写了Controller类返回json数据文件时候报错

This application has no explicit mapping for /error, so you are seeing this as a fallback.

回到idear发现报错：
Error querying database. Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is java.sql.SQLException: Access denied for user ‘root’@‘localhost’ (using password: YES)
The error may exist in edu/xalead/dao/ItemDao.java (best guess)
The error may involve edu.xalead.dao.ItemDao.selectAll
The error occurred while executing a query
Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is java.sql.SQLException: Access denied for user ‘root’@‘localhost’ (using password: YES)] with root cause
java.sql.SQLException: Access denied for user ‘root’@‘localhost’ (using password: YES)

猜测应该是数据库连接的问题，去application.yaml文件下查看数据库连接。

spring:
  application:
    name: item-service
  datasource:
    url: jdbc:mysql://localhost:3306/

路径不完整所以连接有问题

spring:
  application:
    name: item-service
  datasource:
    url: jdbc:mysql://localhost:3306/jdd

补全你的数据库路径，结果还是发现同样的错误！

Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is java.sql.SQLException: Access denied for user ‘root’@‘localhost’ (using password: YES)] with root cause
java.sql.SQLException: Access denied for user ‘root’@‘localhost’ (using password: YES)

再看一遍，原来是数据库的用户名和密码的错误！
这波啊，这波是一石二鸟…

datasource:
    url: jdbc:mysql://localhost:3306/jdd
    username: root
    password: 

把自己的数据库密码和用户名校正就好了！

最后在刷新一下网页，返回的数据与数据库中的数据匹配即成功。