Java cheatsheet

Materialize is wire-compatible with PostgreSQL, which means that Java applications can use common PostgreSQL clients to interact with Materialize. In this guide, we’ll use the PostgreSQL JDBC Driver to connect to Materialize and issue SQL commands.

Connect

To connect to a local Materialize instance using the PostgreSQL JDBC Driver:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;

public class App {

    private final String url = "jdbc:postgresql://localhost:6875/materialize";
    private final String user = "materialize";
    private final String password = "materialize";

    /**
     * Connect to Materialize
     *
     * @return a Connection object
     */
    public Connection connect() {
        Properties props = new Properties();
        props.setProperty("user", user);
        props.setProperty("password", password);
        props.setProperty("ssl","false");
        Connection conn = null;
        try {
            conn = DriverManager.getConnection(url, props);
            System.out.println("Connected to Materialize successfully!");
        } catch (SQLException e) {
            System.out.println(e.getMessage());
        }

        return conn;
    }

    public static void main(String[] args) {
        App app = new App();
        app.connect();
    }
}

To establish the connection to Materialize, call the getConnection() method on the DriverManager class.

Stream

To take full advantage of incrementally updated materialized views from a Java application, instead of querying Materialize for the state of a view at a point in time, use a TAIL statement to request a stream of updates as the view changes.

To read a stream of updates from an existing materialized view, open a long-lived transaction with BEGIN and use TAIL with FETCH to repeatedly fetch all changes to the view since the last query:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;
import java.sql.ResultSet;
import java.sql.Statement;

public class App {

    private final String url = "jdbc:postgresql://localhost:6875/materialize";
    private final String user = "materialize";
    private final String password = "materialize";

    /**
     * Connect to Materialize
     *
     * @return a Connection object
     */
    public Connection connect() throws SQLException {
        Properties props = new Properties();
        props.setProperty("user", user);
        props.setProperty("password", password);
        props.setProperty("ssl","false");

        return DriverManager.getConnection(url, props);

    }

    public void tail() {
        try (Connection conn = connect()) {

            Statement stmt = conn.createStatement();
            stmt.execute("BEGIN");
            stmt.execute("DECLARE c CURSOR FOR TAIL my_view");
            while (true) {
                ResultSet rs = stmt.executeQuery("FETCH ALL c");
                if(rs.next()) {
                    System.out.println(rs.getString(1) + " " + rs.getString(2) + " " + rs.getString(3));
                }
            }
        } catch (SQLException ex) {
            System.out.println(ex.getMessage());
        }
    }

    public static void main(String[] args) {
        App app = new App();
        app.tail();
    }
}

The TAIL output format of rs is a ResultSet of view updates. When a row of a tailed view is updated, two objects will show up in the rows array:

    ...
    1648567756801 1 value_3
    1648567761801 1 value_4
    1648567785802 -1 value_4
    ...

A mz_diff value of -1 indicates that Materialize is deleting one row with the included values. An update is just a retraction (mz_diff: '-1') and an insertion (mz_diff: '1') with the same timestamp.

Query

Querying Materialize is identical to querying a PostgreSQL database: Java executes the query, and Materialize returns the state of the view, source, or table at that point in time.

Because Materialize maintains materialized views in memory, response times are much faster than traditional database queries, and polling (repeatedly querying) a view doesn’t impact performance.

To query a view my_view using a SELECT statement:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;
import java.sql.ResultSet;
import java.sql.Statement;

public class App {

    private final String url = "jdbc:postgresql://localhost:6875/materialize";
    private final String user = "materialize";
    private final String password = "materialize";

    /**
     * Connect to Materialize
     *
     * @return a Connection object
     */
    public Connection connect() throws SQLException {
        Properties props = new Properties();
        props.setProperty("user", user);
        props.setProperty("password", password);
        props.setProperty("ssl","false");

        return DriverManager.getConnection(url, props);

    }

    public void query() {

        String SQL = "SELECT * FROM my_view";

        try (Connection conn = connect();
            Statement stmt = conn.createStatement();
            ResultSet rs = stmt.executeQuery(SQL)) {
            while (rs.next()) {
                System.out.println(rs.getString("my_column"));
            }
        } catch (SQLException ex) {
            System.out.println(ex.getMessage());
        }
    }

    public static void main(String[] args) {
        App app = new App();
        app.query();
    }
}

For more details, see the JDBC documentation.

Insert data into tables

Most data in Materialize will stream in via an external system, but a table can be helpful for supplementary data. For example, you can use a table to join slower-moving reference or lookup data with a stream.

Basic Example: Insert a row of data into a table named countries in Materialize:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;
import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.PreparedStatement;

public class App {

    private final String url = "jdbc:postgresql://localhost:6875/materialize";
    private final String user = "materialize";
    private final String password = "materialize";

    /**
     * Connect to Materialize
     *
     * @return a Connection object
     */
    public Connection connect() throws SQLException {
        Properties props = new Properties();
        props.setProperty("user", user);
        props.setProperty("password", password);
        props.setProperty("ssl","false");

        return DriverManager.getConnection(url, props);

    }

    public void insert() {

        try (Connection conn = connect()) {
            String code = "GH";
            String name = "Ghana";
            PreparedStatement st = conn.prepareStatement("INSERT INTO countries(code, name) VALUES(?, ?)");
            st.setString(1, code);
            st.setString(2, name);
            int rowsDeleted = st.executeUpdate();
            System.out.println(rowsDeleted + " rows inserted.");
            st.close();
        } catch (SQLException ex) {
            System.out.println(ex.getMessage());
        }
    }

    public static void main(String[] args) {
        App app = new App();
        app.insert();
    }
}

Manage sources, views, and indexes

Typically, you create sources, views, and indexes when deploying Materialize, although it is possible to use a Java app to execute common DDL statements.

Create a source from Java

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;
import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.PreparedStatement;

public class App {

    private final String url = "jdbc:postgresql://localhost:6875/materialize";
    private final String user = "materialize";
    private final String password = "materialize";

    /**
     * Connect to Materialize
     *
     * @return a Connection object
     */
    public Connection connect() throws SQLException {
        Properties props = new Properties();
        props.setProperty("user", user);
        props.setProperty("password", password);
        props.setProperty("ssl","false");

        return DriverManager.getConnection(url, props);

    }

    public void source() {

        String SQL = "CREATE SOURCE market_orders_raw_2 FROM PUBNUB "
                   + "SUBSCRIBE KEY 'sub-c-4377ab04-f100-11e3-bffd-02ee2ddab7fe' "
                   + "CHANNEL 'pubnub-market-orders'";

        try (Connection conn = connect()) {
            Statement st = conn.createStatement();
            st.execute(SQL);
            System.out.println("Source created.");
            st.close();
        } catch (SQLException ex) {
            System.out.println(ex.getMessage());
        }
    }

    public static void main(String[] args) {
        App app = new App();
        app.source();
    }
}

For more information, see CREATE SOURCE.

Create a view from Java

    public void view() {

        String SQL = "CREATE VIEW market_orders_2 AS "
                   + "SELECT "
                   + "    val->>'symbol' AS symbol, "
                   + "    (val->'bid_price')::float AS bid_price "
                   + "FROM (SELECT text::jsonb AS val FROM market_orders_raw_2)";

        try (Connection conn = connect()) {
            Statement st = conn.createStatement();
            st.execute(SQL);
            System.out.println("View created.");
            st.close();
        } catch (SQLException ex) {
            System.out.println(ex.getMessage());
        }
    }

For more information, see CREATE VIEW.

Java ORMs

ORM frameworks like Hibernate tend to run complex introspection queries that may use configuration settings, system tables or features not yet implemented in Materialize. This means that even if a tool is compatible with PostgreSQL, it’s not guaranteed that the same integration will work out-of-the-box.

The level of support for these tools will improve as we extend the coverage of pg_catalog in Materialize (#2157) and join efforts with each community to make the integrations Just Work™️.