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MySQL_ JDBC
2022-07-03 13:13:00 【Tolerance speech】
1.JDBC
1. Concept
1. Database driven
drive ： Sound card , The graphics card ……
Our program will deal with the database through database driver .
2.JDBC Concept
SUN In order to simplify the operation of developers on the database , Provides a java Specification of operating database , Be commonly called JDBC.
These specifications are made by specific manufacturers , For developers , We just need to master JDBC Interface can .
So we need to import a database driver package , Download address ：https://dev.mysql.com/downloads/
2. First time to know JDBC Program
stay SQLyog in ：
CREATE DATABASE jdbcStudy CHARACTER SET utf8 COLLATE utf8_general_ci;
USE jdbcStudy;
CREATE TABLE users(
id INT PRIMARY KEY,
`name` VARCHAR(50),
`password` VARCHAR(30),
`email` VARCHAR(60),
birthday DATE
);
INSERT INTO users(`id`,`name`,`password`,`email`,`birthday`) VALUES(1,' Zhang San ','123456','[email protected]','1990-12-4'),(2,' Li Si ','1234567','[email protected]','2000-08-2'),(3,' Zhao Wu ','3456789','[email protected]','2003-07-11');
stay idea in ：
Create a project
Import database driver
- Create a new one lib Catalog , And then put jar The bag dragged in
- Right click add as library Add as library
Write code
import java.sql.*; public class jdbcFirstDemo { public static void main(String[] args) throws ClassNotFoundException, SQLException { //1. The load driver Class.forName("com.mysql.jdbc.Driver");// Fixed writing , The load driver //2. User information and url //useUnicode=true Support Chinese coding ,chaeacterEncoding=utf8 Avoid random code ,useSSL=true Using secure connections String url ="jdbc:mysql://localhost:3306/jdbcStudy?useUnicode=true&chaeacterEncoding=utf8&useSSL=true"; String username = "root"; String password = "1234"; //3. Successful connection , Database objects connection On behalf of the database Connection connection = DriverManager.getConnection(url,username,password); //4. perform SQL The object of Statement Statement statement = connection.createStatement(); //5. perform SQL To execute SQL, View return results String sql= "SELECT * FROM `users`"; ResultSet resultSet = statement.executeQuery(sql);// perform sql, The result set returned , The result set encapsulates all the query results while(resultSet.next()){ System.out.println("id="+resultSet.getObject("id")); System.out.println(" name ="+resultSet.getObject("name")); System.out.println(" password ="+resultSet.getObject("password")); System.out.println(" mailbox ="+resultSet.getObject("email")); System.out.println(" Birthday ="+resultSet.getObject("birthday")); System.out.println("===================="); } //6. Release the connection resultSet.close(); statement.close(); connection.close(); } }result ：
url
String url ="jdbc:mysql://localhost:3306/jdbcStudy?useUnicode=true&chaeacterEncoding=utf8&useSSL=true";
//mysql---3306
//jdbc:mysql:// The host address ： Port number 、 Database name ？ Parameters 1& Parameters 2& Parameters 3
//oralce---1521
//jdbc:oralce:thin:@localhost:1521:sid
connection
//connection Database objects
connection.rollback();
connection.commit();
connection.setAutoCommit();
statement
//statement perform sql The object of
PreparedStatement preparedStatement = connection.prepareStatement();// This is safer
Statement statement = connection.createStatement();
statement.executeQuery();// Query operation , Return result set resultSet
statement.execute();// Carry out any sql
statement.executeLargeUpdate();// to update , Insert , Delete all with this , Returns the number of rows affected
resultSet
// Return result set
//1. Gets the specified data type
resultSet.getObject()// Use when you don't know the column type
resultSet.getInt();
resultSet.getFloat();
resultSet.getDouble();
resultSet.getBoolean();
resultSet.getDate();
//2. Traverse , The pointer
resultSet.next();// Move to the next data
resultSet.beforeFirst();// Move to the front
resultSet.afterLast();// Move to the back
resultSet.previous();// Move to previous line
resultSet.absolute(row);// Move to specified row
Release resources , What has to be done
resultSet.close();
statement.close();
connection.close();// special connection
3.statement object
JDBC Inside statement Object to send... To the database SQL sentence , Want to complete the addition, deletion, modification and query of the database , You only need to send the add, delete, change and query statement to the database through this object .
statement Object's executeUpdate Method , Used to send additions, deletions, and modifications to the specified database sql sentence ,executeUpdate After execution , Will return an integer , That is, several rows of data in the database have changed .
CRUD operation -create
Statement st = conn.ceateStatement();
String sql = "insert into user(...) values(...,...)";
int num = st.executeUpdate(sql);
if(num>0){
System.out.println(" Insert the success ！");
}
CRUD operation -delete
Statement st = conn.ceateStatement();
String sql = "delete from user where id=1";
int num = st.executeUpdate(sql);
if(num>0){
System.out.println(" Delete successful ！");
}
CRUD operation -update
Statement st = conn.ceateStatement();
String sql = "update user set name ='' where name= ''";
int num = st.executeUpdate(sql);
if(num>0){
System.out.println(" Modification successful ！");
}
4. Extract tool class
driver = com.mysql.jdbc.Driver
url =jdbc:mysql://localhost:3306/jdbcStudy?useUnicode=true&chaeacterEncoding=utf8&useSSL=true
username = root
password = 1234
package utils;
import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.Properties;
public class jdbcUtils {
private static String driver = null;
private static String url = null;
private static String username = null;
private static String password = null;
static {
try{
// Access to resources
InputStream in = jdbcUtils.class.getClassLoader().getResourceAsStream("db.properties");
Properties properties = new Properties();
properties.load(in);
driver = properties.getProperty("driver");
url = properties.getProperty("url");
username = properties.getProperty("username");
password = properties.getProperty("password");
//1. The driver can be loaded only once
Class.forName(driver);
} catch (IOException | ClassNotFoundException e) {
e.printStackTrace();
}
}
// Get the connection
public static Connection getConnection() throws SQLException {
return DriverManager.getConnection(url,username,password);
}
// Release the connection
public static void release(Connection conn, Statement st, ResultSet rs){
if (rs != null){
try {
rs.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if (st != null){
try {
rs.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if (conn != null){
try {
rs.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
}
import utils.jdbcUtils;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
public class testInsert {
public static void main(String[] args) {
Connection conn = null;
Statement st = null;
try {
conn = jdbcUtils.getConnection();// Get database connection
st = conn.createStatement();// perform sql The object of
String sql= "INSERT INTO users(`id`,`name`,`password`,`email`,`birthday`) "+"VALUES(6,' cheng ','453','[email protected]','1998-3-1')";
int i = st.executeUpdate(sql);
if (i>0){
System.out.println(" success ！");
}
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
jdbcUtils.release(conn,st,null);
}
}
}
5.sql Injection problem
sql Vulnerability , It can lead to The data reveal that . Nature is ：sql Will be stitched together （or）.
import utils.jdbcUtils;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class sqlInjection {
public static void main(String[] args) {
//login(" Zhang San ","123456"); Normal query ----- name : Zhang San password :123456
login(" 'or' 1=1 "," 'or' 1=1");// All user names and passwords have been found
}
// Log in to business
public static void login(String username ,String password){
Connection conn = null;
Statement st = null;
try {
conn = jdbcUtils.getConnection();// Get database connection
st = conn.createStatement();// perform sql The object of
//SELECT * FROM `users` WHERE `name`=' Zhang San ' AND `password`=123456;
String sql= "SELECT * FROM `users` WHERE `name`='"+username+"' AND `password`='"+password+"'";
ResultSet resultSet = st.executeQuery(sql);// perform sql, The result set returned , The result set encapsulates all the query results
while(resultSet.next()) {
System.out.println(" name :" + resultSet.getObject("name"));
System.out.println(" password :" + resultSet.getObject("password"));
}
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
jdbcUtils.release(conn,st,null);
}
}
}
6.PreparedStatement object
It can prevent sql Injection problem , And more efficient .
import utils.jdbcUtils;
import java.sql.Connection;
import java.util.Date;
import java.sql.PreparedStatement;
import java.sql.SQLException;
public class psInsert {
public static void main(String[] args) {
Connection conn = null;
PreparedStatement st = null;
try {
conn = jdbcUtils.getConnection();
// difference
// Use ？ Placeholders replace specific parameters
String sql = "INSERT INTO users(`id`,`name`,`password`,`email`,`birthday`) "+"VALUES(?,?,?,?,?)";
st = conn.prepareStatement(sql);// precompile sql, First write sql, But it doesn't execute
// Assign parameters manually
st.setInt(1,8);
st.setString(2,"q");
st.setString(3,"2345");
st.setString(4,"[email protected]");
// Be careful ：java.util.Date yes java Of
// java.sql.Date It's database
st.setDate(5,new java.sql.Date(new Date().getTime()));
// perform
int i = st.executeUpdate();
if (i>0){
System.out.println(" Insert the success ！");
}
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
jdbcUtils.release(conn,st,null);
}
}
}
7. Use idea Connect to database
1. Pay attention when connecting ： To put Drive import go in , And there's more Time zone problem You need to add it manually in the advanced settings
2. Add the desired database
3. After importing the database , Double click to view the table
4. Then you can modify the data directly , And submit
5. Enter writing sql Where to code
6. Write code
8. Business
Either they all succeed , Or they all failed .
import utils.jdbcUtils;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
public class transaction {
public static void main(String[] args) throws SQLException {
Connection conn = null;
PreparedStatement st = null;
try {
conn = jdbcUtils.getConnection();
// Turn off automatic submission of the database , Automatically opens the transaction
conn.setAutoCommit(false);// Open transaction
String sql1 = "update account set money = money - 100 where name = 'A' ";
st = conn.prepareStatement(sql1);
st.executeUpdate();
String sql2 = "update account set money = money + 100 where name = 'B' ";
st = conn.prepareStatement(sql2);
st.executeUpdate();
// Business finished , Commit transaction
conn.commit();
System.out.println(" Submit successfully ");
} catch (SQLException throwables) {
conn.rollback();// If it fails, roll back , Don't write this sentence , Failure will also be rolled back automatically by default
throwables.printStackTrace();
}finally {
jdbcUtils.release(conn,st,null);
}
}
}
result ：
9. Database connection pool
We are now database connection ---- perform ---- Release , But the whole process of connection release is a waste of resources . So we need to write a connection pool , To write a connection pool, you only need to implement An interface Datasource( The interface will not change , The method won't change ). After using these data connection pools , When we develop projects , There is no need to write the code to connect to the database ！
Pool technology ： Prepare some Advance resources , Come here, even ready :
Open door — salesman ： wait for ----- service ---- close
How many salesmen do you need here ？ This leads to Minimum connections , This can be set according to your common connection number
maximum connection ： The maximum carrying capacity of the service , If the maximum number of connections is reached , The rest needs to wait in line
Waiting for timeout ： If the waiting time is too long , Just tell the person behind to leave
Some common open source database connection pools ：
DBCP
C3P0
Druid： alibaba.com
1. DBCP
Import jar package , Import and add as library ：
Commons-dbcp.jar： Implementation of connection pool
Commons-pool.jar： Dependency library for connection pool implementation
Download address ：http://commons.apache.org/proper/commons-dbcp/download_dbcp.cgi,http://commons.apache.org/proper/commons-pool/download_pool.cgi
# Database driven , connections setting up ： The name here is DBCP The data source is defined
driverClassName=com.mysql.jdbc.Driver
# Database connection address
url=jdbc:mysql://localhost:3306/jdbcStudy?useUnicode=true&chaeacterEncoding=utf8&useSSL=true
# user name
username=root
# password
password=1234
# Initialize connection
initialSize=10
# Maximum number of database connections to the connection pool . Set to 0 Means unlimited
maxActive=50
# Maximum free connection , Maximum idle time for database connection . More than free time , The database connection will be marked as unavailable , And then it's released . Set to 0 Means unlimited
maxIdle=20
# Minimum free connection
minIdle=5
# Maximum connection setup wait time , Milliseconds . If this time is exceeded, an exception will be received . Set to -1 Means unlimited
maxWait=60000
# Configure monitoring statistics interception filters
#filters=stat
#JDBC The format of the connection attribute attribute attached to the driver when establishing the connection must be as follows ：[ Property name =property;]
# Be careful ："user" And "password" Two attributes are explicitly passed , So there's no need to include them
connectionProperties=useUnicode=true;characterEncoding=UTF8
# Specifies the automatic commit of connections created by the connection pool （auto-commit） state
defaultAutoCommit=true
#driver default Specify the transaction level of the connection created by the connection pool （TransactionIsolation）.
# The available values are one of the following ：（ details javadoc.）NONE,READ_UNCOMMITTED, READ_COMMITTED, REPEATABLE_READ, SERIALIZABLE
defaultTransactionIsolation=READ_UNCOMMITTED
package utils;
import org.apache.commons.dbcp.BasicDataSourceFactory;
import javax.sql.DataSource;
import java.io.InputStream;
import java.sql.*;
import java.util.Properties;
public class dbcpUtils {
private static DataSource dataSource = null;
static {
try{
// Access to resources
InputStream in = dbcpUtils.class.getClassLoader().getResourceAsStream("dbcpconfig.properties");
Properties properties = new Properties();
properties.load(in);
// create data source Factory mode -- Create objects
dataSource = BasicDataSourceFactory.createDataSource(properties);
} catch (Exception e) {
e.printStackTrace();
}
}
// Get the connection
public static Connection getConnection() throws SQLException {
return dataSource.getConnection();
}
// Release the connection
public static void release(Connection conn, Statement st, ResultSet rs){
if (rs != null){
try {
rs.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if (st != null){
try {
st.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if (conn != null){
try {
conn.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
}
test DBCP The code is the same as before , Just change one sentence ：conn = dbcpUtils.getConnection().
2.C3P0
Import jar package , Import and add as library :
- c3p0-0.9.5.2.jar
- mchange-commons-java-0.2.15.jar
<?xml version="1.0" encoding="UTF-8"?>
<!--xml No need to read , Automatically match when loading -->
<c3p0-config>
<!-- The default configuration , If not specified, use this configuration -->
<default-config>
<property name="user">root</property>
<property name="password">1234</property>
<property name="jdbcUrl">jdbc:mysql://localhost:3306/jdbcStudy?useUnicode=true&chaeacterEncoding=utf8&useSSL=true</property>
<property name="driverClass">com.mysql.jdbc.Driver</property>
<property name="checkoutTimeout">30000</property>
<property name="idleConnectionTestPeriod">30</property>
<property name="acquireIncrement">5</property>
<property name="initialPoolSize">10</property>
<property name="maxIdleTime">30</property>
<property name="maxPoolSize">100</property>
<property name="minPoolSize">2</property>
<property name="maxStatements">200</property>
</default-config>
<!-- Named configuration , It can be implemented through method calls -->
<named-config name="MySQL">
<property name="user">root</property>
<property name="password">1234</property>
<property name="jdbcUrl">jdbc:mysql://localhost:3306/jdbcStudy?useUnicode=true&chaeacterEncoding=utf8&useSSL=true</property>
<property name="driverClass">com.mysql.jdbc.Driver</property>
<!-- How many connections in the pool increase at a time if there are not enough connections -->
<property name="acquireIncrement">5</property>
<!-- Number of connections when initializing the database connection pool -->
<property name="initialPoolSize">20</property>
<!-- The maximum number of database connections in the database connection pool -->
<property name="maxPoolSize">25</property>
<!-- The minimum number of database connections in the database connection pool -->
<property name="minPoolSize">5</property>
</named-config>
</c3p0-config>
package utils;
import com.mchange.v2.c3p0.ComboPooledDataSource;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class c3p0Utils {
private static ComboPooledDataSource dataSource = null;
static {
try{
dataSource = new ComboPooledDataSource("MySQL");
} catch (Exception e) {
e.printStackTrace();
}
}
// Get the connection
public static Connection getConnection() throws SQLException {
return dataSource.getConnection();
}
// Release the connection
public static void release(Connection conn, Statement st, ResultSet rs){
if (rs != null){
try {
rs.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if (st != null){
try {
st.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if (conn != null){
try {
conn.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
}
test DBCP The code is the same as before , Just change one sentence ：conn = c3p0Utils.getConnection().
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