JDBC details

JDBC The essence ： An officially defined set of rules for operating all relational databases , Interface . Each database manufacturer to implement this set of interface , Provide database driver .jar package . We can use this interface , To carry out .jar The implementation class in the package .

1、 Implementation steps ：

① Import jar package ： Create under Project lib package , take jar Copy the file to the package , Then right click the package , Select Add to Library

② Registration drive ：Class.forName(“com.mysql.jdbc.Driver”); High version database “com.mysql.cj.jdbc.Driver”

③ Get database connection object          

Connection  c = DriverManager.getConnection(“jdbc:mysql://localhost:3306/ Database name ”,“ user name ”,“ password ”);

  If it's connected to this machine , The default port number is 3306, be localhost:3306 It can be omitted , Slashes cannot be omitted .

④ Definition sql：String sql = “updect Table name set Column = value ”

⑤ Access to perform sql Object of statement Statement：Statement stmt = c.createStatement();

⑥ perform sal, Receive return result ：int num = stmt.executeUpdate(sql);

⑦ Processing results ：System.out.print(num);

⑧ Release resources ：stmt.close();        c.close();

JDBC There is a garbled code solution when connecting to the database

url ="jdbc:mysql://localhost:3306/mydb?characterEncoding=utf8&serverTimezone=Asia/Shanghai";

2、 Detailed explanation of each class ：

Ⅰ、DriverManager class

effect ： Drive management objects       // Drag me Buy a wife

① Registration drive

Method 1 ： Call directly DriverManager Class

               static void registerDriver(Driver driver)//ruai Level dead special

  Method 2  ：Class.forName(“com.mysql.jdbc.Driver”);

                  take Driver Class loading near memory , There is a static code block

Its essence is execution DriverManager Methods in class static void registerDriver​(Driver driver) Do driver registration .

② Get database connection     // But milk can be new

static Connection

getConnection(String url,String user, String password)

url： Specify the path of the connection

url grammar ：jdbc:mysql://ip( domain name ): Port number / Database name

                If it is connected to the local MySQL,url The bold part in the middle can be omitted , But the slash at both ends cannot be omitted

user and password： User name and password .

Ⅱ、Connection Interface ： Database connection object

Function one , Create an implementation sql The object of the class of the statement

Statement	createStatement​()	Get the transmitter , Is used to SQL Statements are sent to the database .
PreparedStatement	prepareStatement​(String sql)	Create a Transmitters , To parameterize SQL Statements are sent to the database .

Function 2 , Manage affairs

void	setAutoCommit​(boolean autoCommit)	Set the parameter to fales, Open transaction
void	commit​()	Commit transaction
void	rollback​()	Roll back

Ⅲ、Statement Interface ： perform sql Object of statement , Transmitters

boolean	execute​(String sql) //A But death kei I'm special	Can execute any sql
int	executeUpdate​(String sql）	perform INSERT , UPDATE , or DELETE Statement , Returns the number of rows affected . perhaps 0, Such as SQL DDL Of the statement SQL sentence .
ResultSet	executeQuery​(String sql) // Kuairi	perform DQL Query statement ,select

Ⅳ、ResultSet Interface ： Result set object , Encapsulate query results // Swiss ra Ott

boolean	next（）	Move the cursor down one line from the current position . The return value is  false Indicates that there is no data in the row where the cursor is located
T	getXXX(int/String  num)	This method gets the contents of the line ,XXX Represents the type of data obtained , There are many kinds of overloads
Object()	getObject(int/String  num)	The ultimate solution

There are probably two types of parameters ：

1. int： Represents the number of the column , from 1 Start , Columns such as getString(1)
2. String： Represents the name of the column . Such as getString(“id”)

When using this class to traverse the contents of the database , Encapsulate the contents of the database as objects , Then load it into the collection , Ergodic set

Ⅴ、PreparedStatement Interface ：Statement Subclasses of , More powerful

sql Inject ： In splicing sql when , Somewhat sql Special keywords participate in string splicing , Can cause security problems .

PreparedStatement

prepareStatement​(String sql)

Incoming sal Statement parameters use ? Place holder

Use PreparedStatement The process of operating the database ：

① Import jar package

② Registration drive

③ Get database connection object         

④ Definition sql：sql Statement parameters use ? Instead of

⑤ Use the database connection object to get the transmitter PrepareStatement(String sql)： to ? The method of assignment ：

        setXXX( Parameter one , Parameter two )//XXX representative ? The type of

                 Parameter one ：? The location of （int type ）, from 1 Start

                 Parameter two ：? Value , String type

        setObject() The ultimate solution

⑥ perform sql, Receive return result , There is no need to pass parameters

boolean	execute（） //A But death kei I'm special	Can execute any sql
int	executeUpdate()	perform INSERT , UPDATE , or DELETE Statement , Returns the number of rows affected . perhaps 0, Such as SQL DDL Of the statement SQL sentence .
ResultSet	executeQuery()	perform DQL Query statement ,select

⑦ Processing results

⑧ Release resources