原文地址： https://www.shanya.world/archives/6f11b78c.html
为了更好的方便使用，我已经上传至jitpack，直接在添加依赖即可。
如何上传 jitpack 参考：
源码地址： https://github.com/Shanyaliux/DownloadUtil
使用方法
- 根目录的
build.gradle添加maven { url 'https://jitpack.io' }， 位置如下
allprojects {
repositories {
...
maven { url 'https://jitpack.io' }
}
}
- 添加依赖
implementation 'com.github.Shanyaliux:DownloadUtil:1.0.0'
- 调用方法
/**
* 下载工具的创建
*@param Url 网络资源路径
*@param Path 本地存储路径
*@param ThreadNum 下载线程数量 （若服务器请求数据没有Content-Type，则默认单线程显示，且无法监听下载进度）
*@param new DownloadUtil.OnDownloadListener() 下载状态监听接口
*/
DownloadUtil downloadUtil = DownloadUtil.getInstance(Url, Path, ThreadNum, new DownloadUtil.OnDownloadListener() {
@Override
public void onDownloadSuccess() {
//下载成功
}
@Override
public void onDownloadProgress(int progress) {
//下载进度（若服务器请求数据没有Content-Type，其无效）
}
@Override
public void onDownloadFailed(Exception e) {
//下载失败
}
});
/**
* 下载开始函数 (目前建议单独放一个线程执行)
*/
new Thread(() -> {
downloadUtil.download();
}).start();
具体源码
- 添加
OkHttp依赖
implementation("com.squareup.okhttp3:okhttp:4.5.0")
DownLoadUtil.java
package com.shanya.downloadutil;
import org.jetbrains.annotations.NotNull;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.util.concurrent.TimeUnit;
import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.Headers;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
public class DownloadUtil {
//资源路径
private String path;
//文件保存位置
private String targetFile;
//下载线程数量（当请求来的Content-Length为null时默认单线程下载）
private int threadNum;
//下载线程对象
private DownloadThread[] threads;
//文件大小（当请求来的Content-Length为null 其没有用）
private int fileSize;
//每个线程已下载数据存储，用来计算进度
private int[] lengths;
//监听下载状态
private OnDownloadListener onDownloadListener;
private static final String TAG = "DownloadUtil";
//Singleton单例化
private static DownloadUtil downloadUtil;
public static DownloadUtil getInstance(String path, String targetFile, int threadNum, OnDownloadListener onDownloadListener){
if (downloadUtil == null) {
downloadUtil = new DownloadUtil(path, targetFile, threadNum,onDownloadListener);
}
return downloadUtil;
}
//构造函数
private DownloadUtil(final String path, final String targetFile, final int threadNum, final OnDownloadListener onDownloadListener) {
this.path = path;
this.targetFile = targetFile;
this.threadNum = threadNum;
threads = new DownloadThread[threadNum];
lengths = new int[threadNum];
this.onDownloadListener = onDownloadListener;
}
//下载
public void download() {
//创建OkHttpClient实例
OkHttpClient client = new OkHttpClient.Builder()
.connectTimeout(5, TimeUnit.SECONDS)
.build();
okhttp3.Request request = new Request.Builder()
.get()
.url(path)
.build();
Call call = client.newCall(request);
//异步请求
call.enqueue(new Callback() {
@Override
public void onFailure(@NotNull Call call, @NotNull IOException e) {
//下载失败回调
onDownloadListener.onDownloadFailed(e);
}
@Override
public void onResponse(@NotNull Call call, @NotNull Response response) throws IOException {
//判断连接是否成功
if (response.code() == HttpURLConnection.HTTP_OK) {
Headers headers = response.headers();
//打印请求来的一些信息
// for (int i = 0; i < headers.size(); i++) {
// Log.d(TAG, "onResponse: ----> " + headers.name(i) + " === " + headers.value(i));
// }
//获取文件大小
if (headers.get("Content-Length") != null){
fileSize = Integer.parseInt(headers.get("Content-Length"));
//根据线程数分解每个线程需下载的文件大小
int currentPartSize = fileSize / threadNum + 1;
//创建RandomAccessFile 填写“rw” 没有文件会自动创建
RandomAccessFile file = new RandomAccessFile(targetFile, "rw");
//设置本地文件大小
file.setLength(fileSize);
file.close();
for (int i = 0; i < threadNum; i++) {
//每条线程使用一个RandomAccessFile 进行下载
RandomAccessFile currentPart = new RandomAccessFile(targetFile, "rw");
//计算每条线程下载的开始位置
int startPos = i * currentPartSize;
//定位该线程的下载位置
currentPart.seek(startPos);
//创建下载线程
threads[i] = new DownloadThread(i,startPos, currentPartSize, currentPart);
//启动下载线程
threads[i].start();
}
}else{//读取不到文件长度则执行以下内容
fileSize = -1;
//创建本地文件
File outFile = new File(targetFile);
//判断文件是否存在 不存在则新建
if (!outFile.getParentFile().exists()) {
outFile.mkdirs();
}
if (!outFile.exists()) {
outFile.createNewFile();
}
//创建文件输出流
FileOutputStream fos = new FileOutputStream(outFile);
//创建输入流
InputStream inputStream = null;
//判断请求数据是否为null
if (response.body() != null) {
//获取InputStream实例
inputStream = response.body().byteStream();
byte[] buffer = new byte[1024];
int len;
//读取网络数据
while ((len = inputStream.read(buffer, 0, buffer.length)) != -1) {
fos.write(buffer, 0, len);
}
//写入文件
fos.flush();
}
fos.close();
inputStream.close();
//下载成功回调
onDownloadListener.onDownloadSuccess();
}
}
}
});
}
/**
* //获取下载百分比（若没有请求到文件大小 则不会调用该方法）
* @return 下载进度
*/
private double getCompleteRate(){
int sumSize = 0;
for (int i = 0; i < threadNum; i++) {
sumSize += lengths[i];
}
return sumSize * 1.0 / fileSize;
}
/**
* 下载线程
*/
private class DownloadThread extends Thread{
//该线程开始下载的位置
private int startPos;
//该线程负责的文件大小
private int currentPartSize;
//该线程下载使用的 RandomAccessFile
private RandomAccessFile currentPart;
//线程序号，计算下载进度时需要
int num;
//构造函数
DownloadThread(int num,int startPos, int currentPartSize, RandomAccessFile currentPart) {
this.num = num;
this.startPos = startPos;
this.currentPartSize = currentPartSize;
this.currentPart = currentPart;
}
@Override
public void run() {
super.run();
//OkHttpClient 实例
OkHttpClient client = new OkHttpClient.Builder()
.connectTimeout(5, TimeUnit.SECONDS)
.build();
okhttp3.Request request = new Request.Builder()
.get()
.url(path)
.build();
Call call = client.newCall(request);
try {
//同步请求
Response execute = call.execute();
int code = execute.code();
//判断是否连接成功
if (code == HttpURLConnection.HTTP_OK) {
InputStream inputStream = null;
if (execute.body() != null) {
inputStream = execute.body().byteStream();
//跳过 startPos 个字节，表明该线程只下载自己负责的那部分
inputStream.skip(startPos);
byte[] buffer = new byte[1024];
int len;
//读取网络数据，并写入本地文件中
while (lengths[num] < currentPartSize && (len = inputStream.read(buffer)) > 0) {
currentPart.write(buffer, 0, len);
//累计该线程下载的总大小
lengths[num] += len;
//更新进度条
if (getCompleteRate() >= 1.0){
onDownloadListener.onDownloadSuccess();
}
onDownloadListener.onDownloadProgress((int)(getCompleteRate() * 100));
}
}
currentPart.close();
inputStream.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* 下载状态回调接口
*/
public interface OnDownloadListener{
//下载成功
void onDownloadSuccess();
//更新进度
void onDownloadProgress(int progress);
//下载失败
void onDownloadFailed(Exception e);
}
}
源码地址： https://github.com/Shanyaliux/DownloadUtil
如有不足之处请多多指正，谢谢