Todos acham que é real.Mar. 30, 1999USA136 Min.
You know, in Java, we can use the classes URLand HttpURLConnection in the package java.net to programmatically download a file from a given URL by following these steps:
http://jdbc.postgresql.org/download/postgresql-9.2-1002.jdbc4.jar
http://myserver.com/download?id=1234
package com.douglas.networking;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.net.HttpURLConnection;import java.net.URL;public class HttpDownloadUtility { private static final int BUFFER_SIZE = 4096; /** * Downloads a file from a URL * @param fileURL HTTP URL of the file to be downloaded * @param saveDir path of the directory to save the file * @throws IOException */ public static void downloadFile(String fileURL, String saveDir) throws IOException { URL url = new URL(fileURL); HttpURLConnection httpConn = (HttpURLConnection) url.openConnection(); int responseCode = httpConn.getResponseCode(); // always check HTTP response code first if (responseCode == HttpURLConnection.HTTP_OK) { String fileName = ""; String disposition = httpConn.getHeaderField("Content-Disposition"); String contentType = httpConn.getContentType(); int contentLength = httpConn.getContentLength(); if (disposition != null) { // extracts file name from header field int index = disposition.indexOf("filename="); if (index > 0) { fileName = disposition.substring(index + 10, disposition.length() - 1); } } else { // extracts file name from URL fileName = fileURL.substring(fileURL.lastIndexOf("/") + 1, fileURL.length()); } System.out.println("Content-Type = " + contentType); System.out.println("Content-Disposition = " + disposition); System.out.println("Content-Length = " + contentLength); System.out.println("fileName = " + fileName); // opens input stream from the HTTP connection InputStream inputStream = httpConn.getInputStream(); String saveFilePath = saveDir + File.separator + fileName; // opens an output stream to save into file FileOutputStream outputStream = new FileOutputStream(saveFilePath); int bytesRead = -1; byte[] buffer = new byte[BUFFER_SIZE]; while ((bytesRead = inputStream.read(buffer)) != -1) { outputStream.write(buffer, 0, bytesRead); } outputStream.close(); inputStream.close(); System.out.println("File downloaded"); } else { System.out.println("No file to download. Server replied HTTP code: "+ responseCode); } httpConn.disconnect(); }}
Note that in the static method downloadFile(), we have to check HTTP response code from the server to make sure the URL is available (HTTP status 200). Then we extract the file name either from the HTTP header Content-Disposition (in case the URL is an indirect link), or from the URL itself (in case the URL is the direct link). We also print out some debugging information like Content-Type, Content-Disposition, Content-Length and file name.And here is a test program which employs the utility class above:12345678910111213141516 package net.codejava.networking; import java.io.IOException; public class HttpDownloader { public static void main(String[] args) { String fileURL = "http://jdbc.postgresql.org/download /postgresql-9.2-1002.jdbc4.jar"; String saveDir = "E:/Download"; try { HttpDownloadUtility.downloadFile(fileURL, saveDir); } catch (IOException ex) { ex.printStackTrace(); } }}
This program downloads the file postgresql-9.2-1002.jdbc4.jar and saves it into the directory E:/Download. It would produce the following output:12345 Content-Type = application/java-archiveContent-Disposition = nullContent-Length = 579785fileName = postgresql-9.2-1002.jdbc4.jarFile downloaded