如何存储Blob变量值？

存储Blob变量值

一、简介

Blob（Binary Large Object）是一种用于存储二进制数据的数据库类型，适用于存储大量数据如图片、音频、视频等，本文将详细介绍如何在Java和JavaScript中存储Blob变量值。

二、在Java中存储Blob变量值

1. 使用PreparedStatement的setBlob()方法

import java.io.File;
import java.io.FileInputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
public class BlobExample {
    public static void main(String[] args) throws Exception {
        // 连接数据库
        String url = "jdbc:mysql://localhost/sampleDB";
        Connection conn = DriverManager.getConnection(url, "root", "password");
        // SQL语句
        String sql = "INSERT INTO table_name (blob_field) VALUES (?)";
        // 创建PreparedStatement对象
        PreparedStatement pstmt = conn.prepareStatement(sql);
        // 文件路径
        File file = new File("path_to_file");
        // 文件输入流
        FileInputStream fis = new FileInputStream(file);
        // 设置Blob字段的值
        pstmt.setBlob(1, fis);
        // 执行SQL语句
        pstmt.executeUpdate();
        // 关闭资源
        fis.close();
        pstmt.close();
        conn.close();
    }
}

2. 使用Blob接口的setBinaryStream()方法

import java.io.File;
import java.io.FileInputStream;
import java.sql.Blob;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
public class BlobExample {
    public static void main(String[] args) throws Exception {
        // 连接数据库
        String url = "jdbc:mysql://localhost/sampleDB";
        Connection conn = DriverManager.getConnection(url, "root", "password");
        // SQL语句
        String sql = "INSERT INTO table_name (blob_field) VALUES (?)";
        // 创建PreparedStatement对象
        PreparedStatement pstmt = conn.prepareStatement(sql);
        // 创建Blob对象
        Blob blob = conn.createBlob();
        // 获取OutputStream对象
        OutputStream os = blob.setBinaryStream(1);
        // 文件路径
        File file = new File("path_to_file");
        // 文件输入流
        FileInputStream fis = new FileInputStream(file);
        // 缓冲区
        byte[] buffer = new byte[1024];
        int len;
        while ((len = fis.read(buffer)) != -1) {
            os.write(buffer, 0, len);
        }
        // 设置Blob字段的值
        pstmt.setBlob(1, blob);
        // 执行SQL语句
        pstmt.executeUpdate();
        // 关闭资源
        fis.close();
        os.close();
        pstmt.close();
        conn.close();
    }
}

从数据库中读取Blob数据

import java.io.File;
import java.io.FileOutputStream;
import java.sql.Blob;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
public class BlobExample {
    public static void main(String[] args) throws Exception {
        // 连接数据库
        String url = "jdbc:mysql://localhost/sampleDB";
        Connection conn = DriverManager.getConnection(url, "root", "password");
        // SQL查询语句
        String sql = "SELECT id, blob_field FROM table_name WHERE id = ?";
        // 创建PreparedStatement对象
        PreparedStatement pstmt = conn.prepareStatement(sql);
        pstmt.setInt(1, 1); // 设置参数值
        // 执行查询语句
        ResultSet rs = pstmt.executeQuery();
        // 处理结果集
        if (rs.next()) {
            Blob blob = rs.getBlob("blob_field");
            File file = new File("output_file");
            FileOutputStream fos = new FileOutputStream(file);
            byte[] buffer = new byte[1024];
            int len;
            while ((len = blob.getBinaryStream().read(buffer)) != -1) {
                fos.write(buffer, 0, len);
            }
            fos.close();
        }
        // 关闭资源
        rs.close();
        pstmt.close();
        conn.close();
    }
}

三、在JavaScript中存储Blob变量值

创建Blob对象并触发下载

let text = "Download this text as a file.";
let blob = new Blob([text], { type: 'text/plain' });
let url = URL.createObjectURL(blob);
let a = document.createElement('a');
a.href = url;
a.download = 'example.txt';
document.body.appendChild(a);
a.click();
document.body.removeChild(a);
URL.revokeObjectURL(url);

let canvas = document.getElementById('myCanvas');
canvas.toBlob(function(blob) {
    let url = URL.createObjectURL(blob);
    let a = document.createElement('a');
    a.href = url;
    a.download = 'canvas_image.png';
    document.body.appendChild(a);
    a.click();
    document.body.removeChild(a);
    URL.revokeObjectURL(url);
}, 'image/png');

let text = "Read this text from a Blob.";
let blob = new Blob([text], { type: 'text/plain' });
let reader = new FileReader();
reader.onload = function(event) {
    console.log(event.target.result);
};
reader.readAsText(blob);

4. 与XMLHttpRequest API集成上传Blob对象

let text = "Upload this text as a file.";
let blob = new Blob([text], { type: 'text/plain' });
let xhr = new XMLHttpRequest();
xhr.open('POST', '/upload', true);
xhr.onload = function() {
    if (xhr.status === 200) {
        console.log('Upload successful');
    } else {
        console.log('Upload failed');
    }
};
xhr.send(blob);

四、相关问题与解答栏目

1. 如何将Blob类型数据转换为字节数组？

答：可以通过以下步骤将Blob类型数据转换为字节数组：从数据库中获取Blob类型的数据；使用Blob对象的length()方法获取Blob类型数据的长度；使用Blob对象的getBinaryStream()方法获取Blob类型数据的输入流；创建一个字节数组，其长度为Blob类型数据的长度，并使用输入流将Blob类型数据读取到字节数组中，以下是示例代码：

import java.sql.*;
public class Main {
    public static void main(String[] args) throws Exception {
        String url = "jdbc:mysql://localhost/test";
        Connection con = DriverManager.getConnection(url, "root", "password");
        String query = "SELECT * FROM my_table WHERE id = ?";
        PreparedStatement pstmt = con.prepareStatement(query);
        pstmt.setInt(1, 1);
        ResultSet rs = pstmt.executeQuery();
        if (rs.next()) {
            Blob blob = rs.getBlob("my_blob_column");
            byte[] bytes = blob.getBytes(1, (int) blob.length());
            // Now you can use the byte array as needed...
        }
    }
}

各位小伙伴们，我刚刚为大家分享了有关“存储blob变量值”的知识，希望对你们有所帮助。如果您还有其他相关问题需要解决，欢迎随时提出哦！