Of course! The term "Java was datasource" seems to be a typo or a misphrasing. I'm going to assume you meant "Java and DataSource" or "Java DataSource", which is a fundamental concept in Java for database connectivity.

Let's break it down from a simple analogy to the technical details.

The Simple Analogy: A Water Company

Imagine your Java application is a city, and your database is a water reservoir.

• Your Java Code: The houses, businesses, and factories in the city that need water.
• The Database: The giant water reservoir.
• java.sql.DataSource: The water company. You don't talk directly to the reservoir. You call the water company.
• The Connection: A specific water pipe that the water company installs to your house.

Why is this better? You don't need to know where the reservoir is, how to build a pipe to it, or how to manage the water pressure. You just call the water company (DataSource), say "I need water," and they give you a working pipe (Connection). If the reservoir moves (you change database servers), you just call the water company and tell them the new address. All the houses in your city don't need to change.

What is a DataSource in Java?

A DataSource is an interface in the Java API (javax.sql.DataSource) that represents a source of database connections. It's the standard, modern, and preferred way for a Java application to get a connection to a database.

Its main purpose is to decouple your application code from the specific details of how to connect to a database (like the driver class name, URL, username, password, etc.).

Why Use a DataSource? (The Benefits)

Using a DataSource instead of manually creating connections has several huge advantages:

1. Abstraction: Your code only interacts with the DataSource interface, not a specific implementation. This makes your code portable and independent of the database vendor (e.g., you can switch from MySQL to PostgreSQL with minimal configuration changes).

2. Connection Pooling: This is the most important benefit. Creating a new database connection is a very slow and resource-intensive process. A DataSource can be configured to maintain a "pool" of pre-created connections. When your code needs a connection, it borrows one from the pool, uses it, and returns it. This dramatically improves application performance and scalability.

   
   （图片来源网络，侵删）

3. Centralized Configuration: All the connection details (URL, user, password, pool size) are configured in one place (often in a configuration file like context.xml for Tomcat or application.properties for Spring Boot). You don't hardcode these details in your Java code, which is a critical best practice.

4. Resource Management: The DataSource and its connection pool are managed by the application server (like Tomcat, JBoss, or WildFly) or a framework (like Spring). This makes it much easier to manage the lifecycle of database connections and prevent resource leaks.

How to Use a DataSource (A Practical Example)

Here’s a step-by-step guide using a standalone Java application and a popular connection pool library, HikariCP, which is considered the best-in-class.

Step 1: Add Dependencies

You need a JDBC driver for your database and a connection pool implementation. HikariCP is a great choice.

If you're using Maven, add this to your pom.xml:

<dependencies>
    <!-- HikariCP Connection Pool -->
    <dependency>
        <groupId>com.zaxxer</groupId>
        <artifactId>HikariCP</artifactId>
        <version>5.0.1</version>
    </dependency>
    <!-- PostgreSQL JDBC Driver (example) -->
    <dependency>
        <groupId>org.postgresql</groupId>
        <artifactId>postgresql</artifactId>
        <version>42.6.0</version>
    </dependency>
</dependencies>

Step 2: Configure the DataSource

Create a properties file (e.g., db.properties) to hold your configuration.

db.properties:

# Database connection details
db.jdbcUrl=jdbc:postgresql://localhost:5432/mydatabase
db.username=postgres
db.password=mysecretpassword
# HikariCP specific settings
db.poolName=MyAppHikariCP
db.maximumPoolSize=10
db.connectionTimeout=30000

Step 3: Create and Use the DataSource in Java

Now, let's write the Java code to load the configuration, create the DataSource, and get a connection.

import com.zaxxer.hikari.HikariConfig;
import com.zaxxer.hikari.HikariDataSource;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;
public class DataSourceExample {
    // The single instance of our DataSource (singleton pattern)
    private static HikariDataSource dataSource;
    // Static block to initialize the DataSource when the class is loaded
    static {
        try (InputStream input = DataSourceExample.class.getClassLoader().getResourceAsStream("db.properties")) {
            Properties props = new Properties();
            if (input == null) {
                throw new RuntimeException("Sorry, unable to find db.properties");
            }
            props.load(input);
            // Configure HikariCP
            HikariConfig config = new HikariConfig();
            config.setJdbcUrl(props.getProperty("db.jdbcUrl"));
            config.setUsername(props.getProperty("db.username"));
            config.setPassword(props.getProperty("db.password"));
            config.setPoolName(props.getProperty("db.poolName"));
            config.setMaximumPoolSize(Integer.parseInt(props.getProperty("db.maximumPoolSize")));
            config.setConnectionTimeout(Long.parseLong(props.getProperty("db.connectionTimeout")));
            // Create the DataSource
            dataSource = new HikariDataSource(config);
        } catch (IOException e) {
            throw new RuntimeException("Failed to load database configuration", e);
        }
    }
    public static Connection getConnection() throws SQLException {
        // Get a connection from the pool
        return dataSource.getConnection();
    }
    public static void main(String[] args) {
        // The 'try-with-resources' statement ensures the connection is always closed
        try (Connection conn = DataSourceExample.getConnection()) {
            System.out.println("Successfully obtained connection from the pool!");
            System.out.println("Connection: " + conn);
            // Example: Execute a simple query
            String sql = "SELECT version();";
            try (PreparedStatement stmt = conn.prepareStatement(sql);
                 ResultSet rs = stmt.executeQuery()) {
                if (rs.next()) {
                    System.out.println("Database Version: " + rs.getString(1));
                }
            }
        } catch (SQLException e) {
            System.err.println("Connection failed!");
            e.printStackTrace();
        } finally {
            // IMPORTANT: Close the entire DataSource when the application shuts down
            if (dataSource != null && !dataSource.isClosed()) {
                dataSource.close();
                System.out.println("DataSource closed.");
            }
        }
    }
}

DataSource in a Java EE / Jakarta EE Environment

If you're running in an application server like WildFly, JBoss, or Payara, the process is even easier. You don't manage the DataSource yourself.

1. Define the Datasource: You configure the DataSource (including the connection pool) directly in the server's admin console or configuration files (e.g., standalone.xml for WildFly).
2. Look it up: Your application code gets a reference to this pre-configured DataSource using JNDI (Java Naming and Directory Interface).

// In a Java EE environment (using JNDI)
InitialContext ctx = new InitialContext();
DataSource ds = (DataSource) ctx.lookup("java:jboss/datasources/ExampleDS"); // The JNDI name
Connection conn = ds.getConnection();

Summary

In short, a DataSource is the cornerstone of robust, high-performance, and maintainable database access in any serious Java application.