JDBC programming of MySQL

MySQL Of JDBC Programming

1. Conditions for database programming

• programing language : Java,C,C++,Python…
• database : Oracle,MySQL,SQLServer…
• Database driver package : Different databases , Different database driver packages are provided for different programming languages ,
  • Such as ：MySQL Provides Java Driver package mysql-connector-java, Need to be based on Java operation MySQL That is, you need the driver package . alike ,
    Based on Java operation Oracle Database is required Oracle Database driver package ojdbc .

2. JDBC Programming

JDBC, namely Java Database Connectivity,java Database connection , It's one for execution SQL Of the statement Java API( A fairly widely used term in computers Application Programming Interface Some functions are provided / Method / class , Programmers can call directly to complete some functions ), be called " database SDK"(software development kit, SDK Broader concept , In addition to providing API outside , There are also some executable programs ( Tools ) Auxiliary development / debugging …), You can use these API Convenient access to database server .

about MySQL/Oracle/SQLServer The client side. / Server structured program , Then the operation database is Through the official command line client / Graphical interface / Code Which one of them ? Now the mainstream way to operate the database is through code manipulation .

In the early days, different databases provided API It's not the same , Very unfriendly to programmers , therefore Java Provide a set of " standard " Interface system of , Let these database manufacturers . Provided API All go to Java In this interface system , So programmers only need to master Java This article API You can adapt to all common mainstream databases .Java This set of operation database API, It's called JDBC.

3. JDBC working principle

JDBC It provides a unified access method for a variety of relational databases , Access as a vendor specific database API A high-level abstraction of , It mainly contains some general interface classes

JDBC Access the database hierarchy :

JDBC advantage ：

• Java Language access database operation is completely oriented to abstract interface programming
• The development of database applications is not limited to the specific database manufacturers API
• The portability of the program is greatly enhanced

4. JDBC Use

4.1 Operating the database - Insert

1. To operate the database , First, connect to the database , To connect to the database , You have to describe the location of the database . stay JDBC in , Use DataSource This class describes MySQL Server location ,

   //DataSource It's a interface, Cannot instantiate directly . and MysqlDataSource Is to achieve DataSource, This class is from the driver package .
   // This operation is  -  Upward transformation 
   DataSource dataSource = new MysqlDataSource();
   // Connect to server  -  Move down 
   ((MysqlDataSource)dataSource).setUrl("jdbc:mysql://127.0.0.1:3306/java104?characterEncoding=utf8&useSSL=false");
   

   Someone here will have questions , Why not use it directly MysqlDataSource To instantiate objects ? Isn't this very convenient ?

   MysqlDataSource dataSource = new MysqlDataSource();
   dataSource.setUrl();
   

   Although there is no difference between the two ways of writing . But in the actual development, we may see the first way more .

   • In the first way , Got The data source is DataSource type . Write other code later , Method / class , If you use a data source , The type of holding is also DataSource type ,DataSource yes General type , It can refer to any database . Once needed in the future Change database , Code changes are very small , Just change the instantiation code , No other code changes .
   • The second way , The data source obtained is MysqlDataSource type . Other subsequent codes , Method / class , If you use a data source , The type of holding is MysqlDataSource, and MysqlDataSource Just for MySQL The type of . Once the database is replaced in the future , You may need to put the scattered in all parts of the code MysqIDataSource Change the type .

   The first method greatly improves the maintainability of the code , Expansibility .

   //MySQL Data connection URL The parameter format is as follows ：
   jdbc:mysql:// Server address : port / Database name ? Parameter name = Parameter values 
   

   

​ Enter your username and password :

((MysqlDataSource)dataSource).setUser("root");
((MysqlDataSource)dataSource).setPassword("123456");

So pass IP Address , Port number , Database name , The user name and password describe the location of the database .

2. Create a connection with the database server

In network communication , There are two styles , One is ’ There is a connection ’, amount to " Make a phone call "; The other is ’ There is no connection ’, amount to " Send wechat ".

The data is based on " There is a connection " The way , Mainly before communication , First, check whether the communication link is smooth , There's a downside , Connections need to be managed , The unused connections need to be released in time ( Like on the phone , Forget to hang up , As a result, the connection cannot be disconnected , The phone bill is kept slowly ~~).

//  Import import java.sql.Connection Under bag Connection class 
Connection connection = dataSource.getConnection();
System.out.println(connection);
// If the output object is  [email protected]  Description of the connection is successful 
// Also pay attention to throwing exceptions   Import import java.sql.SQLException; 

3. Operating the database

Use SQL sentence , utilize JDBC To manipulate the database , The essence is still to use SQL To manipulate the database

//  Create database 
create table student(id int primary key, name varchar(20));

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

adopt PreparedStatement Object to tell SQL The statement executed , Of this object SQL Is from this string .

PreparedStatement statement = connection.prepareStatement(sql);

You can also fill in the following way :

Scanner in = new Scanner(System.in);
System.out.println(" Please enter the student number :");
int id = in.nextInt();
System.out.println(" Please enter a name :");
String name = in.next();
String sql = "insert into student values(?, ?);";//?  As a placeholder 
PreparedStatement statement = connection.prepareStatement(sql);
statement.setInt(1, id); //  The default from the 1 Start 
statement.setString(2, name);

4. perform SQL sentence

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

here insert,update,delete It's through executeUpdate To execute , The return value is an integer , This operation affects several lines ,select It's through executeQuery To execute .

5. disconnect

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

notes : After the creation of the first release

4.2 operation

4.2.1 Modify the record

 public static void main(String[] args) throws SQLException {
    
        //1.  Find the data source 
        DataSource dataSource = new MysqlDataSource();
        ((MysqlDataSource)dataSource).setUrl("jdbc:mysql://127.0.0.1:3306/java_learn?characterEncoding=utf8&useSSL=false");
        ((MysqlDataSource)dataSource).setUser("root");
        ((MysqlDataSource)dataSource).setPassword("123456");

        //2.  Establishing a connection 
        Connection connection = dataSource.getConnection();

        //3.  Enter modification information 
        Scanner in = new Scanner(System.in);
        System.out.println(" Please enter the student ID of the student you want to modify :");
        int id = in.nextInt();
        System.out.println(" The student's revised name :");
        String name = in.next();

        //3.  structure SQL sentence 
        String sql = "update student set name = ? where id = ?";
        PreparedStatement statement = connection.prepareStatement(sql);
        statement.setInt(1,id);
        statement.setString(2, name);

        //4.  perform SQL
        int n = statement.executeUpdate();
        System.out.println(n);

        //5.  close resource 
        statement.close();
        connection.close();

    }

4.2.2 Delete record

public static void main(String[] args) throws SQLException {
    
    //1.  Find the data source 
    DataSource dataSource = new MysqlDataSource();
    ((MysqlDataSource)dataSource).setUrl("jdbc:mysql://127.0.0.1:3306/java_learn?characterEncoding=utf8&useSSL=false");
    ((MysqlDataSource)dataSource).setUser("root");
    ((MysqlDataSource)dataSource).setPassword("123456");

    //2.  Create connection 
    Connection connection = dataSource.getConnection();

    //3.  Enter information about deleting records 
    Scanner in = new Scanner(System.in);
    System.out.println(" Please enter and delete student ID :");
    int id = in.nextInt();

    //4.  structure SQL
    String sql = "delete from student where id = ?";
    PreparedStatement statement = connection.prepareStatement(sql);
    statement.setInt(1, id);

    //5.  perform SQL
    int n = statement.executeUpdate();
    System.out.println(n);

    //6.  close resource 
    statement.close();
    connection.close();
}

4.2.3 find record

    public static void main(String[] args) throws SQLException {
    
        //1.  create data source 
        DataSource dataSource = new MysqlDataSource();
        ((MysqlDataSource)dataSource).setUrl("jdbc:mysql://127.0.0.1:3306/java_learn?characterEncoding=utf8&useSSL=false");
        ((MysqlDataSource)dataSource).setUser("root");
        ((MysqlDataSource)dataSource).setPassword("123456");

        //2.  Establish connection with database 
        Connection connection = dataSource.getConnection();

        //3.  No need to input 

        //4.  structure SQL
        String sql = "select * from student";
        PreparedStatement statement = connection.prepareStatement(sql);

        //5.  perform SQL
        //executeQuery The return value of ResultSet object ,  Think of it as a   A temporary table 
        ResultSet resultSet = statement.executeQuery();

        //6.  Traversal result set 
        // hold  resultSet  As an iterator 
        while (resultSet.next()) {
    
            //  adopt getXXX  Method ,  To get 

            //  take id, id The type is int,  Use getInt
            int id = resultSet.getInt("id");
            // take name,  The type is String  Use getString
            String name = resultSet.getString("name");
            System.out.println(id + ":" + name);
        }

        //7.  close resource 
        statement.close();
        connection.close();
    }

4.2.4 insert record

    public static void main(String[] args) throws SQLException {
    
        //1.  Get the database location 
        DataSource dataSource = new MysqlDataSource();
        ((MysqlDataSource)dataSource).setUrl("jdbc:mysql://127.0.0.1:3306/java_learn?characterEncoding=utf8&useSSL=false");
        ((MysqlDataSource)dataSource).setUser("root");
        ((MysqlDataSource)dataSource).setPassword("123456");

        //2.  Connect to database 
        Connection connection = dataSource.getConnection();
        System.out.println(connection);

        //3.  Use SQL sentence , utilize JDBC To manipulate the database , The essence is still through SQL To operate 
        /*String sql = "insert into student values(3, ' Zhang San ');";*/
        
        Scanner in = new Scanner(System.in);
        System.out.println(" Please enter the student number :");
        int id = in.nextInt();
        System.out.println(" Please enter a name :");
        String name = in.next();
        String sql = "insert into student values(?, ?);";
        PreparedStatement statement = connection.prepareStatement(sql);

        statement.setInt(1, id);
        statement.setString(2, name);
        
        //4.  perform SQL sentence 
        // insert,update,delete It's through  executeUpdate  To execute 
        // select  It's through  executeQuery  To execute 
        //  The return value is an integer ,  This operation affects several lines 
        int n = statement.executeUpdate();
        System.out.println(n);
        
        //5.  disconnect 
        statement.close();
        connection.close();
    }

4.3 Database connection

Connection The interface implementation class is provided by the database , obtain Connection Objects usually have two ways :

• adopt DriverManager（ Driver management ） Static method to get

//  load JDBC The driver 
Class.forName("com.mysql.jdbc.Driver");
//  Create database connection 
Connection connection = DriverManager.getConnection(url);

• adopt DataSource（ data source ） Object acquisition . It will be used in practical application DataSource object

DataSource dataSource = new MysqlDataSource();
((MysqlDataSource)dataSource).setUrl("url");
((MysqlDataSource)dataSource).setUser("root");
((MysqlDataSource)dataSource).setPassword("123456");
Connection connection = dataSource.getConnection();

The difference :

1. DriverManager Class to get Connection Connect , yes Can't reuse Of , Every time you release resources after use , adopt connection.close() Is to close the physical connection .
2. DataSource Provide connection pool support . When the connection pool is initialized, a certain number of database connections will be created , These connections are Reusable , Every time you use the database connection , Release resource call connection.close() All are take Conncetion Connection object recycling .

4.4 Statement object

Statement The object is mainly to SQL Statements are sent to the database .JDBC API There are mainly three kinds of Statement object

The most commonly used in actual development is PreparedStatement object , The following is a summary :

Return value :

• executeQuery() Method returns a single The result set , Usually used for select sentence
• executeUpdate() Method return value is An integer , Indicates the number of lines affected , Usually used for update、insert、delete sentence

4.5 ResultSet object

ResultSet Object, which is called the result set , It represents compliance with SQL All lines of the statement condition , And it passes through a set of getXXX Method provides
Access to the data in these rows .

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Return value :

• executeQuery() Method returns a single The result set , Usually used for select sentence
• executeUpdate() Method return value is An integer , Indicates the number of lines affected , Usually used for update、insert、delete sentence

4.5 ResultSet object

ResultSet Object, which is called the result set , It represents compliance with SQL All lines of the statement condition , And it passes through a set of getXXX Method provides
Access to the data in these rows .

ResultSet The data in the are arranged row by row , Each row has multiple fields , And there are A record pointer , The data row indicated by the pointer is called the current data row , We Only the current data row can be operated . If we want to get a record , Then use ResultSet Of next() Method , If we want to get ResultSet Inside All records , It should be Use while loop