有一个在线文件(如http://www.example.com/information.asp),我需要抓取并保存到一个目录。我知道有几种逐行抓取和读取在线文件(url)的方法,但是否有一种方法可以使用Java下载并保存文件?
当前回答
public class DownloadManager {
static String urls = "[WEBSITE NAME]";
public static void main(String[] args) throws IOException{
URL url = verify(urls);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
InputStream in = null;
String filename = url.getFile();
filename = filename.substring(filename.lastIndexOf('/') + 1);
FileOutputStream out = new FileOutputStream("C:\\Java2_programiranje/Network/DownloadTest1/Project/Output" + File.separator + filename);
in = connection.getInputStream();
int read = -1;
byte[] buffer = new byte[4096];
while((read = in.read(buffer)) != -1){
out.write(buffer, 0, read);
System.out.println("[SYSTEM/INFO]: Downloading file...");
}
in.close();
out.close();
System.out.println("[SYSTEM/INFO]: File Downloaded!");
}
private static URL verify(String url){
if(!url.toLowerCase().startsWith("http://")) {
return null;
}
URL verifyUrl = null;
try{
verifyUrl = new URL(url);
}catch(Exception e){
e.printStackTrace();
}
return verifyUrl;
}
}
其他回答
import java.io.*;
import java.net.*;
public class filedown {
public static void download(String address, String localFileName) {
OutputStream out = null;
URLConnection conn = null;
InputStream in = null;
try {
URL url = new URL(address);
out = new BufferedOutputStream(new FileOutputStream(localFileName));
conn = url.openConnection();
in = conn.getInputStream();
byte[] buffer = new byte[1024];
int numRead;
long numWritten = 0;
while ((numRead = in.read(buffer)) != -1) {
out.write(buffer, 0, numRead);
numWritten += numRead;
}
System.out.println(localFileName + "\t" + numWritten);
}
catch (Exception exception) {
exception.printStackTrace();
}
finally {
try {
if (in != null) {
in.close();
}
if (out != null) {
out.close();
}
}
catch (IOException ioe) {
}
}
}
public static void download(String address) {
int lastSlashIndex = address.lastIndexOf('/');
if (lastSlashIndex >= 0 &&
lastSlashIndex < address.length() - 1) {
download(address, (new URL(address)).getFile());
}
else {
System.err.println("Could not figure out local file name for "+address);
}
}
public static void main(String[] args) {
for (int i = 0; i < args.length; i++) {
download(args[i]);
}
}
}
这个答案几乎和选中的答案完全一样,但是有两个增强:它是一个方法,它关闭了FileOutputStream对象:
public static void downloadFileFromURL(String urlString, File destination) {
try {
URL website = new URL(urlString);
ReadableByteChannel rbc;
rbc = Channels.newChannel(website.openStream());
FileOutputStream fos = new FileOutputStream(destination);
fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
fos.close();
rbc.close();
} catch (IOException e) {
e.printStackTrace();
}
}
下面是一个简洁的、可读的、仅使用jdk的解决方案,其中包含适当的封闭资源:
static long download(String url, String fileName) throws IOException {
try (InputStream in = URI.create(url).toURL().openStream()) {
return Files.copy(in, Paths.get(fileName));
}
}
两行代码,没有依赖关系。
下面是一个完整的文件下载示例程序,包含输出、错误检查和命令行参数检查:
package so.downloader;
import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.nio.file.Files;
import java.nio.file.Paths;
public class Application {
public static void main(String[] args) throws IOException {
if (2 != args.length) {
System.out.println("USAGE: java -jar so-downloader.jar <source-URL> <target-filename>");
System.exit(1);
}
String sourceUrl = args[0];
String targetFilename = args[1];
long bytesDownloaded = download(sourceUrl, targetFilename);
System.out.println(String.format("Downloaded %d bytes from %s to %s.", bytesDownloaded, sourceUrl, targetFilename));
}
static long download(String url, String fileName) throws IOException {
try (InputStream in = URI.create(url).toURL().openStream()) {
return Files.copy(in, Paths.get(fileName));
}
}
}
正如so-downloader存储库README中所指出的:
运行文件下载程序:
java -jar so-downloader.jar <source-URL> <target-filename>
例如:
java -jar so-downloader.jar https://github.com/JanStureNielsen/so-downloader/archive/main.zip so-downloader-source.zip
可以使用Apache的HttpComponents而不是Commons IO来下载文件。这段代码允许您根据URL在Java中下载文件,并将其保存到特定的目的地。
public static boolean saveFile(URL fileURL, String fileSavePath) {
boolean isSucceed = true;
CloseableHttpClient httpClient = HttpClients.createDefault();
HttpGet httpGet = new HttpGet(fileURL.toString());
httpGet.addHeader("User-Agent", "Mozilla/5.0 (Windows NT 6.3; WOW64; rv:34.0) Gecko/20100101 Firefox/34.0");
httpGet.addHeader("Referer", "https://www.google.com");
try {
CloseableHttpResponse httpResponse = httpClient.execute(httpGet);
HttpEntity fileEntity = httpResponse.getEntity();
if (fileEntity != null) {
FileUtils.copyInputStreamToFile(fileEntity.getContent(), new File(fileSavePath));
}
} catch (IOException e) {
isSucceed = false;
}
httpGet.releaseConnection();
return isSucceed;
}
与单行代码相比:
FileUtils.copyURLToFile(fileURL, new File(fileSavePath),
URLS_FETCH_TIMEOUT, URLS_FETCH_TIMEOUT);
这段代码将使您对进程有更多的控制,不仅可以指定超时,还可以指定User-Agent和Referer值,这对许多网站来说都是至关重要的。
在underscore-java库中有一个方法U.fetch(url)。
文件pom.xml:
<dependency>
<groupId>com.github.javadev</groupId>
<artifactId>underscore</artifactId>
<version>1.84</version>
</dependency>
代码示例:
import com.github.underscore.U;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
public class Download {
public static void main(String[] args) throws IOException {
Files.write(Paths.get("data.bin"),
U.fetch("https://stackoverflow.com/questions"
+ "/921262/how-to-download-and-save-a-file-from-internet-using-java").blob());
}
}
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