChange change = changeEvent.getChange(flowRulesKey);
-        //change is never null because the listener will only notify for this key
-        if (change != null) {
-          RecordLog.info("[ApolloDataSource] Received config changes: " + change.toString());
+    private void loadAndUpdateRules() {
+        try {
+            T newValue = loadConfig();
+            if (newValue == null) {
+                RecordLog.warn("[ApolloDataSource] WARN: rule config is null, you may have to check your data source");
+            }
+            getProperty().updateValue(newValue);
+        } catch (Throwable ex) {
+            RecordLog.warn("[ApolloDataSource] Error when loading rule config", ex);
         }
-        loadAndUpdateRules();
-      }
-    }, Sets.newHashSet(flowRulesKey));
-  }
+    }
 
-  @Override
-  public String readSource() throws Exception {
-    return config.getProperty(flowRulesKey, defaultFlowRuleValue);
-  }
+    private void initializeConfigChangeListener() {
+        config.addChangeListener(new ConfigChangeListener() {
+            @Override
+            public void onChange(ConfigChangeEvent changeEvent) {
+                ConfigChange change = changeEvent.getChange(flowRulesKey);
+                //change is never null because the listener will only notify for this key
+                if (change != null) {
+                    RecordLog.info("[ApolloDataSource] Received config changes: " + change.toString());
+                }
+                loadAndUpdateRules();
+            }
+        }, Sets.newHashSet(flowRulesKey));
+    }
 
-  @Override
-  public void close() throws Exception {
-    // nothing to destroy
-  }
+    @Override
+    public String readSource() throws Exception {
+        return config.getProperty(flowRulesKey, defaultFlowRuleValue);
+    }
+
+    @Override
+    public void close() throws Exception {
+        // nothing to destroy
+    }
 }

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

@@ -18,12 +18,20 @@
 import com.alibaba.csp.sentinel.property.DynamicSentinelProperty;
 import com.alibaba.csp.sentinel.property.SentinelProperty;
 
-public abstract class AbstractDataSource<S, T> implements DataSource<S, T> {
+/**
+ * The abstract readable data source provides basic functionality for loading and parsing config.
+ *
+ * @param <S> source data type
+ * @param <T> target data type
+ * @author Carpenter Lee
+ * @author Eric Zhao
+ */
+public abstract class AbstractDataSource<S, T> implements ReadableDataSource<S, T> {
 
-    protected final ConfigParser<S, T> parser;
+    protected final Converter<S, T> parser;
     protected final SentinelProperty<T> property;
 
-    public AbstractDataSource(ConfigParser<S, T> parser) {
+    public AbstractDataSource(Converter<S, T> parser) {
         if (parser == null) {
             throw new IllegalArgumentException("parser can't be null");
         }
@@ -33,24 +41,16 @@ public AbstractDataSource(ConfigParser<S, T> parser) {
 
     @Override
     public T loadConfig() throws Exception {
-        S readValue = readSource();
-        T value = parser.parse(readValue);
-        return value;
+        return loadConfig(readSource());
     }
 
     public T loadConfig(S conf) throws Exception {
-        T value = parser.parse(conf);
+        T value = parser.convert(conf);
         return value;
     }
 
     @Override
     public SentinelProperty<T> getProperty() {
         return property;
     }
-
-    @Override
-    public void writeDataSource(T values) throws Exception {
-        throw new UnsupportedOperationException();
-    }
-
 }

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

@@ -23,7 +23,7 @@
 import com.alibaba.csp.sentinel.log.RecordLog;
 
 /**
- * A {@link DataSource} automatically fetches the backend data.
+ * A {@link ReadableDataSource} automatically fetches the backend data.
  *
  * @param <S> source data type
  * @param <T> target data type
@@ -34,12 +34,12 @@ public abstract class AutoRefreshDataSource<S, T> extends AbstractDataSource<S,
     private ScheduledExecutorService service;
     protected long recommendRefreshMs = 3000;
 
-    public AutoRefreshDataSource(ConfigParser<S, T> configParser) {
+    public AutoRefreshDataSource(Converter<S, T> configParser) {
         super(configParser);
         startTimerService();
     }
 
-    public AutoRefreshDataSource(ConfigParser<S, T> configParser, final long recommendRefreshMs) {
+    public AutoRefreshDataSource(Converter<S, T> configParser, final long recommendRefreshMs) {
         super(configParser);
         if (recommendRefreshMs <= 0) {
             throw new IllegalArgumentException("recommendRefreshMs must > 0, but " + recommendRefreshMs + " get");
@@ -72,5 +72,4 @@ public void close() throws Exception {
             service = null;
         }
     }
-
 }

sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/ConfigParser.java → sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/Converter.java

@@ -16,16 +16,18 @@
 package com.alibaba.csp.sentinel.datasource;
 
 /**
- * Parse config from source data type S to target data type T.
+ * Convert an object from source type {@code S} to target type {@code T}.
  *
  * @author leyou
+ * @author Eric Zhao
  */
-public interface ConfigParser<S, T> {
+public interface Converter<S, T> {
+
     /**
-     * Parse {@code source} to the target format.
+     * Convert {@code source} to the target type.
      *
-     * @param source the source.
-     * @return the target.
+     * @param source the source object
+     * @return the target object
      */
-    T parse(S source);
+    T convert(S source);
 }

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

@@ -19,18 +19,18 @@
 import com.alibaba.csp.sentinel.property.SentinelProperty;
 
 /**
- * A {@link DataSource} based on nothing. {@link EmptyDataSource#getProperty()} will always return the same cached
+ * A {@link ReadableDataSource} based on nothing. {@link EmptyDataSource#getProperty()} will always return the same cached
  * {@link SentinelProperty} that doing nothing.
  * <br/>
- * This class is used when we want to use default settings instead of configs from the {@link DataSource}
+ * This class is used when we want to use default settings instead of configs from the {@link ReadableDataSource}.
  *
  * @author leyou
  */
-public class EmptyDataSource implements DataSource<Object, Object> {
+public final class EmptyDataSource implements ReadableDataSource<Object, Object> {
 
-    public static final DataSource<Object, Object> EMPTY_DATASOURCE = new EmptyDataSource();
+    public static final ReadableDataSource<Object, Object> EMPTY_DATASOURCE = new EmptyDataSource();
 
-    private static final SentinelProperty<Object> property = new NoOpSentinelProperty();
+    private static final SentinelProperty<Object> PROPERTY = new NoOpSentinelProperty();
 
     private EmptyDataSource() { }
 
@@ -46,15 +46,9 @@ public Object readSource() throws Exception {
 
     @Override
     public SentinelProperty<Object> getProperty() {
-        return property;
+        return PROPERTY;
     }
 
     @Override
     public void close() throws Exception { }
-
-    @Override
-    public void writeDataSource(Object config) throws Exception {
-        throw new UnsupportedOperationException();
-    }
-
 }