This beginner example connects a Java application to a local PostgreSQL database and reads rows from a products table. It uses JDBC’s DriverManager, a PreparedStatement, and a ResultSet. The example is useful for learning the read path, but its sample credentials, resource handling, and error reporting need improvement before adapting it for a real application.
What the example does
Saravanan Lakshmanan’s DEV Community lesson, “Java Learning Series – DB connection with Product Management System”, shows a Java application connecting to PostgreSQL and listing products. The indexed example uses these connection details:
- Database URL:
jdbc:postgresql://localhost:5432/productdb - Username:
postgres - Password: a literal value in the source code
The URL points to a PostgreSQL server on the same machine, using port 5432 and a database named productdb. For the query to return product rows, that database and a products table must exist and be accessible to the supplied database account.
How the product read path works
Open a database connection
The lesson’s DBConnection.getPSQLConnection() method calls DriverManager.getConnection with the URL and credentials. JDBC connection URL syntax depends on the database management system and driver; Oracle’s JDBC tutorial describes DriverManager as a straightforward connection option. The Java SE 26 DriverManager API says that getConnection selects an appropriate registered driver and may throw SQLException if a database access error occurs.
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Run a query and read its rows
ProductService.viewProduct() obtains the connection, prepares select * from products, executes it with executeQuery(), and iterates over the returned ResultSet. For each row, it reads the id, name, category, and price fields.
The article’s indexed sample output reports a successful connection and displays two illustrative rows: 1 / chair / furniture / 10000 and 2 / mobile / electronics / 20000. Those are the article’s example output, not independently verified results; the excerpt does not establish the table schema or database setup needed to reproduce them.
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What to change before reusing the pattern
Keep credentials out of source code
The tutorial’s username and password are sample values. Do not copy a password literal into an application that will be shared or deployed. Load secrets from configuration managed outside the source code, and avoid printing them in error messages or logs.
Close JDBC resources reliably
The indexed code does not show the connection, statement, or result set inside try-with-resources blocks. These are closeable resources; use try-with-resources so they are released when processing finishes or an exception occurs. For example, the structure can be:
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String sql = "select id, name, category, price from products";
try (Connection connection = DriverManager.getConnection(url, user, password);
PreparedStatement statement = connection.prepareStatement(sql);
ResultSet results = statement.executeQuery()) {
while (results.next()) {
int id = results.getInt("id");
String name = results.getString("name");
String category = results.getString("category");
BigDecimal price = results.getBigDecimal("price");
// Use the product values here.
}
}This illustrates resource cleanup and selecting named columns; it is not a complete application or a substitute for configuring a PostgreSQL JDBC driver. The lesson excerpt does not specify a driver dependency or version, Java version, PostgreSQL server version, or schema setup, so those must be chosen and configured for the environment in which you run the code.
Select only the columns you use
select * from products is concise for demonstrating row iteration, but it requests every column. Listing the needed columns, as in the example above, makes the query’s requirements explicit and avoids retrieving unrelated fields.
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Preserve useful diagnostics
The article’s generic SQLException catch message gives the beginner a visible failure branch, but it does not identify the cause. During troubleshooting, retain the exception details for authorized diagnostic logs while ensuring credentials and other secrets are excluded. Common points to check are whether PostgreSQL is running at the configured host and port, whether productdb exists, whether the account can connect, and whether the table and requested columns are present.
When to use DriverManager or DataSource
DriverManager keeps a small learning example direct: supply a URL and credentials and request a connection. For an application that needs connection configuration separated from application logic, Oracle’s JDBC tutorial recommends the DataSource interface, stating: “This interface is preferred over DriverManager because it allows details about the underlying data source to be transparent to your application.” The right approach depends on the application’s connection-management needs; the lesson demonstrates DriverManager for instruction, not a production connection-management design.
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