samples/connectors/src/main/java/org/apache/edgent/samples/connectors/jdbc/SimpleReaderApp.java

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to you under the Apache License, Version 2.0 (the
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  http://www.apache.org/licenses/LICENSE-2.0

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package org.apache.edgent.samples.connectors.jdbc;

import java.io.File;
import java.nio.file.Files;
import java.util.List;
import java.util.Properties;

import org.apache.edgent.connectors.jdbc.JdbcStreams;
import org.apache.edgent.providers.direct.DirectProvider;
import org.apache.edgent.topology.TStream;
import org.apache.edgent.topology.Topology;

/**
 * A simple JDBC connector sample demonstrating streaming read access
 * of a dbms table and creating stream tuples from the results.
 */
public class SimpleReaderApp {
    private final Properties props;

    public static void main(String[] args) throws Exception {
        if (args.length != 1)
            throw new Exception("missing pathname to jdbc.properties file");
        SimpleReaderApp reader = new SimpleReaderApp(args[0]);
        reader.run();
    }

    /**
     * @param jdbcPropsPath pathname to properties file
     */
    SimpleReaderApp(String jdbcPropsPath) throws Exception {
        props = new Properties();
        props.load(Files.newBufferedReader(new File(jdbcPropsPath).toPath()));
    }
    
    /**
     * Create a topology for the writer application and run it.
     */
    private void run() throws Exception {
        DirectProvider tp = new DirectProvider();
        
        // build the application/topology
        
        Topology t = tp.newTopology("jdbcSampleWriter");

        // Create the JDBC connector
        JdbcStreams myDb = new JdbcStreams(t,
                () -> DbUtils.getDataSource(props),
                dataSource -> dataSource.getConnection());
        
        // Create a sample stream of tuples containing a person id
        List<PersonId> personIdList = PersonData.toPersonIds(PersonData.loadPersonData(props));
        personIdList.add(new PersonId(99999));
        TStream<PersonId> personIds = t.collection(personIdList);
        
        // For each tuple on the stream, read info from the db table
        // using the "id", and create a Person tuple on the result stream.
        TStream<Person> persons = myDb.executeStatement(personIds,
                () -> "SELECT id, firstname, lastname FROM persons WHERE id = ?",
                (personId,stmt) -> stmt.setInt(1, personId.id),
                (personId,rSet,exc,resultStream) -> {
                        if (exc != null) {
                            // some failure processing this tuple. an error was logged.
                            System.err.println("Unable to process id="+personId+": "+exc);
                            return;
                        }
                        if (rSet.next()) {
                            resultStream.accept(
                                    new Person(rSet.getInt("id"),
                                            rSet.getString("firstname"),
                                            rSet.getString("lastname")));
                        }
                        else {
                            System.err.println("Unknown person id="+personId.id);
                        }
                    }
                );
        
        // print out Person tuples as they are retrieved 
        persons.sink(person -> System.out.println("retrieved person: "+person));
        
        // run the application / topology
        tp.submit(t);
    }
}