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Getting started with JDBC
2022-07-03 18:35:00 【Bieyunchao】
One 、 What is? JDBC？
Concept ：Java DataBase Connectivity Java Database connection , Java Language operation database
Two 、JDBC The essence
JDBC The essence ： Actually, it's official （sun company ） A set of rules defined to operate all relational databases , Interface . Each database manufacturer to implement this set of interface , Provide database driver jar package . We can use this interface （JDBC） Programming , The code that actually executes is the driver jar The implementation class in the package .
3、 ... and 、JDBC Quick start
1.JDBC Six steps to programming
First step ： Registration drive （ effect ： tell Java Program , Which brand database will be connected soon ）
The second step ： Get database connection （ Express JVM The channel between the database process and the database process is opened , This belongs to communication between processes , A heavyweight , Be sure to close the channel after use .）
The third step ： Get database operation object （ Special execution sql Object of statement ）
Step four ： perform SQL sentence （DQL DML....）
Step five ： Process query result set （ Only if the fourth step is select At the time of statement , The fifth step is to process the query result set .）
Step six ： Release resources （ Be sure to close the resource after using it .Java And database belong to the communication between processes , Be sure to turn it off after you turn it on .）
2.JDBC Quick start
package com.aynu.jdbc;
import cn.aynu.pojo.User;
import java.sql.*;
/** * Inquire about tab_user surface */
public class JDBCTest04 {
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
ResultSet resultSet = null;
try {
// 1. Registration drive
Class.forName("com.mysql.jdbc.Driver");
// 2. Get the connection
conn = DriverManager.getConnection(
"jdbc:mysql://localhost:3306/db",
"root",
"root");
// 3. Get database operation object
stmt = conn.createStatement();
// 4. perform sql sentence
String sql = "select * from tab_user";
resultSet = stmt.executeQuery(sql);
// 5. Process query result set
User u = new User();
while (resultSet.next()){
String id = resultSet.getString("id");
String name = resultSet.getString("name");
int age = resultSet.getInt("age");
Date birthday = resultSet.getDate("birthday");
u.setId(id);
u.setName(name);
u.setAge(age);
u.setBirthday(birthday);
System.out.println(u);
}
} catch (SQLException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
} finally {
// 6. Release resources
if (resultSet != null){
try {
resultSet.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (stmt != null){
try {
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (conn != null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
}
Four 、 Detailed explanation JDBC Each object
1.DriverManager
DriverManager： Drive management objects
function ：
1. Registration drive ： Tell the driver of the corresponding database used by the program
Code :Class.forName("com.mysql.jdbc.Driver");
Source code analysis ： stay com.mysql.jdbc.Driver Class has static code blocks
static {
try {
java.sql.DriverManager.registerDriver(new Driver());
} catch (SQLException E) {
throw new RuntimeException("Can't register driver!");
}
}
Be careful ：mysql5 After the drive jar Packages can omit the steps of registering drivers .
2. Get database connection
Method ：static Connection getConnection(String url, String user, String password)
Parameters ：
url： Specify the path of the connection
grammar ：jdbc:mysql://ip Address ( domain name ): Port number / Database name
Example ：jdbc:mysql://localhost:3306/db
user： user name （mysql The user name of the database ）
root： password （mysql Database password ）
2.Connection
Connection： Database connection object
Access method ：conn = DriverManager.getConnection(url, user, password);
function ：
1. Access to perform sql Object of statement
conn.createStatement()
conn.prepareStatement(sql);
2. Manage affairs
Open transaction ：conn.setAutoCommit(false);
Commit transaction ：conn.commit();
Transaction rollback ：conn.rollback();
Be careful ： Here conn Generation refers to Connection object
3.Statement
Statement： perform sql The object of
Access method ：Statement stmt = conn.createStatement();
1. perform sql
1. boolean execute(String sql) ：
You can do whatever you want sql
2. int executeUpdate(String sql) ：
It can be executed DML（insert、update、delete） sentence 、
DDL(create,alter、drop) sentence
* Return value ： Number of rows affected , It can be judged by the number of rows affected DML Is the statement executed successfully
* Return value >0 Then the execution is successful , conversely , The failure .
3. ResultSet executeQuery(String sql) ：
perform DQL（select) sentence
4.ResultSet
ResultSet： Result set object , Encapsulate query results
Access method ：ResultSet resultSet = stmt.executeQuery(sql);
boolean next(): Move the cursor down one line , Determine whether the current line is the end of the last line ( Is there any data ),
If it is , Then return to false, If not, return true
* getXxx( Parameters ): get data
* Xxx： Representative data type Such as ： int getInt() , String getString()
* Parameters ：
1. int： Represents the number of the column , from 1 Start Such as ： getString(1)
2. String： Name of representative column . Such as ： getDouble("balance")
while (resultSet.next()){
// Get the data of this row in the database
String id = resultSet.getString("id");
String name = resultSet.getString("name");
int age = resultSet.getInt("age");
Date birthday = resultSet.getDate("birthday");
}
5. PreparedStatement
PreparedStatement： perform sql The object of （ Precompiled objects ）
Access method ：PrepareStatement pstmt = conn.prepareStatement(sql);
1. SQL Injection problem ： In splicing sql when , Somewhat sql Special keywords participate in string splicing .
Can cause security problems
2 solve sql Injection problem ： Use PreparedStatement Object to solve
2. precompiled SQL： Parameters use ? As placeholder
package com.aynu.jdbc;
import java.sql.*;
import java.util.Scanner;
/** * Practice using PreparedStatement * Implement login function id name */
public class JDBCTest05 {
public static void main(String[] args) {
Connection conn = null;
PreparedStatement pstmt = null;
ResultSet resultSet = null;
try {
// 1. Registration drive
Class.forName("com.mysql.jdbc.Driver");
// 2. Get the connection
conn = DriverManager.getConnection(
"jdbc:mysql://localhost:3306/day04",
"root", "root");
// 3. Get database operation object
// Definition sql sentence
String sql = "select * from tab_user where id = ? and name = ?";
pstmt = conn.prepareStatement(sql);
System.out.print("id：");
String id = new Scanner(System.in).nextLine();
System.out.print("name：");
String name = new Scanner(System.in).nextLine();
// to ？ assignment
pstmt.setString(1, id);
pstmt.setString(2, name);
// 4. perform sql sentence
resultSet = pstmt.executeQuery();
// 5. Process query result set
if (resultSet.next()){
System.out.println(" Landing successful ");
} else{
System.out.println(" Login failed ");
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
} finally {
// 6. Release resources
if (resultSet != null){
try {
resultSet.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (pstmt != null){
try {
pstmt.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (conn != null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
}
5、 ... and 、 Extract tool class
It is obvious from the above two code cases ,JDBC Code is not complicated , however Duplicate code A lot , So we need to extract a tool class , The following is a tool class I extracted in this stage of study , And configuration files （ take driver,url,user,password Extract a properties in ）, You can also use it .
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/db?useUnicode=true&characterEncoding=utf-8
user=root
password=root
Be careful ： In daily study
?useUnicode=true&characterEncoding=utf-8user=root
To deal with the problem of Chinese garbled code
package com.aynu.util;
import java.io.FileInputStream;
import java.io.FileReader;
import java.io.IOException;
import java.net.URL;
import java.sql.*;
import java.util.Properties;
/** * JDBC Tool class */
public class JDBCUtils {
private static String url;
private static String user;
private static String password;
private static String driver;
/** * Static code block , Used to load configuration files */
static {
try {
Properties pro = new Properties();
String path = Thread.currentThread().getContextClassLoader().getResource("jdbc.properties").getPath();
pro.load(new FileInputStream(path));
url = pro.getProperty("url");
user = pro.getProperty("user");
password = pro.getProperty("password");
driver = pro.getProperty("driver");
// Registration drive
Class.forName(driver);
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
/** * Get the connection * @return Connection object */
public static Connection getConnection() throws SQLException {
return DriverManager.getConnection(url, user, password);
}
/** * Release resources * @param stmt * @param conn */
public static void close(Statement stmt, Connection conn){
if (stmt != null){
try {
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (conn != null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
/** * Release resources * @param rs * @param stmt * @param conn */
public static void close(ResultSet rs,Statement stmt, Connection conn){
if (rs != null){
try {
rs.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (stmt != null){
try {
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (conn != null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
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