为什么无法完成下载？下载几个字节后停止。为什么会这样呢？
import java.io.BufferedInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.Authenticator;
import java.net.HttpURLConnection;
import java.net.InetSocketAddress;
import java.net.PasswordAuthentication;
import java.net.Proxy;
import java.net.URL;
import java.util.Scanner;
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
/**
*
* @author prashanth
*/
public class downloadManager {
public static void main(String[] args) {
String url;
Proxy myproxy;
HttpURLConnection uc;
String downloadDir, file, filename;
byte[] data;
Scanner inp = new Scanner(System.in);
System.out.println("Enter the URL of the file to be downloaded: ");
url = inp.nextLine();
if (url.isEmpty()) {
System.out.println("URL is not provided, please enter the url and try again");
System.exit(-1);
}
try {
myproxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress("172.31.102.14", 3128));
Authenticator auth = new Authenticator() {
@Override
public PasswordAuthentication getPasswordAuthentication() {
return (new PasswordAuthentication("edcguest", "edcguest".toCharArray()));
}
};
Authenticator.setDefault(auth);
URL u = new URL(url);
uc = (HttpURLConnection) u.openConnection(myproxy);
uc.setRequestProperty("User-Agent", "Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.4; en-US; rv:1.9.2.2) Gecko/20100316 Firefox/3.6.2");
downloadDir = System.getProperty("user.home") + System.getProperty("file.separator") + "Downloads" + System.getProperty("file.separator");
file = u.getFile();
filename = file.substring(file.lastIndexOf('/') + 1);
System.out.println("Waiting for connection...");
if (uc.getResponseCode() == 200) {
System.out.println("Connection OK!\nFile: " + filename + "\nFile Size: " + uc.getContentLength() + " bytes\nDownloading file...");
data = new byte[uc.getContentLength()];
int bytesRead = 0;
int offset = 0;
InputStream in = new BufferedInputStream(uc.getInputStream());
while (offset < uc.getContentLength()) {
bytesRead += in.read(data, offset, data.length - offset);
if (bytesRead == -1) {
break;
}
offset += bytesRead;
System.out.println("Finished downloading: " + bytesRead + " Bytes");
}
in.close();
if (offset != uc.getContentLength()) {
throw new IOException("Only read " + offset + " bytes. Expected " + uc.getContentLength() + " bytes");
}
System.out.println("Finishing Download...");
FileOutputStream out = new FileOutputStream(downloadDir + filename);
out.write(data);
System.out.println("Download Completed! Find the file in your Downloads folder");
out.flush();
out.close();
} else {
System.out.println("Download failed! Error: " + uc.getResponseCode());
}
} catch (Exception e) {
System.err.println("Exception: "+e.getMessage());
}
}
}
我哪里做错了？ while循环不会完全执行，并且代码执行将在那里停止，而不会继续进行。
编辑：
这是例子
Enter the URL of the file to be downloaded:
http://psthomas.com/solutions/Liar_Truth.pdf
Waiting for connection...
Connection OK!
File: Liar_Truth.pdf
File Size: 60326 bytes
Downloading file...
Finished downloading: 3709 Bytes
Finished downloading: 8053 Bytes
Finished downloading: 12397 Bytes
Finished downloading: 13845 Bytes
Finished downloading: 16741 Bytes
Finished downloading: 20093 Bytes
Exception: Only read 74838 bytes. Expected 60326 bytes
就是这样，我回到了提示。
最佳答案
看起来您的byteRead相互添加（使用+ =运算符）。
while (offset < uc.getContentLength()) {
bytesRead += in.read(data, offset, data.length - offset);
if (bytesRead == -1) {
break;
}
offset += bytesRead;
System.out.println("Finished downloading: " + bytesRead + " Bytes");
}
这是您的代码，这是每个循环的bytesRead和offset的实际值：
Loop count bytesRead offset
1 3709 Bytes 3709
2 8053 Bytes 11762
3 12397 Bytes 24159
4 13845 Bytes 38004
5 16741 Bytes 54745
6 20093 Bytes 74838
您可以看到偏移量在每个循环中都将bytesRead添加到其自身，这就是为什么看到大量数字跳跃的原因。
将while循环的第一行更改为：
bytesRead = in.read(data, offset, data.length - offset);
因此，bytesRead不再追加其自身，而offset为其自身添加了正确的值。
在当前的实现中，因为bytesRead是添加到自身中，所以当您处于EOF时，它将永远不会具有值-1。
关于java - HttpURLConnection在Java中意外断开连接，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/32784434/