JDBC tutorial

JDBC Concept

1.1 JDBC Concept
JDBC Is the use of Java A set of language operation relational database API. Full name ：( Java DataBase Connectivity ) Java Database connection .

1.2 JDBC The essence ：

• official （sun company ） A set of rules defined to operate all relational databases , Interface
• Each database manufacturer to implement this set of interface , Provide database driver jar package
• We can use this interface （JDBC） Programming , The code that actually executes is the driver jar The implementation class in the package

1.3 Benefits of use

• Each database manufacturer uses the same interface ,Java The code does not need to be developed separately for different databases
• The underlying database can be replaced at any time , Access database Java The code is basically unchanged

JDBC introduction

Use steps

 First step ： To write Java Code 

 The second step ：Java Code will SQL Send to MySQL Server side 

 The third step ：MySQL The server receives SQL Statement and execute the SQL sentence 

 Step four ： take SQL The result of statement execution is returned to Java Code 

step1： Create a new empty project

Create a module




newly build lib package

step2: Import driver package
take mysql The driver package is placed under the module lib Catalog （ Name at will ） Next , And put the jar Add package as library file

take mysql-connector-java-5.1.48.jar Put it in lib Inside the directory ,Ctrl+V Put it in for

Make it effective

When adding as a library file , There are three options

• Global Library ： Global availability
• Project Library : The project works
• Module Library ： Module valid

step3: stay src Create a class

/** * JDBC Quick start  */
public class JDBCDemo {
    

    public static void main(String[] args) throws Exception {
    
        //1.  Registration drive 
        //Class.forName("com.mysql.jdbc.Driver");
        //2.  Get the connection 
        String url = "jdbc:mysql://127.0.0.1:3306/db1";
        String username = "root";
        String password = "12348765";
        Connection conn = DriverManager.getConnection(url, username, password);
        //3.  Definition sql
        String sql = "update account set money = 2000 where id = 1";
        //4.  Access to perform sql The object of  Statement
        Statement stmt = conn.createStatement();
        //5.  perform sql
        int count = ((Statement) stmt).executeUpdate(sql);// Rows affected 
        //6.  Processing results 
        System.out.println(count);
        //7.  Release resources 
        stmt.close();
        conn.close();
    }
}

JDBC API Detailed explanation

1.DriverManager

• Registration drive
  
  
  In the static code block in this class DriverManager Object's registerDriver() Method to register the driver , Then we just need to load Driver class , The static code block will execute . and Class.forName(“com.mysql.jdbc.Driver”); It can be loaded Driver class .
  Be careful ：
  1.MySQL 5 Later driver package , You can omit the steps of registering the driver
  2. Automatic loading jar In bag META-INF/services/java.sql.Driver Driver class in file

• Get database connection
  
  

2.Connection

Connection（ Database connection object ） effect ：1. Access to perform SQL The object of 2. Manage affairs

• Access to perform SQL object

Common execution SQL object

Statement createStatement()

precompile SQL Implementation SQL object ： prevent SQL Inject

PreparedStatement  prepareStatement(sql)

The object that executes the stored procedure

CallableStatement prepareCall(sql)

• Business management
  MySQL Operation of transaction management
  Open transaction ： BEGIN; perhaps START TRANSACTION;
  Commit transaction ： COMMIT;
  Roll back the transaction ： ROLLBACK;
  JDBC Methods of transaction management
  Open transaction
  
  Commit transaction
  
  Roll back the transaction
  

/** * JDBC API  Detailed explanation ：Connection */
public class JDBCDemo3_Connection {
    

    public static void main(String[] args) throws Exception {
    
        //1.  Registration drive 
        //Class.forName("com.mysql.jdbc.Driver");
        //2.  Get the connection ： If the connection is local mysql And the port is the default  3306  Can simplify writing 
        String url = "jdbc:mysql:///db1?useSSL=false";
        String username = "root";
        String password = "1234";
        Connection conn = DriverManager.getConnection(url, username, password);
        //3.  Definition sql
        String sql1 = "update account set money = 3000 where id = 1";
        String sql2 = "update account set money = 3000 where id = 2";
        //4.  Access to perform sql The object of  Statement
        Statement stmt = conn.createStatement();

        try {
    
            // ============ Open transaction ==========
            conn.setAutoCommit(false);
            //5.  perform sql
            int count1 = stmt.executeUpdate(sql1);// Rows affected 
            //6.  Processing results 
            System.out.println(count1);
            int i = 3/0;
            //5.  perform sql
            int count2 = stmt.executeUpdate(sql2);// Rows affected 
            //6.  Processing results 
            System.out.println(count2);

            // ============ Commit transaction ==========
            // The program runs here , Indicates that there are no problems , Then you need to commit the transaction 
            conn.commit();
        } catch (Exception e) {
    
            // ============ Roll back the transaction ==========
            // When an exception occurs, the program will execute to this place , At this point, the transaction needs to be rolled back 
            conn.rollback();
            e.printStackTrace();
        }

        //7.  Release resources 
        stmt.close();
        conn.close();
    }
}

3.Statement

/** *  perform DML sentence  * @throws Exception */
@Test
public void testDML() throws  Exception {
    
    //1.  Registration drive 
    //Class.forName("com.mysql.jdbc.Driver");
    //2.  Get the connection ： If the connection is local mysql And the port is the default  3306  Can simplify writing 
    String url = "jdbc:mysql:///db1?useSSL=false";
    String username = "root";
    String password = "1234";
    Connection conn = DriverManager.getConnection(url, username, password);
    //3.  Definition sql
    String sql = "update account set money = 3000 where id = 1";
    //4.  Access to perform sql The object of  Statement
    Statement stmt = conn.createStatement();
    //5.  perform sql
    int count = stmt.executeUpdate(sql);// After execution DML sentence , Rows affected 
    //6.  Processing results 
    //System.out.println(count);
    if(count > 0){
    
        System.out.println(" Modification successful ~");
    }else{
    
        System.out.println(" Modification failed ~");
    }
    //7.  Release resources 
    stmt.close();
    conn.close();
}

without junit If you depend , It can be run directly as a function or

4.ResultSet

ResultSet（ Result set object ） effect ： Encapsulates the SQL The result of the query statement .
And executed DQL Statement will return the object , Corresponding execution DQL The method of statement is as follows ：

ResultSet  executeQuery(sql)： perform DQL  sentence , return  ResultSet  object 

that , We can traverse and view the contents of the result set .ResultSet Object provides methods to manipulate query result data .

boolean next()
 explain ：
 Move the cursor forward one line from the current position 
 Judge whether the current line is a valid line 
 Method return value description ：true ：  Effective navigation , There is data in the current row false ：  Invalid line , There is no data in the current row 

xxx getXxx( Parameters )： get data 
xxx :  data type ; Such as ： int getInt( Parameters ) ;String getString( Parameters )
 Parameters : int Parameters of type ： Number of columns , from 1 Start .  String Parameters of type ：  Column name 

/** *  perform DQL * @throws Exception */
@Test
public void testResultSet() throws  Exception {
    
    //1.  Registration drive 
    //Class.forName("com.mysql.jdbc.Driver");
    //2.  Get the connection ： If the connection is local mysql And the port is the default  3306  Can simplify writing 
    String url = "jdbc:mysql:///db1?useSSL=false";
    String username = "root";
    String password = "1234";
    Connection conn = DriverManager.getConnection(url, username, password);
    //3.  Definition sql
    String sql = "select * from account";
    //4.  obtain statement object 
    Statement stmt = conn.createStatement();
    //5.  perform sql
    ResultSet rs = stmt.executeQuery(sql);
    //6.  Processing results ,  Traverse rs All data in 
    /* // 6.1  Move the cursor down one line , And judge whether there is data in the current line  while (rs.next()){ //6.2  get data  getXxx() int id = rs.getInt(1); String name = rs.getString(2); double money = rs.getDouble(3); System.out.println(id); System.out.println(name); System.out.println(money); System.out.println("--------------"); }*/
    // 6.1  Move the cursor down one line , And judge whether there is data in the current line 
    while (rs.next()){
    
        //6.2  get data  getXxx()
        int id = rs.getInt("id");
        String name = rs.getString("name");
        double money = rs.getDouble("money");

        System.out.println(id);
        System.out.println(name);
        System.out.println(money);

        System.out.println("--------------");
    }

    //7.  Release resources 
    rs.close();
    stmt.close();
    conn.close();
}

5.PreparedStatement

PreparedStatement effect ：  precompile SQL Statement and execute ： The prevention of SQL Injection problem 

SQL Injection concept ： Modify pre-defined by operating input SQL sentence , The method used to execute code to attack the server .
PreparedStatement The function is to precompile SQL Statement and execute , So as to prevent SQL Injection problem .

public class JDBCDemo_Statement {
    
    private static void testDML() throws  Exception {
    
        //1.  Registration drive 
        //Class.forName("com.mysql.jdbc.Driver");
        //2.  Get the connection ： If the connection is local mysql And the port is the default  3306  Can simplify writing 
        String url = "jdbc:mysql:///db1?useSSL=false";
        String username = "root";
        String password = "12348765";
        Connection conn = DriverManager.getConnection(url, username, password);
        //3.  Definition sql
        String sql = "select * from tb_user where username = ? and password = ?";
        //4.  obtain pstmt object 
        PreparedStatement pstmt = conn.prepareStatement(sql);
        String name="zhangsan";
        String pwd="123";
        // Set up ？ Value 
        pstmt.setString(1,name);
        pstmt.setString(2,pwd);
        //5.  perform sql
        ResultSet rs = pstmt.executeQuery();
        //6.  Processing results ,  Traverse rs All data in 
        // 6.1  Move the cursor down one line , And judge whether there is data in the current line 
        if (rs.next()){
    
            System.out.println("OKKK!");
        }else{
    
            System.out.println("Error!");
        }

    }
    public static void main(String[] args) throws Exception {
    
        testDML();
    }

}

 In obtaining PreparedStatement Object time , take sql The statement is sent to mysql The server checks , compile （ These steps are time-consuming ）
 You don't have to do these steps when executing , Faster 
 If sql It's like a template , You only need to check once 、 compile 

Database connection pool

Concept

Concept ： Database connection pool is a container , To be responsible for the distribution of 、 Manage database connections (Connection). It allows applications to reuse an existing database connection , Instead of building a new . Release database connection with idle time exceeding the maximum idle time to avoid missing database connection caused by no free database connection

benefits ： 1. Resource reuse 2. Improve system response speed 3. Avoid missing database connections

Realization

Database connection pool implementation

• Standard interface ：DataSource

  official (SUN) Database connection pool standard interface provided , This interface is implemented by a third-party organization . This interface provides the function of obtaining connection ：

Connection getConnection()

• Common database connection pool
  DBCP C3P0 Druid

• We use Druid,Druid Connection pool is an open source database connection pool project of Alibaba . Powerful , Excellent performance , yes Java One of the best database connection pools in language

Driud Use steps

1. Import jar package  druid-1.1.12.jar
2. Define configuration file 
3. Load profile 
4. Get database connection pool object 
5. Get the connection 

download druid Of jar package ： Database connection pool druid Of jar Download from Bao official website - Download the latest version

When adding as a library file , There are three options

• Global Library ： Global availability
• Project Library : The project works
• Module Library ： Module valid
  Selection module is valid

New file DruidDemo

druid.properties
The contents of the configuration file are as follows ：

driverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql:///db1?useSSL=false&useServerPrepStmts=true
username=root
password=1234
#  Initialize the number of connections 
initialSize=5
#  maximum connection 
maxActive=10
#  Maximum waiting time 
maxWait=3000

DruidDemo.java

/** * Druid Database connection pool demo  */
public class DruidDemo {
    

    public static void main(String[] args) throws Exception {
    
        //1. Import jar package 
        //2. Define configuration file 
        //3.  Load profile 
        Properties prop = new Properties();
        prop.load(new FileInputStream("jdbc-demo/src/druid.properties"));
        //4.  Get connection pool object 
        DataSource dataSource = DruidDataSourceFactory.createDataSource(prop);

        //5.  Get database connection  Connection
        Connection connection = dataSource.getConnection();
        System.out.println(connection); // After obtaining the connection, you can continue to do other operations 

        //System.out.println(System.getProperty("user.dir"));
    }
}

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