diff --git a/app/src/main/java/com/kunfei/bookshelf/base/BaseModelImpl.java b/app/src/main/java/com/kunfei/bookshelf/base/BaseModelImpl.java
index a9bc0302ed..0236998f5a 100644
--- a/app/src/main/java/com/kunfei/bookshelf/base/BaseModelImpl.java
+++ b/app/src/main/java/com/kunfei/bookshelf/base/BaseModelImpl.java
@@ -32,7 +32,7 @@
 import retrofit2.adapter.rxjava2.RxJava2CallAdapterFactory;
 
 public class BaseModelImpl {
-    private static OkHttpClient.Builder clientBuilder;
+    private static OkHttpClient httpClient;
 
     public static BaseModelImpl getInstance() {
         return new BaseModelImpl();
@@ -66,7 +66,7 @@ public Retrofit getRetrofitString(String url) {
                 .addConverterFactory(EncodeConverter.create())
                 //增加返回值为Observable<T>的支持
                 .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
-                .client(getClientBuilder().build())
+                .client(getClient())
                 .build();
     }
 
@@ -76,13 +76,13 @@ public Retrofit getRetrofitString(String url, String encode) {
                 .addConverterFactory(EncodeConverter.create(encode))
                 //增加返回值为Observable<T>的支持
                 .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
-                .client(getClientBuilder().build())
+                .client(getClient())
                 .build();
     }
 
-    public static OkHttpClient.Builder getClientBuilder() {
-        if (clientBuilder == null) {
-            clientBuilder = new OkHttpClient.Builder()
+    synchronized public static OkHttpClient getClient() {
+        if (httpClient == null) {
+            httpClient = new OkHttpClient.Builder()
                     .connectTimeout(15, TimeUnit.SECONDS)
                     .writeTimeout(15, TimeUnit.SECONDS)
                     .readTimeout(15, TimeUnit.SECONDS)
@@ -90,9 +90,10 @@ public static OkHttpClient.Builder getClientBuilder() {
                     .sslSocketFactory(SSLSocketClient.getSSLSocketFactory(), SSLSocketClient.createTrustAllManager())
                     .hostnameVerifier(SSLSocketClient.getHostnameVerifier())
                     .protocols(Collections.singletonList(Protocol.HTTP_1_1))
-                    .addInterceptor(getHeaderInterceptor());
+                    .addInterceptor(getHeaderInterceptor())
+                    .build();
         }
-        return clientBuilder;
+        return httpClient;
     }
 
     private static Interceptor getHeaderInterceptor() {
diff --git a/app/src/main/java/com/kunfei/bookshelf/utils/webdav/WebDav.kt b/app/src/main/java/com/kunfei/bookshelf/utils/webdav/WebDav.kt
index 368c76efb4..284ee67b2a 100644
--- a/app/src/main/java/com/kunfei/bookshelf/utils/webdav/WebDav.kt
+++ b/app/src/main/java/com/kunfei/bookshelf/utils/webdav/WebDav.kt
@@ -130,7 +130,7 @@ constructor(urlStr: String) {
                 )
             }
             request.header("Depth", if (depth < 0) "infinity" else depth.toString())
-            return BaseModelImpl.getClientBuilder().build().newCall(request.build()).execute()
+            return BaseModelImpl.getClient().newCall(request.build()).execute()
         }
         return null
     }
@@ -225,7 +225,7 @@ constructor(urlStr: String) {
                     Credentials.basic(it.user, it.pass)
             )
         }
-        val response = BaseModelImpl.getClientBuilder().build().newCall(requestBuilder.build()).execute()
+        val response = BaseModelImpl.getClient().newCall(requestBuilder.build()).execute()
         return response.isSuccessful
     }
 
@@ -236,7 +236,7 @@ constructor(urlStr: String) {
                 request.header("Authorization", Credentials.basic(it.user, it.pass))
             }
             try {
-                return BaseModelImpl.getClientBuilder().build().newCall(request.build()).execute().body?.byteStream()
+                return BaseModelImpl.getClient().newCall(request.build()).execute().body?.byteStream()
             } catch (e: IOException) {
                 e.printStackTrace()
             } catch (e: IllegalArgumentException) {