Spring数据中的java JpaRepository方法被卡住，没有返回响应或错误

Question

我正在使用Spring数据连接MySql数据库。 下面是我的实体类

package seller.entity;

import javax.persistence.*;

@Entity
@Table(name="seller")
public class SELLER {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column
    private Integer seller_id;
    @Column(name = "username")
    private String Username;
    @Column(name = "password")
    private String Password;
    @Column(name = "name")
    private String Name;
    @Column(name = "loggedin")
    private Integer LoggedIn;
    @Column(name = "upvotes")
    private Integer Upvotes;
    @Column(name = "downvotes")
    private Integer Downvotes;
    @Column(name = "itemssold")
    private Integer ItemsSold;

    public SELLER() {
    }

    public SELLER(String username, String password, String name, int loggedIn, int upvotes, int downvotes, int itemsSold) {
        this.Username = username;
        this.Password = password;
        this.Name = name;
        this.LoggedIn = loggedIn;
        this.Upvotes = upvotes;
        this.Downvotes = downvotes;
        this.ItemsSold = itemsSold;
    }

    public int getSellerId() {
        return seller_id;
    }

    public String getUsername() {
        return Username;
    }

    public void setUsername(String username) {
        this.Username = username;
    }

    public String getPassword() {
        return Password;
    }

    public void setPassword(String password) {
        this.Password = password;
    }

    public String getName() {
        return Name;
    }

    public void setName(String name) {
        this.Name = name;
    }

    public int getLoggedIn() {
        return LoggedIn;
    }

    public void setLoggedIn(int loggedIn) {
        this.LoggedIn = loggedIn;
    }

    public int getUpvotes() {
        return Upvotes;
    }

    public void setUpvotes(int upvotes) {
        this.Upvotes = upvotes;
    }

    public int getDownvotes() {
        return Downvotes;
    }

    public void setDownvotes(int downvotes) {
        this.Downvotes = downvotes;
    }

    public int getItemsSold() {
        return ItemsSold;
    }

    public void setItemsSold(int itemsSold) {
        this.ItemsSold = itemsSold;
    }
}

我正在使用JpaRepository进行DB操作。下面是我的存储库文件

package seller.repo;

import seller.entity.SELLER;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;


@Repository
public interface SellerRepository extends JpaRepository<SELLER, Integer> {
}

我已自动连接SellerRepositoy并尝试调用DB方法。我尝试调用save（）和findAll（）方法。它们都被无限期地卡住，既不返回错误也不返回响应。（我也尝试过使用Crudepository，也遇到了同样的问题）。我正在使用Maven并添加了以下依赖项

 <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>

我在应用程序中使用Java15，不确定在这种情况下它是否真的重要。我在应用程序属性中添加了以下行，因为表已经创建

spring.jpa.hibernate.ddl-auto=none

我不知道这里发生了什么事。有人能告诉我这里发生了什么事吗？ 提前谢谢