Java大文件下载方案(vue+饿了么)：分片下载、断点续载!

本文主要是介绍Java大文件下载方案(vue+饿了么)：分片下载、断点续载!，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

前言

本篇文章是基于其他文章的基础上结合自己的理解写出来的,如果哪里有问题请指出!

详细教程

分片下载

1.什么是分片下载

分片下载是指将一个大的文件分成多个较小的部分（分片或块），然后并行地从服务器下载这些部分到客户端的过程。

2.分片下载的场景

1.大文件下载

2.网络环境环境不好，存在需要重新下载风险的场景.

断点续传

1、什么是断点续传

断点续传是在下载时，将下载任务（一个文件或一个压缩包）人为的划分为几个部分，每一个部分采用一个线程进行下载，如果碰到网络故障，可以从已经下载的部分开始继续下载未完成的部分，而没有必要从头开始上传或者下载。

实现流程步骤

1.本文实现的步骤

前端（客户端）需要根据固定大小对文件进行分片，请求后端（服务端）时要带上分片开始位置,结束位置以及文件位置.
服务端根据上分片开始位置,结束位置以及文件位置.将文件读取成流的形式返回前端（
前端（客户端）需要将每次分片请求的流暂时存储到前端(这步是实现断点续传的核心步骤,本文是丢到indexedDB里面)最后读取完所有分片,组合为下载的文件。

2.分片上传/断点上传代码实现

a、前端框架使用的是vue+饿了么UI，进行分片下载。

b、后端实现文件读取，是用MappedByteBuffer实现。

前端(客户端)大概流程:

根据点击下载的文件获取行数据->通过特定字符串+id初始化indexedDB库,以及store->获取indexedDB库存储的数据->计算分片参数->循环调用分片下载请求->记录下载数据到indexedDB->分片下载成功->是?->合并分片下载的数据,返回下载文件,同时删除indexedDB库

前端代码片段(代码垃圾,大佬勿怪,有哪里需要改的帮忙指出下谢谢)

<template><div><!-- 文件进度条 --><fileProgressBar :data="progressData"></fileProgressBar><el-table :data="fileData.list" style="width: 100%"><el-table-column prop="fileName" label="文件名称" /><el-table-column prop="fileSize" label="文件大小" /><el-table-column prop="fileType" label="文件类型" /><el-table-column label="操作"><template #default="scope"><el-button size="small" icon="Position" type="success"@click="startDownload(scope.$index, scope.row)">下载</el-button></template></el-table-column></el-table></div>
</template><script setup>import {ref,watch,reactive,onMounted} from 'vue';import useIndexedDB from '../../assets/common/useIndexedDB.js';import fileProgressBar from '../../components/fileProgressBar.vue';import {ElMessage} from 'element-plus';import {useStore} from 'vuex';import {fileDownload} from "../../api/photo.js";import {getAllFile} from "../../api/test.js";const {initializeDB,addData,getData,getAllData,clearObjectStore,requestAdditionalStorage,deleteDatabase,} = useIndexedDB();const store = useStore();/*** 总分片数*/let totalChunks = ref(0);/*** 当前分片数量*/let currentChunk = ref(0);/*** 组装下载文件参数*/const downFileJson = reactive({"filePath": "","start": 0,"end": 0,});/*** 行id当作indexedDB唯一解*/const rowId = ref(null);/*** 文件列表数据*/const fileData = ref([]);/*** indexedDB前缀*/const fileDatabase = "fileDatabase:";/*** 进度条对象*/const progressData = reactive({progressBar: false, //是否显示进度条percentage: store.state.downloadProgress //进度条});//监听进度条变化watch(() => store.state.downloadProgress, (value) => {//(100/总块数/100)*变化值+(100/总块数*当前块数)progressData.percentage = Math.ceil((Math.floor((100 / totalChunks.value)) / 100) * value) + (Math.floor((100 /totalChunks.value)) * currentChunk.value);});/*** 初始化数据*/async function initParam() {//显示进度条progressData.progressBar = true;//进度条值为0progressData.percentage = 0;//当前块数轻灵currentChunk.value = 0;}/**下载文件按钮* @param {Object} index* @param {Object} row 行数据*/async function startDownload(index, row) {try {rowId.value = row.id;initParam();// 初始化 IndexedDBawait initializeDB(fileDatabase + row.id, row.id, 1);// 文件分片await downloadFileChunks(row);// 合并文件分片await mergeFileChunks(row);} catch (e) {console.error('Failed to download file:', e);ElMessage.error("文件下载失败!");} finally {progressData.progressBar = false;}}/**下载分片文件* @param {Object} row*/async function downloadFileChunks(row) {// 每个分片的大小const chunkSize = store.state.config.fileChunkSize;// 文件总数const fileSize = row.fileSize;// 总分片数totalChunks.value = Math.ceil(fileSize / chunkSize);console.log("分片大小:" + chunkSize + "文件总大小:" + fileSize + "分片数量:" + totalChunks.value);//设置文件得下载路径downFileJson.filePath = row.filePath;//先从获取本地所有分片const localData = await getAllData(row.id);//这里相当于设置初始下载得位置if (localData.length != 0) {console.log("文件续载!!!");//获取最后一条.取出start位置const lastData = localData[localData.length - 1];//id为当前得分片开始数currentChunk.value = lastData.id;currentChunk.value++;}//在这里我需要循环请求分片数据(块数从0开始)while (currentChunk.value < totalChunks.value) {console.log("=====总分片数:" + totalChunks.value + "=====当前下载分片:" + (currentChunk.value + 1) + "=====");await assembleParameter(row);await downloadFile();}}/**组装服务器请求参数* @param {Object} row*/async function assembleParameter(row) {// 每个分片的大小const chunkSize = store.state.config.fileChunkSize;// 文件总数const fileSize = row.fileSize;// 当前分片的起始位置let start = currentChunk.value * chunkSize;// 当前分片的结束位置let end = Math.min(start + chunkSize, fileSize);downFileJson.start = start;downFileJson.end = end;}/*** 调用服务器下载接口*/async function downloadFile() {console.log("请求参数", downFileJson);//请求接口const result = await fileDownload(downFileJson);if (result.status == 200) {// 将分片下载得数据添加到 IndexedDBawait addIndexedDbData(result.data);currentChunk.value++;}}/**将分片数据添加到 IndexedDB* @param {Object} data*/async function addIndexedDbData(data) {// 请求额外的存储空间//await requestAdditionalStorage(store.state.config.fileChunkSize);// 组装分片数据const fileChunk = {id: currentChunk.value,start: downFileJson.start,end: downFileJson.end,data: data};//添加到 IndexedDBawait addData(rowId.value, fileChunk);}async function mergeFileChunks(row) {// 从 IndexedDB 获取所有分片数据const allChunks = await getAllData(row.id);if (allChunks.length == 0) {ElMessage.error("文件内容为空!");return;}// 合并所有分片const mergedBlob = new Blob(allChunks.map(chunk => chunk.data), {type: 'application/octet-stream'});// 下载合并后的文件const link = document.createElement('a');link.href = URL.createObjectURL(mergedBlob);link.download = row.fileName + "." + row.fileType;link.click();URL.revokeObjectURL(link.href);link.remove();//下载完成清空数据库await deleteDatabase(fileDatabase + row.id);}/*** 获取所有文件列表*/function getAllList() {getAllFile().then(result => {fileData.value = result.data;})}//初始化onMounted(() => {getAllList();});
</script>

useIndexedDB.js

import {ref
} from 'vue';export default function useIndexedDB() {const db = ref(null);const error = ref(null);// 初始化数据库const initializeDB = (databaseName, storeName, version) => {return new Promise((resolve, reject) => {let request = indexedDB.open(databaseName, version);request.onerror = (event) => {error.value = event.target.errorCode;reject(event.target.error);};request.onsuccess = (event) => {db.value = event.target.result;resolve(db.value);};request.onupgradeneeded = (event) => {let db = event.target.result;if (!db.objectStoreNames.contains(storeName)) {db.createObjectStore(storeName, {keyPath: 'id'});}};});};// 添加数据const addData = (objectStoreName, data) => {return new Promise((resolve, reject) => {let transaction = db.value.transaction([objectStoreName], 'readwrite');let objectStore = transaction.objectStore(objectStoreName);let request = objectStore.add(data);request.onsuccess = () => resolve(true);request.onerror = () => reject(false);});};// 查询数据const getData = (objectStoreName, key) => {return new Promise((resolve, reject) => {let transaction = db.value.transaction([objectStoreName], 'readonly');let objectStore = transaction.objectStore(objectStoreName);let request = objectStore.get(key);request.onsuccess = () => resolve(request.result);request.onerror = () => reject(null);});};// 查询数据const getAllData = (objectStoreName) => {return new Promise((resolve, reject) => {let transaction = db.value.transaction([objectStoreName], 'readonly');let objectStore = transaction.objectStore(objectStoreName);let request = objectStore.getAll();request.onsuccess = () => resolve(request.result);request.onerror = () => reject(null);});};// 删除数据const deleteData = (objectStoreName, key) => {return new Promise((resolve, reject) => {let transaction = db.value.transaction([objectStoreName], 'readwrite');let objectStore = transaction.objectStore(objectStoreName);let request = objectStore.delete(key);request.onsuccess = () => resolve(true);request.onerror = () => reject(false);});};// 删除数据库const deleteDatabase = (databaseName) => {const request = indexedDB.deleteDatabase(databaseName);db.value.close();request.onsuccess = (event) => {console.log(`Database ${databaseName} has been deleted successfully.`);db.value = null;};request.onerror = (event) => {console.error(`Error deleting database ${databaseName}:`, event.target.errorCode);};request.onblocked = (event) => {console.warn(`Delete operation is blocked for database ${databaseName}.`);};};// 清空整个 objectStoreconst clearObjectStore = (objectStoreName) => {return new Promise((resolve, reject) => {let transaction = db.value.transaction([objectStoreName], 'readwrite');let objectStore = transaction.objectStore(objectStoreName);let request = objectStore.clear();request.onsuccess = () => resolve(true);request.onerror = () => reject(false);});};// 请求额外的空间const requestAdditionalStorage = (quotaInBytes) => {return new Promise((resolve, reject) => {if (typeof navigator.webkitTemporaryStorage !== 'undefined') {// WebKit-based browsers (Chrome, Safari)navigator.webkitTemporaryStorage.requestQuota(quotaInBytes, function(grantedQuota) {console.log('Granted temporary storage quota:', grantedQuota);// 进行进一步的操作}, function(error) {console.error('Error requesting temporary storage quota:', error);});} else if (typeof navigator.webkitPersistentStorage !== 'undefined') {// WebKit-based browsers (Chrome, Safari)navigator.webkitPersistentStorage.requestQuota(quotaInBytes, function(grantedQuota) {console.log('Granted persistent storage quota:', grantedQuota);// 进行进一步的操作}, function(error) {console.error('Error requesting persistent storage quota:', error);});} else if (typeof indexedDB.requestQuota === 'function') {// Modern browsers that support IndexedDB 2.0indexedDB.requestQuota(quotaInBytes, function(grantedQuota) {console.log('Granted storage quota:', grantedQuota);// 进行进一步的操作}, function(error) {console.error('Error requesting storage quota:', error);});} else {console.warn('Storage quota request not supported.');// 在不支持的情况下采取备用方案}});};return {db,error,initializeDB,addData,getData,deleteData,clearObjectStore,requestAdditionalStorage,getAllData,deleteDatabase};
}

后端(服务端)大概流程:

获取到前端传递的参数->通过文件开始位置,结束位置,读取文件->流的形式返回前端.

后端代码片段(代码垃圾,大佬勿怪,有哪里需要改的帮忙指出下谢谢)

 public ResponseEntity<InputStreamResource>  fileShardingDownload(FileDownloadRequest req) {// 根据文件路径获取文件File file = new File(req.getFilePath());if (!file.exists()) {throw new RuntimeException("文件丢失");}//获取文件偏移量long position = req.getStart();//获取文件读取大小long size= req.getEnd() - position;MappedByteBuffer mappedByteBuffer = null;try (FileChannel fileChannel = FileChannel.open(Paths.get(file.toURI()), StandardOpenOption.READ)) {// 映射文件到内存(从那个位置开始,读取多少数据.)mappedByteBuffer = fileChannel.map(FileChannel.MapMode.READ_ONLY, position, size);// 读取数据byte[] buffer = new byte[(int) size];// 将数据从 ByteBuffer 复制到 byte 数组mappedByteBuffer.get(buffer);// 转换为 InputStreamInputStreamResource inputStreamResource = new InputStreamResource(new ByteArrayInputStream(buffer));return ResponseEntity.ok().contentType(MediaType.APPLICATION_OCTET_STREAM).contentLength(size).header("Content-Disposition", "attachment; filename=part-of-file.zip").body(inputStreamResource);} catch (IOException e) {log.error(e.getMessage(), e);throw new RuntimeException("文件下载失败！");} finally {//这是一个坑不关闭,会一直占用try {Method m = FileChannelImpl.class.getDeclaredMethod("unmap", MappedByteBuffer.class);m.setAccessible(true);m.invoke(FileChannelImpl.class, mappedByteBuffer);} catch (Exception e) {log.error(e.getMessage(), e);}}}

FileDownloadRequest类

@Data
public class FileDownloadRequest {/*** 文件名称*/private String fileName;/*** 文件临时路径*/private String filePath;/*** 文件大小*/private String fileSize;/*** 当前分片开始位置*/private Long start;/*** 当前分片结束位置*/private Long end;/*** 当前分片位置*/private Long offset;}