chore: change to final fields

src/main/java/com/qcloud/im/IMClient.java

@@ -15,8 +15,8 @@ import java.util.concurrent.ThreadLocalRandom;
  * @since 2021/07/29 16:11
  */
 public class IMClient {
-    private static ConcurrentHashMap<String, IMClient> imClient = new ConcurrentHashMap<>();
-    private static String FORMAT_URL = "https://console.tim.qq.com/%s/%s/%s?sdkappid=%d&identifier=%s&usersig=%s&random=%d&contenttype=json";
+    private static final ConcurrentHashMap<String, IMClient> IM_CLIENT = new ConcurrentHashMap<>();
+    private static final String FORMAT_URL = "https://console.tim.qq.com/%s/%s/%s?sdkappid=%d&identifier=%s&usersig=%s&random=%d&contenttype=json";
     /**
      * core methods
      */
@@ -27,25 +27,25 @@ public class IMClient {
     /**
      * init property
      */
-    private String version = "v4";
-    private Long sdkAppId;
-    private String userId;
-    private String userSig;
+    private final String version = "v4";
+    private final Long sdkAppId;
+    private final String userId;
+    private final String userSig;
 
     public static IMClient getInstance(Long sdkAppId, String userId, String key, Long expire) {
         String identify = sdkAppId + "_" + userId;
-        if (imClient.get(identify) == null) {
-            imClient.putIfAbsent(identify, new IMClient(sdkAppId, userId, key, expire));
+        if (IM_CLIENT.get(identify) == null) {
+            IM_CLIENT.putIfAbsent(identify, new IMClient(sdkAppId, userId, key, expire));
         }
-        return imClient.get(identify);
+        return IM_CLIENT.get(identify);
     }
 
     public static IMClient getInstance(Long sdkAppId, String userId, String key) {
         String identify = sdkAppId + "_" + userId;
-        if (imClient.get(identify) == null) {
-            imClient.putIfAbsent(identify, new IMClient(sdkAppId, userId, key, 24 * 60 * 60L));
+        if (IM_CLIENT.get(identify) == null) {
+            IM_CLIENT.putIfAbsent(identify, new IMClient(sdkAppId, userId, key, 24 * 60 * 60L));
         }
-        return imClient.get(identify);
+        return IM_CLIENT.get(identify);
     }
 
     public IMClient(Long sdkAppId, String userId, String key, Long expire) {

src/main/java/com/qcloud/im/core/Account.java

@@ -22,7 +22,7 @@ public class Account {
     private static final String KICK = "kick";
     private static final String QUERY_STATE = "querystate";
 
-    private IMClient imClient;
+    private final IMClient imClient;
 
     public Account(IMClient imClient) {
         this.imClient = imClient;

src/main/java/com/qcloud/im/core/Message.java

@@ -19,7 +19,7 @@ public class Message {
     private static final String SEND_MSG_COMMAND = "sendmsg";
     private static final String IMPORT_MSG_COMMAND = "importmsg";
 
-    private IMClient imClient;
+    private final IMClient imClient;
 
     public SendMsgResult sendMsg(SendMsgRequest sendMsgRequest) throws IOException {
         String url = imClient.getUrl(SERVICE_NAME, SEND_MSG_COMMAND);

src/main/java/com/qcloud/im/core/Profile.java

@@ -16,7 +16,7 @@ public class Profile {
     private static final String SERVICE_NAME = "profile";
     private static final String PORTRAIT_SET_COMMAND = "portrait_set";
 
-    private IMClient imClient;
+    private final IMClient imClient;
 
     public PortraitSetResult portraitSet(PortraitSetRequest portraitSetRequest) throws IOException {
         String url = imClient.getUrl(SERVICE_NAME, PORTRAIT_SET_COMMAND);

src/main/java/com/qcloud/im/core/SNS.java

@@ -16,7 +16,7 @@ public class SNS {
     private static final String SERVICE_NAME = "sns";
     private static final String FRIEND_IMPORT_COMMAND = "friend_import";
 
-    private IMClient imClient;
+    private final IMClient imClient;
 
     public FriendImportResult friendImport(FriendImportRequest friendImportRequest) throws IOException {
         String url = imClient.getUrl(SERVICE_NAME, FRIEND_IMPORT_COMMAND);

src/test/java/com/qcloud/im/AccountTest.java

@@ -15,8 +15,8 @@ import java.util.Properties;
  * @since 2021/7/30 16:17
  */
 public class AccountTest {
-    private static Properties properties = new Properties();
-    private static IMClient client;
+    private static final Properties properties = new Properties();
+    private static final IMClient client;
 
     static {
         InputStream resourceAsStream = AccountTest.class.getClassLoader().getResourceAsStream("app.properties");