ORIGIN

JDBC Database Connection

2023-02-11

JDBC Java Database Connection 2 mins476 words

I’m currently learning JDBC to operate database. This article is an note of what I learnt.

What Is JDBC

Java™ database connectivity (JDBC) is the JavaSoft specification of a standard application programming interface (API) that allows Java programs to access database management systems. The JDBC API consists of a set of interfaces and classes written in the Java programming language.

This helps Java developer to write code more easily when coming to different database. You don’t need to write a new code to adapt the different database, it can be done in almost the same code using JDBC.

How to connect to DB

read config information

We use a config file to set user and password and database URL information, so that when we change database, we don’t need to compile the code again, and we separate the code and data.

Because we use Properties to get the file, we can store file in jdbc.properties in src folder.

We set four properties for the database:

user=root
password=123
url=jdbc:mysql://localhost:3306/test
driverClass=com.mysql.jdbc.Driver

The URL is different for different database, you can search the format in each database driver’s README file.

InputStream is = db_conn.class.getClassLoader().getResourceAsStream("jdbc.properties");

Properties pros = new Properties();
pros.load(is);

String user = pros.getProperty("user");
String password = pros.getProperty("password");
String url = pros.getProperty("url");
String driver = pros.getProperty("driverClass");

load drive

We can just write Class.forName(driver);

We don’t need to write

1
2
3

Driver driver = (Driver) clazz.NewInstance();
// Register driver:
DriverManager.registerDriver(driver)

Because In MySQL driver class, there is the code, so we don’t need to write them, the code in MySQL driver is :

static {
	try{
        java.sql.DriverManager.registerDriver(new Driver());
    } catch (SQLException E) {
        throw new RuntimeException("Can't register driver!")；
    }
}

Get connection

1	Connection conn = DriverManager.getConnection(url, user, password);

Close connection

public void closeResource(Connection conn) {
	try {
        if(conn != null) {
            conn.close();
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

Complete Code

import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.util.Properties;

public class JDBCUtils {
    public Connection getConnection() throws Exception{
        // 1. read config information
        InputStream is = db_conn.class.getClassLoader().getResourceAsStream("jdbc.properties");
        
        Properties pros = new Properties();
        pros.load(is);

        String user = pros.getProperty("user");
        String password = pros.getProperty("password");
        String url = pros.getProperty("url");
        String driver = pros.getProperty("driverClass");

        // 2. load drive
        Class.forName(driver);

        // 3. get connection
        Connection conn = DriverManager.getConnection(url, user, password);
        return conn;
    }
    public void closeResource(Connection conn) {
    	try {
            if(conn != null) {
                conn.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}