+
−/*
+
− * SPDX-License-Identifier: MPL-2.0
+
− *
+
− * This Source Code Form is subject to the terms of the Mozilla Public
+
− * License, v. 2.0.  If a copy of the MPL was not distributed with this
+
− * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
− *
+
− * Copyright 2024, 2025 MonetDB Foundation;
+
− * Copyright August 2008 - 2023 MonetDB B.V.;
+
− * Copyright 1997 - July 2008 CWI.
+
− */
+
−
+
−import org.monetdb.jdbc.MonetConnection;
+
−
+
−import java.io.BufferedReader;
+
−import java.io.BufferedWriter;
+
−import java.io.IOException;
+
−import java.io.InputStream;
+
−import java.io.InputStreamReader;
+
−import java.io.OutputStream;
+
−import java.io.OutputStreamWriter;
+
−import java.io.PrintStream;
+
−import java.nio.charset.Charset;
+
−import java.nio.charset.StandardCharsets;
+
−import java.nio.file.FileSystems;
+
−import java.nio.file.Files;
+
−import java.nio.file.Path;
+
−import java.sql.Connection;
+
−import java.sql.DriverManager;
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−import java.sql.ResultSet;
+
−import java.sql.SQLException;
+
−import java.sql.SQLNonTransientException;
+
−import java.sql.Statement;
+
−
+
−public class OnClientExample {
+
−
+
−	public static void main(String[] args) {
+
−		int status;
+
−		try {
+
−			// Ideally this would not be hardcoded..
+
−			final String dbUrl = "jdbc:monetdb://localhost:50000/demo";
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−			final String userName = "monetdb";
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−			final String password = "monetdb";
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−			final String uploadDir = "/home/jvr/mydata";
+
−			final boolean filesAreUtf8 = false;
+
−			String[] queries = {
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−					"DROP TABLE IF EXISTS mytable",
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−					"CREATE TABLE mytable(i INT, t TEXT)",
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−
+
−					// with this filename our handler will make up data by itself
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−					"COPY INTO mytable FROM 'generated.csv' ON CLIENT",
+
−
+
−					// with this filename our handler will access the file system
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−					"COPY INTO mytable FROM 'data.csv' ON CLIENT",
+
−
+
−					// with this statement, the server will ask the handler to stop halfway
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−					"COPY 20 RECORDS OFFSET 5 INTO mytable FROM 'generated.csv' ON CLIENT",
+
−
+
−					// this demonstrates sending errors
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−					"COPY INTO mytable FROM 'nonexistentfilethatdoesnotexist.csv' ON CLIENT",
+
−
+
−					// downloads but does not write to file, only counts the lines
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−					"COPY SELECT * FROM mytable INTO 'justcount.csv' ON CLIENT",
+
−
+
−					// downloads to actual file
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−					"COPY SELECT * FROM mytable INTO 'download.csv' ON CLIENT",
+
−
+
−					// demonstrate that the connection is still alive
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−					"SELECT COUNT(*) FROM mytable",
+
−			};
+
−
+
−			status = run(dbUrl, userName, password, uploadDir, filesAreUtf8, queries);
+
−
+
−		} catch (Exception e) {
+
−			status = 1;
+
−			e.printStackTrace();
+
−		}
+
−		System.exit(status);
+
−	}
+
−
+
−	private static int run(String dbUrl, String userName, String password, String uploadDir, boolean filesAreUtf8, String[] queries) throws ClassNotFoundException, SQLException {
+
−		int status = 0;
+
−
+
−		// Connect
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−		Class.forName("org.monetdb.jdbc.MonetDriver");
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−		Connection conn = DriverManager.getConnection(dbUrl, userName, password);
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−
+
−		// Register upload- and download handler
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−		MyHandler handler = new MyHandler(uploadDir, filesAreUtf8);
+
−		MonetConnection monetConnection = conn.unwrap(MonetConnection.class);
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−		monetConnection.setUploadHandler(handler);
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−		monetConnection.setDownloadHandler(handler);
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−
+
−		Statement stmt = conn.createStatement();
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−		for (String q : queries) {
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−			System.out.println(q);
+
−			try {
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−				boolean hasResultSet = stmt.execute(q);
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−				if (hasResultSet) {
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−					ResultSet rs = stmt.getResultSet();
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−					long count = 0;
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−					while (rs.next()) {
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−						count++;
+
−					}
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−					rs.close();
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−					System.out.printf("  OK, returned %d rows%n", count);
+
−				} else {
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−					System.out.printf("  OK, updated %d rows%n", stmt.getUpdateCount());
+
−				}
+
−			} catch (SQLNonTransientException e) {
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−				throw e;
+
−			} catch (SQLException e) {
+
−				System.out.println("  => SQL ERROR " + e.getMessage());
+
−				status = 1;
+
−			}
+
−		}
+
−
+
−		return status;
+
−	}
+
−
+
−
+
−	private static class MyHandler implements MonetConnection.UploadHandler, MonetConnection.DownloadHandler {
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−		private final Path uploadDir;
+
−		private final boolean filesAreUtf8;
+
−		private boolean stopUploading = false;
+
−
+
−		public MyHandler(String uploadDir, boolean filesAreUtf8) {
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−			this.uploadDir = FileSystems.getDefault().getPath(uploadDir).normalize();
+
−			this.filesAreUtf8 = filesAreUtf8;
+
−		}
+
−
+
−		@Override
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−		public void uploadCancelled() {
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−			System.out.println("  CANCELLATION CALLBACK: server cancelled the upload");
+
−			stopUploading = true;
+
−		}
+
−
+
−		@Override
+
−		public void handleUpload(MonetConnection.Upload handle, String name, boolean textMode, long linesToSkip) throws IOException {
+
−			// We can upload data read from the file system but also make up our own data
+
−			if (name.equals("generated.csv")) {
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−				uploadGeneratedData(handle, linesToSkip);
+
−			} else {
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−				uploadFileData(handle, name, textMode, linesToSkip);
+
−			}
+
−		}
+
−
+
−		@Override
+
−		public void handleDownload(MonetConnection.Download handle, String name, boolean textMode) throws IOException {
+
−			if (name.equals("justcount.csv")) {
+
−				justCountLines(handle);
+
−			} else {
+
−				downloadFileData(handle, name, textMode);
+
−			}
+
−		}
+
−
+
−		private Path securelyResolvePath(String name) {
+
−			Path p = uploadDir.resolve(name).normalize();
+
−			if (p.startsWith(uploadDir)) {
+
−				return p;
+
−			} else {
+
−				return null;
+
−			}
+
−		}
+
−
+
−		private void uploadGeneratedData(MonetConnection.Upload handle, long toSkip) throws IOException {
+
−			// Set the chunk size to a tiny amount, so we can demonstrate
+
−			// cancellation handling. The default chunk size is one megabyte.
+
−			// DO NOT DO THIS IN PRODUCTION!
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−			handle.setChunkSize(50);
+
−
+
−			// Make up some data and upload it.
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−			PrintStream stream = handle.getStream();
+
−			long n = 100;
+
−			System.out.printf("  HANDLER: uploading %d generated lines, numbered %d to %d%n", n - toSkip, toSkip + 1, n);
+
−			long i;
+
−			for (i = toSkip + 1; i <= n; i++) {
+
−				if (stopUploading) {
+
−					System.out.printf("  HANDLER: at line %d we noticed the server asked us to stop sending%n", i);
+
−					break;
+
−				}
+
−				stream.printf("%d|the number is %d%n", i, i);
+
−			}
+
−			System.out.println("  HANDLER: done uploading");
+
−			stream.close();
+
−		}
+
−
+
−		private void uploadFileData(MonetConnection.Upload handle, String name, boolean textMode, long linesToSkip) throws IOException {
+
−			// Validate the path, demonstrating two ways of dealing with errors
+
−			Path path = securelyResolvePath(name);
+
−			if (path == null || !Files.exists(path)) {
+
−				// This makes the COPY command fail but keeps the connection
+
−				// alive. Can only be used if we haven't sent any data yet
+
−				handle.sendError("Invalid path");
+
−				return;
+
−			}
+
−			if (!Files.isReadable(path)) {
+
−				// As opposed to handle.sendError(), we can throw an IOException
+
−				// at any time. Unfortunately, the file upload protocol does not
+
−				// provide a way to indicate to the server that the data sent so
+
−				// far is incomplete, so for the time being throwing an
+
−				// IOException from {@handleUpload} terminates the connection.
+
−				throw new IOException("Unreadable: " + path);
+
−			}
+
−
+
−			boolean binary = !textMode;
+
−			if (binary) {
+
−				uploadAsBinary(handle, path);
+
−			} else if (linesToSkip == 0 && filesAreUtf8) {
+
−				// Avoid unnecessary UTF-8 -> Java String -> UTF-8 conversions
+
−				// by pretending the data is binary.
+
−				uploadAsBinary(handle, path);
+
−			} else {
+
−				// Charset and skip handling are really necessary
+
−				uploadAsText(handle, path, linesToSkip);
+
−			}
+
−		}
+
−
+
−		private void uploadAsText(MonetConnection.Upload handle, Path path, long toSkip) throws IOException {
+
−			BufferedReader reader = Files.newBufferedReader(path);// Converts from system encoding to Java text
+
−			for (long i = 0; i < toSkip; i++) {
+
−				reader.readLine();
+
−			}
+
−			// This variant of uploadFrom takes a Reader
+
−			handle.uploadFrom(reader); // Converts from Java text to UTF-8 as required by MonetDB
+
−		}
+
−
+
−		private void uploadAsBinary(MonetConnection.Upload handle, Path path) throws IOException {
+
−			// No charset conversion whatsoever..
+
−			// Use this for binary data or when you are certain the file is UTF-8 encoded.
+
−			InputStream stream = Files.newInputStream(path);
+
−			// This variant of uploadFrom takes a Stream
+
−			handle.uploadFrom(stream);
+
−		}
+
−
+
−		private void justCountLines(MonetConnection.Download handle) throws IOException {
+
−			System.out.println("  HANDLER: not writing the download to file, just counting the lines");
+
−			InputStream stream = handle.getStream();
+
−			InputStreamReader reader = new InputStreamReader(stream, StandardCharsets.UTF_8); // MonetDB always sends UTF-8
+
−			BufferedReader bufreader = new BufferedReader(reader);
+
−			long count = 0;
+
−			while (bufreader.readLine() != null) {
+
−				count++;
+
−			}
+
−			System.out.println("  HANDLER: file had " + count + " lines");
+
−		}
+
−
+
−		private void downloadFileData(MonetConnection.Download handle, String name, boolean textMode) throws IOException {
+
−			Path path = securelyResolvePath(name);
+
−			if (path == null) {
+
−				handle.sendError("Illegal path");
+
−				return;
+
−			}
+
−
+
−			OutputStream stream = Files.newOutputStream(path);
+
−			if (!textMode || filesAreUtf8) {
+
−				handle.downloadTo(stream);
+
−				stream.close(); // do not forget this
+
−			} else {
+
−				OutputStreamWriter writer = new OutputStreamWriter(stream, Charset.defaultCharset()); // let system decide the encoding
+
−				BufferedWriter bufwriter = new BufferedWriter(writer);
+
−				handle.downloadTo(bufwriter);
+
−				bufwriter.close(); // do not forget this
+
−			}
+
−		}
+
−	}
+
−}