无法从Java中的URL下载文件

您

byte

    while (fileIn.read() != -1) {     //1st read        fileOut.write(fileIn.read());     //2nd read - 1st write    }

您正在阅读两次，只写一次。

您需要做的是

    int x;    while ((x = fileIn.read()) != -1) {   //1st read        fileOut.write(x);     //1st write    }

这是您的完整代码

import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.net.URL;import java.net.URLConnection;import java.util.Scanner;public class FileDownloader {    public static void main(String[] args) throws IOException {        InputStream fileIn;        FileOutputStream fileOut;        Scanner s = new Scanner(System.in);        System.out.println("Enter URL: ");        String urlStr = s.nextLine();        URL url = new URL(urlStr);        URLConnection urlConnect = url.openConnection();        fileIn = urlConnect.getInputStream();        System.out.println("Enter file name: ");        String fileStr = s.nextLine();        fileOut = new FileOutputStream(fileStr);        int x;        while ((x = fileIn.read()) != -1) { fileOut.write(x);        }        System.out.println("File is downloaded");}