Let’s break this down for your exact stack—since you’re on JDK 8, you need a driver that supports JDBC 4.2 (the spec tied to JDK 8). All the versions below work seamlessly with PostgreSQL 10 and Tomcat 8:

Top Recommended Driver Versions #

• PostgreSQL JDBC Driver 42.2.20 (final stable release of the 42.2.x series): This version supports PostgreSQL 9.4 through 14, works with JDK 6+, and is fully compatible with Tomcat 8. It’s far more stable than the early 42.2.2 release you tried, with bug fixes that likely resolve your issues.
• PostgreSQL JDBC Driver 42.3.x series (e.g., 42.3.9): This line requires JDK 8+ (perfect for your setup) and supports PostgreSQL 9.6 through 15. It includes minor improvements over 42.2.x without breaking compatibility.
• PostgreSQL JDBC Driver 42.1.4 (mature stable option): If you prefer a long-supported, battle-tested version, this works with PostgreSQL 9.3 through 12 and JDK 6+. It’s a reliable pick if you don’t need the latest features.

Why Your 42.2.2 Driver Might Be Failing #

The 42.2.x series should work for your stack, so the issue is likely not the version itself. Here are the most common pitfalls to check:

• Incorrect driver placement: Ensure the .jar file is in $CATALINA_HOME/lib (Tomcat’s global lib directory) or your web app’s WEB-INF/lib folder. If it’s in the wrong spot, Tomcat won’t load it, leading to ClassNotFoundException for org.postgresql.Driver.
• Malformed JDBC URL: Double-check your connection string follows the format: jdbc:postgresql://localhost:5432/your_database_name (replace your_database_name with your actual DB name, and adjust the port if you changed PostgreSQL’s default 5432).
• Dependency conflicts: If your web app includes other JDBC drivers or duplicate PostgreSQL driver versions, they can interfere with the new driver. Run a dependency scan (e.g., with Maven/Gradle) to spot conflicts.
• Database permissions: Verify the user account your app uses has proper access to the PostgreSQL database (e.g., run GRANT ALL PRIVILEGES ON DATABASE your_db TO your_user; in PostgreSQL).
• Tomcat connection pool misconfiguration: If you’re using Tomcat’s Resource setup in context.xml, confirm all attributes are correct. Example snippet:

  <Resource name="jdbc/YourDB"
            auth="Container"
            type="javax.sql.DataSource"
            driverClassName="org.postgresql.Driver"
            url="jdbc:postgresql://localhost:5432/your_db"
            username="your_user"
            password="your_pass"
            maxTotal="100"
            maxIdle="20"
            maxWaitMillis="10000"/>
  

Quick Test to Isolate the Issue #

To rule out Tomcat-specific problems, write a simple standalone Java class to test the JDBC connection:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class PGTest {
    public static void main(String[] args) {
        String url = "jdbc:postgresql://localhost:5432/your_db";
        String user = "your_user";
        String password = "your_pass";

        try (Connection conn = DriverManager.getConnection(url, user, password)) {
            System.out.println("Connected successfully!");
        } catch (SQLException e) {
            System.err.println("Connection failed: " + e.getMessage());
        }
    }
}

Compile and run this with JDK 8 and your 42.2.2 driver in the classpath. If it fails, the issue is with the driver or database setup; if it works, the problem lies in your Tomcat configuration.

内容的提问来源于stack exchange，提问作者Hani Draidi