Creating a java.sql.Connection using JDBC and Spring Boot

Question

I wanted to create two static functions: java.sql.Connection Connection.getConnection() and void Connection.closeConection() to obtain and terminate connections so that I can execute JDBC queries on my remote RDS instance. Here's what I wrote:

application.properties

spring.datasource.url=jdbc:mysql://myRDSEndpoint:3306/mySchemaName
spring.datasource.username=myUsername
spring.datasource.password=myPassword
spring.datasource.driver-class-name=com.mysql.jdbc.Driver

RDSConnection.java:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class RDSConnection {
    public static String driver;
    public static String url;
    public static String user;
    public static String pass;

    @Autowired
    public RDSConnection getRDSConnection(@Value("${spring.datasource.driver-class-name}") String driver,
                                          @Value("${spring.datasource.url}") String url,
                                          @Value("${spring.datasource.username}") String user,
                                          @Value("${spring.datasource.password}") String pass) {
        RDSConnection.driver = driver;
        RDSConnection.url = url;
        RDSConnection.user = user;
        RDSConnection.pass = pass;

        return this;
    }
}

Connection.java

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;

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

@Component
@Slf4j
public class Connection {
    private static java.sql.Connection sqlConnection;

    public static java.sql.Connection getConnection() {
        String driver = RDSConnection.driver;
        String url = RDSConnection.url;
        String user = RDSConnection.user;
        String pass = RDSConnection.pass;

        if(sqlConnection != null) return sqlConnection;

        try {
            Class.forName(driver);
            sqlConnection =  DriverManager.getConnection(url, user, pass);
        } catch (ClassNotFoundException | SQLException e) {
            log.error(e.getMessage());
        }

        return sqlConnection;
    }

    public static void closeConnection(java.sql.Connection sqlConnection) {
        try {
            sqlConnection.close();
        } catch (SQLException e) {
            log.error(e.getMessage());
        }
    }
}

This works, but I was wondering if there is a better way to do this. Is there a way to make the static variables in RDSConection final as well, since I know that the spring.datasource.* values are not going to change? If so, how do I inject the values from application.properties?

You don't want that. Instead use the pre-configured JdbcTemplate to execute queries — M. Deinum
– M. Deinum, Commented Oct 17, 2018 at 7:14
Why do you want to do that?! Configure a connection pooling datasource (which is the normal way of doing this in spring boot), and get connections in a try-with-resources block. You also really should not just ignore exceptions like you do and continue as if nothing happened. And you should most definitely not use a static field for a connection. Especially (but not only) in web applications that is a sure way to get race conditions and other weird behavior for concurrent requests. — Mark Rotteveel
– Mark Rotteveel, Commented Oct 18, 2018 at 18:34

Thiago Bomfim · Accepted Answer · 2018-10-17 00:41:12Z

There are some things that can be improved...

First, I you recommend you using SPRING DATA, you can use EntityManager and get the connection with this:

@PersistenceContext
private EntityManager entityManager;

public void method() {
    ... entityManager.unwrap(Session.class) ...
}

For more info: https://docs.spring.io/spring-data/jpa/docs/current/reference/html/

For use spring data with spring boot, just use:

@SpringBootApplication
@EntityScan(basePackages = {
            "com.your.project"
            })
@EnableJpaRepositories(basePackages = {
            "com.your.project"
            })
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);    
    }

}

Second, if you really want to use JDBC, I hope you use JAVA 7 / +

In this case, first use try-with-resources, this will close the connection automatically.

Something like:

try (Connection sqlConnection  =  DriverManager.getConnection(url, user, pass);
         PreparedStatement ps = sqlConnection.createPreparedStatement(sql); 
         ResultSet rs = ps.executeQuery()) {

         // process the resultset here, all resources will be cleaned up

    } catch (SQLException e) {
        log.error(e.getMessage());
    }
}

For more info: How should I use try-with-resources with JDBC?

And Class.forName(driver); It is no longer necessary. In Java 6+ because DriverManager will auto-load drivers found on the classpath. For more info: Why do I need to explicitly write Class.forName() when using JDK 8?

Finally, if you really do not want to use the Spring settings, you do not have a reason to use application.properties. You can use constants that will be static and final.

PS: Remember that you have to close all ResultSet and PreparedStatement, not just connection as a precaution.

Using DriverManager in a web application is not really a proper way, use of a data source is better, especially because that can be backed by a connection pool.

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