JDBC & Databases (`pkg11jdbc`)

Runnable demos: `pkg11jdbc`. Run with java pkg11jdbc/jdbc1JdbcOverview.java.

This repo has no external jars, so no JDBC driver is registered by default. The CRUD/transaction demos run for real if an in-memory driver is on the classpath, and otherwise print the exact SQL + setup steps. To run them live:

bashCopy

1# download h2.jar, then:2java -cp ".;h2.jar" pkg11jdbc/jdbc2CrudStatements.java   # Windows (use ':' on macOS/Linux)

What is JDBC?

JDBC (java.sql) is a vendor-neutral API for relational databases. Each DB ships a driver implementing the API for its wire protocol.

The lifecycle

1DriverManager / DataSource ──► Connection ──► Statement/PreparedStatement ──► ResultSet ──► close()

JDBC URLs

1jdbc:postgresql://host:5432/db2jdbc:mysql://host:3306/db3jdbc:sqlite:app.db          (file)4jdbc:h2:mem:test            (in-memory)

Files in this package

Best practices

• Always use PreparedStatement with ? params — never concatenate user input (SQL injection!).
• Wrap everything in try-with-resources so connections/statements/result sets close.
• Group related writes in a transaction: setAutoCommit(false) → work → commit() / rollback().
• Batch bulk inserts (addBatch/executeBatch) to cut round trips.
• In production use a connection pool (HikariCP) via a DataSource, not DriverManager.