Corda节点运行时能否添加额外数据库驱动JAR？如何操作？

Hey there, great questions about Corda's database driver handling—let's break this down clearly, since this is a common point of confusion when working with external databases in Corda.

1. Including Extra Database Drivers During Node Startup #

First, let's clarify: when people talk about "runtime" here, they usually mean making the driver available as the node starts (since Corda initializes its database connection pool on startup). Here's the standard, supported way to add an external database driver:

• Drop the driver JAR in the node's drivers folder: Every Corda node has a dedicated drivers directory in its root. Just place your database driver JAR (like postgresql-42.6.0.jar for PostgreSQL or mysql-connector-java-8.0.33.jar for MySQL) here before firing up the node. The node's classloader automatically scans this directory on startup and loads the driver.
• Update your node.conf to use the driver: You need to configure the database connection details to point to your external DB and specify the driver class. For example, a PostgreSQL config would look like this:

  dataSourceProperties = {
      dataSourceClassName = "org.postgresql.ds.PGSimpleDataSource"
      dataSource.url = "jdbc:postgresql://localhost:5432/corda_node_db"
      dataSource.user = "corda_admin"
      dataSource.password = "your_secure_password"
  }
  database = {
      transactionIsolationLevel = "READ_COMMITTED"
  }
  

  Make sure the dataSourceClassName matches the fully qualified class name of your driver—double-check the driver's docs if you're unsure.

2. Loading Driver JARs After the Node Has Started #

Can you dynamically load a new database driver JAR once the node is already running? The short answer is: it's not officially supported by Corda, and it's not a good idea for production. Here's why:

• Corda's classloader is built to load all dependencies at startup. Trying to inject a JAR post-startup can cause class conflicts, broken connections, or even crash the node.
• The node's database connection pool is initialized when it starts. There's no built-in way to reconfigure or restart this pool without stopping and restarting the node.

That said, if you're doing experimental work or testing, you could hack together a solution using Java's dynamic classloading APIs (like URLClassLoader), but this is totally unsupported:

1. Create a custom Corda service or flow that uses URLClassLoader to load the JAR from a specified file path.
2. Register the driver class with Class.forName("com.mysql.cj.jdbc.Driver") after loading the JAR.
3. Even then, you'd need to reconfigure the node's data source to use the new driver—which isn't possible without restarting the node anyway, making the dynamic loading part pointless for most use cases.

Final Recommendation #

Stick to the supported method: add the driver JAR to the drivers directory, update your node.conf, and restart the node. Dynamic runtime loading is risky, unsupported, and rarely necessary.

内容的提问来源于stack exchange，提问作者Joel