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Abstract of this article ： Upgrade driver to mysql-connector-java 8.0.28 Precautions for
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Problem description

Upgrade driver to mysql-connector-java 8.0.28 after , Deploy and execute various error reports , But switch the connector to mysql-connector-java-5.1.48 No problem , It's very confusing ！

Most of the information reported in error is that such information cannot be found 、 Unable to connect

It is mainly configured , There was no screenshot , Just pay attention to the differences from the old version

Official download address

Through all kinds of difficulties and dangers , Finally solved , Successfully connected , The solution is given below

Solution

The first is an example of a rookie , More comprehensive ; If you feel troublesome , The second option can be used

1. Full version

Here quote Novice tutorial Example

1. Database environment construction

--  Building a database  demo1
CREATE DATABASE IF NOT EXISTS demo1;

--  establish  websites  surface 
CREATE TABLE websites (
  id int(11) NOT NULL AUTO_INCREMENT,
  name char(20) NOT NULL DEFAULT '' COMMENT ' Site name ',
  url varchar(255) NOT NULL DEFAULT '',
  alexa int(11) NOT NULL DEFAULT '0' COMMENT 'Alexa  ranking ',
  country char(10) NOT NULL DEFAULT '' COMMENT ' Country ',
  PRIMARY KEY (id)
) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8;

--  Write data 
INSERT INTO websites
VALUES ('1', 'Google', 'https://www.google.cm/', '1', 'USA'), 
('2', ' TaoBao ', 'https://www.taobao.com/', '13', 'CN'), 
('3', ' Novice tutorial ', 'http://www.runoob.com', '5892', ''), 
('4', ' Microblogging ', 'http://weibo.com/', '20', 'CN'), 
('5', 'Facebook', 'https://www.facebook.com/', '3', 'USA');

2. Test class connection

The most important thing is here MySQL Version problem , The new version updates the name of the driver class to com.mysql.cj.jdbc.Driver

import java.sql.*;

public class JDBCTest {
    

    // MySQL 8.0  The following versions  - JDBC  Driver name and database  URL
    // static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
    // static final String DB_URL = "jdbc:mysql://localhost:3306/RUNOOB";

    // MySQL 8.0  Above version  - JDBC  Driver name and database  URL
    static final String JDBC_DRIVER = "com.mysql.cj.jdbc.Driver";
    static final String DB_URL = "jdbc:mysql://localhost:3306/demo1?useSSL=false&allowPublicKeyRetrieval=true&serverTimezone=UTC&useServerPrepStmts=true";
                                                            //  Pay attention to modifying the database name  

    //  User name and password of database , It needs to be based on your own settings 
    static final String USER = "your db login name";
    static final String PASS = "your db password";

    public static void main(String[] args) {
    
        Connection conn = null;
        Statement stmt = null;
        try {
    
            //  register  JDBC  drive 
            Class.forName(JDBC_DRIVER);

            //  Open the link 
            System.out.println(" Connect to database ...");
            conn = DriverManager.getConnection(DB_URL, USER, PASS);

            //  Execute the query 
            System.out.println("  Instantiation Statement object ...");
            stmt = conn.createStatement();
            String sql;
            sql = "SELECT id, name, url FROM websites";
            ResultSet rs = stmt.executeQuery(sql);

            //  Expand the result set database 
            while (rs.next()) {
    
                //  Retrieve... By fields 
                int id = rs.getInt("id");
                String name = rs.getString("name");
                String url = rs.getString("url");

                //  Output data 
                System.out.print("ID: " + id);
                System.out.print(",  Site name : " + name);
                System.out.print(",  Site  URL: " + url);
                System.out.print("\n");
            }
            //  Close... When done 
            rs.close();
            stmt.close();
            conn.close();
        } catch (SQLException se) {
    
            //  Handle  JDBC  error 
            se.printStackTrace();
        } catch (Exception e) {
    
            //  Handle  Class.forName  error 
            e.printStackTrace();
        } finally {
    
            //  close resource 
            try {
    
                if (stmt != null) stmt.close();
            } catch (SQLException se2) {
    
            }//  Don't do anything? 
            try {
    
                if (conn != null) conn.close();
            } catch (SQLException se) {
    
                se.printStackTrace();
            }
        }
        System.out.println("Goodbye!");
    }
}

Execution results , Successful connection

2. Lite version

The above example considers the overall , Use more exceptions , For ease of understanding , Let's simplify the amount of code

1. Database environment construction

--  Building a database  demo1
CREATE DATABASE IF NOT EXISTS demo1;

--  Create data tables  accounts
CREATE TABLE accounts (
			id int(3) NOT NULL PRIMARY KEY auto_increment,
			name varchar(5),
			money FLOAT(4,2)
			);

--  Write data 
INSERT INTO accounts VALUES('1','jason','10000'),('2','you','99999');

2. Test class connection

Note that version 、 The order in which resources are released （ Call first , Final release , The release order is opposite to the call order ）

package com.jason.jdbc;

import java.sql.*;

public class JDBCDemo {
    public static void main(String[] args) throws Exception { //psvm  Quickly generate 
        //1.  Registration drive 
        Class.forName("com.mysql.cj.jdbc.Driver");
        //2.  Get the connection 
        String url = "jdbc:mysql://localhost:3306/demo1?useSSL=false&allowPublicKeyRetrieval=true&serverTimezone=UTC&useServerPrepStmts=true";
        String username = "your db login name";
        String password = "your db password";
        Connection conn = DriverManager.getConnection(url, username, password);
        //3.  Definition sql
        String sql = "update accounts set money = 1000 where id = 2";
        //4.  Access to perform sql The object of  Statement
        Statement stmt = conn.createStatement();
        //5.  perform sql
        int count = stmt.executeUpdate(sql);// Rows affected 
        //6.  Processing results 
        System.out.println("Affected rows: "+count);
        //7.  Release resources  Statement  and  Connection  Pay attention to the release sequence 
        stmt.close();
        conn.close();
    }
}

Execution results , Successful connection

summary

After all, it's an update , There will be some changes , We need to learn to see what's updated 、 Learn to go to the authorities to find solutions

For example, this error report can be from the latest jar Found in the package

stay 5.x After the version , Registration driver code can be omitted without writing , This is the passage

//1.  Registration drive 
//Class.forName("com.mysql.cj.jdbc.Driver");

as a result of ： drive jar It's a bag , Default META-INF services The corresponding driver class name is recorded in the directory , No need to write again

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Maybe the version I use is too old , Can't keep up with the development of the times ~~