Java

You can connect to and interact with Databend from various client tools and applications through a native interface designed for Java programming language, the Databend JDBC driver.

Installing Databend JDBC Driver

This topic outlines the steps to download and install the Databend JDBC driver for use in Java-based projects. The driver requires Java LTS (Long-Term Support) versions 1.8 or higher. If your client machine does not have the minimum required version of Java, install Oracle Java or OpenJDK.

To download the Databend JDBC driver:

1. Go to the Maven Central Repository at https://repo1.maven.org/maven2/com/databend/databend-jdbc/
2. Click on the directory of the latest version.
3. Download the jar file, for example, databend-jdbc-0.1.1.jar.

To verify the version of Databend JDBC driver, for example, databend-jdbc-0.1.1.jar, run the following command in the terminal:

java -jar databend-jdbc-0.2.1.jar --version

The Databend JDBC driver is provided as a JAR file and can be integrated directly into your Java-based projects. Alternatively, you can declare a Maven dependency in your project's pom.xml file, like so:

<dependency>
    <groupId>com.databend</groupId>
    <artifactId>databend-jdbc</artifactId>
    <version>0.2.1</version>
</dependency>

DID YOU KNOW?

You can also connect to Databend from DBeaver through the Databend JDBC driver. For more information, see Connecting to Databend with JDBC.

Data Type Mappings

This table illustrates the correspondence between Databend data types and their corresponding Java equivalents:

Databend	Java
TINYINT	Byte
SMALLINT	Short
INT	Integer
BIGINT	Long
UInt8	Short
UInt16	Integer
UInt32	Long
UInt64	BigInteger
Float32	Float
Float64	Double
String	String
Date	String
TIMESTAMP	String
Bitmap	byte[]
Array	String
Decimal	BigDecimal
Tuple	String
Map	String
VARIANT	String

Databend JDBC Driver Behavior Summary

Databend's JDBC Driver generally follows the JDBC specifications. Below is a list of some common basic behaviors, their associated key functions, and the principles behind them.

Basic Behavior	Key Functions	Principle
Establishing a Connection	DriverManager.getConnection, Properties.setProperty	getConnection establishes a connection with Databend using the provided connection string. The Properties object is used to construct connection parameters, such as user and password, which can also be specified within the connection string.
Executing Queries	Statement.createStatement(), Statement.execute()	Statement.execute() performs queries using the v1/query interface.
Batch Inserting	Connection.prepareStatement(), PrepareStatement.setInt(), PrepareStatement.setString(), PrepareStatement.addBatch(), PrepareStatement.executeBatch(), etc.	Databend supports batch insertions and replacements (INSERT INTO and REPLACE INTO) using PrepareStatement objects. The PrepareStatement.setXXX() methods are used for binding values to the parameters of the statement. PrepareStatement.addBatch() adds as much data as possible to the batch for the created statement object. PrepareStatement.executeBatch() uploads data to the built-in Stage and executes insert/replace operations, utilizing Stage Attachment.
Uploading Files to an Internal Stage	Connection.uploadStream	Data will be uploaded to a Stage. By default, the PRESIGN UPLOAD is used to obtain a URL, or if PRESIGN is disabled, the v1/upload_to_stage API is used.
Downloading Files from an Internal Stage	Connection.downloadStream	Data will be downloaded from a Stage using the PRESIGN DOWNLOAD to obtain a URL.

Configuring Connection String

Once the driver is installed and integrated into your project, you can use it to connect to Databend using the following JDBC connection string format:

jdbc:databend://<username>:<password>@<host_port>/<database>?<connection_params>

The connection_params refers to a series of one or more parameters in the format of param=value. Each parameter should be separated by the ampersand character (&), and there should be no spaces anywhere in the connection string. These parameters can be set either in the connection string or in a Properties object passed to the DriverManager.getConnection() method. For example:

Properties props = new Properties();
props.put("parameter1", parameter1Value);
props.put("parameter2", parameter2Value);
Connection con = DriverManager.getConnection("jdbc:databend://user:pass@host/database", props);

For the available connection parameters and their descriptions, see https://github.com/databendcloud/databend-jdbc/blob/main/docs/Connection.md#connection-parameters

Examples

Example: Creating a Database and Table

package com.example;

import java.sql.*;
import java.util.Properties;

public class Main {
    // Connecting to a local Databend with a SQL user named 'user1' and password 'abc123' as an example.
    // Feel free to use your own values while maintaining the same format.
    static final String DB_URL = "jdbc:databend://127.0.0.1:8000";

    public static void main(String[] args) throws Exception {
        Properties properties = new Properties();
        properties.setProperty("user", "user1");
        properties.setProperty("password", "abc123");
        properties.setProperty("SSL", "false");

        Connection conn = DriverManager.getConnection(DB_URL, properties);

        Statement stmt = conn.createStatement();
        String create_sql = "CREATE DATABASE IF NOT EXISTS book_db";
        stmt.execute(create_sql);

        String use_sql = "USE book_db";
        stmt.execute(use_sql);

        String ct_sql = "CREATE TABLE IF NOT EXISTS books(title VARCHAR, author VARCHAR, date VARCHAR)";
        stmt.execute(ct_sql);
        stmt.close();
        conn.close();
        System.exit(0);
    }
}

Example: Copy into or merge into table

    public void copyInto(String tableName, List<String> files) throws Exception {
        String filesStr = "'" + String.join("','", files) + "'";
        String copyIntoSql = String.format("copy into %s from @~ files=(%s) file_format=(type=NDJSON) purge=true;", tableName, filesStr);
        Connection connection = createConnection();
        try (Statement statement = connection.createStatement()) {
            Instant copyIntoStart = Instant.now();
            statement.execute(copyIntoSql);
            ResultSet r = statement.getResultSet();
            while (r.next()) {
            }
            Instant copyIntoEnd = Instant.now();
            System.out.println("Copied files into: " + files.size() + " , time elapsed: " + (copyIntoEnd.toEpochMilli() - copyIntoStart.toEpochMilli()) + "ms");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            connection.close();
        }
    }
// For merge into just replace the copyIntoSql.

tip

1. Because the SQL commands such as SELECT, COPY INTO, and MERGE INTO return a ResultSet object, it is necessary to call rs.next() before accessing the data. Failure to do so may result in the query being canceled. If you don't intend to retrieve the results, you can iterate over the ResultSet using a while loop (while (r.next())) to avoid this issue.
2. For other SQL commands such as CREATE TABLE or DROP TABLE, which are non-query type SQL, you can call statement.execute() directly.

Example: Batch Inserting

In your Java application code, you can insert multiple rows in a single batch by binding parameters in an INSERT statement and calling addBatch() and executeBatch().

As an example, the following code inserts two rows into a table that contains an INT column and a VARCHAR column. The example binds values to the parameters in the INSERT statement and calls addBatch() and executeBatch() to perform a batch insert.

Connection connection = DriverManager.getConnection(url, prop);

PreparedStatement pstmt = connection.prepareStatement("INSERT INTO t(c1, c2) VALUES(?, ?)");
pstmt.setInt(1, 101);
pstmt.setString(2, "test1");
pstmt.addBatch();

pstmt.setInt(1, 102);
pstmt.setString(2, "test2");
pstmt.addBatch();

int[] count = pstmt.executeBatch(); // After execution, count[0]=1, count[1]=1
...
pstmt.close();

Example: Uploading Files to an Internal Stage

 /**
     * Upload inputStream to the databend internal stage, the data would be uploaded as one file with no split.
     * Caller should close the input stream after the upload is done.
     *
     * @param stageName the stage which receive uploaded file
     * @param destPrefix the prefix of the file name in the stage
     * @param inputStream the input stream of the file
     * @param destFileName the destination file name in the stage
     * @param fileSize the file size in the stage
     * @param compressData whether to compress the data
     * @throws SQLException failed to upload input stream
     */
    public void uploadStream(String stageName, String destPrefix, InputStream inputStream, String destFileName, long fileSize, boolean compressData) throws SQLException;

Uploading CSV File to Databend:

        File f = new File("test.csv");
        try (InputStream fileInputStream = Files.newInputStream(f.toPath())) {
            Logger.getLogger(OkHttpClient.class.getName()).setLevel(Level.ALL);
            Connection connection = createConnection();
            String stageName = "test_stage";
            DatabendConnection databendConnection = connection.unwrap(DatabendConnection.class);
            PresignContext.createStageIfNotExists(databendConnection, stageName);
            databendConnection.uploadStream(stageName, "jdbc/test/", fileInputStream, "test.csv", f.length(), false);
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            f.delete();
        }

Example: Downloading Files from an Internal Stage

 /**
     * Download a file from the databend internal stage, the data would be downloaded as one file with no split.
     *
     * @param stageName the stage which contains the file
     * @param sourceFileName the file name in the stage
     * @param decompress whether to decompress the data
     * @return the input stream of the file
     * @throws SQLException
     */
    public InputStream downloadStream(String stageName, String sourceFileName, boolean decompress) throws SQLException;

Downloading CSV File from Databend:

        File f = new File("test.csv");
        try (InputStream fileInputStream = Files.newInputStream(f.toPath())) {
            Logger.getLogger(OkHttpClient.class.getName()).setLevel(Level.ALL);
            Connection connection = createConnection(true);
            String stageName = "test_stage";
            DatabendConnection databendConnection = connection.unwrap(DatabendConnection.class);
            PresignContext.createStageIfNotExists(databendConnection, stageName);
            databendConnection.uploadStream(stageName, "jdbc/test/", fileInputStream, "test.csv", f.length(), false);
            InputStream downloaded = databendConnection.downloadStream(stageName, "jdbc/test/test.csv", false);
            byte[] arr = streamToByteArray(downloaded);
            System.out.println(arr);
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            f.delete();
        }

Example: Integrating with Databend Cloud

Before you start, make sure you have successfully created a warehouse and obtained the connection information. For how to do that, see Connecting to a Warehouse.

Step 1. Add Dependencies with Maven

<dependency>
    <groupId>com.databend</groupId>
    <artifactId>databend-jdbc</artifactId>
    <version>0.2.8</version>
</dependency>

Step 2. Connect with databend-jdbc

Create a file named sample.java with the following code:

package databend_cloud;

import java.sql.*;
import java.util.Properties;

public class sample {
    public static void main(String[] args) throws Exception {

        String url = "jdbc:databend://{WAREHOUSE_HOST}:443/{DATABASE}";
        Properties properties = new Properties();
        properties.setProperty("user", "{USER}");
        properties.setProperty("password", "{PASSWORD}");
        properties.setProperty("SSL", "true");
        Connection connection = DriverManager.getConnection(url, properties);

        // Execute
        connection.createStatement().execute("CREATE TABLE IF NOT EXISTS sample_test(id TINYINT, obj VARIANT, d TIMESTAMP, s String, arr ARRAY(INT64)) Engine = Fuse");

        // SELECT
        Statement statement = connection.createStatement();
        statement.execute("SELECT number from numbers(200000) order by number");
        ResultSet r = statement.getResultSet();
        r.next();
        for (int i = 1; i < 1000; i++) {
            r.next();
            System.out.println(r.getInt(1));
        }

        // INSERT INTO Using executeBatch()
        connection.setAutoCommit(false);
        PreparedStatement ps = connection.prepareStatement("insert into sample_test values");
        ps.setInt(1, 1);
        ps.setString(2, "{\"a\": 1,\"b\": 2}");
        ps.setTimestamp(3, Timestamp.valueOf("1983-07-12 21:30:55.888"));
        ps.setString(4, "hello world, 你好");
        ps.setString(5, "[1,2,3,4,5]");
        ps.addBatch();
        int[] ans = ps.executeBatch();
        Statement s = connection.createStatement();

        System.out.println("execute select on table");
        statement.execute("SELECT * from sample_test");
        ResultSet r2 = statement.getResultSet();

        while (r2.next()) {
            System.out.println(r2.getInt(1));
            System.out.println(r2.getString(2));
            System.out.println(r2.getTimestamp(3).toString());
            System.out.println(r2.getString(4));
            System.out.println(r2.getString(5));
        }
        connection.close();
    }
}

tip

Replace {USER}, {PASSWORD}, {WAREHOUSE_HOST}, and {DATABASE} in the code with your connection information. For how to obtain the connection information, see Connecting to a Warehouse.

Step 3. Run sample with Maven

$ mvn compile
$ mvn exec:java -D exec.mainClass="databend_cloud.sample"