How do I read CLOBs data from database?

package org.kodejava.example.jdbc;

import java.io.File;
import java.io.FileWriter;
import java.io.Reader;
import java.sql.*;

public class ClobReadDemo {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "";

    public static void main(String[] args) {
        try (Connection conn =
                 DriverManager.getConnection(URL, USERNAME, PASSWORD)) {

            String sql = "SELECT book_isbn, data FROM book_excerpts";
            PreparedStatement stmt = conn.prepareStatement(sql);

            ResultSet resultSet = stmt.executeQuery();
            while (resultSet.next()) {
                String bookIsbn = resultSet.getString("book_isbn");
                // Get the character stream of our CLOB file
                Reader reader = resultSet.getCharacterStream("data");

                File file = new File(bookIsbn + ".txt");
                try (FileWriter writer = new FileWriter(file)) {
                    char[] buffer = new char[1];
                    while (reader.read(buffer) > 0) {
                        writer.write(buffer);
                    }
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

The structure of book_excerpts table.

CREATE TABLE `book_excerpts` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `book_isbn` varchar(50) NOT NULL,
  `description` varchar(255)  NOT NULL,
  `data` longtext,
  PRIMARY KEY (`id`),
  KEY `book_isbn` (`book_isbn`),
  CONSTRAINT `book_excerpts_ibfk_1` FOREIGN KEY (`book_isbn`) REFERENCES `books` (`isbn`)
) ENGINE=InnoDB;

Maven dependencies

<!-- https://search.maven.org/remotecontent?filepath=mysql/mysql-connector-java/5.1.47/mysql-connector-java-5.1.47.jar -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.47</version>
</dependency>

Wayan Saryada

Founder at Kode Java Org
I am a programmer, a runner, a recreational diver, currently live in the island of Bali, Indonesia. Mostly programming in Java, Spring Framework, Hibernate / JPA. You can support my works by donating here. Thank you 🥳

1 Comments

  1. Worked like magic.. Thank you for this great code snippet. Keep posting such nice stuff and keep empowering the community.

    Reply

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