Refactor SpiLoader and enhance SPI mechanism (alibaba#1383)

* Add `@Spi` annotation as the general annotation for SPI definition.
* Add isDefault in @SPI, add loadDefaultInstance and improve loadFirstInstanceOrDefault method, improve test cases
* Add SpiLoaderException class for thrown when something goes wrong while loading Provider
* Rearrange packages of base SPI mechanism

NOTE: this PR contains breaking changes regarding API.

sentinel-adapter/sentinel-api-gateway-adapter-common/src/main/java/com/alibaba/csp/sentinel/adapter/gateway/common/api/GatewayApiDefinitionManager.java

@@ -27,7 +27,7 @@
 import com.alibaba.csp.sentinel.property.PropertyListener;
 import com.alibaba.csp.sentinel.property.SentinelProperty;
 import com.alibaba.csp.sentinel.util.AssertUtil;
-import com.alibaba.csp.sentinel.util.SpiLoader;
+import com.alibaba.csp.sentinel.spi.SpiLoader;
 import com.alibaba.csp.sentinel.util.StringUtil;
 
 /**
@@ -59,7 +59,7 @@ public final class GatewayApiDefinitionManager {
     }
 
     private static void initializeApiChangeObserverSpi() {
-        List<ApiDefinitionChangeObserver> listeners = SpiLoader.loadInstanceList(ApiDefinitionChangeObserver.class);
+        List<ApiDefinitionChangeObserver> listeners = SpiLoader.of(ApiDefinitionChangeObserver.class).loadInstanceList();
         for (ApiDefinitionChangeObserver e : listeners) {
             API_CHANGE_OBSERVERS.put(e.getClass().getCanonicalName(), e);
             RecordLog.info("[GatewayApiDefinitionManager] ApiDefinitionChangeObserver added: {}"

sentinel-adapter/sentinel-api-gateway-adapter-common/src/main/java/com/alibaba/csp/sentinel/adapter/gateway/common/slot/GatewayFlowSlot.java

@@ -27,13 +27,13 @@
 import com.alibaba.csp.sentinel.slots.block.flow.param.ParamFlowException;
 import com.alibaba.csp.sentinel.slots.block.flow.param.ParamFlowRule;
 import com.alibaba.csp.sentinel.slots.block.flow.param.ParameterMetricStorage;
-import com.alibaba.csp.sentinel.spi.SpiOrder;
+import com.alibaba.csp.sentinel.spi.Spi;
 
 /**
  * @author Eric Zhao
  * @since 1.6.1
  */
-@SpiOrder(-4000)
+@Spi(order = -4000)
 public class GatewayFlowSlot extends AbstractLinkedProcessorSlot<DefaultNode> {
 
     @Override

sentinel-adapter/sentinel-api-gateway-adapter-common/src/main/java/com/alibaba/csp/sentinel/adapter/gateway/common/slot/GatewaySlotChainBuilder.java

@@ -21,8 +21,9 @@
  * @author Eric Zhao
  * @since 1.6.1
  *
- * @deprecated since 1.7.2, we can use @SpiOrder(-4000) to adjust the order of {@link GatewayFlowSlot},
+ * @deprecated since 1.7.2, we can use @Spi(order = -4000) to adjust the order of {@link GatewayFlowSlot},
  * this class is reserved for compatibility with older versions.
+ *
  * @see GatewayFlowSlot
  * @see DefaultSlotChainBuilder
  */

sentinel-cluster/sentinel-cluster-client-default/src/main/java/com/alibaba/csp/sentinel/cluster/client/codec/ClientEntityCodecProvider.java

@@ -15,7 +15,7 @@
  */
 package com.alibaba.csp.sentinel.cluster.client.codec;
 
-import com.alibaba.csp.sentinel.util.SpiLoader;
+import com.alibaba.csp.sentinel.spi.SpiLoader;
 import com.alibaba.csp.sentinel.cluster.codec.request.RequestEntityWriter;
 import com.alibaba.csp.sentinel.cluster.codec.response.ResponseEntityDecoder;
 import com.alibaba.csp.sentinel.log.RecordLog;
@@ -34,15 +34,15 @@ public final class ClientEntityCodecProvider {
     }
 
     private static void resolveInstance() {
-        RequestEntityWriter writer = SpiLoader.loadFirstInstance(RequestEntityWriter.class);
+        RequestEntityWriter writer = SpiLoader.of(RequestEntityWriter.class).loadFirstInstance();
         if (writer == null) {
             RecordLog.warn("[ClientEntityCodecProvider] No existing request entity writer, resolve failed");
         } else {
             requestEntityWriter = writer;
             RecordLog.info("[ClientEntityCodecProvider] Request entity writer resolved: {}",
                 requestEntityWriter.getClass().getCanonicalName());
         }
-        ResponseEntityDecoder decoder = SpiLoader.loadFirstInstance(ResponseEntityDecoder.class);
+        ResponseEntityDecoder decoder = SpiLoader.of(ResponseEntityDecoder.class).loadFirstInstance();
         if (decoder == null) {
             RecordLog.warn("[ClientEntityCodecProvider] No existing response entity decoder, resolve failed");
         } else {

sentinel-cluster/sentinel-cluster-server-default/src/main/java/com/alibaba/csp/sentinel/cluster/flow/DefaultTokenService.java

@@ -22,6 +22,7 @@
 import com.alibaba.csp.sentinel.cluster.flow.rule.ClusterParamFlowRuleManager;
 import com.alibaba.csp.sentinel.slots.block.flow.FlowRule;
 import com.alibaba.csp.sentinel.slots.block.flow.param.ParamFlowRule;
+import com.alibaba.csp.sentinel.spi.Spi;
 
 import java.util.Collection;
 
@@ -31,6 +32,7 @@
  * @author Eric Zhao
  * @since 1.4.0
  */
+@Spi(isDefault = true)
 public class DefaultTokenService implements TokenService {
 
     @Override

sentinel-cluster/sentinel-cluster-server-default/src/main/java/com/alibaba/csp/sentinel/cluster/server/TokenServiceProvider.java

@@ -16,9 +16,8 @@
 package com.alibaba.csp.sentinel.cluster.server;
 
 import com.alibaba.csp.sentinel.cluster.TokenService;
-import com.alibaba.csp.sentinel.cluster.flow.DefaultTokenService;
 import com.alibaba.csp.sentinel.log.RecordLog;
-import com.alibaba.csp.sentinel.util.SpiLoader;
+import com.alibaba.csp.sentinel.spi.SpiLoader;
 
 /**
  * @author Eric Zhao
@@ -37,7 +36,7 @@ public static TokenService getService() {
     }
 
     private static void resolveTokenServiceSpi() {
-        service = SpiLoader.loadFirstInstanceOrDefault(TokenService.class, DefaultTokenService.class);
+        service = SpiLoader.of(TokenService.class).loadFirstInstanceOrDefault();
         if (service != null) {
             RecordLog.info("[TokenServiceProvider] Global token service resolved: "
                 + service.getClass().getCanonicalName());

sentinel-cluster/sentinel-cluster-server-default/src/main/java/com/alibaba/csp/sentinel/cluster/server/codec/ServerEntityCodecProvider.java

@@ -18,7 +18,7 @@
 import com.alibaba.csp.sentinel.cluster.codec.request.RequestEntityDecoder;
 import com.alibaba.csp.sentinel.cluster.codec.response.ResponseEntityWriter;
 import com.alibaba.csp.sentinel.log.RecordLog;
-import com.alibaba.csp.sentinel.util.SpiLoader;
+import com.alibaba.csp.sentinel.spi.SpiLoader;
 
 /**
  * @author Eric Zhao
@@ -34,15 +34,15 @@ public final class ServerEntityCodecProvider {
     }
 
     private static void resolveInstance() {
-        ResponseEntityWriter writer = SpiLoader.loadFirstInstance(ResponseEntityWriter.class);
+        ResponseEntityWriter writer = SpiLoader.of(ResponseEntityWriter.class).loadFirstInstance();
         if (writer == null) {
             RecordLog.warn("[ServerEntityCodecProvider] No existing response entity writer, resolve failed");
         } else {
             responseEntityWriter = writer;
             RecordLog.info("[ServerEntityCodecProvider] Response entity writer resolved: {}",
                 responseEntityWriter.getClass().getCanonicalName());
         }
-        RequestEntityDecoder decoder = SpiLoader.loadFirstInstance(RequestEntityDecoder.class);
+        RequestEntityDecoder decoder = SpiLoader.of(RequestEntityDecoder.class).loadFirstInstance();
         if (decoder == null) {
             RecordLog.warn("[ServerEntityCodecProvider] No existing request entity decoder, resolve failed");
         } else {

sentinel-cluster/sentinel-cluster-server-default/src/main/java/com/alibaba/csp/sentinel/cluster/server/processor/RequestProcessorProvider.java

@@ -15,12 +15,12 @@
  */
 package com.alibaba.csp.sentinel.cluster.server.processor;
 
+import java.util.List;
 import java.util.Map;
-import java.util.ServiceLoader;
 import java.util.concurrent.ConcurrentHashMap;
 
 import com.alibaba.csp.sentinel.cluster.annotation.RequestType;
-import com.alibaba.csp.sentinel.spi.ServiceLoaderUtil;
+import com.alibaba.csp.sentinel.spi.SpiLoader;
 import com.alibaba.csp.sentinel.util.AssertUtil;
 
 /**
@@ -31,15 +31,13 @@ public final class RequestProcessorProvider {
 
     private static final Map<Integer, RequestProcessor> PROCESSOR_MAP = new ConcurrentHashMap<>();
 
-    private static final ServiceLoader<RequestProcessor> SERVICE_LOADER = ServiceLoaderUtil.getServiceLoader(
-        RequestProcessor.class);
-
     static {
         loadAndInit();
     }
 
     private static void loadAndInit() {
-        for (RequestProcessor processor : SERVICE_LOADER) {
+        List<RequestProcessor> processors = SpiLoader.of(RequestProcessor.class).loadInstanceList();
+        for (RequestProcessor processor : processors) {
             Integer type = parseRequestType(processor);
             if (type != null) {
                 PROCESSOR_MAP.put(type, processor);

sentinel-core/src/main/java/com/alibaba/csp/sentinel/Constants.java

@@ -70,5 +70,17 @@ public final class Constants {
      */
     public static volatile boolean ON = true;
 
+    /**
+     * Order of default processor slots
+     */
+    public static final int ORDER_NODE_SELECTOR_SLOT = -10000;
+    public static final int ORDER_CLUSTER_BUILDER_SLOT = -9000;
+    public static final int ORDER_LOG_SLOT = -8000;
+    public static final int ORDER_STATISTIC_SLOT = -7000;
+    public static final int ORDER_AUTHORITY_SLOT = -6000;
+    public static final int ORDER_SYSTEM_SLOT = -5000;
+    public static final int ORDER_FLOW_SLOT = -2000;
+    public static final int ORDER_DEGRADE_SLOT = -1000;
+
     private Constants() {}
 }

sentinel-core/src/main/java/com/alibaba/csp/sentinel/cluster/client/TokenClientProvider.java

@@ -16,7 +16,7 @@
 package com.alibaba.csp.sentinel.cluster.client;
 
 import com.alibaba.csp.sentinel.log.RecordLog;
-import com.alibaba.csp.sentinel.util.SpiLoader;
+import com.alibaba.csp.sentinel.spi.SpiLoader;
 
 /**
  * Provider for a universal {@link ClusterTokenClient} instance.
@@ -38,7 +38,7 @@ public static ClusterTokenClient getClient() {
     }
 
     private static void resolveTokenClientInstance() {
-        ClusterTokenClient resolvedClient = SpiLoader.loadFirstInstance(ClusterTokenClient.class);
+        ClusterTokenClient resolvedClient = SpiLoader.of(ClusterTokenClient.class).loadFirstInstance();
         if (resolvedClient == null) {
             RecordLog.info(
                 "[TokenClientProvider] No existing cluster token client, cluster client mode will not be activated");

sentinel-core/src/main/java/com/alibaba/csp/sentinel/cluster/server/EmbeddedClusterTokenServerProvider.java

@@ -16,7 +16,7 @@
 package com.alibaba.csp.sentinel.cluster.server;
 
 import com.alibaba.csp.sentinel.log.RecordLog;
-import com.alibaba.csp.sentinel.util.SpiLoader;
+import com.alibaba.csp.sentinel.spi.SpiLoader;
 
 /**
  * @author Eric Zhao
@@ -31,7 +31,7 @@ public final class EmbeddedClusterTokenServerProvider {
     }
 
     private static void resolveInstance() {
-        EmbeddedClusterTokenServer s = SpiLoader.loadFirstInstance(EmbeddedClusterTokenServer.class);
+        EmbeddedClusterTokenServer s = SpiLoader.of(EmbeddedClusterTokenServer.class).loadFirstInstance();
         if (s == null) {
             RecordLog.warn("[EmbeddedClusterTokenServerProvider] No existing cluster token server, cluster server mode will not be activated");
         } else {

sentinel-core/src/main/java/com/alibaba/csp/sentinel/config/SentinelConfig.java

@@ -41,6 +41,11 @@ public final class SentinelConfig {
      */
     public static final int APP_TYPE_COMMON = 0;
 
+    /**
+     * Parameter value for using context classloader.
+     */
+    private static final String CLASSLOADER_CONTEXT = "context";
+
     private static final Map<String, String> props = new ConcurrentHashMap<>();
 
     private static int appType = APP_TYPE_COMMON;
@@ -307,6 +312,15 @@ private static void resolveAppName() {
     private static String toEnvKey(/*@NotBlank*/ String propKey) {
         return propKey.toUpperCase().replace('.', '_');
     }
+    /**
+     * Whether use context classloader via config parameter
+     *
+     * @return Whether use context classloader
+     */
+    public static boolean shouldUseContextClassloader() {
+        String classloaderConf = SentinelConfig.getConfig(SentinelConfig.SPI_CLASSLOADER);
+        return CLASSLOADER_CONTEXT.equalsIgnoreCase(classloaderConf);
+    }
 
     private SentinelConfig() {}
 }

sentinel-core/src/main/java/com/alibaba/csp/sentinel/init/InitExecutor.java

@@ -21,7 +21,7 @@
 import java.util.concurrent.atomic.AtomicBoolean;
 
 import com.alibaba.csp.sentinel.log.RecordLog;
-import com.alibaba.csp.sentinel.spi.ServiceLoaderUtil;
+import com.alibaba.csp.sentinel.spi.SpiLoader;
 
 /**
  * Load registered init functions and execute in order.
@@ -43,9 +43,9 @@ public static void doInit() {
             return;
         }
         try {
-            ServiceLoader<InitFunc> loader = ServiceLoaderUtil.getServiceLoader(InitFunc.class);
+            List<InitFunc> initFuncs = SpiLoader.of(InitFunc.class).loadInstanceListSorted();
             List<OrderWrapper> initList = new ArrayList<OrderWrapper>();
-            for (InitFunc initFunc : loader) {
+            for (InitFunc initFunc : initFuncs) {
                 RecordLog.info("[InitExecutor] Found init func: {}", initFunc.getClass().getCanonicalName());
                 insertSorted(initList, initFunc);
             }

sentinel-core/src/main/java/com/alibaba/csp/sentinel/metric/extension/MetricExtensionProvider.java

@@ -19,7 +19,7 @@
 import java.util.List;
 
 import com.alibaba.csp.sentinel.log.RecordLog;
-import com.alibaba.csp.sentinel.util.SpiLoader;
+import com.alibaba.csp.sentinel.spi.SpiLoader;
 
 /**
  * Get all {@link MetricExtension} via SPI.
@@ -35,7 +35,7 @@ public class MetricExtensionProvider {
     }
 
     private static void resolveInstance() {
-        List<MetricExtension> extensions = SpiLoader.loadInstanceList(MetricExtension.class);
+        List<MetricExtension> extensions = SpiLoader.of(MetricExtension.class).loadInstanceList();
 
         if (extensions.isEmpty()) {
             RecordLog.info("[MetricExtensionProvider] No existing MetricExtension found");

sentinel-core/src/main/java/com/alibaba/csp/sentinel/slotchain/SlotChainProvider.java

@@ -17,7 +17,7 @@
 
 import com.alibaba.csp.sentinel.log.RecordLog;
 import com.alibaba.csp.sentinel.slots.DefaultSlotChainBuilder;
-import com.alibaba.csp.sentinel.util.SpiLoader;
+import com.alibaba.csp.sentinel.spi.SpiLoader;
 
 /**
  * A provider for creating slot chains via resolved slot chain builder SPI.
@@ -41,7 +41,7 @@ public static ProcessorSlotChain newSlotChain() {
         }
 
         // Resolve the slot chain builder SPI.
-        slotChainBuilder = SpiLoader.loadFirstInstanceOrDefault(SlotChainBuilder.class, DefaultSlotChainBuilder.class);
+        slotChainBuilder = SpiLoader.of(SlotChainBuilder.class).loadFirstInstanceOrDefault();
 
         if (slotChainBuilder == null) {
             // Should not go through here.

sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/DefaultSlotChainBuilder.java

@@ -21,7 +21,8 @@
 import com.alibaba.csp.sentinel.slotchain.ProcessorSlot;
 import com.alibaba.csp.sentinel.slotchain.ProcessorSlotChain;
 import com.alibaba.csp.sentinel.slotchain.SlotChainBuilder;
-import com.alibaba.csp.sentinel.util.SpiLoader;
+import com.alibaba.csp.sentinel.spi.Spi;
+import com.alibaba.csp.sentinel.spi.SpiLoader;
 
 import java.util.List;
 
@@ -31,14 +32,14 @@
  * @author qinan.qn
  * @author leyou
  */
+@Spi(isDefault = true)
 public class DefaultSlotChainBuilder implements SlotChainBuilder {
 
     @Override
     public ProcessorSlotChain build() {
         ProcessorSlotChain chain = new DefaultProcessorSlotChain();
 
-        // Note: the instances of ProcessorSlot should be different, since they are not stateless.
-        List<ProcessorSlot> sortedSlotList = SpiLoader.loadPrototypeInstanceListSorted(ProcessorSlot.class);
+        List<ProcessorSlot> sortedSlotList = SpiLoader.of(ProcessorSlot.class).loadInstanceListSorted();
         for (ProcessorSlot slot : sortedSlotList) {
             if (!(slot instanceof AbstractLinkedProcessorSlot)) {
                 RecordLog.warn("The ProcessorSlot(" + slot.getClass().getCanonicalName() + ") is not an instance of AbstractLinkedProcessorSlot, can't be added into ProcessorSlotChain");

sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/block/authority/AuthoritySlot.java

@@ -18,20 +18,21 @@
 import java.util.Map;
 import java.util.Set;
 
+import com.alibaba.csp.sentinel.Constants;
 import com.alibaba.csp.sentinel.context.Context;
 import com.alibaba.csp.sentinel.node.DefaultNode;
 import com.alibaba.csp.sentinel.slotchain.AbstractLinkedProcessorSlot;
 import com.alibaba.csp.sentinel.slotchain.ProcessorSlot;
 import com.alibaba.csp.sentinel.slotchain.ResourceWrapper;
-import com.alibaba.csp.sentinel.spi.SpiOrder;
+import com.alibaba.csp.sentinel.spi.Spi;
 
 /**
  * A {@link ProcessorSlot} that dedicates to {@link AuthorityRule} checking.
  *
  * @author leyou
  * @author Eric Zhao
  */
-@SpiOrder(-6000)
+@Spi(order = Constants.ORDER_AUTHORITY_SLOT)
 public class AuthoritySlot extends AbstractLinkedProcessorSlot<DefaultNode> {
 
     @Override

sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/block/degrade/DegradeSlot.java

@@ -17,6 +17,7 @@
 
 import java.util.List;
 
+import com.alibaba.csp.sentinel.Constants;
 import com.alibaba.csp.sentinel.Entry;
 import com.alibaba.csp.sentinel.context.Context;
 import com.alibaba.csp.sentinel.node.DefaultNode;
@@ -25,15 +26,15 @@
 import com.alibaba.csp.sentinel.slotchain.ResourceWrapper;
 import com.alibaba.csp.sentinel.slots.block.BlockException;
 import com.alibaba.csp.sentinel.slots.block.degrade.circuitbreaker.CircuitBreaker;
-import com.alibaba.csp.sentinel.spi.SpiOrder;
+import com.alibaba.csp.sentinel.spi.Spi;
 
 /**
  * A {@link ProcessorSlot} dedicates to circuit breaking.
  *
  * @author Carpenter Lee
  * @author Eric Zhao
  */
-@SpiOrder(-1000)
+@Spi(order = Constants.ORDER_DEGRADE_SLOT)
 public class DegradeSlot extends AbstractLinkedProcessorSlot<DefaultNode> {
 
     @Override