Add get preview and next post feature

src/main/java/run/halo/app/repository/PostRepository.java

@@ -1,10 +1,15 @@
 package run.halo.app.repository;
 
+import org.springframework.data.domain.Page;
+import org.springframework.data.domain.Pageable;
 import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
 import org.springframework.data.jpa.repository.Query;
+import org.springframework.lang.NonNull;
 import run.halo.app.model.entity.Post;
 import run.halo.app.repository.base.BasePostRepository;
 
+import java.util.Date;
+
 
 /**
  * Post repository.
@@ -19,4 +24,10 @@ public interface PostRepository extends BasePostRepository<Post>, JpaSpecificati
 
     @Query("select sum(p.likes) from Post p")
     Long countLike();
+
+    @NonNull
+    Page<Post> findAllByStatusAndCreateTimeBefore(Date createTime, @NonNull Pageable pageable);
+
+    @NonNull
+    Page<Post> findAllByStatusAndCreateTimeAfter(Date createTime, @NonNull Pageable pageable);
 }

src/main/java/run/halo/app/service/PostService.java

@@ -15,7 +15,9 @@ import run.halo.app.model.vo.PostDetailVO;
 import run.halo.app.model.vo.PostListVO;
 import run.halo.app.service.base.CrudService;
 
+import java.util.Date;
 import java.util.List;
+import java.util.Optional;
 import java.util.Set;
 
 /**
@@ -211,4 +213,10 @@ public interface PostService extends CrudService<Post, Integer> {
      */
     @NonNull
     Post filterIfEncrypt(@NonNull Post post);
+
+    @NonNull
+    Optional<Post> getPrePost(@NonNull Date createTime);
+
+    @NonNull
+    Optional<Post> getNextPost(@NonNull Date createTime);
 }

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

@@ -437,6 +437,32 @@ public class PostServiceImpl extends AbstractCrudService<Post, Integer> implemen
         return post;
     }
 
+    @Override
+    public Optional<Post> getPrePost(Date createTime) {
+        Assert.notNull(createTime, "Create time must not be null");
+
+        Page<Post> prePostPage = postRepository.findAllByStatusAndCreateTimeAfter(createTime, PageRequest.of(0, 1));
+
+        if (prePostPage.isEmpty()) {
+            return Optional.empty();
+        }
+
+        return Optional.of(prePostPage.getContent().get(0));
+    }
+
+    @Override
+    public Optional<Post> getNextPost(Date createTime) {
+        Assert.notNull(createTime, "Create time must not be null");
+
+        Page<Post> prePostPage = postRepository.findAllByStatusAndCreateTimeBefore(createTime, PageRequest.of(0, 1));
+
+        if (prePostPage.isEmpty()) {
+            return Optional.empty();
+        }
+
+        return Optional.of(prePostPage.getContent().get(0));
+    }
+
     /**
      * Converts to post minimal output dto.
      *