一、前言

各位亲爱的们，之前介绍过了上传超大文件到MinIO：

• MinIO分片上传超大文件（纯服务端）
• MinIO分片上传超大文件（非纯服务端）

这里最后再补充一下从MinIO下载超大文件。

二、从MinIO分片下载大文件

2.1、确定文件大小

根据文件名查找MinIO上对应文件的大小。

核心API：minioClient.statObject(StatObjectArgs args)。

StatObjectResponse statObjectResponse = minioClient.statObject(StatObjectArgs.builder().bucket(bucketName).object(fileName).build());
long totalLength = statObjectResponse.size();
System.out.println("目标文件总大小: " + totalLength);

2.2、分片下载

这里举例分片大小为1000个字节，根据文件总大小计算出分片数，最后将每个分片保存下来。

核心API：minioClient.getObject(GetObjectArgs args)。

final long CHUNK_LENGTH = 1000;
// 从目标文件开始下载
long startByte = 0l;
long chunkCount = (long) Math.ceil((double) totalLength / CHUNK_LENGTH);
System.out.println("预计总分片数: " + chunkCount);
String targetPath = "C://tmp";
for (long i = 0; i < chunkCount; i++) {GetObjectResponse response = minioClient.getObject(GetObjectArgs.builder().bucket(bucketName).object(fileName).offset(startByte).length(CHUNK_LENGTH).build());String chunkFilePath = targetPath + "//" + (i + 1) + ".part";FileOutputStream fileOutputStream = new FileOutputStream(chunkFilePath);byte[] buffer = new byte[1024];int bytesRead;while ((bytesRead = response.read(buffer)) != -1) {fileOutputStream.write(buffer, 0, bytesRead);}System.out.println("分片已下载: " + chunkFilePath + " 大小: " + new File(chunkFilePath).length());startByte = (i + 1) * CHUNK_LENGTH;
}

2.3、合并分片

将每个分片文件合并到一个文件里。

String mergedFilePath = targetPath + "//" + "result.txt";
BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(mergedFilePath));
for (long i = 0; i < chunkCount; i++) {String chunkFilePath = targetPath + "//" + (i + 1) + ".part";BufferedInputStream bis = new BufferedInputStream(new FileInputStream(chunkFilePath));byte[] buffer = new byte[1024];int bytesRead;while ((bytesRead = bis.read(buffer)) != -1) {bos.write(buffer, 0, bytesRead);}bis.close();
}
bos.close();

三、完整测试代码

import io.minio.*;
import java.io.*;public class MinioMain4Download {static CustomMinioClient minioClient = new CustomMinioClient(MinioClient.builder().endpoint("http://192.168.2.195:9000").credentials("minioUser", "minioUser123").build());// 测试桶static String bucketName = "test";static {try {boolean found = minioClient.bucketExists(BucketExistsArgs.builder().bucket(bucketName).build());if (!found) {minioClient.makeBucket(MakeBucketArgs.builder().bucket(bucketName).build());}} catch (Exception e) {throw new RuntimeException(e);}}public static void main(String[] args) throws Exception {// 大小 1295 ByteString fileName = "202410181656357348160";// 第一步：查询目标文件大小StatObjectResponse statObjectResponse = minioClient.statObject(StatObjectArgs.builder().bucket(bucketName).object(fileName).build());long totalLength = statObjectResponse.size();System.out.println("目标文件总大小: " + totalLength);// 第二步：分片下载(最简单的同步方式)// 假设1000个字节作为一个分片final long CHUNK_LENGTH = 1000;// 从目标文件开始下载long startByte = 0l;long chunkCount = (long) Math.ceil((double) totalLength / CHUNK_LENGTH);System.out.println("预计总分片数: " + chunkCount);String targetPath = "C://tmp";for (long i = 0; i < chunkCount; i++) {GetObjectResponse response = minioClient.getObject(GetObjectArgs.builder().bucket(bucketName).object(fileName).offset(startByte).length(CHUNK_LENGTH).build());String chunkFilePath = targetPath + "//" + (i + 1) + ".part";FileOutputStream fileOutputStream = new FileOutputStream(chunkFilePath);byte[] buffer = new byte[1024];int bytesRead;while ((bytesRead = response.read(buffer)) != -1) {fileOutputStream.write(buffer, 0, bytesRead);}System.out.println("分片已下载: " + chunkFilePath + " 大小: " + new File(chunkFilePath).length());startByte = (i + 1) * CHUNK_LENGTH;}// 第三步：合并String mergedFilePath = targetPath + "//" + "result.txt";BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(mergedFilePath));for (long i = 0; i < chunkCount; i++) {String chunkFilePath = targetPath + "//" + (i + 1) + ".part";BufferedInputStream bis = new BufferedInputStream(new FileInputStream(chunkFilePath));byte[] buffer = new byte[1024];int bytesRead;while ((bytesRead = bis.read(buffer)) != -1) {bos.write(buffer, 0, bytesRead);}bis.close();}bos.close();System.out.println("合并完成");}
}