Alibaba Druid database connection pool take-off directly

1. What is a database connection pool

Why use connection pooling: When we develop in Java, we need to access the database, but Java can't access the database directly. We have to establish a connection between the program and the database through JDBC. Performing a transaction requires creating a connection. The process of establishing a connection between the program and the database is the most time consuming, and when the program becomes large, Frequent connections between programs and databases can be time consuming, so programmers have the concept of connection pools

Connection pool: Stores the channels to connect to the database, that is, Connections in JDBC. n connections are defined beforehand. These connections are initialized when the program starts, taken directly from the connection pool later on, and put back into the connection pool. A large number of repetitive connections and release operations are omitted.

2. Druid Connection Pool

Druid: The Druid connection pool was developed by the Alibaba team and introduced the concept of "slow loading".

Slow load: When creating a connection pool object, the database is not connected to the number of connection channels that have been defined beforehand. Instead, when the first connection channel is taken from the middle connection pool, the connection pool checks to see if there are any useful connection channels inside, and if so, if there are no connections to the database, it performs n connection channels that have been defined beforehand.

3. jar/dependency of Druid connection pool

1. Download Druid.jar


2. Import Dependency

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Either way.

4. Code representation

4.1. Create a properties file

Create a properties Files, mainly for Druid Connection pool one constraint
driverClassName = com.mysql.cj.jdbc.Driver
url = jdbc:mysql://localhost:3306/javaweb?characterEncoding=utf8&zeroDateTimeBehavior=convertToNull
username = root
password = 123456
initialSize = 5 //Number of Initialized Connection Channels
maxActive = 5 //Maximum number of available connection channels
maxWait = 3000 //The maximum time, in milliseconds, to wait when all connection channels are occupied

4.2, Create a DruidUtils class

Read the configuration file into memory and wait for the connection channel to be fetched

public class DruidUtils {

    private static DataSource dataSource = null;
    private static Properties properties = null;

        properties = new Properties();
        try {
            //Load profile into memory using reflection technology
            //Get a connection pool object from factory design mode, get a connection pool object, not a connection object
            dataSource = DruidDataSourceFactory.createDataSource(properties);
        } catch (Exception e) {
            throw new RuntimeException("Connection pool profile loading failed");
    //Open Connection Pool Objects for External Use
    public static DataSource getDataSource(){
        return dataSource;
    //Get Connection from Connection Pool Object
    public static Connection getConnection() throws SQLException {
        return dataSource.getConnection();

4.3, Testing

1. You need to first get a connection pool object and then get a connection from the connection pool object
2. Once connected, the operation is the same as JDBC operation database

4.3.0, Print, View Connection Pool

private static DataSource dataSource = DruidUtils.getDataSource(); //Get Connection Pool Object

public static void main(String[] args){



4.3.1, Add User Method

    private static String addUser(User user){
        String sql = "INSERT INTO user VALUES(?,?,?,?,?)";//SQL statement
        int result = 0; //Results after execution
        try {
        //Get Connection Channel from Connection Pool Object
            Connection connection = dataSource.getConnection();
		//The following actions execute the SQL statement as in JDBC
            PreparedStatement preparedStatement = connection.prepareStatement(sql);
            result = preparedStatement.executeUpdate();
            //Be sure to put the connection in the connection pool again after the operation is completed, or the connection pool will remain occupied and cannot be used by other things.
        } catch (SQLException e) {
        return result > 0 ? "Successfully added user" : "Failed to add user";

4.3.1, Get all user information

    private static List<User> getUserList() {
        List<User> userList = new ArrayList<>();
        ResultSet result = null;
        String sql = "SELECT * FROM user";
        try {
        	//Get Connection Channel from Connection Pool
            Connection connection = dataSource.getConnection();
            PreparedStatement preparedStatement = connection.prepareStatement(sql);
            result = preparedStatement.executeQuery();
            User user = null;
            while ( {
                user = new User(result.getString("id"),result.getString("username"),
                        result.getString("password"), result.getString("sex"), result.getString("phone"));
        } catch (SQLException e) {
        return userList;

4.3.3, Main method

public class DruidPoolTest {
    private static DataSource dataSource = null;

    public static void main(String[] args) {
        dataSource = DruidUtils.getDataSource(); //Get Connection Pool Object

        System.out.println("-----------Add a user to the database-----------------");
        User user = new User("6","Boiling in King water","999999","female","13888887878");

     	System.out.println("--------------Query all-------------");
        List<User> userList = getUserList();
        for(User user : userList){


There are currently five pieces of user information in the database

After performing the operation in the Main method

There are six pieces of data, and the data was added successfully. Because of the "slow-loading" technology used by Druid connection pools, N connection channels need to be initialized when the program gets the connection channel for the first time because there is no connection in the connection pool, so it will start slowly.

5. Exception thrown by not returning connection to connection pool

The number of connection channel bars I defined in the properties file beforehand is five, and the maximum number of active bars is five.
And now I want to get six:

    public static void main(String[] args) {
        dataSource = DruidUtils.getDataSource(); //Get Connection Pool Object
        try {
            Connection connection1 = dataSource.getConnection();//First Connection
            Connection connection2 = dataSource.getConnection();//Second Connection
            Connection connection3 = dataSource.getConnection();//Third Connection
            Connection connection4 = dataSource.getConnection();//Fourth Connection
            Connection connection5 = dataSource.getConnection();//Fifth Connection
            Connection connection6 = dataSource.getConnection();//Sixth Connection
        } catch (SQLException e) {

Direct error


Reason 1: There are no available connection channels in the connection pool. Five channels are defined. The maximum available is also five channels. All are not available.
Reason 2: I did not release the connection after a transaction, which prevented other transactions from getting the connection channel.


Solution 1: Expand the maximum number of connections available in the connection pool
initialSize = 5 //Initialize five connection channels
maxActive = 10 // Maximum available connection channels are 10

Solution 2: After the transaction is executed, the connection is returned to the connection pool.

Solution 2 is recommended because in large projects, it is not recommended to move around and increase the number of connection channels

6. Summary

Druid connection pooling is also a popular connection pooling technology, but it only solves the performance optimization of connection channels in connection and release. Other ways of operating databases are the same as JDBC, so there are framework technologies such as MyBatis on the market.

Tags: Java Database JDBC jar

Posted on Thu, 25 Nov 2021 12:07:34 -0500 by PastorHank