As RisingWave is wire-compatible with PostgreSQL, you can use third-party PostgreSQL drivers to interact with RisingWave from your Java applications. In this guide, we use the PostgreSQL JDBC driver to connect to RisingWave.

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Run RisingWave

To learn about how to run RisingWave, see Run RisingWave.
You do not need to connect to RisingWave at this stage.

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Download the PostgreSQL JDBC driver

Download the correct version of the PostgreSQL JDBC driver from the PostgreSQL JDBC website based on the Java version in your environment. Ensure the JDBC driver is added to your Java project.

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Connect to RisingWave

To connect to RisingWave with the JDBC driver, specify the connection parameters by passing either a connection URL or a Properties object parameter to DriverManager.getConnection. 
import java.sql.*;
import java.util.Properties;

public class RisingWaveConnect {

    public static void main (String arg[]) throws SQLException{
        String url = "jdbc:postgresql://localhost:4566/dev";
        Properties props = new Properties();
        props.setProperty("user", "root");
        props.setProperty("password", "secret");
        props.setProperty("ssl", "false");
        Connection conn = DriverManager.getConnection(url, props);

        //If needed, add the code for issuing queries here.
        conn.close();
    }   
}

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Create a source

The code below creates a source walk with the datagen connector. The datagen connector is used to generate mock data. The walk source consists of two columns, distance and duration, which respectively represent the distance and the duration of a walk. The source is a simplified version of the data that is tracked by smart watches. 
import java.sql.*;
import java.util.Properties;

public class source {

    public static void main (String arg[]) throws SQLException {

        //If necessary, add the code for connecting to RisingWave here.

        String sqlQuery = "CREATE TABLE walk (distance INT, duration INT) WITH " +
        "(connector = 'datagen'," +
        "fields.distance.kind = 'sequence'," +
        "fields.distance.start = '1'," +
        "fields.distance.end  = '60'," +
        "fields.duration.kind = 'sequence'," +
        "fields.duration.start = '1'," +
        "fields.duration.end = '30'," +
        "datagen.rows.per.second='15'," +
        "datagen.split.num = '1') " +
        "FORMAT PLAIN ENCODE JSON";
        PreparedStatement st = conn.prepareStatement(sqlQuery); //Define a query and pass it to a PreparedStatement object.
        st.executeQuery(); //Execute the query.
        conn.close();  //Close the connection.
    }
}

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Create a materialized view

The code in this section creates a materialized view counter to capture the latest total distance and duration. 
import java.sql.*;
import java.util.Properties;

public class create_mv {

    public static void main (String arg[]) throws SQLException {

        //If necessary, add the code for connecting to RisingWave here.

        String sqlQuery = "CREATE MATERIALIZED VIEW counter AS " +
        "SELECT sum(distance) AS total_distance, sum(duration) AS total_duration " +
        "FROM walk; ";
        PreparedStatement st = conn.prepareStatement(sqlQuery); 
        st.executeQuery();
        conn.close();
    }
}

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Query a materialized view

The code in this section queries the materialized view counter to get the real-time data. 
import java.sql.*;
import java.util.Properties;

public class retrieve {

    public static void main (String arg[]) throws SQLException {

        //If necessary, add the code for connecting to RisingWave here.

        PreparedStatement showMV = conn.prepareStatement("SELECT * FROM counter;");
        ResultSet rs = showMV.executeQuery();
        while (rs.next()) {
            System.out.println("Total distance: " + rs.getString("total_distance"));
            System.out.println("Total duration: " + rs.getString("total_duration"));
        }
    }
}