1.首先建立数据库。。。建立一个名为books的数据库，建立一个fs表。

create database if not exists books;
use books;
create table fs(
    id int unsigned auto_increment primary key ,
    name varchar(50) not null ,
    files longblob
);

假如你不喜欢代码建立，也可以直接用数据库管理工机来建立，注意数据类型。

我用的是navicat这个工具。。。

 一定不要把数据类型搞错了

 准备工作完成后我们建立一个maven项目。。。（不会的小伙伴可以参考这篇博客）

maven的下载安装与配置环境变量！！！（全网最详细）_明天更新的博客-CSDN博客

2.建立好maven项目我们要添加依赖：

 <dependencies>
        <!-- com.mysql/mysql-connector-j -->
        <dependency>
            <groupId>com.mysql</groupId>
            <artifactId>mysql-connector-j</artifactId>
            <version>8.1.0</version>
        </dependency>

        <!-- org.junit.jupiter/junit-jupiter-api -->
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>5.10.0</version>
            <scope>test</scope>
        </dependency>

    </dependencies>

3.建立Java文件。这里用到JDBC的内容和单元测试这两个部分。

（一定要注意我们是在这个包下面建立的Java文件）

 4.编写Java程序。（这是将jpg存入数据库）我用的是本地照片。。。

写Java程序时注意你的数据库名字是否正确。

@Test @DisplayName("将文件存入数据库中")
    void savefile() {
        InputStream is = null;
        String file = "C:\\Users\\admin\\Desktop\\girl.jpg";
        File f = new File(file);
        String fn = f.getName();
        try {
            is = new FileInputStream(f);
        } catch (FileNotFoundException e) {
            throw new RuntimeException(e);
        }
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            try {
                Connection conn = DriverManager.getConnection("jdbc:mysql:/books", "root", "");
                PreparedStatement ps = conn.prepareStatement("insert into fs(name,files) values (?,?)");
                ps.setString(1, fn);
                ps.setBlob(2, is);
                int result = ps.executeUpdate();
                if (result > 0) {
                    System.out.println("成功将" + fn + "存入数据库");
                }
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
    }

 你可以点击鼠标右键将文件保存下来，看是否正确。

你以为这就完了？？？？

远远不够，我们再写一个读取程序，将这个照片读取出来。。。。

5.从数据库中读取文件。

 @Test@DisplayName("从数据库中读取文件")
    void readfile() {
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            try {
                Connection conn = DriverManager.getConnection("jdbc:mysql:/books", "root", "");
                PreparedStatement ps = conn.prepareStatement("select * from fs");
                ResultSet rs = ps.executeQuery();
                while (rs.next()) {
                    InputStream inputStream = rs.getBinaryStream(3);
                    OutputStream out = new FileOutputStream(UUID.randomUUID().toString().concat(".jpg"));
                    byte[] bytes = new byte[10240];
                    while (inputStream.read(bytes) > 0) {
                        out.write(bytes);
                    }
                }
            } catch (SQLException e) {
                throw new RuntimeException(e);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
    }

读取完成你会发现：

 什么你说你想要照片？？？

照片没有，代码倒是有。。。

Java：

/*
 * Copyright (c) 2020, 2023,  All rights reserved.
 *
 */
package cn.scl;

import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;

import java.io.*;
import java.sql.*;
import java.util.UUID;

/**
 * <p>Project: filesJDBC - Dome</p>
 * <p>Powered by scl On 2023-08-03 19:30:58</p>
 * <p>描述：<p>
 *
 * @author scl [1846080280@qq.com]
 * @version 1.0
 * @since 17
 */
public class Dome {

    @Test@DisplayName("从数据库中读取文件")
    void readfile() {
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            try {
                Connection conn = DriverManager.getConnection("jdbc:mysql:/books", "root", "");
                PreparedStatement ps = conn.prepareStatement("select * from fs");
                ResultSet rs = ps.executeQuery();
                while (rs.next()) {
                    InputStream inputStream = rs.getBinaryStream(3);
                    OutputStream out = new FileOutputStream(UUID.randomUUID().toString().concat(".jpg"));
                    byte[] bytes = new byte[10240];
                    while (inputStream.read(bytes) > 0) {
                        out.write(bytes);
                    }
                }
            } catch (SQLException e) {
                throw new RuntimeException(e);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
    }


    @Test @DisplayName("将文件存入数据库中")
    void savefile() {
        InputStream is = null;
        String file = "C:\\Users\\admin\\Desktop\\girl.jpg";
        File f = new File(file);
        String fn = f.getName();
        try {
            is = new FileInputStream(f);
        } catch (FileNotFoundException e) {
            throw new RuntimeException(e);
        }
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            try {
                Connection conn = DriverManager.getConnection("jdbc:mysql:/books", "root", "");
                PreparedStatement ps = conn.prepareStatement("insert into fs(name,files) values (?,?)");
                ps.setString(1, fn);
                ps.setBlob(2, is);
                int result = ps.executeUpdate();
                if (result > 0) {
                    System.out.println("成功将" + fn + "存入数据库");
                }
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
    }

}

 xml: 

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>filesJDBC</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>17</maven.compiler.source>
        <maven.compiler.target>17</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>
    <dependencies>
        <!-- com.mysql/mysql-connector-j -->
        <dependency>
            <groupId>com.mysql</groupId>
            <artifactId>mysql-connector-j</artifactId>
            <version>8.1.0</version>
        </dependency>

        <!-- org.junit.jupiter/junit-jupiter-api -->
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>5.10.0</version>
            <scope>test</scope>
        </dependency>

    </dependencies>
</project>