Fetching Data

To start fetching data with JPAstreamer you need to initialize an instance of JPAStreamer. This section describes how that is accomplished.

Obtaining a JPAstreamer instance

JPAstreamer is initialized with the name of the persistence unit like so:

JPAStreamer jpaStreamer = JPAStreamer.of("sakila"); (1)
1 "sakila" is to be replaced with the name of your persistence unit that can be found in a configuration-file

In the example, the String "sakila" should refer to the name of your persistance unit. Assuming you are already using a JPA provider, your project should contain an XML-file like the one below, describing the persistence unit:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.2"

    <persistence-unit name="sakila" transaction-type="RESOURCE_LOCAL"> (1)
        <description>MySQL Sakila Example Database</description>
            <!-- Configuring The Database Connection Details -->
            <property name="javax.persistence.jdbc.driver" value="com.mysql.cj.jdbc.Driver" />
            <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/sakila" />

            <!-- ... -->

1 The name of the persistence unit, in this case "sakila", is used to initialize JPAstreamer.
This configuration is just an example configuration for the MySQL Sakila example database. You should use the configuration you already have in place.
If you have multiple persistence units, you can initiate several instances of JPAStreamer to establish connections with different sources.

JPAstreamer does not need any additional configuration and depends solely on this file to establish a database connection. If your starting a project from scratch, make sure to set up your JPA project before trying to use JPAstreamer.

Having obtained a JPAStreamer instance, you are ready to go. Here is an example that includes both the instantiation and the querying:

public static void main(String[] args) {

    JPAStreamer jpaStreamer = JPAStreamer.createJPAStreamerBuilder("sakila") (1)

    long count = jpaStreamer.stream(Film.class)

    System.out.format("There are %d films with a title that starts with A", count);

The next section demonstrates use of the available Stream operators and how they map to SQL constructs.