The way to get database connection & the disadvantages of Statement operating database

1. How to get a database connection

TestConnection

package com.aff.connection;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;
import org.junit.Test;

public  class TestConnection {
     // Method 1 
    @Test
     public  void testConnection () throws SQLException {
         // Get Driver implementation object 
        Driver driver = new com.mysql.jdbc.Driver ();
         // jdbc: mysql protocol
         // localhost ip Address
         // 3306 default mysql port number
         // test database name 
        String url = "jdbc: mysql: // localhost: 3306 / test" ;
         // username and password are encapsulated in Properties 
        Properties info = new Properties ();
        info.setProperty("user", "root");
        info.setProperty("password", "123456");
        Connection conn = driver.connect(url, info);
        System.out.println(conn);
    }

    // Method 2: For iteration of method 1, no third-party APIs appear in the following program, making the program more portable 
    @Test
     public  void testConnection2 () throws Exception {
         // Get Driver implementation class object : Use reflection 
        Class clazz = Class.forName ("com.mysql.jdbc.Driver" );
        Driver driver = (Driver) clazz.newInstance();

        // Database required for connection 
        String url = "jdbc: mysql: // localhost: 3306 / test" ;

        // Provide the username and password required for connection 
        Properties info = new Properties ();
        info.setProperty("user", "root");
        info.setProperty("password", "123456");

        // Get connection 
        Connection conn = driver.connect (url, info);
        System.out.println(conn);
    }

    // Method 3: Use DriverManager to manage 
    @Test
     public  void testConnection3 () throws Exception {
         // Get the object of Driver implementation class 
        Class clazz = Class.forName ("com.mysql.jdbc.Driver" );
        Driver driver = (Driver) clazz.newInstance();

        // Provide basic information for three connections 
        String url = "jdbc: mysql: // localhost: 3306 / test" ;
        String user = "root";
        String password = "123456";

        // Get DriverManager Driver
         // Register Driver 
        DriverManager.registerDriver (driver);

        // Get connection 
        Connection conn = DriverManager.getConnection (url, user, password);
        System.out.println(conn);
    }

    // Method four: Optimize 
    @Test
     public  void testConnection4 () throws Exception on the basis of three {
         // 1. Provide basic information of three connections 
        String url = "jdbc: mysql: // localhost: 3306 / test" ;
        String user = "root";
        String password = "123456";

        // 2. Load the driver. In the driver's implementation class of mysql, the driver has been registered 
        Class.forName ("com.mysql.jdbc.Driver" );

        // 3. Get connection 
        Connection conn = DriverManager.getConnection (url, user, password);
        System.out.println(conn);
    }

    
    
    
    // Method 5: Final version, declare the 4 information needed for database connection in the configuration file, and connect to the database by reading the configuration file
    /*
     * Benefits: 1. Realize the separation of data and code, realize decoupling
     * 2. If you need to modify the configuration information, you can avoid re-packaging the program
     */
    @Test
    public  void testConnection5 () throws Exception {
         // 1. Read the 4 basic information in the configuration file, through the class loader 
        InputStream is = TestConnection. class .getClassLoader (). getResourceAsStream ("jdbc.properties" );
        Properties pro = new Properties ();
         // Load the is file 
        pro.load (is);
         // Read the configuration information in it 
        String user = pro.getProperty ("user" );
        String url = pro.getProperty("url");
        String password = pro.getProperty("password");
        String driverClass = pro.getProperty("driverClass");

        // 2. Load the driver 
        Class.forName (driverClass);

        // 3. Get connection 
        Connection conn = DriverManager.getConnection (url, user, password);
        System.out.println(conn);
    }
}

 

 

2. The disadvantages of Statement operation database: need to spell sql statement, and there is a problem of SQL injection

Example: testLogin

package com.aff.connection;
import java.io.InputStream;
import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;
import java.util.Scanner;
import org.junit.Test;

public class StatementTest {

    // Disadvantages of using Statement: need to spell sql statement, and there is a problem of SQL injection 
    @Test
     public  void testLogin () {
        Scanner scan = new Scanner(System.in);

        System.out.print ( "User name:" );
        String userName = scan.nextLine();
        System.out.print ( "Password:" );
        String password = scan.nextLine();

         // SELECT user,password FROM user_table WHERE USER = '1' or ' AND
        // PASSWORD = '
        // ='1' or '1' = '1';
        String sql = "SELECT user,password FROM user_table WHERE user = '" + userName + "' AND PASSWORD = '" + password
                + "'";
        User user = get(sql, User.class);
        if (user != null) {
            System.out.println ( "Login successful!" );
        } else {
            System.out.println ( "Wrong username or password!" );
        }
    }

    // Use Statement to query the data table 
    public <T> T get (String sql, Class <T> clazz) {
        T t = null;

        Connection conn = null;
        Statement st = null;
        ResultSet rs = null ;
         try {
             // 1. Load configuration file 
            InputStream is = StatementTest. Class .getClassLoader (). GetResourceAsStream ("jdbc.properties" );
            Properties pros = new Properties();
            pros.load(is);

            // 2. Read configuration information 
            String user = pros.getProperty ("user" );
            String password = pros.getProperty("password");
            String url = pros.getProperty("url");
            String driverClass = pros.getProperty("driverClass");

            // 3. Load the driver 
            Class.forName (driverClass);

            // 4. Get connection 
            conn = DriverManager.getConnection (url, user, password);
            st = conn.createStatement();
            rs = st.executeQuery(sql);

            // Get the metadata of the result set 
            ResultSetMetaData rsmd = rs.getMetaData ();

            // Get the number of columns in the result set 
            int columnCount = rsmd.getColumnCount ();

            if (rs.next()) {

                t = clazz.newInstance();

                for ( int i = 0; i <columnCount; i ++ ) {
                     //  // 1. Get the name of the column
                     // String columnName = rsmd.getColumnName (i + 1);

                    // 1. Get the alias of the column 
                    String columnName = rsmd.getColumnLabel (i + 1 );

                    // 2. Obtain the data in the corresponding data table according to the column name 
                    Object columnVal = rs.getObject (columnName);

                    // 3. Pack the data obtained in the data table into the object 
                    Field field = clazz.getDeclaredField (columnName);
                    field.setAccessible(true);
                    field.set(t, columnVal);
                }
                return t;
            }
        } catch (Exception e) {
            e.printStackTrace ();
        } finally {
             // Close resource 
            if (rs! = null ) {
                 try {
                    rs.close();
                } catch (SQLException e) {
                    e.printStackTrace ();
                }
            }
            if (st != null) {
                try {
                    st.close();
                } catch (SQLException e) {
                    e.printStackTrace ();
                }
            }
            if (conn != null) {
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace ();
                }
            }
        }
        return null;
    }
}

User 

package com.aff.connection;

public class User {
    private String user;
    private String password;

    public User() {
    }
    public User(String user, String password) {
        super();
        this.user = user;
        this.password = password;
    }
    @Override
    public String toString() {
        return "User [user=" + user + ", password=" + password + "]";
    }
    public String getUser() {
        return user;
    }
    public void setUser(String user) {
        this.user = user;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
}