JDBC JDBC

DriverManager： Used to manage JDBC Driven service class . The main function of using this class in the program is obtain Connection object , This class contains the following methods ：

public static synchronized Connection getConnection（String url,String user,String pass）throws SQLException
// This method obtains url The connection to the database 

Connection： representative Database connection object , Every Connection Represents a physical connection session . Want to access the database , You have to get a database connection first . The common methods of this interface are as follows .

Statement creatStatement()throws SQLExcetpion
// This method returns a Statement object 

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JDBC Programming steps （ Six steps ）

        1. The load driver

2. Get the connection

         3. Get database operation object

4. perform sql

        5. Process query result set

6. Release resources

1. Load database driver

Usually use Class Class forName（） Static method to load the driver . for example

Class.forName(driverClass)

In code driverClass Is the string corresponding to the database driver class .

load MYSQL The driver ：

Class.forName("com.mysql.cj.jdbc.Driver");

 2. Get the connection

adopt DriverManager Get database connection .

// Get database connection 
DriverManager.getConnection（String url,String user,String pass）;

URL： database

database URL Usually follow the following wording

jdbc:subprotocol:other stuff

above URL In writing jdbc Is constant , and subprotocol Specifies the driver that connects to a specific database , And then there's other stuff It's not fixed either . for example MYSQL Database URL It is written as follows ：

jdbc：mysql：//hostname：port/databasename

url What are the components of ：
            agreement ,IP, Port number , Resource name

for example ：  jdbc:mysql://localhost:3366/bjpowernode
            jdbc:mysql://   agreement
            localhost      IP Address
            3366           Port number
            chatroom    Database instance name  

3.  Get database operation object

adopt Connection objects creating Statement object .

Connection establish Statement There are three ways

creatStatement（）： Create basic Statement object 
prepareStatement（String sql）： Based on the incoming SQL Statement to create precompiled Statement object 
prepareCall（String sql）： Based on the incoming SQL Sentence creation CallableStatement object 

take 3.4. Operation merge ：

eg：

 Connection con= DriverManager.getConnection("jdbc:mysql://localhost:3306/xxx", "root", "123456");
                                                               // What you enter here is the database name xxx
        Statement state=con.createStatement();

 4. perform sql

Use Statement perform SQL sentence . be-all Statement There are three ways to execute SQL sentence .

execute（）： You can do anything SQL sentence . But it's troublesome .
executeUpdata（）： Mainly used for execution DML and DDL sentence . perform DML Statement to return by SQL Number of rows affected , perform DDL Statement returns 0.
executeQuery（）： Only query statements can be executed , After execution, it returns the query result ResultSet object .

5. Process query result set

If executed SQL Statement is a query statement , The execution structure will return a ResultSet object . The object contains SQL Structure of statement query , The program can operate the REsultSet Object to retrieve the query results .（ Get data as needed according to the situation ）

6. Release resources

Reclaim database resources , Including closing ResultSet,Statement and Connection And so on .