A brief introduction to DriverManager in Java

happy smile

爱神和月老

A: "Do you know why there are more divorces in Western countries than in China?"

B: "This It’s not simple, because the Western Cupid is a doll, while the Chinese one is an old man under the moon, and of course he has much more experience! "

Ask a question

Simple learning of the DriverManager class? ? ?

Solve the problem

DriverManager manages a set of basic services of the JDBC driver in the java.sql package

[code]package com.evada.de;
import java.sql.Connection;
import java.sql.Driver;
import java.sql.DriverManager;
import java.util.Enumeration;

/**
 * 用静态工厂方法管理一个唯一的可重用的连接
 * Created by Ay on 2016/5/1.
 */
public class ConnUtils{

private ConnUtils(){}
private static Connection con;
//在静态代码块中创建与数据库的连接
static{
    try{
        //postgresql驱动名称
        Class.forName("org.postgresql.Driver");
        //数据库连接路径
        String url = "jdbc:postgresql://127.0.0.1:5432/postgres";
        //用户名和密码
        con = DriverManager.getConnection(url, "postgres", "888888");
    }catch(Exception e){
        throw new RuntimeException(e.getMessage(),e);
    }
}
//使用一个静态方法－静态工厂方法，返回connection实例
public static Connection getCon(){
    return con;
}

//main函数测试用
public static void main(String[] args) {
    //获取所有的数据库驱动
    Enumeration<Driver> driverEnum = DriverManager.getDrivers();
    //打印出所有驱动信息
    while(driverEnum.hasMoreElements()){
        System.out.println(driverEnum.nextElement());
    }
}
}

Running results:

[code]org.mariadb.jdbc.Driver@7cef4e59
com.alibaba.druid.proxy.DruidDriver@3ada9e37
com.alibaba.druid.mock.MockDriver@4ec6a292
org.postgresql.Driver@71c7db30

Explanation , because our project package has the database driver as shown below, the following information will be printed

##The difference between the two:

DriverManager.registerDriver(new Driver()); 
Class.forName(“com.mysql.jdbc.Driver”);

org.postgresql.Driver class source code is as follows. It can be seen that postgresql uses a singleton form and a new driver Driver, which means that when connecting to the database, only After creating a new Driver

[code]static {
        sharedTimer = new SharedTimer(logger);

        try {
            //注册
            register();
        } catch (SQLException var1) {
            throw new ExceptionInInitializerError(var1);
        }

        protocols = new String[]{"jdbc", "postgresql"};
    }

    public static void register() throws SQLException {
        if(isRegistered()) {
            throw new IllegalStateException("Driver is already registered......);
        } else {
            Driver registeredDriver = new Driver();
            DriverManager.registerDriver(registeredDriver);
            registeredDriver = registeredDriver;
        }
    }

, let’s take a look at the source code of DriverManager. It will package the Driver into DriverInfo,

[code]//
public static synchronized void registerDriver(java.sql.Driver driver,
            DriverAction da)
        throws SQLException {

        /* Register the driver if it has not already been added to our list */
        if(driver != null) {
            //将驱动包装到DriverInfo中
            registeredDrivers.addIfAbsent(new DriverInfo(driver, da));
        } else {
            // This is for compatibility with the original DriverManager
            throw new NullPointerException();
        }

        println("registerDriver: " + driver);

    }

Class.forName(“com.mysql.jdbc.Driver” );

Conclusion: DriverManager.registerDriver(new Driver()); Adding a new Driver is a waste; and Class.forName("com.mysql.jdbc.Driver"); singleton form is more recommended...

The above is a brief introduction to Java’s DriverManager. For more related content, please pay attention to the PHP Chinese website (www.php.cn)!