JDBC programming of MySQL database

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This article will introduce JDBC Programming ,JDBC(Java DataBase Connectivity,java Database connection ) It's one for execution SQL Of the statement Java API, It can provide unified access for a variety of relational databases , It's used by a group Java Language written classes and interfaces .

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1.JDBC Front work

1.1 Get ready MySQL Drive pack

MySQL Of jdbc We can download the driver package on the official website , We can maven Central warehouse download , This maven What is the central warehouse ？ You can understand it as “ The app store ” Software , Its function is similar to that of the app store , It's just that there are mobile apps in the mobile app store , and maven There are many in the central warehouse API And dependency packages .

Now? MySQL Has been Oracle Acquired ,Oracle Of “ table manners ” It's a little ugly , You can find it on the official website , But I feel maven The central warehouse is better , So we arrived maven Central warehouse download jdbc Drive pack .

website ：maven The central warehouse

First step , Click the website to enter maven The central warehouse .

The second step , Search for MySQL, Choose the one shown below .

The third step , Click to enter , Find the corresponding large version jdbc Drive pack , If your MySQL yes 5 Version of the driver package also choose 5 Version of , Of course if your MySQL yes 8 edition , Then choose your driver package 8 edition .

my MySQL yes 5 So I choose the larger version as 5 Driver package .

Step four , Click in , Follow the diagram below , Download the driver package .

After downloading, our driver package is ready .

1.2 Create project

Use the compiler to create a project , After the project is created , Follow the steps below ：

First step , Create a directory , Name at will , It might as well be called lib Catalog .

The second step , Copy the downloaded driver package to this directory .

The third step , set an option , Right click the directory that you just created and copied the driver package , find As a Lib…


In this way, our driver package will be imported into our project , Then we can write jdbc Code. .

2.JDBC Programming steps

2.1 create data source DataSource

First step , establish DataSource object , To describe where the database is .

DataSource dataSource = new MysqlDataSource();

among DataSource by java.sql One of the inside jdbc Interface ,MysqlDataSource It comes from an implementation in the driver package we downloaded DataSource The class of the interface .

The second step , Set the “ Location ”(URL), Login database account name and password .

        // Set the address of the database 
        ((MysqlDataSource)dataSource).setURL("jdbc:mysql://127.0.0.1:3306/jdbctest/characterEncoding=utf8&useSSL=false");
        // Set the account name for logging into the database 
        ((MysqlDataSource)dataSource).setUser("root");
        // Set the password to log in to the database 
        ((MysqlDataSource)dataSource).setPassword("123456");

jdbc:mysql://127.0.0.1:3306/jdbctest?characterEncoding=utf8&useSSL=false It's just one. URL, Also called unique resource locator .
jdbc:mysql It means that we should url Is used for jdbc mysql Of URL, Because there are many databases , More than jdbc A kind of , So it needs to be subdivided .

Specific meaning independent comparison ：URL Type declaration :// The address of the database / Database name ? Character set encoding & Is it encrypted .

2.2 Connect to database

The third step , Establish a connection with the server , Create a data source DataSource After the object , Calling the getConnection() Method , obtain java.sql.Connection object , This will establish a connection with the database .

Connection connection = dataSource.getConnection();

2.3 Construct and execute sql sentence （ Insert operation as an example ）

Step four , structure sql Statement string , And wrap the statement as PreparedStatement object , That is to call Connection Object's prepareStatement Method , Parameter is sql character string , Will return a PreparedStatement object , Then we call PreparedStatement Object executeUpdate Method or executeQuery Method execution sql sentence .

Let's take the insertion operation as an example .

        // Operating the database   The key is to construct sql sentence 
        //jdbc  Tectonic sql Statements do not need to be accompanied by ;
        String sql = "insert into student values(1, ' Zhang San ')";
        // take sql String wrapped into a statement object , Indicates to be executed sql The object of 
        PreparedStatement statement = connection.prepareStatement(sql);

        // perform sql
        // If it is to be implemented sql Statement operation is insert, update, delete, Then use executeUpdate Method execution , The return value is the number of rows that affect the data 
        // If it is to be implemented sql Statement operation is select, Then use executeQuery Method execution 
        int ret = statement.executeUpdate();

among , If it is to be implemented sql Statement operation is insert, update, delete, Then use executeUpdate Method execution , The return value is the number of rows that affect the data , If it is to be implemented sql Statement operation is select, Then use executeQuery Method execution , The return value is one ResultSet Result table object .

2.4 Release resources in time

Step five , Release resources , We are finished sql You need to release resources in time after the statement , stay JDBC Programming , The most common classes or interfaces that need to be released are three , Namely Connection,PreparedStatement,ResultSet, The first two of them are jdbc It has been used in the insert operation , And the last one , namely ResultSet, It is used when executing query statements , call executeQuery Method after executing the query statement , Will return a “ A temporary table ”, The “ A temporary table ” The results of the query are stored on , We can get the result of querying the database by traversing the result table .

// here sql The statement has been executed , Need to release resources 
statement.close();
connection.close();

Use jdbc Program to insert all the code ：

import com.mysql.jdbc.jdbc2.optional.MysqlDataSource;

import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.Scanner;

public class TestJdbc {
    

    public static void main(String[] args) throws SQLException {
    
        DataSource dataSource = new MysqlDataSource();
        // Set the address of the database 
        ((MysqlDataSource)dataSource).setURL("jdbc:mysql://127.0.0.1:3306/jdbctest?characterEncoding=utf8&useSSL=false");
        // Set the account name for logging into the database 
        ((MysqlDataSource)dataSource).setUser("root");
        // Set the password to log in to the database 
        ((MysqlDataSource)dataSource).setPassword("123456");

        // Establishing a connection 
        Connection connection = dataSource.getConnection();

        // Operating the database   The key is to construct sql sentence 
        //jdbc  Tectonic sql Statements do not need to be accompanied by ;
        String sql = "insert into student values(1, ' Zhang San ')";
        // take sql String wrapped into a statement object , Indicates to be executed sql The object of 
        PreparedStatement statement = connection.prepareStatement(sql);

        // perform sql
        // If it is to be implemented sql Statement operation is insert, update, delete, Then use executeUpdate Method execution , The return value is the number of rows that affect the data 
        // If it is to be implemented sql Statement operation is select, Then use executeQuery Method execution 
        int ret = statement.executeUpdate();

        // here sql The statement has been executed , Need to release resources 
        statement.close();
        connection.close();
    }
}

Running results , We observe by querying the results of the tables in the database ：

mysql> create database jdbctest;
Query OK, 1 row affected (0.01 sec)

mysql> use jdbctest;
Database changed
mysql> create table student(id int, name varchar(20));
Query OK, 0 rows affected (0.02 sec)

mysql> show tables;
+--------------------+
| Tables_in_jdbctest |
+--------------------+
| student            |
+--------------------+
1 row in set (0.00 sec)
--  perform jdbc Query after code 
mysql> select * from student;
+------+--------+
| id   | name   |
+------+--------+
|    1 |  Zhang San    |
+------+--------+
1 row in set (0.00 sec)

Program run results , Express 1 The line has been affected .

2.5 Don't write dead code （ Take insertion, for example ）

We found our sql The sentence is completely written , This is not good , We can use the input operation to let users input information for insertion , Then we need to use Scanner The class .

After we get the information entered by the user , We need to integrate information , The easiest way to think of is string splicing , But it has the following disadvantages , First, it is easy to make mistakes , Especially when there are many single and double quotation marks , Second, it's not safe , Hackers can use sql Injection to modify the database .

So a better way is to sql The information to be input in the string uses ? Instead of or called space occupying , And then through PreparedStatement Medium setXXX A series of methods to set each ? What is the content of .

This series of methods , First parameter representation sql How many objects to be executed ?, The second parameter indicates that this ? What to set up . such as ：

        // Operating the database   The key is to construct sql sentence 
        //jdbc  Tectonic sql Statements do not need to be accompanied by ;
        String sql = "insert into student values(?, ?)";
        // take sql String wrapped into a statement object , Indicates to be executed sql The object of 
        PreparedStatement statement = connection.prepareStatement(sql);
        statement.setInt(1, id);
        statement.setString(2, name);

Complete code ：jdbc Insert operation source code

Running results ：

Database query results ：

mysql> select * from student;
+------+--------+
| id   | name   |
+------+--------+
|    1 |  Zhang San    |
|    2 |  Li Si    |
+------+--------+
2 rows in set (0.00 sec)

2.6JDBC Delete , update operation

stay jdbc Programming , Delete operation and update operation , Its steps are exactly the same as the insertion operation , It's just constructed sql Statements are different , Everything else is the same .

Delete operation key code ：

        // User input 
        System.out.println(" Please enter the student number to be deleted ：");
        int id = sc.nextInt();

        // Operating the database   The key is to construct sql sentence 
        //jdbc  Tectonic sql Statements do not need to be accompanied by ;
        String sql = "delete from student where id = ?";
        PreparedStatement statement = connection.prepareStatement(sql);
        statement.setInt(1, id);
        System.out.println("statement" + statement);

jdbc Delete operation complete code ： Source code address

Program run results ：

Database query results ：

mysql> select * from student;
+------+--------+
| id   | name   |
+------+--------+
|    1 |  Zhang San    |
+------+--------+
1 row in set (0.00 sec)

Update operation key code ：

        // User input   What needs to be revised id  And the modified name 
        System.out.println(" Please enter the student number to be modified ：");
        int id = sc.nextInt();
        sc.nextLine();
        System.out.println(" Please enter the modified name ：");
        String afterName = sc.nextLine();

        // Operating the database   The key is to construct sql sentence 
        //jdbc  Tectonic sql Statements do not need to be accompanied by ;
        String sql = "update student set name = ? where id = ?";
        PreparedStatement statement = connection.prepareStatement(sql);
        statement.setString(1, afterName);
        statement.setInt(2, id);
        System.out.println("statement" + statement);

jdbc Update operation complete code ： Source code address

Program run results ：

Database query results ：

mysql> select * from student;
+------+--------+
| id   | name   |
+------+--------+
|    1 |  Wang Wu    |
+------+--------+
1 row in set (0.00 sec)

2.7JDBC Query operation

jdbc The query operation of is a little different from the insert, delete and update operation , Execute the query sql Statement is called executeQuery Method to execute the statement , And it will bring back the query results , We can obtain the results of the query through operations similar to iterators , After using this result set, you need to release it .

Key code ：

        // Operating the database   The key is to construct sql sentence 
        //jdbc  Tectonic sql Statements do not need to be accompanied by ;
        String sql = "select * from student";
        PreparedStatement statement = connection.prepareStatement(sql);

        // perform sql  The query operation does not return int  It's a temporary table   Use ResultSet Object represents this temporary table 
        ResultSet ret = statement.executeQuery();

        // Convenient result set 
        // Expected result format 
// +------+--------+
// | id | name |
// +------+--------+
// | 1 |  Wang Wu  |
// +------+--------+
        while (ret.next()) {
    
            int id = ret.getInt("id");
            String name = ret.getString("name");
            System.out.println("id:" + id + ", name:" + name);
        }
        // close resource 
        ret.close();
        statement.close();
        connection.close();

jdbc Query operation complete code ： Source code address

Program run results ：

Okay ,JDBC The whole content of is almost these , All complete code links ： Address .

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Next up ： Database transactions

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