Troubleshooting Java Connection to MySQL

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本讲座将解释从Java连接到MySQL工作所需的步骤，并强调可能遇到的潜在问题。它将涵盖所有组件、安装和配置。
About the Author
Rodrigo Trindade
Master in Computer Science by the Rio Grande do Sul Federal University (Brazil). Over 10 years experience as CS Professor. Started as Software Developer then moved to Support Engineering working for Netscape, Sun Microsystems and Oracle. Joined Percona in 2018 as a Service Delivery Manager. Solaris, Java and Weblogic certified.

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9 .Vagrant file ```# -*- mode: ruby -*- # vi: set ft=ruby : Vagrant.configure(2) do |config| config.vm.define "node-1" do |node| node.vm.box = "centos/7" node.vm.host_name = "node1" node.vm.network "private_network", ip: "192.168.33.10" end end Vagrant.configure(2) do |config| config.vm.define "jvm-1" do |node| node.vm.box = "centos/7" node.vm.host_name = "jvm1" node.vm.network "private_network", ip: "192.168.33.11" end end``` 9 9 © 2019 Percona

10 .VMs Installation $ vagrant up Bringing machine 'node-1' up with 'virtualbox' provider... ==> node-1: Checking if box 'centos/7' is up to date... (...) ==> node-1: Booting VM... ==> node-1: Waiting for machine to boot. This may take a few minutes... (...) ==> node-1: Machine booted and ready! (...) ==> node-1: Setting hostname... ==> node-1: Configuring and enabling network interfaces... node-1: SSH address: 127.0.0.1:2222 node-1: SSH username: vagrant node-1: SSH auth method: private key 1 10 © 2019 Percona 0

11 .VMs Installation Bringing machine 'jvm-1' up with 'virtualbox' provider... ==> jvm-1: Importing base box 'centos/7'... ==> jvm-1: Matching MAC address for NAT networking... ==> jvm-1: Checking if box 'centos/7' is up to date... ==> jvm-1: Setting the name of the VM: CentOS7_jvm_1542309057193_62910 (...) ==> jvm-1: Booting VM... ==> jvm-1: Waiting for machine to boot. This may take a few minutes... (...) ==> jvm-1: Machine booted and ready! (...) ==> jvm-1: Setting hostname... ==> jvm-1: Configuring and enabling network interfaces... jvm-1: SSH address: 127.0.0.1:2200 jvm-1: SSH username: vagrant jvm-1: SSH auth method: private key 1 11 © 2019 Percona 1

13 .Percona Server Installation [root@node1 ~]# yum install http://www.percona.com/downloads/percona- release/redhat/0.1-6/percona-release-0.1-6.noarch.rpm Loaded plugins: fastestmirror (...) Is this ok [y/d/N]: y Downloading packages: (...) Running transaction Installing : percona-release-0.1-6.noarch Verifying : percona-release-0.1-6.noarch Installed: percona-release.noarch 0:0.1-6 Complete! 1 3 13 © 2019 Percona

14 .Percona Server Installation [root@node1 ~]# yum install Percona-Server-server-57 Loaded plugins: fastestmirror Loading mirror speeds from cached hostfile (...) Resolving Dependencies --> Running transaction check ---> Package Percona-Server-server-57.x86_64 0:5.7.23-24.1.el7 will be installed (...) Installed: Percona-Server-server-57.x86_64 0:5.7.23-24.1.el7 Percona-Server-shared-compat-57.x86_64 0:5.7.23-24.1.el7 (...) Complete! 1 4 14 © 2019 Percona

15 .Percona Server Installation [root@node1 ~]# systemctl start mysql [root@node1 ~]# ps -ef | grep mysqld mysql 23699 1 18 20:55 ? 00:00:01 /usr/sbin/mysqld -- daemonize --pid-file=/var/run/mysqld/mysqld.pid [root@node1 ~]# grep -i 'password' /var/log/mysqld.log 2018-11-15T20:55:36.680897Z 1 [Note] A temporary password is generated for root@localhost: ;s_ZcHwfR5r1 1 5 15 © 2019 Percona

16 .Percona Server Installation [root@node1 ~]# mysql -u root -p Enter password: Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 4 Server version: 5.7.23-24 (...) mysql> set PASSWORD = 'Passw0rd!'; Query OK, 0 rows affected (0.00 sec) mysql> exit Bye 1 6 16 © 2019 Percona

23 .MySQL JDBC Connector JDBC provides a standard interface for interacting with any RDBMS. The API consists of the following 4 main components: 1. JDBC Driver 2. Connection 3. Statement 4. ResultSet 2 23 © 2019 Percona 3

24 .Java Source code Conn.java import java.sql.*; class Conn { private static String Driver = "com.mysql.jdbc.Driver"; private static String ConnectionURL = "jdbc:mysql://192.168.33.10:3306/plive"; private static String User = "root"; private static String Password = "Passw0rd!"; private static String SQL_Statement = "SELECT * FROM emp"; public static void main(String args[]){ try { Class.forName(Driver); Connection con=DriverManager.getConnection(ConnectionURL,User,Password); Statement stmt=con.createStatement(); ResultSet rs=stmt.executeQuery(SQL_Statement); while(rs.next()) System.out.println(rs.getInt(1)+" "+rs.getString(2)+" "+rs.getString(3)); con.close(); } catch(Exception e){ System.out.println(e);} } } 2 24 © 2019 Percona 4

25 .Java Source code 1. Class.forName(Driver); 2. Connection con=DriverManager.getConnection(ConnectionURL,User,Passw ord); 3. Statement stmt=con.createStatement(); 4. ResultSet rs=stmt.executeQuery(SQL_Statement); 2 25 © 2019 Percona 5

26 .Java Source code Where does that come from??? Class.forName(Driver); Class.forName loads a class using Classloader, including running its static initializers. ● The goal is to allow instanciation of a Connection from a static string, potentially from a configuration file. ● Takes a Class or Interface as parameter. 2 26 © 2019 Percona 6

27 .MySQL Sample Data Creation mysql> create database plive; mysql> use plive; Database changed mysql> create table emp(id int(10),name varchar(40),age int(3)); mysql> insert into emp(id,name,age) values (1,'Percona Live',10); mysql> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | mysql | | performance_schema | | plive | | sys | +--------------------+ 6 rows in set (0.00 sec) 2 27 © 2019 Percona 7

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