Add common module for Sentinel default cluster implementation

- Add a `ClusterTransportClient` for transport abstraction of Sentinel cluster
- Add universal request/response interface and common ClusterRequest/ClusterResponse abstraction
- Add common request/response data entity
- Add basic abstraction of codec (EntityWriter and EntityDecoder)

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

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/ClusterConstants.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster;
+
+/**
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public final class ClusterConstants {
+
+    public static final int MSG_TYPE_PING = 0;
+    public static final int MSG_TYPE_FLOW = 1;
+    public static final int MSG_TYPE_PARAM_FLOW = 2;
+
+    public static final int RESPONSE_STATUS_BAD = -1;
+    public static final int RESPONSE_STATUS_OK = 0;
+
+    public static final int PARAM_TYPE_INTEGER = 0;
+    public static final int PARAM_TYPE_LONG = 1;
+    public static final int PARAM_TYPE_BYTE = 2;
+    public static final int PARAM_TYPE_DOUBLE = 3;
+    public static final int PARAM_TYPE_FLOAT = 4;
+    public static final int PARAM_TYPE_SHORT = 5;
+    public static final int PARAM_TYPE_BOOLEAN = 6;
+    public static final int PARAM_TYPE_STRING = 7;
+
+    public static final int DEFAULT_CLUSTER_SERVER_PORT = 8730;
+    public static final int DEFAULT_REQUEST_TIMEOUT = 20;
+
+    private ClusterConstants() {}
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/ClusterErrorMessages.java

@@ -0,0 +1,32 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster;
+
+/**
+ * @author jialiang.ljl
+ * @since 1.4.0
+ */
+public final class ClusterErrorMessages {
+
+    public static final String BAD_REQUEST = "bad request";
+    public static final String UNEXPECTED_STATUS = "unexpected status";
+    public static final String TOO_MANY_REQUESTS = "too many requests (client side)";
+    public static final String REQUEST_TIME_OUT = "request time out";
+    public static final String CLIENT_NOT_READY = "client not ready (not running or initializing)";
+    public static final String NO_RULES_IN_SERVER = "no rules in token server";
+
+    private ClusterErrorMessages() {}
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/ClusterTransportClient.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster;
+
+import com.alibaba.csp.sentinel.cluster.request.ClusterRequest;
+import com.alibaba.csp.sentinel.cluster.response.ClusterResponse;
+
+/**
+ * Synchronous transport client for distributed flow control.
+ *
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public interface ClusterTransportClient {
+
+    /**
+     * Send request to remote server and get response.
+     *
+     * @param request Sentinel cluster request
+     * @return response from remote server
+     * @throws Exception some error occurs
+     */
+    ClusterResponse sendRequest(ClusterRequest request) throws Exception;
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/codec/EntityDecoder.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster.codec;
+
+/**
+ * @param <S> source stream type
+ * @param <T> target entity type
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public interface EntityDecoder<S, T> {
+
+    /**
+     * Decode target object from source stream.
+     *
+     * @param source source stream
+     * @return decoded target object
+     */
+    T decode(S source);
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/codec/EntityWriter.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster.codec;
+
+/**
+ * A universal interface for publishing entities to a target stream.
+ *
+ * @param <E> entity type
+ * @param <T> target stream type
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public interface EntityWriter<E, T> {
+
+    /**
+     * Write the provided entity to target stream.
+     *
+     * @param entity entity to publish
+     * @param target the target stream
+     */
+    void writeTo(E entity, T target);
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/codec/request/RequestEntityDecoder.java

@@ -0,0 +1,27 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster.codec.request;
+
+import com.alibaba.csp.sentinel.cluster.codec.EntityDecoder;
+import com.alibaba.csp.sentinel.cluster.request.Request;
+
+/**
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public interface RequestEntityDecoder<S, T extends Request> extends EntityDecoder<S, T> {
+
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/codec/request/RequestEntityWriter.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster.codec.request;
+
+import com.alibaba.csp.sentinel.cluster.codec.EntityWriter;
+import com.alibaba.csp.sentinel.cluster.request.Request;
+
+/**
+ * A universal {@link EntityWriter} interface for publishing {@link Request} to a target stream.
+ *
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public interface RequestEntityWriter<E extends Request, T> extends EntityWriter<E, T> {
+
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/codec/response/ResponseEntityDecoder.java

@@ -0,0 +1,27 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster.codec.response;
+
+import com.alibaba.csp.sentinel.cluster.codec.EntityDecoder;
+import com.alibaba.csp.sentinel.cluster.response.Response;
+
+/**
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public interface ResponseEntityDecoder<S, T extends Response> extends EntityDecoder<S, T> {
+
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/codec/response/ResponseEntityWriter.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster.codec.response;
+
+import com.alibaba.csp.sentinel.cluster.codec.EntityWriter;
+import com.alibaba.csp.sentinel.cluster.response.Response;
+
+/**
+ * A universal {@link EntityWriter} interface for publishing {@link Response} to a target stream.
+ *
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public interface ResponseEntityWriter<E extends Response, T> extends EntityWriter<E, T> {
+
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/exception/SentinelClusterException.java

@@ -0,0 +1,32 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster.exception;
+
+/**
+ * @author jialiang.ljl
+ * @since 1.4.0
+ */
+public class SentinelClusterException extends Exception {
+
+    public SentinelClusterException(String errorMsg) {
+        super(errorMsg);
+    }
+
+    @Override
+    public Throwable fillInStackTrace() {
+        return this;
+    }
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/request/ClusterRequest.java

@@ -0,0 +1,79 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster.request;
+
+/**
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public class ClusterRequest<T> implements Request {
+
+    private int id;
+    private int type;
+
+    private T data;
+
+    public ClusterRequest() {}
+
+    public ClusterRequest(int id, int type, T data) {
+        this.id = id;
+        this.type = type;
+        this.data = data;
+    }
+
+    public ClusterRequest(int type, T data) {
+        this.type = type;
+        this.data = data;
+    }
+
+    @Override
+    public int getId() {
+        return id;
+    }
+
+    public ClusterRequest<T> setId(int id) {
+        this.id = id;
+        return this;
+    }
+
+    @Override
+    public int getType() {
+        return type;
+    }
+
+    public ClusterRequest<T> setType(int type) {
+        this.type = type;
+        return this;
+    }
+
+    public T getData() {
+        return data;
+    }
+
+    public ClusterRequest<T> setData(T data) {
+        this.data = data;
+        return this;
+    }
+
+    @Override
+    public String toString() {
+        return "ClusterRequest{" +
+            "id=" + id +
+            ", type=" + type +
+            ", data=" + data +
+            '}';
+    }
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/request/Request.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster.request;
+
+/**
+ * Cluster transport request interface.
+ *
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public interface Request {
+
+    /**
+     * Get request type.
+     *
+     * @return request type
+     */
+    int getType();
+
+    /**
+     * Get request ID.
+     *
+     * @return unique request ID
+     */
+    int getId();
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/request/data/FlowRequestData.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster.request.data;
+
+/**
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public class FlowRequestData {
+
+    private long flowId;
+    private int count;
+    private boolean priority;
+
+    public long getFlowId() {
+        return flowId;
+    }
+
+    public FlowRequestData setFlowId(long flowId) {
+        this.flowId = flowId;
+        return this;
+    }
+
+    public int getCount() {
+        return count;
+    }
+
+    public FlowRequestData setCount(int count) {
+        this.count = count;
+        return this;
+    }
+
+    public boolean isPriority() {
+        return priority;
+    }
+
+    public FlowRequestData setPriority(boolean priority) {
+        this.priority = priority;
+        return this;
+    }
+
+    @Override
+    public String toString() {
+        return "FlowRequestData{" +
+            "flowId=" + flowId +
+            ", count=" + count +
+            ", priority=" + priority +
+            '}';
+    }
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/request/data/ParamFlowRequestData.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster.request.data;
+
+import java.util.Collection;
+
+/**
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public class ParamFlowRequestData {
+
+    private long flowId;
+    private int count;
+    private Collection<Object> params;
+
+    public long getFlowId() {
+        return flowId;
+    }
+
+    public ParamFlowRequestData setFlowId(long flowId) {
+        this.flowId = flowId;
+        return this;
+    }
+
+    public int getCount() {
+        return count;
+    }
+
+    public ParamFlowRequestData setCount(int count) {
+        this.count = count;
+        return this;
+    }
+
+    public Collection<Object> getParams() {
+        return params;
+    }
+
+    public ParamFlowRequestData setParams(Collection<Object> params) {
+        this.params = params;
+        return this;
+    }
+
+    @Override
+    public String toString() {
+        return "ParamFlowRequestData{" +
+            "flowId=" + flowId +
+            ", count=" + count +
+            ", params=" + params +
+            '}';
+    }
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/response/ClusterResponse.java

@@ -0,0 +1,87 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster.response;
+
+/**
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public class ClusterResponse<T> implements Response {
+
+    private int id;
+    private int type;
+    private int status;
+
+    private T data;
+
+    public ClusterResponse() {}
+
+    public ClusterResponse(int id, int type, int status, T data) {
+        this.id = id;
+        this.type = type;
+        this.status = status;
+        this.data = data;
+    }
+
+    @Override
+    public int getId() {
+        return id;
+    }
+
+    public ClusterResponse<T> setId(int id) {
+        this.id = id;
+        return this;
+    }
+
+    @Override
+    public int getType() {
+        return type;
+    }
+
+    public ClusterResponse<T> setType(int type) {
+        this.type = type;
+        return this;
+    }
+
+    @Override
+    public int getStatus() {
+        return status;
+    }
+
+    public ClusterResponse<T> setStatus(int status) {
+        this.status = status;
+        return this;
+    }
+
+    public T getData() {
+        return data;
+    }
+
+    public ClusterResponse<T> setData(T data) {
+        this.data = data;
+        return this;
+    }
+
+    @Override
+    public String toString() {
+        return "ClusterResponse{" +
+            "id=" + id +
+            ", type=" + type +
+            ", status=" + status +
+            ", data=" + data +
+            '}';
+    }
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/response/Response.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster.response;
+
+/**
+ * Cluster transport response interface.
+ *
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public interface Response {
+
+    /**
+     * Get response ID.
+     *
+     * @return response ID
+     */
+    int getId();
+
+    /**
+     * Get response type.
+     *
+     * @return response type
+     */
+    int getType();
+
+    /**
+     * Get response status.
+     *
+     * @return response status
+     */
+    int getStatus();
+}

sentinel-cluster/sentinel-cluster-common-default/src/main/java/com/alibaba/csp/sentinel/cluster/response/data/FlowTokenResponseData.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.cluster.response.data;
+
+/**
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public class FlowTokenResponseData {
+
+    private int remainingCount;
+    private int waitInMs;
+
+    public int getRemainingCount() {
+        return remainingCount;
+    }
+
+    public FlowTokenResponseData setRemainingCount(int remainingCount) {
+        this.remainingCount = remainingCount;
+        return this;
+    }
+
+    public int getWaitInMs() {
+        return waitInMs;
+    }
+
+    public FlowTokenResponseData setWaitInMs(int waitInMs) {
+        this.waitInMs = waitInMs;
+        return this;
+    }
+
+    @Override
+    public String toString() {
+        return "FlowTokenResponseData{" +
+            "remainingCount=" + remainingCount +
+            ", waitInMs=" + waitInMs +
+            '}';
+    }
+}

sentinel-core/src/main/java/com/alibaba/csp/sentinel/util/SpiLoader.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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 com.alibaba.csp.sentinel.util;
+
+import java.util.Iterator;
+import java.util.Map;
+import java.util.ServiceLoader;
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public final class SpiLoader {
+
+    private static final Map<String, ServiceLoader> SERVICE_LOADER_MAP = new ConcurrentHashMap<String, ServiceLoader>();
+
+    public static <T> T loadFirstInstance(Class<T> clazz) {
+        String key = clazz.getName();
+        // Not thread-safe, as it's expected to be resolved in a thread-safe context.
+        ServiceLoader<T> serviceLoader = SERVICE_LOADER_MAP.get(key);
+        if (serviceLoader == null) {
+            serviceLoader = ServiceLoader.load(clazz);
+            SERVICE_LOADER_MAP.put(key, serviceLoader);
+        }
+
+        Iterator<T> iterator = serviceLoader.iterator();
+        if (iterator.hasNext()) {
+            return iterator.next();
+        } else {
+            return null;
+        }
+    }
+
+    private SpiLoader() {}
+}