MySQL JDBC programming

Blog home page ：Lockey-s Welcome to thumb up Collection Leaving a message. Welcome to discuss ！ This paper is written by 【Lockey-s】 original ！ First appeared in CSDN Because the blogger is learning Xiaobai one , There are bound to be mistakes , If you have any questions, please leave a message in the comment area to point out , Thank you no all ！ Boutique column （ Update from time to time ）

Concept

JDBC Is a kind and method , It's a kind of execution SQL Of the statement Java API, It can realize unified access to a variety of databases , It's like the monitor agreeing on the statistical format of the data . The advantage is that the portability of the program is greatly enhanced , Not limited to specific database vendors API.

Use

Introduce dependencies

Introducing dependencies requires MySQL Driver package （ hold MySQL Self api To convert into JDBC style ）.

Download the driver package

The best way is to MySQL Official website , however MySQL By Oracle After the acquisition , It's hard to find , So you can go maven The central warehouse To install , And then the search MySQL, The first result is ：
Then click in to choose 5.1.x Series is OK , Because of my MySQL yes 5.7 Series of , So it uses 5 Series of , If MySQL yes 8 Series of , Then use 8 Series of , Be sure to communicate with your MySQL Version match , If it doesn't match , May lead to bug ：
Then click the previous version number , Then enter the page ：
Then order that jar Button , Will download the driver package ,jar It's written by others class file .

Import into project

1. After entering the project , You can create a directory , What's created here is lib
   
2. Just download jar Copy the file to the directory just now , Directly copy the file and click lib, Then paste it
   
3. Right click the directory just now , There is one add as library Then click this option , That's what makes jar The package is introduced into the project , Items will be read jar Inside .class file . Otherwise the code will not find jar There are some classes .

Write code

JDBC Basic process of insertion

establish DataSource object

This object describes where the database server is . The code is as follows ：

DataSource dataSource = new MysqlDataSource();

among DataSource yes JDBC The interface with , hinder MysqlDataSource From previously downloaded jar package , It is an upward transformation .

Set the database address ： The database address here can be copied directly ,127.0.0.1 Indicating the machine IP ,3306 It's the port number ,user It's the database name , Followed by the character set ,SSL Is whether the transmission process is encrypted .

((MysqlDataSource) dataSource).setURL("jdbc:mysql://127.0.0.1:3306/user?characterEncoding=utf8&useSSL=false");

Set the database user name ：

((MysqlDataSource) dataSource).setUser();

Set the password of the database ：

((MysqlDataSource) dataSource).setPassword();

It can also be written like this , In this way, there is no transformation ：

MysqlDataSource dataSource = new MysqlDataSource();
dataSource.setURL();
dataSource.setUser();
dataSource.setPassword();

Because the instance held in our code is DataSource type , If other codes need to be used later DataSource , Relevant parameters are also DataSource, The code hardly needs to be changed , Namely “ Low coupling ”.

Establish a connection with the database server

adopt dataSource.Connection To establish a connection ：

Connection connection = dataSource.getConnection();

It should be noted that , It uses java.sql Inside Connection：

Operating the database

1. When operating the database , The key is to construct a SQL sentence , structure String Class , Don't write a semicolon ：

String sql = "insert into student values(1,' Zhang San ')";

2. And then through Connection Inside prepareStatement Method , hold String Style sql The sentence is translated into JDBC The object in it ：

PreparedStatement statement = connection.prepareStatement(sql);

3. perform sql , If it is inserted , Namely executeUpdate, If you choose , Namely executeQuery：

int line = statement.executeUpdate();

there line Is the return value , Just a few lines were affected .

4. Release resources , Create first and release later , After the creation of the first release .

statement.close();
connection.close();

Execute code , The return value is 1, It means that one line has been affected ：

After three executions , Return to the database to view the contents , Found three more records ：

The user enters the content to insert

adopt Scanner To let users input ：

int id = scanner.nextInt();
String name = scanner.next();

After user input , hold id, and name Replace the sql Statement inside , stay sql sentence Of values In the middle ？ Instead of ：

String sql1 = "insert into student values(?,?)";

these two items. ？ It means that the value of the current field has not been determined , Take a seat first , Reuse PreparedStatement Of setXXX Replace with a series of methods ：

PreparedStatement statement1 = connection.prepareStatement(sql1);
statement1.setInt(1,id);
statement1.setString(2,name);

there 1,2 It's the subscript , from 1 Start calculating , Take the first one. ？ Replace with id Value , Put the second one ？ Replace with name Value . Then print the replacement object ：

System.out.println("statement1" + statement1);

Assembled SQL The output value of is below ：


In the database lisi Also successfully inserted .

JDBC Basic process of deletion

1. create data source ：

DataSource dataSource = new MysqlDataSource();
((MysqlDataSource)dataSource).setURL("jdbc:mysql://127.0.0.1:3306/user?characterEncoding=utf8&useSSL=false");
((MysqlDataSource)dataSource).setUser("root");
((MysqlDataSource)dataSource).setPassword("");

2. Establishing a connection ：

Connection connection = dataSource.getConnection();

3. User input id：

Scanner scanner = new Scanner(System.in);
int id = scanner.nextInt();

4. assemble sql sentence ：

String sql = "delete from student where id = ?";
PreparedStatement statement = connection.prepareStatement(sql);
statement.setInt(1, id);

5. perform sql ：

int line = statement.executeUpdate();
System.out.println(line);

6. Recycle resources ：

statement.close();
connection.close();

The operation results are as follows ：

The database data is as follows ：

You can see id by 1 All of them have been deleted .

JDBC The basic process of updating

1. create data source ：

DataSource dataSource = new MysqlDataSource();
((MysqlDataSource)dataSource).setURL("jdbc:mysql://127.0.0.1:3306/user?characterEncoding=utf8&useSSL=false");
((MysqlDataSource)dataSource).setUser("root");
((MysqlDataSource)dataSource).setPassword("");

2. Establishing a connection

Connection connection = dataSource.getConnection();

3. User input id

Scanner scanner = new Scanner(System.in);
int id = scanner.nextInt();
String name = scanner.next();

4. assemble sql sentence

String sql = "update student set name = ? where id = ?";
PreparedStatement statement = connection.prepareStatement(sql);
statement.setString(1, name);
statement.setInt(2, id);
System.out.println("statement" + statement);

5. perform sql

int line = statement.executeUpdate();
System.out.println("line" + line);

6. Recycle resources

statement.close();
connection.close();

In the database id be equal to 2 The name of is ：lisi

The results are as follows ：

You can see that the data in the database has also been modified ：

JDBC Basic process of searching

1. create data source ：

DataSource dataSource = new MysqlDataSource();
((MysqlDataSource)dataSource).setURL("jdbc:mysql://127.0.0.1:3306/user?characterEncoding=utf8&useSSL=false");
((MysqlDataSource)dataSource).setUser("root");
((MysqlDataSource)dataSource).setPassword("");

2. Establishing a connection

Connection connection = dataSource.getConnection();

3. assemble sql sentence

String sql = "select * from student order by id";
PreparedStatement statement = connection.prepareStatement(sql);

4. perform sql, Because the query operation returns a temporary table , So use executeQuery, The returned temporary table is used ResultSet To express .

ResultSet resultSet = statement.executeQuery();

5. Traverse the result set , That is, traverse the returned temporary table , Get each returned row first , Then get every column of this result .

while (resultSet.next()) {
    
    // First, get the columns for one row 
    int id = resultSet.getInt("id");
    String name = resultSet.getString("name");
    System.out.println("id= " + id + " ,name= " + name);
}

6. close resource

resultSet.close();
statement.close();
connection.close();

The database resources are as follows ：

Code execution result ( Press id Sequential arrangement ) as follows ：