Prevent to create one more users

src/main/java/run/halo/app/controller/admin/api/InstallController.java

@@ -5,8 +5,11 @@ import lombok.extern.slf4j.Slf4j;
 import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.lang.NonNull;
 import org.springframework.stereotype.Controller;
-import org.springframework.web.bind.annotation.*;
-import org.springframework.web.multipart.MultipartFile;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.ResponseBody;
+import run.halo.app.cache.lock.CacheLock;
 import run.halo.app.event.logger.LogEvent;
 import run.halo.app.exception.BadRequestException;
 import run.halo.app.model.entity.*;
@@ -72,6 +75,7 @@ public class InstallController {
 
     @PostMapping
     @ResponseBody
+    @CacheLock
     public BaseResponse<String> installBlog(@RequestBody @Valid InstallParam installParam) {
         // TODO Install blog.
         // Check is installed

src/main/java/run/halo/app/service/impl/UserServiceImpl.java

@@ -8,6 +8,7 @@ import org.springframework.stereotype.Service;
 import org.springframework.util.Assert;
 import org.springframework.util.CollectionUtils;
 import run.halo.app.cache.StringCacheStore;
+import run.halo.app.cache.lock.CacheLock;
 import run.halo.app.event.logger.LogEvent;
 import run.halo.app.exception.BadRequestException;
 import run.halo.app.exception.NotFoundException;
@@ -202,6 +203,17 @@ public class UserServiceImpl extends AbstractCrudService<User, Integer> implemen
         return create(user);
     }
 
+    @Override
+    @CacheLock
+    public User create(User user) {
+        // Check user
+        if (count() != 0) {
+            throw new BadRequestException("This blog already exists a blogger");
+        }
+
+        return super.create(user);
+    }
+
     @Override
     public User update(User user) {
         User updatedUser = super.update(user);