fix bug: PrivateWSClient npe because apiKeyVersion is null.

src/main/java/com/kucoin/sdk/KucoinClientBuilder.java

@@ -7,6 +7,7 @@
 
 import com.kucoin.sdk.rest.adapter.*;
 import com.kucoin.sdk.rest.interfaces.*;
+import com.kucoin.sdk.websocket.KucoinAPICallback;
 import org.apache.commons.lang3.StringUtils;
 
 import com.kucoin.sdk.constants.APIConstants;
@@ -69,6 +70,9 @@ public class KucoinClientBuilder {
 
     private LoanAPI loanAPI;
 
+    private KucoinAPICallback connectedCallback;
+    private KucoinAPICallback disConnectedCallback;
+
     public KucoinRestClient buildRestClient() {
         if (StringUtils.isBlank(baseUrl)) baseUrl = APIConstants.API_BASE_URL;
         if (userAPI == null) userAPI = new UserAPIAdapter(baseUrl, apiKey, secret, passPhrase, apiKeyVersion);
@@ -92,7 +96,12 @@ public KucoinRestClient buildRestClient() {
     public KucoinPublicWSClient buildPublicWSClient() throws IOException {
         if (StringUtils.isBlank(baseUrl)) baseUrl = APIConstants.API_BASE_URL;
         if (chooseServerStrategy == null) chooseServerStrategy = new RandomChooseStrategy();
-        KucoinPublicWSClientImpl client = new KucoinPublicWSClientImpl(this);
+        KucoinPublicWSClientImpl client;
+        if (connectedCallback == null) {
+            client = new KucoinPublicWSClientImpl(this);
+        } else {
+            client = new KucoinPublicWSClientImpl(this, connectedCallback, disConnectedCallback);
+        }
         client.connect();
         return client;
     }
@@ -181,4 +190,12 @@ public KucoinClientBuilder withChooseServerStrategy(ChooseServerStrategy chooseS
         this.chooseServerStrategy = chooseServerStrategy;
         return this;
     }
+
+    public KucoinClientBuilder withCallback(KucoinAPICallback connectedCallback,
+                                            KucoinAPICallback disconnectedCallback) {
+        this.connectedCallback = connectedCallback;
+        this.disConnectedCallback = disconnectedCallback;
+        return this;
+    }
+
 }

src/main/java/com/kucoin/sdk/factory/HttpClientFactory.java

@@ -8,6 +8,8 @@
 import okhttp3.Interceptor;
 import okhttp3.OkHttpClient;
 
+import java.util.concurrent.TimeUnit;
+
 /**
  * Created by chenshiwei on 2019/1/18.
  */
@@ -26,7 +28,8 @@ private static OkHttpClient buildHttpClient(Interceptor interceptor) {
         dispatcher.setMaxRequestsPerHost(100);
         dispatcher.setMaxRequests(100);
         OkHttpClient.Builder builder = new OkHttpClient.Builder()
-                .dispatcher(dispatcher);
+                .dispatcher(dispatcher)
+                .pingInterval(20, TimeUnit.SECONDS);
         if (interceptor != null) {
             builder.addInterceptor(interceptor);
         }

src/main/java/com/kucoin/sdk/impl/KucoinPublicWSClientImpl.java

@@ -38,6 +38,15 @@ public KucoinPublicWSClientImpl(KucoinClientBuilder kucoinClientBuilder) {
                 new WebsocketPublicAPIAdaptor(kucoinClientBuilder.getBaseUrl()));
     }
 
+    public KucoinPublicWSClientImpl(KucoinClientBuilder kucoinClientBuilder,
+                                    KucoinAPICallback connectedCallback, KucoinAPICallback disconnectedCallback) {
+        this(
+                HttpClientFactory.getPublicClient(),
+                new KucoinPublicWebsocketListener(connectedCallback, disconnectedCallback),
+                kucoinClientBuilder.getChooseServerStrategy(),
+                new WebsocketPublicAPIAdaptor(kucoinClientBuilder.getBaseUrl()));
+    }
+
     private KucoinPublicWSClientImpl(OkHttpClient client,
                                      KucoinPublicWebsocketListener listener,
                                      ChooseServerStrategy chooseServerStrategy,

src/main/java/com/kucoin/sdk/rest/impl/retrofit/AbstractRetrofitAPIImpl.java

@@ -97,4 +97,12 @@ public String getPassPhrase() {
     public void setPassPhrase(String passPhrase) {
         this.passPhrase = passPhrase;
     }
+
+    public Integer getApiKeyVersion() {
+        return apiKeyVersion;
+    }
+
+    public void setApiKeyVersion(Integer apiKeyVersion) {
+        this.apiKeyVersion = apiKeyVersion;
+    }
 }

src/main/java/com/kucoin/sdk/websocket/event/AccountChangeEvent.java

@@ -27,12 +27,20 @@ public class AccountChangeEvent {
 
     private String relationEvent;
 
-    private String relationContext;
+    private RelationContext relationContext;
 
     private String relationEventId;
 
     private String time;
 
     private String accountId;
 
+    @Data
+    public static class RelationContext {
+
+        private String symbol;
+
+        private String orderId;
+    }
+
 }

src/main/java/com/kucoin/sdk/websocket/listener/KucoinPublicWebsocketListener.java

@@ -39,9 +39,21 @@ public class KucoinPublicWebsocketListener extends WebSocketListener {
     private KucoinAPICallback<KucoinEvent<Level3Event>> level3V2Callback = new PrintCallback<>();
     private KucoinAPICallback<KucoinEvent<SnapshotEvent>> snapshotCallback = new PrintCallback<>();
 
+    private KucoinAPICallback<String> connectedCallback;
+    private KucoinAPICallback<String> disConnectedCallback;
+
+    public KucoinPublicWebsocketListener() {}
+
+    public KucoinPublicWebsocketListener(KucoinAPICallback<String> connectedCallback,
+                                         KucoinAPICallback<String> disConnectedCallback) {
+        this.connectedCallback = connectedCallback;
+        this.disConnectedCallback = disConnectedCallback;
+    }
+
     @Override
     public void onOpen(WebSocket webSocket, Response response) {
         LOGGER.debug("web socket open");
+        this.connectedCallback.onResponse(response.message());
     }
 
     @Override
@@ -94,7 +106,18 @@ public void onMessage(WebSocket webSocket, String text) {
 
     @Override
     public void onFailure(WebSocket webSocket, Throwable t, Response response) {
-        LOGGER.error("Error on private socket", t);
+        LOGGER.error("Error on public socket", t);
+        this.disConnectedCallback.onResponse(response.message());
+    }
+
+    @Override
+    public void onClosing(WebSocket webSocket, int code, String reason) {
+        this.disConnectedCallback.onResponse(reason);
+    }
+
+    @Override
+    public void onClosed(WebSocket webSocket, int code, String reason) {
+        this.disConnectedCallback.onResponse(reason);
     }
 
     private JsonNode tree(String text) {