springboot 实现增删改查，分页查询的mapper层，service层，serviceIpml层，controller层以及前端js的代码

以下是一个简单的示例：

Mapper层代码：

@Mapper
public interface UserMapper {
    @Select("SELECT * FROM user")
    List<User> findAll();

    @Select("SELECT * FROM user WHERE id = #{id}")
    User findById(@Param("id") Long id);

    @Insert("INSERT INTO user(username, password) VALUES(#{username}, #{password})")
    void save(User user);

    @Update("UPDATE user SET username=#{username}, password=#{password} WHERE id=#{id}")
    void update(User user);

    @Delete("DELETE FROM user WHERE id=#{id}")
    void deleteById(@Param("id") Long id);

    @Select("SELECT COUNT(*) FROM user")
    int count();
}

Service层代码：

public interface UserService {
    List<User> findAll();

    User findById(Long id);

    void save(User user);

    void update(User user);

    void deleteById(Long id);

    int count();
}

@Service
public class UserServiceImpl implements UserService {
    @Autowired
    private UserMapper userMapper;

    @Override
    public List<User> findAll() {
        return userMapper.findAll();
    }

    @Override
    public User findById(Long id) {
        return userMapper.findById(id);
    }

    @Override
    public void save(User user) {
        userMapper.save(user);
    }

    @Override
    public void update(User user) {
        userMapper.update(user);
    }

    @Override
    public void deleteById(Long id) {
        userMapper.deleteById(id);
    }

    @Override
    public int count() {
        return userMapper.count();
    }
}

Controller层代码：

@RestController
public class UserController {
    @Autowired
    private UserService userService;

    @GetMapping("/users")
    public List<User> findAll() {
        return userService.findAll();
    }

    @GetMapping("/users/{id}")
    public User findById(@PathVariable Long id) {
        return userService.findById(id);
    }

    @PostMapping("/users")
    public void save(@RequestBody User user) {
        userService.save(user);
    }

    @PutMapping("/users")
    public void update(@RequestBody User user) {
        userService.update(user);
    }

    @DeleteMapping("/users/{id}")
    public void deleteById(@PathVariable Long id) {
        userService.deleteById(id);
    }

    @GetMapping("/users/count")
    public int count() {
        return userService.count();
    }
}

前端js代码：

$(function() {
    // 获取用户列表
    $.get("/users", function(data) {
        // 处理数据
    });

    // 获取指定用户
    $.get("/users/1", function(data) {
        // 处理数据
    });

    // 新增用户
    $.ajax({
        url: "/users",
        type: "POST",
        contentType: "application/json",
        data: JSON.stringify({username: "test", password: "123456"}),
        success: function() {
            // 处理成功
        }
    });

    // 修改用户
    $.ajax({
        url: "/users",
        type: "PUT",
        contentType: "application/json",
        data: JSON.stringify({id: 1, username: "test", password: "abcdef"}),
        success: function() {
            // 处理成功
        }
    });

    // 删除用户
    $.ajax({
        url: "/users/1",
        type: "DELETE",
        success: function() {
            // 处理成功
        }
    });

    // 获取用户数量
    $.get("/users/count", function(data) {
        // 处理数据
    });
});

以上代码仅供参考，实际应用中需要根据具体情况进行调整。