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JDBC knowledge

2022-06-29 18:23:00 【Spirit Lord sinner】

One 、 know jdbc

jdbc What can ？ What can be done
JDBC brief introduction - JDBC（Java DataBase Connectivity,java Database connection ） It's one for execution SQL Of the statement Java API, It can provide unified access for a variety of relational databases , It's used by a group Java Language written classes and interfaces .JDBC It provides a benchmark , From this, you can build more advanced tools and interfaces , Enable database developers to write database applications

For me ,jdbc It's a kind of toolbox encapsulated in a shelf bag

Commonly used tools

There are many common tools in this toolbox ：

1. DriverManager – class ： Used to obtain Connection
2. Connection – Interface ; Used to obtain Statement perhaps PreparedStatement Object's
3. Statement – Interface ; Used to perform sql Sentence method 1
4. PreparedStatement Interface ： Used to perform sql Sentence method 2
5. ResultSet – Interface ： Get the result set returned by executing the query statement

What's the use of these tools ？

First of all, we need to know this jdbc It's a tool , Connect java With the database , By means of java Direct operation database on program

-1、

This is not jdbc Of

The first one is ： Suppose there is no jdbc This kind of APL Provide a unified operating language , So the application is operating MySql When using the database MySQL Special driver language , Use operation Oracle When you need it Oracle Database operation language , Besides, there are other databases , For a programmer , Spend too much time learning the language of other applications operating database Libraries , No doubt a waste of energy , and , Easy to confuse , The code is easy to couple , Deposition

-2、

There is jdbc Of

The second is , A is added in the middle Jdbc drive , In this set of drivers, there is a set of specialized and perfect language and interface to manage various databases , So , A set of programmer student numbers is enough , And liberate the application from direct contact with the database , This greatly reduces the coupling between the application and the database , Even when the application interfaces with other databases , It won't change much , Directly modifying jdbc Just fine

And what we need to learn is the second

Second, first download mysql Drive pack

open cmd Input :mysql -V
see mysql edition , there ’V’ It's in capital letters V

1, stay maven Warehouse downloading ：dbc website : https://mvnrepository.com/artifact/mysql/mysql-connector-java
Then download the corresponding version of the rack package
–> After go in
2. stay Official website Another method step downloaded in ： Download from the official website
Import the downloaded rack package into
Create a new empty package , Choose a name at will ,lib Import shelf package
Right click on the lib Folder , And then click add as library… Jump out of this and click OK

such jdbc The environment is the first time

3、 ... and 、 Database connection steps

use jdbc Operating the data path is equivalent to turning the visual operation into a line of sorted code for operation

1. The load driver

A1、 Load driven in mysql6.0 The following versions use the following driver statements

Class.forName("com.mysql.jdbc.Driver");

A2、 After the update mysql6.0 For the above

Class.forName("com.mysql.cj.jdbc.Driver");

The original writing was ：

DriverManager.registerDriver(new com.mysql.jdbc.Driver())

Because in Driver It encapsulates static code blocks , Once called, it will execute , If created in this way, it will be executed twice , So we don't advocate

The above line of code is equivalent to opening and loading the database >

2. User information and address

 	    String url = "jdbc:mysql://localhost:3306/school?useUnicode=true&characterEncoding=utf8&usrSSL=true&serverTimezone=Asia/Shanghai";
        String username = "root";
        String userpassword = "123456";

For address url There are a lot of things to pay attention to ：url Some introductions

jdbc:mysql://localhost:3306/school?useUnicode=true&characterEncoding=utf8&usrSSL=true&serverTimezone=Asia/Shanghai
jdbc:mysql:// : agreement
localhost: IP Address
3306: Port number
school: Database instance name
useUnicode=true&characterEncoding=utf8 Introduce :

usrSSL=true: Is the use of JDBC When connecting to your database , Yours JDBC Version and MySQL Version incompatible ,MySQL The version of is higher , Add... After the join statement “useSSL=‘true’” , You can connect to the database . Higher version .

serverTimezone=Asia/Shanghai: Set time zone , For Shanghai

“？”： Equivalent to a spliced character
“&”: amount to and

Format ：
url=“ agreement :// This machine IP Address : Port number / Database name ”
Equivalent to the basic information of database application connection
Of course, databases are usually in their own mysql It's built inside , Even which database is up to you
3. Get database connection
Connection connection = DriverManager.getConnection(url, username, userpassword);
4. Create execution sql Of the statement statement object
Statement statement = connection.createStatement();
5. use statement Object to perform sql sentence
Be careful ：
-1. Yes statement perform sql object
-2. Yes PreparedStatement perform sql object
There are two ways Related introduction
1 、 First there must be execution statements
String sql= "SELECT * FROM grade";
2 、 Created with statement Object to perform
ResultSet resultSet = statement.executeQuery(sql);
Yes
statement.excuteQuery() ：（ Inquire about ） After execution, a resultset
statement.excute() ： You can do anything sql sentence , Determine whether the first result is ResultSet object , If it is , be return true, Otherwise return to false
statement.excuteUpdate() ：（ Insert , to update . Delete ） Use this one to execute , A number of affected rows will be returned
6. Release resources
resultSet.close(); statement.close(); connection.close();
Close resources in order , It's equivalent to exiting in order mysql Visual interface for operation
Four 、jdbc Addition, deletion and modification of
use statement complete increase 、 Delete 、 Change 、 check
The following is a simplified addition, deletion, modification and query without packaging tools
1、 check yes select sentence
package Zer.demo.util; import java.sql.*; // My first one jdbc Program public class Select { public static void main(String[] args) throws ClassNotFoundException, SQLException { //1. The load driver //DriverManager.registerDriver(new com.mysql.jdbc.Driver());// Achieved two registrations Class.forName("com.mysql.cj.dbc.Driver"); //2. Appliance information and address String url = "jdbc:mysql://localhost:3306/school?useUnicode=true&characterEncoding=utf8&useSSL=true&serverTimezone=Asia/Shanghai"; String username = "root"; String userpassword = "123456"; //3. Successful connection , Create database objects Connection connection = DriverManager.getConnection(url, username, userpassword); //4. Database object creation execution sq The object of , Write lost statements Statement statement = connection.createStatement(); String sql= "SELECT * FROM grade"; //5、 Created with statement Object to perform sql sentence , ResultSet resultSet = statement.executeQuery(sql);// use executeQuery() Method , Will return a result set while (resultSet.next()){ System.out.println("gradeid="+resultSet.getInt("gradeid")); System.out.println("gradename="+resultSet.getString("gradename")); System.out.println("………………………………………………………………………………………………………………………………………"); } // System.out.println(i); //6. Release the connection resultSet.close(); statement.close(); connection.close(); } }
2、 increase yes insert sentence
package Zer.demo.util; import java.sql.*; // My first one jdbc Program public class Insert { public static void main(String[] args) throws ClassNotFoundException, SQLException { //1. The load driver //DriverManager.registerDriver(new com.mysql.jdbc.Driver());// Achieved two registrations Class.forName("com.mysql.cj.jdbc.Driver"); //2. Appliance information and address String url = "jdbc:mysql://localhost:3306/school?useUnicode=true&characterEncoding=utf8&useSSL=true&serverTimezone=Asia/Shanghai"; String username = "root"; String userpassword = "123456"; //3. Successful connection , Create database objects Connection connection = DriverManager.getConnection(url, username, userpassword); //4. Database object creation execution sq The object of , Write lost statements Statement statement = connection.createStatement(); String sql= "insert into grade values(25,' How about this ')"; //5、 Created with statement Object to perform sql sentence , int i = statement.executeUpdate(sql);// For increment 、 Delete 、 Change , use executeUpdate() Method execution , Will return a number of affected rows if (i>0){ System.out.println(" Insert the success "); }else { System.out.println(" Insert the failure "); } // System.out.println(i); //6. Release the connection statement.close(); connection.close(); } }
3、 Change yes update sentence
package Zer.demo.util; import java.sql.*; // My first one jdbc Program public class Update { public static void main(String[] args) throws ClassNotFoundException, SQLException { //1. The load driver //DriverManager.registerDriver(new com.mysql.jdbc.Driver());// Achieved two registrations Class.forName("com.mysql.cj.jdbc.Driver"); //2. Appliance information and address String url = "jdbc:mysql://localhost:3306/school?useUnicode=true&characterEncoding=utf8&useSSL=true&serverTimezone=Asia/Shanghai"; String username = "root"; String userpassword = "123456"; //3. Successful connection , Create database objects Connection connection = DriverManager.getConnection(url, username, userpassword); //4. Database object creation execution sq The object of , Write lost statements Statement statement = connection.createStatement();// Perform the operation of the query String sql= "update grade set gradename=' Everybody's the same , Even if it's different , It doesn't hurt to be a little tired ' where gradeid= 22"; //5、 Created with statement Object to perform sql sentence , int i = statement.executeUpdate(sql);// For increment 、 Delete 、 Change , use executeUpdate() Method execution , Will return a number of affected rows if (i>0){ System.out.println(" The update is successful "); }else { System.out.println(" Update failed "); } // System.out.println(i); //6. Release the connection statement.close(); connection.close(); } }
4、 Delete yes delete sentence
package Zer.demo.util; import java.sql.*; // My first one jdbc Program public class Delete { public static void main(String[] args) throws ClassNotFoundException, SQLException { //1. The load driver //DriverManager.registerDriver(new com.mysql.jdbc.Driver());// Achieved two registrations Class.forName("com.mysql.cj.jdbc.Driver"); //2. Appliance information and address String url = "jdbc:mysql://localhost:3306/school?useUnicode=true&characterEncoding=utf8&useSSL=true&serverTimezone=Asia/Shanghai"; String username = "root"; String userpassword = "123456"; //3. Successful connection , Create database objects Connection connection = DriverManager.getConnection(url, username, userpassword); //4. Database object creation execution sq The object of , Write lost statements Statement statement = connection.createStatement(); String sql= "delete from grade where gradeid =22"; //5、 Created with statement Object to perform sql sentence , int i = statement.executeUpdate(sql);// For increment 、 Delete 、 Change , use executeUpdate() Method execution , Will return a number of affected rows if (i>0){ System.out.println(" Delete successful "); }else { System.out.println(" Delete failed "); } // System.out.println(i); //6. Release the connection statement.close(); connection.close(); } }
Picture reference changed to
Connection made by tools
If you also find the law ,
Only ：
1.sql Statement change
2. Execution time , The query is different from the addition, deletion and modification ：（1） One is executeQuery() Return a result set , You can use while Circular display
（2） One is executeUpdate() Returns the number of affected rows , It can be used to judge whether the execution is successful
To this end, we can build a Tool class
https://blog.csdn.net/qq_45898383/article/details/118399812
5、 ... and 、SQL Injection problem
SQL A brief introduction
Use statement There is SQL Injection problem , There are security risks , So , If you want to know something about it, you can learn it by yourself

Computers have two languages ：
1、 Interpretive language ： When the computer is running , A running component interprets the running code , And execute the instructions contained therein （ Execute while parsing ）
2、 Compiled language ： When the code is generated, it is transformed into mechanical language , At run time, the instructions in the language are executed directly （ Direct execution ）
In interpretative language ： If the program interacts with the user . The user can construct special input to splice into the program to execute , So that the program executes according to the information entered by the user, and there may be malicious code .
Like this column
SQL After injection
1、SQL Injection gets more information
2、SQL Injection problems will lead to more information easy to leak
’or 1=1 – : One of the single quotes ’ In order to splice the previous user input information , parallel bars “–” An empty space can be followed by a comment . Don't comment , Parallel bars can not write
6、 ... and PreparedStatemen object
Can prevent SQL Injection and higher efficiency ,
about preparedstatement The object is ：
Multiple placeholders , Replace the original data with question marks “?”, Use a question mark to occupy a space
Assign values manually , In the order of question marks , Assign values one by one from the first
1、 check
package Zer.demo.util1; import java.sql.*; public class Select1 { public static void main(String[] args) throws ClassNotFoundException, SQLException { //1. The load driver Class.forName("com.mysql.cj.jdbc.Driver"); //2. User information String url="jdbc:mysql://localhost:3306/school?useUnicode=true&characterEncoding=utf8&useSSL=true&serverTimezone=Asia/Shanghai"; String username = "root"; String userpassword = "123456"; //3. Successful connection , Create database objects Connection connection = DriverManager.getConnection(url, username, userpassword); //4、 To write sql sentence String sql= "select * from grade where gradeid = ? "; //String sql= "select * from grade "; If there is no placeholder , You don't have to assign values , Just do it directly //5. Precompile , Precompiled but not executed PreparedStatement preparedStatement = connection.prepareStatement(sql);// Precompiled without execution // After manual assignment , Will execute preparedStatement.setInt(1,24); //6. Execute the manually assigned statement ResultSet resultSet = preparedStatement.executeQuery(); while (resultSet.next()){ System.out.println(resultSet.getInt("gradeid")); System.out.println(resultSet.getString("gradename")); } //7. Release resources resultSet.close(); preparedStatement.close(); connection.close(); } }
2、 increase
package Zer.demo.util1; import java.sql.*; public class Insert { public static void main(String[] args) throws ClassNotFoundException, SQLException { //1. The load driver Class.forName("com.mysql.cj.jdbc.Driver"); //2. User information String url="jdbc:mysql://localhost:3306/school?useUnicode=true&characterEncoding=utf8&useSSL=true&serverTimezone=Asia/Shanghai"; String username = "root"; String userpassword = "123456"; //3. Successful connection , Create database objects Connection connection = DriverManager.getConnection(url, username, userpassword); //4、 To write sql sentence String sql= "insert into grade(gradeid,gradename) values(?,?)"; //5. Precompile , Precompiled but not executed PreparedStatement preparedStatement = connection.prepareStatement(sql);// Precompiled without execution // After manual assignment , Will execute preparedStatement.setInt(1,27); preparedStatement.setString(2," Do you still want to learn "); //6. Execute the manually assigned statement int i = preparedStatement.executeUpdate();// Returns the number of rows affected by an execution if (i>0) { System.out.println(" Insert the success "); }else { System.out.println(" Insert the failure "); } //7. Release resources preparedStatement.close(); connection.close(); } }
3、 Change
package Zer.demo.util1; import java.sql.*; public class Update1 { public static void main(String[] args) throws ClassNotFoundException, SQLException { //1. The load driver Class.forName("com.mysql.cj.jdbc.Driver"); //2. User information String url = "jdbc:mysql://localhost:3306/school?useUnicode=true&characterEncoding=utf8&useSSL=true&serverTimezone=Asia/Shanghai"; String username = "root"; String userpassword = "123456"; //3. Successful connection , Create database objects Connection connection = DriverManager.getConnection(url, username, userpassword); //4、 To write sql sentence String sql = "update grade set gradename = ? where gradeid = ? "; //5. Precompile , Precompiled but not executed PreparedStatement preparedStatement = connection.prepareStatement(sql);// Precompiled without execution // After manual assignment , Will execute preparedStatement.setString(1, " If you want to learn, of course you want to learn "); preparedStatement.setInt(2, 27); //6. Execute the manually assigned statement int i = preparedStatement.executeUpdate();// Returns the number of rows affected by an execution if (i > 0) { System.out.println(" The update is successful "); } else { System.out.println(" Update failed "); } //7. Release resources preparedStatement.close(); connection.close(); } }
4、 Delete
package Zer.demo.util1; import java.sql.*; public class Delete1 { public static void main(String[] args) throws ClassNotFoundException, SQLException { //1. The load driver Class.forName("com.mysql.cj.jdbc.Driver"); //2. User information String url = "jdbc:mysql://localhost:3306/school?useUnicode=true&characterEncoding=utf8&useSSL=true&serverTimezone=Asia/Shanghai"; String username = "root"; String userpassword = "123456"; //3. Successful connection , Create database objects Connection connection = DriverManager.getConnection(url, username, userpassword); //4、 To write sql sentence String sql = "delete from grade where gradeid = ?"; //5. Precompile , Precompiled but not executed PreparedStatement preparedStatement = connection.prepareStatement(sql);// Precompiled without execution // After manual assignment , Will execute preparedStatement.setInt(1,27); //6. Execute the manually assigned statement int i = preparedStatement.executeUpdate();// Returns the number of rows affected by an execution , The number of lines is greater than 0, Nature is success if (i > 0) { System.out.println(" Delete successful "); } else { System.out.println(" Delete failed "); } //7. Release resources preparedStatement.close(); connection.close(); } }
Tool class connection
preparedstatement The utility class simplifies the connection
Tool class :https://blog.csdn.net/qq_45898383/article/details/118399812
These are written by individuals at will , You guys, just take a look at it at will