Java如何从数据库读取BLOB数据？

本示例说明如何从数据库表读取BLOB数据。

package org.nhooo.example.jdbc;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.sql.*;

public class BlobReadDemo {
    private static final String URL = "jdbc:mysql://localhost/nhooo";
    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 name, image FROM product_images";

            PreparedStatement stmt = conn.prepareStatement(sql);
            ResultSet rs = stmt.executeQuery();
            while (rs.next()) {
                String name = rs.getString("name");

                File image = new File(name);
                try (FileOutputStream fos = new FileOutputStream(image)) {
                    byte[] buffer = new byte[1024];

                    // 获取我们的BLOB数据的二进制流
                    InputStream is = rs.getBinaryStream("image");
                    while (is.read(buffer) > 0) {
                        fos.write(buffer);
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

表结构 product_images

CREATE TABLE `product_images` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `product_id` bigint(20) unsigned NOT NULL,
  `name` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `description` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `image` blob,
  PRIMARY KEY (`id`),
  KEY `product_id` (`product_id`),
  CONSTRAINT `product_images_ibfk_1` FOREIGN KEY (`product_id`) REFERENCES `products` (`id`)
) ENGINE=InnoDB;

Maven依赖

<!-- https://search.maven.org/remotecontent?filepath=mysql/mysql-connector-java/8.0.17/mysql-connector-java-8.0.17.jar -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.17</version>
</dependency>