idea java return 报错

package com.gem.student.dao.impl;

import com.gem.student.dao.UserDao;
import com.gem.student.entity.User;
import com.gem.student.template.JdbcTemplate;

import java.sql.PreparedStatement;
import java.sql.ResultSet;

public class UserDAOImpl implements UserDao {
    @Override
    public User selectOne(final String username) {
        JdbcTemplate jdbcTemplate = new JdbcTemplate<>();
        return jdbcTemplate.query((conn)->{
            PreparedStatement pst =null;
            ResultSet rs = null;
            User user = null;
            try{
                String sql = "select * from t_user where username = ?";
                pst = conn.prepareStatement(sql);
                pst.setString(1,username);
                if(rs.next()){
                    user = new User();
                    user.setId(rs.getInt("id"));
                    user.setUsername(rs.getString("username"));
                    user.setPassword(rs.getString("password"));
                }
            }catch (Exception e){
                e.printStackTrace();
            }
            return user;     // return 报错Lambda expressions are not supported at language level 7
        });

    }
}

Lambda expressions are not supported at language level 7

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