PostgreSQL JDBC: Call Stored Functions

Summary: in this tutorial, you will learn how to call PostgreSQL stored functions using JDBC.

Calling a built-in stored function example

We will call a built-in string function initcap() that capitalizes the first letter of each word in a string.

To call the initcap() function, you follow these steps:

First, establish a database connection.
Second, create a CallableStatement object by calling the prepareCall() method of the Connection object.
Register OUT parameters if applicable.
Bind values to the statement if applicable.
Third, execute the function call and obtain the result.

The following example creates a new class named Util and defines a static method properCase() that calls the initcap() function in PostgreSQL:

import java.sql.SQLException;
import java.sql.Types;

public class Util {
    public static String properCase(String s) {
        try (var conn = DB.connect();
             var stmt = conn.prepareCall("{ ? = call initcap( ? ) }")) {
            stmt.registerOutParameter(1, Types.VARCHAR);
            stmt.setString(2, s);
            stmt.execute();
            return stmt.getString(1);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }
}

The following illustrates how to use the properCase() method of the Util class:

public class Main {
    public static void main(String[] args) {
        var greeting = Util.properCase("hello joe");
        System.out.println(greeting);
    }
}

Output:

Hello Joe

Calling a stored function example

Let’s take an example of calling a stored function in PostgreSQL from a Java program using JDBC.

Creating a stored function

First, open Command Prompt on Windows or Terminal on Unix-like systems and connect to the sales database on your PostgreSQL server:

psql -U postgres -d sales

Second, create a function that finds the products by name based on a specified pattern:

create or replace function find_products (
	p_pattern varchar
)
returns table (
	p_id int,
	p_name varchar,
	p_price decimal
)
language plpgsql
as $$
declare
    var_r record;
begin
	for var_r in(
		select id, name, price
		from products
		where name ilike p_pattern
    )
	loop
		p_id := var_r.id;
		p_name := var_r.name;
		p_price := var_r.price;
        return next;
	end loop;
end; $$

Third, exit the psql:

exit

Calling a stored function

The following defines the findByName() method in the ProductDB class that calls the find_products stored function to find the products by names based on a pattern:

import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

public class ProductDB {
    public static List<Product> findByName(String pattern) {
        String SQL = "SELECT * FROM find_products (?)";

        var products = new ArrayList<Product>();

        try (var conn = DB.connect();
             var pstmt = conn.prepareStatement(SQL)) {

            pstmt.setString(1, pattern);
            var rs = pstmt.executeQuery();

            while (rs.next()) {
                var product = new Product(
                        rs.getInt("p_id"),
                        rs.getString("p_name"),
                        rs.getDouble("p_price")
                );
                products.add(product);
            }
        } catch (SQLException e) {
            System.out.println(e.getMessage());
        }
        return products;
    }

// ...
}

The following uses the findByName() method of the ProductDB class to search for products with the name containing the string "phone":

public class Main {
    public static void main(String[] args) {

        var products = ProductDB.findByName("%phone%");

        for (var product: products) {
            System.out.println(product);
        }
    }
}

Output:

Product{id=5, name='Bluetooth Headphones', price=199.0}
Product{id=6, name='Phone Stand', price=24.99}

Summary

Use the CallableStatement to call a built-in function from PostgreSQL.