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[JDBC] API parsing
2022-07-03 16:48:00 【Hold on for a long time】
Catalog
demonstration jdbc The business of
PreparedStatement solve SQL Inject
One 、DriverManager
DriverManager( Driver management ) effect ：
1、 Registration drive
2、 Get database connection
1、 Registration drive ：
Class.forName("com.mysql.jdbc.Driver");Registration driven writing method , Not used on the surface DriverManager class , Choose Driver,ctrl+b Look at the source
package com.mysql.jdbc;
import java.sql.DriverManager;
import java.sql.SQLException;
public class Driver extends NonRegisteringDriver implements java.sql.Driver {
public Driver() throws SQLException {
}
static {
try {
DriverManager.registerDriver(new Driver());
} catch (SQLException var1) {
throw new RuntimeException("Can't register driver!");
}
}
}
It has been used. DriverManager.registerDriver（） Methods
stay MySQL5 Later driver package , You can omit the steps of registering the driver
Automatic loading jar In bag META-INF/services/java.sql.Driver File driver class
2、 Get the connection
static Connection getConnection(String url,String user,String password)
Parameters
1、url： Connection path
grammar ：jdbc:mysql://ip Address ( domain name ): Port number / Database name ？ Parameter key value pair 1& Parameter key value pair 2....
give an example ：jdbc:mysql://127.0.0.1:3306/db1( This machine 127.0.0.1, Local domain name ：localhost)
details ： If the connection is local mysql The server , also mysql The default port number is 3306 , be url I could just write it as :jdbc:mysql:// Database name ？ Parameter key value pairs, such as ：jdbc:mysql:///db1
To configure userSSL=false Parameters , Disable secure connection mode , Resolve warning tips
2、user: user name
3、password： password
Resolve warning tips ：
?userSSL=false
String url="jdbc:mysql://127.0.0.1:3306/db1？useSSL=false";Two 、Connection
Connection（ Database connection object ） effect ：
1、 Access to perform SQL The object of
2、 Manage affairs
1、 Get hold sql object
- Common execution SQL object
Statement createStatement()
- precompile SQL Implementation SQL object ： prevent SQL Inject
PrepareStatement prepareStatement(sql)
- Objects execute stored procedures
CallableStatement prepareCall(sql)
2、 Business management
mysql Business management
Open transaction ：BEGIN;/START TRANSACTION(start transaction)
Commit transaction ：COMMIT;
Roll back the transaction ：ROLLBACK;
(MySQL Automatically commit transactions by default )
JDBC Business management ：
Connection Interface defined 3 Corresponding methods
Open transaction :setAutoCommit(boolean autoCommit);true For auto commit transactions ,false For manual commit transactions （ Open transaction ）
Commit transaction ：commit()
Roll back the transaction ：rollback()
demonstration jdbc The business of
Copy the previous classes to the package
package com.jdbc;
import com.mysql.jdbc.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
public class JDBCConnectionDemo {
public static void main(String[] args) throws Exception {
//1、 Registration drive
Class.forName("com.mysql.jdbc.Driver");
//2、 Get the connection
//url The format is ："jdbc:mysql://mysql Of ip: Port number / Operational database "
String url="jdbc:mysql://127.0.0.1:3306/kc_db01";
//username Is your mysql user name
String username="root";
//password Is your mysql password
String password="123456";
Connection conn= (Connection) DriverManager.getConnection(url, username, password);
//3、 Definition sql
String sql1="update emp set salary=6666 where ename='zhangsan'";
String sql2="update emp set salary=6666 where ename='lisi'";
//4、 Access to perform sql Of Statement object
Statement stat=conn.createStatement();
// Select the exception part to handle ,ctrl+alt+t Shortcut key generation
try {
// Open transaction
conn.setAutoCommit(false);
// perform sql
int count1=stat.executeUpdate(sql1);
// Processing results
System.out.println(" Number of rows affected :"+count1);
// Execution time sql
int count2=stat.executeUpdate(sql2);
// Processing results
System.out.println(" Number of rows affected :"+count2);
// Commit transaction
conn.commit();
} catch (Exception e) {
e.printStackTrace();
// Roll back the transaction ( Back before starting the transaction , That is, before dealing with anything )
conn.rollback();
}finally {
//7、 Release resources ( Open first and then release )
stat.close();
conn.close();
}
}
}
Before running the database emp surface ：
Running results ：
After running, the database emp surface ：
try An exception occurred in , will By catch Capture , A rollback occurred , Rollback to before the transaction has been started , That is, before the data is modified , If it doesn't work , It may lead to one success and one failure , This is something we don't want to see . Transaction enabled , Rollback transaction is used , Multiple transactions can be guaranteed to succeed at the same time , Or fail at the same time .
3、 ... and 、Statement
Statemen effect ：
1、 perform sql sentence
int executeUpdate(sql): perform DML( Addition, deletion and modification of data )、DDL( Addition, deletion and modification of tables and libraries ) sentence
Return value :(1)DML The number of lines affected by the statement （2）DDL After statement execution , Successful execution may also return 0
ResultSet executeQuery（sql）: perform DQL( Query data ) sentence
Return value ：ResultSet Result object
Four 、ResultSet
ResultSet( Result set object ) effect ：
1. Encapsulates the DQL The result of the query statement
ResultSet stmt.executeQuery(sql): perform DQL sentence , return ResultSet object
Get query results
boolean next():（1） Move the cursor forward one line from the current position （2） Judge whether the current line is a valid line
Return value ： The current row has data returned true, There is currently no data returned false.
xxx getXxx( Parameters )： get data
explain ：xxx Represents the data type ; Such as int getInt( Parameters );String getString( Parameters );
Parameters ： about int Is the number of the column , from 1 Start , about String Is the name of the column .
Use steps ：
1、 Move the cursor down one line , And judge whether the line has data ：next()
2、 get data ：getXxx( Parameters )
Example ：
while(rs.next()){
rs.getXxx( Parameters );
}example ：
package com.jdbc;
import com.mysql.jdbc.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
public class JDBCDemo3_ResultSet {
public static void main(String[] args) throws Exception {
//1、 Registration drive
Class.forName("com.mysql.jdbc.Driver");
//2、 Get the connection
//url The format is ："jdbc:mysql://mysql Of ip: Port number / Operational database "
String url="jdbc:mysql://127.0.0.1:3306/kc_db01";
//username Is your mysql user name
String username="root";
//password Is your mysql password
String password="123456";
Connection conn= (Connection) DriverManager.getConnection(url, username, password);
//3、 Definition sql
String sql="select *from emp";
//4、 Access to perform sql Of Statement object
Statement stmt=conn.createStatement();
//5、 perform sql sentence
ResultSet rs=stmt.executeQuery(sql);
//6 Processing results
while(rs.next()){
// get data getXxx(); You can write the line in parentheses , You can also write column names
int id=rs.getInt(1);
String ename=rs.getString(2);
int salary=rs.getInt(3);
// Another way of writing ： Write the name of the line
// int id=rs.getInt("id");
// String ename=rs.getString("ename");
// int salary=rs.getInt("salary");
System.out.println(id);
System.out.println(ename);
System.out.println(salary);
System.out.println("-----------");
}
//7、 Release resources ( Open first and then release )
rs.close();
stmt.close();
conn.close();
}
}
In the database emp surface
After running ：
ResultSet Case study
demand ： Inquire about account Account data , Encapsulated in the Account In the object , And store it in ArrayList Collection
Create a pojo package , Used to store objects .
Created a class , Provide getSet Method
package com.pojo;
public class Account {
private int id;
private String ename;
private int salary;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getEname() {
return ename;
}
public void setEname(String ename) {
this.ename = ename;
}
public int getSalary() {
return salary;
}
public void setSalary(int salary) {
this.salary = salary;
}
// In order to better show , rewrite toString() Method
@Override
public String toString() {
return "Account{" +
"id=" + id +
", ename='" + ename + '\'' +
", salary=" + salary +
'}'+"\n";
}
}
jdbc In the class created under the package
package com.jdbc;
import com.mysql.jdbc.Connection;
import com.pojo.Account;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
public class JDBCDemo4_ResultSet {
public static void main(String[] args) throws Exception {
//1、 Registration drive
Class.forName("com.mysql.jdbc.Driver");
//2、 Get the connection
//url The format is ："jdbc:mysql://mysql Of ip: Port number / Operational database "
String url="jdbc:mysql://127.0.0.1:3306/kc_db01";
//username Is your mysql user name
String username="root";
//password Is your mysql password
String password="123456";
Connection conn= (Connection) DriverManager.getConnection(url, username, password);
//3、 Definition sql
String sql="select *from emp";
//4、 Access to perform sql Of Statement object
Statement stmt=conn.createStatement();
//5、 perform sql sentence
ResultSet rs=stmt.executeQuery(sql);
//6 Processing results
// Create a collection object
List<Account> list=new ArrayList<>();
while(rs.next()){
// establish Account object
Account account=new Account();
// get data getXxx(); You can write the line in parentheses , You can also write column names
int id=rs.getInt(1);
String ename=rs.getString(2);
int salary=rs.getInt(3);
// Assignment data
account.setId(id);
account.setEname(ename);
account.setSalary(salary);
list.add(account);
}
System.out.println(list);
//7、 Release resources ( Open first and then release )
rs.close();
stmt.close();
conn.close();
}
}
Running results ：
5、 ... and 、PreparedStatement
PreparedStatement effect ：
1、 precompile SQL Statement and execute ： The prevention of SQL Injection problem
SQL Inject
SQL Injection is to modify pre-defined by operating input SQL sentence , The method used to execute code to attack the server .
Demonstrate normal login ：
First, data record kc_db1 Under the emp The table is ：
package com.jdbc;
import com.mysql.jdbc.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
public class JDBCDemo5_UserLogin {
public static void main(String[] args) throws Exception {
//2、 Get the connection
//url The format is ："jdbc:mysql://mysql Of ip: Port number / Operational database "
String url="jdbc:mysql://127.0.0.1:3306/kc_db01";
//username Is your mysql user name
String username="root";
//password Is your mysql password
String password="123456";
Connection conn= (Connection) DriverManager.getConnection(url, username, password);
String name="zhangsan";
String pwd="1233";
//3、 Definition sql
String sql="select *from emp where ename='"+name+"'and password='"+pwd+"'" ;
System.out.println(" This article SQL The sentence is :"+sql);
//4、 Access to perform sql Of Statement object
Statement stat=conn.createStatement();
//5、 perform sql sentence
ResultSet rs = stat.executeQuery(sql);
//6 Processing results ,rs A value indicates that the search is successful
if(rs.next()){
System.out.println(" Login successful ");
}else{
System.out.println(" Login failed ");
}
//7、 Release resources ( Open first and then release )
rs.close();
stat.close();
conn.close();
}
}
Running results ：
Enter other ( The reason for the failure is that there is no account with this password in the database )：
sql Inject Demo ：
For this article sql It's not about passwords , Any account number
String name=" A casual name ";
String pwd=" ' or '1'='1"; Running results ：
This article SQL The sentence is :select *from emp where ename=' A casual name 'and password=' ' or '1'='1'
sql The essence of injection is to change the original SQL sentence , Join in or after 1=1 Always true , So this sentence is true
PreparedStatement solve SQL Inject
① obtain PreparedStatement object
//sql Parameters in statement , Use ？ Instead of
String sql="select *from user where username=? and password=?";
// adopt Connection Object acquisition , And pass in the corresponding sql sentence
PreparedStatement pstmt=conn.prepareStatement(sql);② Set parameters
PreparedStatement object ：setXxx( Parameters 1, Parameters 2)： Expressed as a parameter 1(? The location of ) Assign value to parameter 2
Xxx： data type ; arbitrarily setInt( Parameters 1, Parameters 2)
Parameters ：
- Parameters 1： Express ？ Location number of , from 1 Start
- Parameters 2： ？ Value
③ perform sql
executeUpdate();/excuteQuery(); There is no need to pass... In parentheses sql.
Create a class ：
package com.jdbc;
import com.mysql.jdbc.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Scanner;
public class JDBCDemo5_UserLogin {
public static void main(String[] args) throws Exception {
//2、 Get the connection
//url The format is ："jdbc:mysql://mysql Of ip: Port number / Operational database "
String url="jdbc:mysql://127.0.0.1:3306/kc_db01";
//username Is your mysql user name
String username="root";
//password Is your mysql password
String password="123456";
Connection conn= (Connection) DriverManager.getConnection(url, username, password);
String name=" A casual name ";
String pwd=" ' or '1'='1";
//3、 Definition sql
String sql="select *from emp where ename=? and password=?" ;
//4、 Acquired PreparedStatement object
PreparedStatement pstmt = conn.prepareStatement(sql);
// Set parameters
pstmt.setString(1, name);
pstmt.setString(2, pwd);
//5、 perform sql sentence
ResultSet rs =pstmt.executeQuery();
System.out.println(" This article SQL The sentence is :"+sql);
//6 Processing results ,rs A value indicates that the search is successful
if(rs.next()){
System.out.println(" Login successful ");
}else{
System.out.println(" Login failed ");
}
//7、 Release resources ( Open first and then release )
rs.close();
pstmt.close();
conn.close();
}
}
Running results ：
This prevents sql Inject ,setXxx The parameters passed in will be escaped , Not spliced into strings, but \' or\ ' 1\' = \' 1\'
Enter the correct ：
PrepareStatement principle
PrepareStatement benefits ：
1、 precompile SQL, Higher performance
2、 prevent sql Inject .
my.ini The configuration file can see the log
log-output=FILE
general-log=1
general_log_file="D:\mysql.log"
slow-query-log=1
slow_query_log_file="D:\mysql_slow.log"
long_query_time=2
The precompile function is off by default
①：PreparedStatement Precompile function Turn on ：userServerPrepStmts=true
stay sql sentence ? Then write the parameters
String url="jdbc:mysql://127.0.0.1:3306/kc_db01"?userServerPrepStmts=true;When you open it, you will prepare precompile ：
After closing, there is no Prepare Stage
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