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Create a Data Access Object for PostgreSQL Data using JDBI

A brief overview of creating a SQL Object API for PostgreSQL data in JDBI.

JDBI is a SQL convenience library for Java that exposes two different style APIs, a fluent style and a SQL object style. The CData JDBC Driver for PostgreSQL integrates connectivity to live PostgreSQL data in Java applications. By pairing these technologies, you gain simple, programmatic access to PostgreSQL data. This article walks through building a basic Data Access Object (DAO) and the accompanying code to read and write PostgreSQL data.

Create a DAO for the PostgreSQL Orders Entity

The interface below declares the desired behavior for the SQL object to create a single method for each SQL statement to be implemented.

public interface MyOrdersDAO { //insert new data into PostgreSQL @SqlUpdate("INSERT INTO Orders (ShipCountry, ShipCity) values (:shipCountry, :shipCity)") void insert(@Bind("shipCountry") String shipCountry, @Bind("shipCity") String shipCity); //request specific data from PostgreSQL (String type is used for simplicity) @SqlQuery("SELECT ShipCity FROM Orders WHERE ShipCountry = :shipCountry") String findShipCityByShipCountry(@Bind("shipCountry") String shipCountry); /* * close with no args is used to close the connection */ void close(); }

Open a Connection to PostgreSQL

Collect the necessary connection properties and construct the appropriate JDBC URL for connecting to PostgreSQL.

To connect to PostgreSQL, set the Server, Port (the default port is 5432), and Database connection properties and set the User and Password you wish to use to authenticate to the server. If the Database property is not specified, the data provider connects to the user's default database.

Built-in Connection String Designer

For assistance in constructing the JDBC URL, use the connection string designer built into the PostgreSQL JDBC Driver. Either double-click the JAR file or execute the jar file from the command-line.

java -jar cdata.jdbc.postgresql.jar

Fill in the connection properties and copy the connection string to the clipboard.

A connection string for PostgreSQL will typically look like the following:

jdbc:postgresql:User=postgres;Password=admin;Database=postgres;Server=127.0.0.1;Port=5432;

Use the configured JDBC URL to obtain an instance of the DAO interface. The particular method shown below will open a handle bound to the instance, so the instance needs to be closed explicitly to release the handle and the bound JDBC connection.

DBI dbi = new DBI("jdbc:postgresql:User=postgres;Password=admin;Database=postgres;Server=127.0.0.1;Port=5432;"); MyOrdersDAO dao = dbi.open(MyOrdersDAO.class); //do stuff with the DAO dao.close();

Read PostgreSQL Data

With the connection open to PostgreSQL, simply call the previously defined method to retrieve data from the Orders entity in PostgreSQL.

//disply the result of our 'find' method String shipCity = dao.findShipCityByShipCountry("USA"); System.out.println(shipCity);

Write PostgreSQL Data

It is also simple to write data to PostgreSQL, using the previously defined method.

//add a new entry to the Orders entity dao.insert(newShipCountry, newShipCity);

Since the JDBI library is able to work with JDBC connections, you can easily produce a SQL Object API for PostgreSQL by integrating with the CData JDBC Driver for PostgreSQL. Download a free trial and work with live PostgreSQL data in custom Java applications today.