java - 无法从java中的URL下载文件

Question

我正在制作一个从 URL 下载文件的程序。下载总是开始，但没有完成。例如，如果文件大小为 3 MB，程序只下载一半，所以我无法打开下载的文件。但是程序说文件下载成功。

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);

        while (fileIn.read() != -1) {   
            fileOut.write(fileIn.read());
        }
        System.out.println("File is downloaded");
    }
}

那我该如何解决呢？是否应该使用其他方式下载？

Answer 1

由于

，您正在丢失每个备用 字节

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

你读了两次，只写了一次。

你需要做的是

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

这是你的完整代码

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");

}