如何從http URL下載文件

Question

這是我下載文件的servlet代碼。但其下載只有本地文件，我想從http url下載文件，如：
（「http://www.java2s.com/Code/JarDownload/sqljdbc4/sqljdbc4-3.0.jar.zip」）。

package net.codejava; 

import java.io.File; 
import java.io.FileInputStream; 
import java.io.IOException; 
import java.io.OutputStream; 

    import javax.servlet.ServletContext; 
    import javax.servlet.ServletException; 
    import javax.servlet.http.HttpServlet; 
    import javax.servlet.http.HttpServletRequest; 
    import javax.servlet.http.HttpServletResponse; 

    public class DownloadFileServlet extends HttpServlet { 

    protected void doGet(HttpServletRequest request, 
     HttpServletResponse response) throws ServletException, IOException { 
    // reads input file from an absolute path 
    String filePath = "E:/Test/Download/MYPIC.JPG"; 
    File downloadFile = new File(filePath); 
    FileInputStream inStream = new FileInputStream(downloadFile); 

    // if you want to use a relative path to context root: 
    String relativePath = getServletContext().getRealPath(""); 
    System.out.println("relativePath = " + relativePath); 

    // obtains ServletContext 
    ServletContext context = getServletContext(); 

    // gets MIME type of the file 
    String mimeType = context.getMimeType(filePath); 
    if (mimeType == null) {   
     // set to binary type if MIME mapping not found 
     mimeType = "application/octet-stream"; 
    } 
    System.out.println("MIME type: " + mimeType); 

    // modifies response 
    response.setContentType(mimeType); 
    response.setContentLength((int) downloadFile.length()); 

    // forces download 
    String headerKey = "Content-Disposition"; 
    String headerValue = String.format("attachment; 
    filename=\"%s"",downloadFile.getName()); 
    response.setHeader(headerKey, headerValue); 

    // obtains response's output stream 
    OutputStream outStream = response.getOutputStream(); 

    byte[] buffer = new byte[4096]; 
    int bytesRead = -1; 

    while ((bytesRead = inStream.read(buffer)) != -1) { 
     outStream.write(buffer, 0, bytesRead); 
    } 

    inStream.close(); 
    outStream.close();  
     } 
    } 

Answer 1

首先確保您的防火牆不阻止您的應用程序。 您可以在Apache中使用FileUtils類將url作爲文件下載。

FileUtils.copyURLToFile(your_URL, file);

Answer 2

public class DownloadServlet extends HttpServlet { 
/** 
* 
*/ 
private static final long serialVersionUID = 1L; 

protected void doGet(HttpServletRequest request, HttpServletResponse 
    response) throws ServletException, IOException { 

    /*final GetData data = new HttpGetData(); 
    String downloadFile=data.getContent("http://www.java2s.com 
     /Code/JarDownload/spring-/spring-2.5.jar.zip"); 
    System.out.println("download file is:"+downloadFile);*/ 
    String filePath = "http://www.java2s.com/Code/JarDownload/spring- 
     /spring-2.5.jar.zip"; 
     //URL url = new URL(filePath); 
     //Scanner scan = new Scanner(System.in); 
     //filePath=scan.nextLine(); 
    URL url = new URL(filePath); 
     HttpURLConnection httpConn = (HttpURLConnection) 
     url.openConnection(); 
     //File downloadFile = new File(filePath); 
     //FileInputStream inStream = new FileInputStream(downloadFile); 

     InputStream inStream = httpConn.getInputStream(); 

     // if you want to use a relative path to context root: 
     String relativePath = getServletContext().getRealPath(""); 
     System.out.println("relativePath = " + relativePath); 

     // obtains ServletContext 
     ServletContext context = getServletContext(); 

     // gets MIME type of the file 
     String mimeType = context.getMimeType(filePath); 
     if (mimeType == null) {   
      // set to binary type if MIME mapping not found 
      mimeType = "application/octet-stream"; 
     } 
     System.out.println("MIME type: " + mimeType); 

     // modifies response 
     response.setContentType(mimeType); 
     response.setContentLength((int) httpConn.getContentLength()); 

     String fileName = filePath.substring(filePath.lastIndexOf("/") + 1, 
       filePath.length()); 

     // forces download 
     String headerKey = "Content-Disposition"; 
     String headerValue = String.format("attachment; filename=\"%s\"", 
     fileName); 
     response.setHeader(headerKey, headerValue); 

     // obtains response's output stream 
     OutputStream outStream = response.getOutputStream(); 

     byte[] buffer = new byte[4096]; 
     int bytesRead = -1; 

     while ((bytesRead = inStream.read(buffer)) != -1) { 
      outStream.write(buffer, 0, bytesRead); 
     } 

     inStream.close(); 
     outStream.close(); 
      } 

     }