Database error collection

1. Virtual machine database part

1.1 idea

• First use the datasource tool here to connect

1.2 The virtual machine cannot connect to the virtual machine mysql through IP

• unsolved

1.3 Database time zone setting

mysql database time zone configuration

1.4 Check the current database time

select now();

1.5 Database connection dependencies

• Mybatis, jpa, jdbc any dependency
• mysql-connector-java is required

1.6 spring boot database connection test

• Note the package referenced by the @Test annotation:

import org.junit.jupiter.api.Test;

package com.example.demo;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import javax.sql.DataSource;
import java.sql.SQLException;

@SpringBootTest
class DemoApplicationTests {
    
    
    @Autowired
    DataSource dataSource;
    @Test
    public void testMysqlConn() throws SQLException {
    
    
        System.out.println(dataSource.getConnection());
    }
}

• 报错:The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.

The remote database service is not logged in, you can log in through mysql -uroot -p

1.6 Pay attention to the spring boot version

• About test annotation import
• There was one version before 2.2, and a different version after 2.2.

在Spring Boot 2.2.X以后使用import org.junit.jupiter.api.Test Junit5

在Spring Boot 2.2.x之前使用import org.junit.Test Junit4

1.7 mybatis-plus settings

• Note that you must add time zone configuration

spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/shopping?serverTimezone=GMT%2B8
    username: root
    password: ******

#mybatis输出日志
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

1.8 Pay attention to the datasource package

import javax.sql.DataSource;

1.9 Complete testing

package com.ybx.sunshine;

import com.ybx.sunshine.entity.User;
import com.ybx.sunshine.mapper.UserMapper;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import javax.sql.DataSource;
import java.sql.SQLException;


@SpringBootTest
public class Usertest {
    @Autowired
    UserMapper userMapper;
    @Test
    public void testUser(){
        User user = userMapper.selectById(1);
        System.out.println(user.getName());

    }
    @Autowired
    DataSource dataSource;
    @Test
    public void testMysqlConn() throws SQLException {
        System.out.println(dataSource.getConnection());
    }
}

1.10 Database link configuration

spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
#    url: jdbc:mysql://localhost:3306/shopping?serverTimezone=GMT%2B8
    url: jdbc:mysql://localhost:3306/shopping?serverTimezone=GMT%2B8
    username: root
    password: ******
#mybatis输出日志
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

2. Java part

2.1Chasret

• Get all encoding formats

 SortedMap<String, Charset> stringCharsetSortedMap = Charset.availableCharsets();
        Set<Map.Entry<String, Charset>> entries = stringCharsetSortedMap.entrySet();
        for(Map.Entry<String, Charset> key : entries){
    
    
            System.out.println(key.getKey() + " " + key.getValue());
        }

• Get the Charset class of the corresponding format

3. mysql

3.1 Host ‘192.168.16.104’ is blocked because of many connection errors; unblock with ‘mysqladmin flush-hosts’

4. Commonly used configuration commands

4.1 View mysql installation location command

 select @@basedir;

4.2 mysql data storage command

 select @@datadir;

4.3 The mysql configuration file and data are in the same directory

4.4 Restart the mysql service

service mysql restart;

4.5 flush-hosts

• To be executed on the remotely connected host
• For example, when connecting to 192.168.16.103 on the computer of 192.168.16.104, pymysql.err.OperationalError: (1129, "192.168.16.104' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'"), you need to Do this on the computer at 192.168.16.104:
• Cannot be added;

mysqladmin -uroot -p flush-hosts

4.6 Set database time zone

 set global time_zone = "+00:00";

• It will only take effect after re-entering mysql for the second time.