在本教程中，我们将看到如何从Java中从URL下载文件。
它可以使用Java自动从URL自动下载任何文件时使用。

有很多方法可以做到这一点，其中一些是：

• 使用Java输入输出流
• 使用apache common io
• 使用nio.

Java程序：

package org.igi.theitroad;
 
import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.nio.channels.Channels;
import java.nio.channels.ReadableByteChannel;
 
import org.apache.commons.io.FileUtils;
 
/*
 * @author igi Mandliya
 */
public class FileDownloadFromURLMain {
 
 public static void main(String[] args) {
 
 
  String dirName = "/Users/igi/Desktop/Blog";
 
  try {
 
   System.out.println("---------------------------");
   System.out.println("Downloading file from github using java file IO");
   
   //Using java IO
   downloadFileFromUrlWithJavaIO(
     dirName + "/sampleFile1.zip",
     "https://github.com/igimandliya/SpringRestfulWebServicesWithJSONExample/archive/master.zip");
 
   System.out.println("Downloaded file from github using java file IO");
   System.out.println("---------------------------");
   System.out.println("Downloading file from github using apache common IO");
 
   //Using Apache common IO
   downloadFileFromUrlWithCommonsIO(
     dirName + "/sampleFile2.zip",
     "https://github.com/igimandliya/SpringSecurityHelloWorldExample/archive/master.zip");
 
   System.out.println("Downloaded file from github using apache common IO");
   System.out.println("---------------------------");
   System.out.println("Downloading file from github using NIO");
 
   //Using NIO
   downloadFileFromURLUsingNIO(
     dirName + "/sampleFile3.zip",
     "https://github.com/igimandliya/SpringMVCHelloWorldExample/archive/master.zip");
 
   System.out.println("Downloaded file from github using NIO");
   System.out.println("---------------------------");
 
  } catch (MalformedURLException e) {
   e.printStackTrace();
  } catch (IOException e) {
   e.printStackTrace();
  }
 
 }
 
 //Using Java IO
 public static void downloadFileFromUrlWithJavaIO(String fileName, String fileUrl)
   throws MalformedURLException, IOException {
  BufferedInputStream inStream = null;
  FileOutputStream outStream = null;
  try {
   URL fileUrlObj=new URL(fileUrl);
   inStream = new BufferedInputStream(fileUrlObj.openStream());
   outStream = new FileOutputStream(fileName);
 
   byte data[] = new byte[1024];
   int count;
   while ((count = inStream.read(data, 0, 1024)) != -1) {
    outStream.write(data, 0, count);
   }
  } finally {
   if (inStream != null)
    inStream.close();
   if (outStream != null)
    outStream.close();
  }
 }
 
 //Using common IO
 public static void downloadFileFromUrlWithCommonsIO(String fileName,
   String fileUrl) throws MalformedURLException, IOException {
  FileUtils.copyURLToFile(new URL(fileUrl), new File(fileName));
 }
 
 //Using NIO
 private static void downloadFileFromURLUsingNIO(String fileName,String fileUrl) throws IOException {
  URL url = new URL(fileUrl);
  ReadableByteChannel rbc = Channels.newChannel(url.openStream());
  FileOutputStream fOutStream = new FileOutputStream(fileName);
  fOutStream.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
  fOutStream.close();
  rbc.close();
 }
 
}

运行上面的程序时，文件将在上面提到的目录中下载。
我们将在输出之后获取：

--------------------------
Downloading file from github using java file IO
Downloaded file from github using java file IO
--------------------------
Downloading file from github using apache common IO
Downloaded file from github using apache common IO
--------------------------
Downloading file from github using NIO
Downloaded file from github using NIO
--------------------------