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JDBC courses
2022-07-03 01:12:00 【__ Miracle__】
MVC
SELECT * from emp;
insert INTO emp VALUES(8888, 'ERIC', 'CLERK', 7902, '2000-01-12',40000 ,0, 40)
UPDATE EMP SET SAL = 70000 WHERE EMPNO = 8888;
DELETE FROM EMP WHERE EMPNO = 8888;
JDBC：
JDBC：Java DataBase Connectivity Java Database connection , Java Language operation database .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 .
Quick start ：
- step ：
- Import driver jar package mysql-connector-java-5.1.37-bin.jar
1. Copy mysql-connector-java-5.1.37-bin.jar To the project libs Under the table of contents
2. Right click –>Add As Library - Registration drive
- Get database connection object Connection
- Definition sql
- Access to perform sql Object of statement Statement
- perform sql, Accept the return result
- Processing results
- Release resources
- Code implementation ：
public class JDBCDemo1 {
public static void main(String[] args) throws Exception{
//1. Import driver jar package
//2. Registration drive
Class.forName("com.mysql.jdbc.Driver");
//3. Get database connection object
Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/info", "root", "root");
//4. Definition sql sentence
String sql = "update account set balance = 500 where id = 1";
//5. Access to perform sql The object of Statement
Statement stmt = conn.createStatement();
//6. perform sql
int count = stmt.executeUpdate(sql);
//7. Processing results
System.out.println(count);
//8. Release resources
stmt.close();
conn.close();
}
}
Explain the objects in detail ：
- DriverManager： Drive management objects
- function ：
- Registration drive ： Tell the program which database driver to use jar
static void registerDriver(Driver driver) : Register with given driver DriverManager .
Write code using ： Class.forName(“com.mysql.jdbc.Driver”);
Discover by looking at the source code ： 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/db3
- details ： If the connection is local mysql The server , also mysql The default port for the service is 3306, be url I could just write it as ：jdbc:mysql:/// Database name
- user： user name
- password： password
- url： Specify the path of the connection
- Connection： Database connection object
- function ：
- Access to perform sql The object of
- Statement createStatement()
- PreparedStatement prepareStatement(String sql)
- Manage affairs ：
- Open transaction ：setAutoCommit(boolean autoCommit) ： Call this method to set the parameter to false, That is, start the transaction
- Commit transaction ：commit()
- Roll back the transaction ：rollback()
- Statement： perform sql The object of
- perform sql
- boolean execute(String sql) ： You can do whatever you want sql understand
- int executeUpdate(String sql) ： perform 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 .
- ResultSet executeQuery(String sql) ： perform DQL（select) sentence
- practice ：
- account surface Add a record
- account surface Modify the record
- account surface Delete a record
Code ：
public class JDBCDemo2 {
public static void main(String[] args) {
Statement stmt = null;
Connection conn = null;
try {
//1. Registration drive
Class.forName("com.mysql.jdbc.Driver");
//2. Definition sql
String sql = "insert into account values(' Wang Wu ',null,3000)";
String sql = "update account set balance = 1 where id = 2";
String sql = "delete from account where id = 2";
//3. obtain Connection object
conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/info", "root", "root");
//4. Access to perform sql The object of Statement
stmt = conn.createStatement();
//5. perform sql
int count = stmt.executeUpdate(sql);// Number of rows affected
//6. Processing results
System.out.println(count);
if(count > 0){
System.out.println(" Add success ！");
}else{
System.out.println(" Add failure ！");
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}finally {
//stmt.close();
//7. Release resources
// Avoid null pointer exceptions
if(stmt != null){
try {
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if(conn != null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
}
- ResultSet： Result set object , Encapsulate query results
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 ：
- int： Represents the number of the column , from 1 Start Such as ： getString(1)
- String： Name of representative column . Such as ： getDouble(“balance”)
Be careful ：
- Use steps ：
- Move the cursor down one line
- Judge whether there is data
- get data
- Use steps ：
// Loop to determine whether the cursor is at the end of the last line .
while(rs.next()){
// get data
//6.2 get data
int id = rs.getInt(1);
String name = rs.getString("name");
double balance = rs.getDouble(3);
System.out.println(id + "---" + name + "---" + balance);
}
- practice ：
- Define a method , Inquire about emp The table's data encapsulates it as an object , Then load the collection , return .
Definition Emp class
Define methods public List findAll(){}
Implementation method select * from emp;
PreparedStatement： perform sql The object of
SQL Injection problem ： In splicing sql when , Somewhat sql Special keywords participate in string splicing . Can cause security problems
- Input users casually , Input password ：a’ or ‘a’ = 'a
- sql：select * from user where username = ‘fhdsjkf’ and password = ‘a’ or ‘a’ = ‘a’
solve sql Injection problem ： Use PreparedStatement Object to solve
precompiled SQL： Parameters use ? As placeholder
step ：
- Import driver jar package mysql-connector-java-5.1.37-bin.jar
- Registration drive
- Get database connection object Connection
- Definition sql
- Be careful ：sql Parameter usage of ？ As placeholder . Such as ：select * from user where username = ? and password = ?;
- Access to perform sql Object of statement PreparedStatement Connection.prepareStatement(String sql)
- to ？ assignment ：
- Method ： setXxx( Parameters 1, Parameters 2)
- Parameters 1：？ Location number of from 1 Start
- Parameters 2：？ Value
- Method ： setXxx( Parameters 1, Parameters 2)
- perform sql, Accept the return result , There is no need to pass on sql sentence
- Processing results
- Release resources
Be careful ： It will be used later PreparedStatement To complete all operations of addition, deletion, modification and query
- Can prevent SQL Inject
- More efficient
extract JDBC Tool class ： JDBCUtils
- Purpose ： Simplify writing
- analysis ：
Registration drivers also extract
Extract a method to get the connection object
- demand ： Don't want to pass parameters （ trouble ）, We also need to ensure the universality of tool class .
- solve ： The configuration file
jdbc.properties
url=
user=
password=
Extract a method to release resources
Druid： Database connection pool implementation technology , Provided by Alibaba
- step ：
- Import jar package druid-1.0.9.jar
- Define configuration file ：
- yes properties Formal
- You can call it anything , It can be placed in any directory
- Load profile .Properties
- Get database connection pool object ： From the factory DruidDataSourceFactory
- Get the connection ：getConnection
- Code ：
//3. Load profile
Properties pro = new Properties();
InputStream is = DruidDemo.class.getClassLoader().getResourceAsStream(“druid.properties”);
pro.load(is);
//4. Get connection pool object
DataSource ds = DruidDataSourceFactory.createDataSource(pro);
//5. Get the connection
Connection conn = ds.getConnection();
- Define tool classes
- Define a class JDBCUtils
- Provide static code block loading configuration file , Initialize connection pool object
- Provide methods
- Get the connection method ： Get the connection through the database connection pool
- Release resources
- How to get the connection pool
- step ：
- Code implementation ：
package com.neusoft.utils;
import com.alibaba.druid.pool.DruidDataSourceFactory;
import javax.sql.DataSource;
import java.io.IOException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;
/** * Druid Connection pool tool class */
public class JDBCUtils {
//1. Define member variables DataSource
private static DataSource ds ;
static{
try {
//1. Load profile
Properties pro = new Properties();
pro.load(JDBCUtils.class.getClassLoader().getResourceAsStream("druid.properties"));
//2. obtain DataSource
ds = DruidDataSourceFactory.createDataSource(pro);
} catch (IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
}
/** * Get the connection */
public static Connection getConnection() throws SQLException {
return ds.getConnection();
}
/** * Release resources */
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();// Return connection } catch (SQLException e) { e.printStackTrace(); } }*/
close(null,stmt,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();// Return connection
} catch (SQLException e) {
e.printStackTrace();
}
}
}
/** * Get connection pool method */
public static DataSource getDataSource(){
return ds;
}
}
druid.properties
driverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/info
username=root
password=root
# Initialize the number of connections
initialSize=5
# maximum connection
maxActive=10
# Maximum waiting time
maxWait=3000
JDBC Inquire about
public class JDBCDemo6 {
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
try {
//1. Registration drive
Class.forName("com.mysql.jdbc.Driver");
//2. Get the connection object
conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/info", "root", "root");
//3. Definition sql
String sql = "select * from account";
//4. Access to perform sql object
stmt = conn.createStatement();
//5. perform sql
rs = stmt.executeQuery(sql);
//6. Processing results
//6.1 Move the cursor down one line
rs.next();
//6.2 get data
int id = rs.getInt(2);
String name = rs.getString("name");
double balance = rs.getDouble(3);
System.out.println(id + "---" + name + "---" + balance);
//6.1 Move the cursor down one line
rs.next();
//6.2 get data
int id2 = rs.getInt(2);
String name2 = rs.getString("name");
double balance2 = rs.getDouble(3);
System.out.println(id2 + "---" + name2 + "---" + balance2);
//6.1 Move the cursor down one line
rs.next();
//6.2 get data
int id3 = rs.getInt(2);
String name3 = rs.getString("name");
double balance3 = rs.getDouble(3);
System.out.println(id3 + "---" + name3 + "---" + balance3);
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
} finally {
//7. Release resources
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();
}
}
}
}
}
Rewrite to cycle
package com.neusoft.jdbc1;
import java.sql.*;
public class JDBCDemo7 {
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
try {
//1. Registration drive
Class.forName("com.mysql.jdbc.Driver");
//2. Get the connection object
conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/info", "root", "root");
//3. Definition sql
String sql = "select * from account";
//4. Access to perform sql object
stmt = conn.createStatement();
//5. perform sql
rs = stmt.executeQuery(sql);
//6. Processing results
// Loop to determine whether the cursor is at the end of the last line .
while(rs.next()){
// get data
//6.2 get data
int id = rs.getInt(2);
String name = rs.getString("name");
double balance = rs.getDouble(3);
System.out.println(id + "---" + name + "---" + balance);
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
} finally {
//7. Release resources
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();
}
}
}
}
}
Use common methods and connection pools to query emp
domain It usually represents the relationship with database tables – One to one correspondence javaBean
private Integer id;
private String ename;
private String job;
private Integer mgr;
private Date hiredate;
private int salary;
private int bonus;
private Integer deptno;
package com.neusoft.jdbc1;
import com.neusoft.domain.Emp;
import com.neusoft.utils.JDBCUtils;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
/** * * Define a method , Inquire about emp The table's data encapsulates it as an object , Then load the collection , return . */
public class JDBCDemo8 {
public static void main(String[] args) {
// List<Emp> list = new JDBCDemo8().findAll();
List<Emp> list = new JDBCDemo8().findAll2();
System.out.println(list);
System.out.println(list.size());
}
/** * Query all emp object * @return */
public List<Emp> findAll(){
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
List<Emp> list = null;
try {
//1. Registration drive
Class.forName("com.mysql.jdbc.Driver");
//2. Get the connection
conn = DriverManager.getConnection("jdbc:mysql:///info", "root", "root");
//3. Definition sql
String sql = "select * from emp";
//4. Access to perform sql The object of
stmt = conn.createStatement();
//5. perform sql
rs = stmt.executeQuery(sql);
//6. Traversal result set , Encapsulated object , Load collection
Emp emp = null;
list = new ArrayList<Emp>();
while(rs.next()){
// get data
int id = rs.getInt("empno");
String ename = rs.getString("ename");
String job = rs.getString("job");
int mgr = rs.getInt("mgr");
Date hiredate = rs.getDate("HIREDATE");
int salary = rs.getInt("sal");
int bonus = rs.getInt("comm");
int deptno = rs.getInt("deptno");
// establish emp object , And the assignment
emp = new Emp();
emp.setId(id);
emp.setEname(ename);
emp.setJob(job);
emp.setMgr(mgr);
emp.setHiredate(hiredate);
emp.setSalary(salary);
emp.setBonus(bonus);
emp.setDeptno(deptno);
// Load collection
list.add(emp);
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}finally {
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();
}
}
}
return list;
}
/** * demonstration JDBC Tool class * @return */
public List<Emp> findAll2(){
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
List<Emp> list = null;
try {
conn = JDBCUtils.getConnection();
//3. Definition sql
String sql = "select * from emp";
//4. Access to perform sql The object of
stmt = conn.createStatement();
//5. perform sql
rs = stmt.executeQuery(sql);
//6. Traversal result set , Encapsulated object , Load collection
Emp emp = null;
list = new ArrayList<Emp>();
while(rs.next()){
int id = rs.getInt("empno");
String ename = rs.getString("ename");
String job = rs.getString("job");
int mgr = rs.getInt("mgr");
Date hiredate = rs.getDate("HIREDATE");
int salary = rs.getInt("sal");
int bonus = rs.getInt("comm");
int deptno = rs.getInt("deptno");
// establish emp object , And the assignment
emp = new Emp();
emp.setId(id);
emp.setEname(ename);
emp.setJob(job);
emp.setMgr(mgr);
emp.setHiredate(hiredate);
emp.setSalary(salary);
emp.setBonus(bonus);
emp.setDeptno(deptno);
// Load collection
list.add(emp);
}
} catch (SQLException e) {
e.printStackTrace();
}finally {
JDBCUtils.close(rs,stmt,conn);
}
return list;
}
}
SQL Inject
SQL Injection is one of the most common network attacks , It's not using the operating system BUG To achieve an attack , It's about the negligence of programmers , adopt SQL sentence , Login without account , Even tampering with the database .
select * from user where username = 'OR 1=1 -- and password= ';
This condition is bound to succeed
select * from user where username = ' ; Drop Database java9 -- and password= ';
How to solve sql Inject
- practice ：
- demand ：
- Enter the user name and password through the keyboard
- Determine whether the user has successfully logged in
- select * from user where username = “” and password = “”;
- If this sql There are query results , The successful , conversely , The failure
- step ：
- Create database tables user
CREATE TABLE USER(
id INT PRIMARY KEY AUTO_INCREMENT,
username VARCHAR(32),
PASSWORD VARCHAR(32)
);
INSERT INTO USER VALUES(NULL,‘zhangsan’,‘123’);
INSERT INTO USER VALUES(NULL,‘lisi’,‘234’);
package com.neusoft.jdbc1;
import com.neusoft.utils.JDBCUtils;
import java.sql.*;
import java.util.Scanner;
/** * practice ： * * demand ： * 1. Enter the user name and password through the keyboard * 2. Determine whether the user has successfully logged in */
public class JDBCDemo9 {
public static void main(String[] args) {
//1. Keyboard Entry , Accept user name and password
Scanner sc = new Scanner(System.in);
System.out.println(" Please enter a user name ：");
String username = sc.nextLine();
System.out.println(" Please input a password ：");
String password = sc.nextLine();
//2. Calling method
boolean flag = new JDBCDemo9().login2(username, password);
//3. Judge the result , Output different statements
if(flag){
// Login successful
System.out.println(" Login successful ！");
}else{
System.out.println(" Wrong user name or password ！");
}
}
/** * Login method */
public boolean login(String username ,String password){
if(username == null || password == null){
return false;
}
// Connect the database to determine whether the login is successful
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
//1. Get the connection
try {
conn = JDBCUtils.getConnection();
//2. Definition sql
String sql = "select * from user where username = '"+username+"' and password = '"+password+"' ";
System.out.println(sql);
//3. Access to perform sql The object of
stmt = conn.createStatement();
//4. Execute the query
rs = stmt.executeQuery(sql);
//5. Judge
/* if(rs.next()){// If there's a next line , Then return to true return true; }else{ return false; }*/
return rs.next();// If there's a next line , Then return to true
} catch (SQLException e) {
e.printStackTrace();
}finally {
JDBCUtils.close(rs,stmt,conn);
}
return false;
}
/** * Login method , Use PreparedStatement Realization */
public boolean login2(String username ,String password){
if(username == null || password == null){
return false;
}
// Connect the database to determine whether the login is successful
Connection conn = null;
PreparedStatement pstmt = null;
ResultSet rs = null;
//1. Get the connection
try {
conn = JDBCUtils.getConnection();
//2. Definition sql
String sql = "select * from user where username = ? and password = ?";
//3. Access to perform sql The object of
pstmt = conn.prepareStatement(sql);
// to ? assignment
pstmt.setString(1,username);
pstmt.setString(2,password);
//4. Execute the query , There is no need to pass on sql
rs = pstmt.executeQuery();
//5. Judge
/* if(rs.next()){// If there's a next line , Then return to true return true; }else{ return false; }*/
return rs.next();// If there's a next line , Then return to true
} catch (SQLException e) {
e.printStackTrace();
}finally {
JDBCUtils.close(rs,pstmt,conn);
}
return false;
}
}
JDBC Control the transaction ：
- Business ： A business operation with multiple steps . If the business operation is managed by a transaction , Then these multiple steps will either succeed at the same time , Or fail at the same time .
- operation ：
- Open transaction
- Commit transaction
- Roll back the transaction
- Use Connection Object to manage affairs
- Open transaction ：setAutoCommit(boolean autoCommit) ： Call this method to set the parameter to false, That is, start the transaction
- In execution sql Before opening the transaction
- Commit transaction ：commit()
- When all sql All commit transactions are completed
- Roll back the transaction ：rollback()
- stay catch Rollback transaction
package com.neusoft.jdbc1;
import com.neusoft.utils.JDBCUtils;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
/**
* The transaction operations
*/
public class JDBCDemo10 {
public static void main(String[] args) {
Connection conn = null;
PreparedStatement pstmt1 = null;
PreparedStatement pstmt2 = null;
try {
//1. Get the connection
conn = JDBCUtils.getConnection();
// Open transaction
conn.setAutoCommit(false);
//2. Definition sql
//2.1 Zhang San - 500
String sql1 = "update account set balance = balance - ? where id = ?";
//2.2 Li Si + 500
String sql2 = "update account set balance = balance + ? where id = ?";
//3. Access to perform sql object
pstmt1 = conn.prepareStatement(sql1);
pstmt2 = conn.prepareStatement(sql2);
//4. Set parameters
pstmt1.setDouble(1,500);
pstmt1.setInt(2,1);
pstmt2.setDouble(1,500);
pstmt2.setInt(2,3);
//5. perform sql
pstmt1.executeUpdate();
// Manual manufacturing abnormality
int i = 3/0;
pstmt2.executeUpdate();
// Commit transaction
conn.commit();
} catch (Exception e) {
// Transaction rollback
try {
if(conn != null) {
conn.rollback();
}
} catch (SQLException e1) {
e1.printStackTrace();
}
e.printStackTrace();
}finally {
JDBCUtils.close(pstmt1,conn);
JDBCUtils.close(pstmt2,conn);
}
}
}
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