Answers:
提供的Java NIO一试:
URL website = new URL("http://www.website.com/information.asp");
ReadableByteChannel rbc = Channels.newChannel(website.openStream());
FileOutputStream fos = new FileOutputStream("information.html");
fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
使用transferFrom()
是可能不是一个简单的循环从源信道的读取和写入这个频道有效得多。许多操作系统可以直接将字节从源通道传输到文件系统缓存中,而无需实际复制它们。
在这里查看更多信息。
注意:transferFrom中的第三个参数是要传输的最大字节数。 Integer.MAX_VALUE
将最多传输2 ^ 31个字节,Long.MAX_VALUE
最多允许2 ^ 63个字节(大于现有文件)。
8388608
结核病?
transferFrom()
指定为“ isnt”以在单个呼叫中完成整个转移。这就是为什么它返回一个计数。你必须循环。
URL::openStream()
仅返回常规流,这意味着整个流量仍将通过Java byte []数组进行复制,而不是保留在本机缓冲区中。fos.getChannel()
实际上只有一个本机通道,因此开销保持完整。在这种情况下,使用NIO的收益为零。正如EJP和Ben MacCann正确注意到的那样,除了被打破之外。
使用apache commons-io,只需一行代码:
FileUtils.copyURLToFile(URL, File)
Nio的用法更简单:
URL website = new URL("http://www.website.com/information.asp");
try (InputStream in = website.openStream()) {
Files.copy(in, target, StandardCopyOption.REPLACE_EXISTING);
}
InputStream.read()
除非提供了长度为零的缓冲区或计数,“小暂停”或其他方式,否则不可能返回零。它将阻塞,直到已传输至少一个字节或流结束或发生错误为止。您对的内部说法Files.copy()
是毫无根据的。
public void saveUrl(final String filename, final String urlString)
throws MalformedURLException, IOException {
BufferedInputStream in = null;
FileOutputStream fout = null;
try {
in = new BufferedInputStream(new URL(urlString).openStream());
fout = new FileOutputStream(filename);
final byte data[] = new byte[1024];
int count;
while ((count = in.read(data, 0, 1024)) != -1) {
fout.write(data, 0, count);
}
} finally {
if (in != null) {
in.close();
}
if (fout != null) {
fout.close();
}
}
}
您需要处理可能在此方法外部的异常。
in.close
抛出异常,fout.close
则不调用。
BufferedInputStream
对套接字超时的影响为零。在我对您引用的“背景细节”的评论中,我已经将其视为“城市神话”。三年前
BufferedInputStream
“可能导致不可预测的失败”)。
这是一个古老的问题,但这是一个简洁,易读,仅JDK的解决方案,具有适当封闭的资源:
public static void download(String url, String fileName) throws Exception {
try (InputStream in = URI.create(url).toURL().openStream()) {
Files.copy(in, Paths.get(fileName));
}
}
两行代码,没有依赖关系。
import java.io.InputStream; import java.net.URI; import java.nio.file.Files; import java.nio.file.Paths;
使用时,请Java 7+
使用以下方法从Internet下载文件并将其保存到某个目录:
private static Path download(String sourceURL, String targetDirectory) throws IOException
{
URL url = new URL(sourceURL);
String fileName = sourceURL.substring(sourceURL.lastIndexOf('/') + 1, sourceURL.length());
Path targetPath = new File(targetDirectory + File.separator + fileName).toPath();
Files.copy(url.openStream(), targetPath, StandardCopyOption.REPLACE_EXISTING);
return targetPath;
}
文档在这里。
这个答案几乎与选择的答案完全一样,但是有两个增强:这是一个方法,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();
}
}
transferFrom()
指定为“ isnt”以在单个呼叫中完成整个转移。这就是为什么它返回一个计数。你必须循环。
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]);
}
}
}
in.close
抛出异常,out.close
则不调用。
这是另一个基于Brian Risk的 try-with语句的java7变体:
public static void downloadFileFromURL(String urlString, File destination) throws Throwable {
URL website = new URL(urlString);
try(
ReadableByteChannel rbc = Channels.newChannel(website.openStream());
FileOutputStream fos = new FileOutputStream(destination);
){
fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
}
}
transferFrom()
指定为“ isnt”以在单个呼叫中完成整个转移。这就是为什么它返回一个计数。你必须循环。
可以使用Apache HttpComponents
代替来下载文件Commons-IO
。该代码允许您根据URL下载Java文件并将其保存在特定的目标位置。
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;
}
与单行代码相反:
FileUtils.copyURLToFile(fileURL, new File(fileSavePath),
URLS_FETCH_TIMEOUT, URLS_FETCH_TIMEOUT);
这段代码会给你更多的控制权的过程,让你不仅指定超时,但User-Agent
和Referer
值,这对于许多Web站点的关键。
这里有许多优雅而有效的答案。但是,简洁会使我们失去一些有用的信息。特别是,人们通常不希望将连接错误视为一种异常。,并且可能希望以不同方式对待某些与网络相关的错误-例如,决定是否应重试下载。
这是一种不会因网络错误而引发异常的方法(仅适用于真正异常的问题,例如格式错误的url或写入文件的问题)
/**
* Downloads from a (http/https) URL and saves to a file.
* Does not consider a connection error an Exception. Instead it returns:
*
* 0=ok
* 1=connection interrupted, timeout (but something was read)
* 2=not found (FileNotFoundException) (404)
* 3=server error (500...)
* 4=could not connect: connection timeout (no internet?) java.net.SocketTimeoutException
* 5=could not connect: (server down?) java.net.ConnectException
* 6=could not resolve host (bad host, or no internet - no dns)
*
* @param file File to write. Parent directory will be created if necessary
* @param url http/https url to connect
* @param secsConnectTimeout Seconds to wait for connection establishment
* @param secsReadTimeout Read timeout in seconds - trasmission will abort if it freezes more than this
* @return See above
* @throws IOException Only if URL is malformed or if could not create the file
*/
public static int saveUrl(final Path file, final URL url,
int secsConnectTimeout, int secsReadTimeout) throws IOException {
Files.createDirectories(file.getParent()); // make sure parent dir exists , this can throw exception
URLConnection conn = url.openConnection(); // can throw exception if bad url
if( secsConnectTimeout > 0 ) conn.setConnectTimeout(secsConnectTimeout * 1000);
if( secsReadTimeout > 0 ) conn.setReadTimeout(secsReadTimeout * 1000);
int ret = 0;
boolean somethingRead = false;
try (InputStream is = conn.getInputStream()) {
try (BufferedInputStream in = new BufferedInputStream(is); OutputStream fout = Files
.newOutputStream(file)) {
final byte data[] = new byte[8192];
int count;
while((count = in.read(data)) > 0) {
somethingRead = true;
fout.write(data, 0, count);
}
}
} catch(java.io.IOException e) {
int httpcode = 999;
try {
httpcode = ((HttpURLConnection) conn).getResponseCode();
} catch(Exception ee) {}
if( somethingRead && e instanceof java.net.SocketTimeoutException ) ret = 1;
else if( e instanceof FileNotFoundException && httpcode >= 400 && httpcode < 500 ) ret = 2;
else if( httpcode >= 400 && httpcode < 600 ) ret = 3;
else if( e instanceof java.net.SocketTimeoutException ) ret = 4;
else if( e instanceof java.net.ConnectException ) ret = 5;
else if( e instanceof java.net.UnknownHostException ) ret = 6;
else throw e;
}
return ret;
}
以下是使用Java代码从互联网下载电影的示例代码:
URL url = new
URL("http://103.66.178.220/ftp/HDD2/Hindi%20Movies/2018/Hichki%202018.mkv");
BufferedInputStream bufferedInputStream = new BufferedInputStream(url.openStream());
FileOutputStream stream = new FileOutputStream("/home/sachin/Desktop/test.mkv");
int count=0;
byte[] b1 = new byte[100];
while((count = bufferedInputStream.read(b1)) != -1) {
System.out.println("b1:"+b1+">>"+count+ ">> KB downloaded:"+new File("/home/sachin/Desktop/test.mkv").length()/1024);
stream.write(b1, 0, count);
}
简单使用存在一个问题:
org.apache.commons.io.FileUtils.copyURLToFile(URL, File)
如果您需要下载并保存非常大的文件,或者通常情况下需要自动重试以防连接断开。
在这种情况下,我建议使用Apache HttpClient以及org.apache.commons.io.FileUtils。例如:
GetMethod method = new GetMethod(resource_url);
try {
int statusCode = client.executeMethod(method);
if (statusCode != HttpStatus.SC_OK) {
logger.error("Get method failed: " + method.getStatusLine());
}
org.apache.commons.io.FileUtils.copyInputStreamToFile(
method.getResponseBodyAsStream(), new File(resource_file));
} catch (HttpException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
method.releaseConnection();
}
总结(并以某种方式完善和更新)以前的答案。以下三种方法实际上是等效的。(我添加了明确的超时,因为我认为这是必须的,没有人希望在连接断开时永久冻结下载。)
public static void saveUrl1(final Path file, final URL url,
int secsConnectTimeout, int secsReadTimeout))
throws MalformedURLException, IOException {
// Files.createDirectories(file.getParent()); // optional, make sure parent dir exists
try (BufferedInputStream in = new BufferedInputStream(
streamFromUrl(url, secsConnectTimeout,secsReadTimeout) );
OutputStream fout = Files.newOutputStream(file)) {
final byte data[] = new byte[8192];
int count;
while((count = in.read(data)) > 0)
fout.write(data, 0, count);
}
}
public static void saveUrl2(final Path file, final URL url,
int secsConnectTimeout, int secsReadTimeout))
throws MalformedURLException, IOException {
// Files.createDirectories(file.getParent()); // optional, make sure parent dir exists
try (ReadableByteChannel rbc = Channels.newChannel(
streamFromUrl(url, secsConnectTimeout,secsReadTimeout)
);
FileChannel channel = FileChannel.open(file,
StandardOpenOption.CREATE,
StandardOpenOption.TRUNCATE_EXISTING,
StandardOpenOption.WRITE)
) {
channel.transferFrom(rbc, 0, Long.MAX_VALUE);
}
}
public static void saveUrl3(final Path file, final URL url,
int secsConnectTimeout, int secsReadTimeout))
throws MalformedURLException, IOException {
// Files.createDirectories(file.getParent()); // optional, make sure parent dir exists
try (InputStream in = streamFromUrl(url, secsConnectTimeout,secsReadTimeout) ) {
Files.copy(in, file, StandardCopyOption.REPLACE_EXISTING);
}
}
public static InputStream streamFromUrl(URL url,int secsConnectTimeout,int secsReadTimeout) throws IOException {
URLConnection conn = url.openConnection();
if(secsConnectTimeout>0) conn.setConnectTimeout(secsConnectTimeout*1000);
if(secsReadTimeout>0) conn.setReadTimeout(secsReadTimeout*1000);
return conn.getInputStream();
}
我没有发现重大差异,所有这些对我来说似乎都是正确的。他们是安全和有效的。(速度差异似乎无关紧要-我将本地服务器的180Mb写入SSD磁盘的时间大约在1.2到1.5段之间波动)。他们不需要外部库。所有这些都可以使用任意大小和(以我的经验)HTTP重定向来工作。
此外,FileNotFoundException
如果找不到资源(通常为错误404),则会抛出所有异常,并且java.net.UnknownHostException
DNS解析失败则会。其他IOException对应于传输期间的错误。
(标记为社区Wiki,随时添加信息或更正)
underscore-java库中有方法U.fetch(url)。
pom.xml:
<groupId>com.github.javadev</groupId>
<artifactId>underscore</artifactId>
<version>1.45</version>
代码示例:
import com.github.underscore.lodash.U;
public class Download {
public static void main(String ... args) {
String text = U.fetch("https://stackoverflow.com/questions"
+ "/921262/how-to-download-and-save-a-file-from-internet-using-java").text();
}
}
Java
,但您的答案像JavaScript
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;
}
}
您可以使用netloader for Java在1行中完成此操作:
new NetFile(new File("my/zips/1.zip"), "https://example.com/example.zip", -1).load(); //returns true if succeed, otherwise false.
如果您在代理后面,则可以在Java程序中设置代理,如下所示:
Properties systemSettings = System.getProperties();
systemSettings.put("proxySet", "true");
systemSettings.put("https.proxyHost", "https proxy of your org");
systemSettings.put("https.proxyPort", "8080");
如果您不是代理人,请不要在代码中包含以上几行。当您在代理服务器后面时,完整的工作代码可下载文件。
public static void main(String[] args) throws IOException {
String url="https://raw.githubusercontent.com/bpjoshi/fxservice/master/src/test/java/com/bpjoshi/fxservice/api/TradeControllerTest.java";
OutputStream outStream=null;
URLConnection connection=null;
InputStream is=null;
File targetFile=null;
URL server=null;
//Setting up proxies
Properties systemSettings = System.getProperties();
systemSettings.put("proxySet", "true");
systemSettings.put("https.proxyHost", "https proxy of my organisation");
systemSettings.put("https.proxyPort", "8080");
//The same way we could also set proxy for http
System.setProperty("java.net.useSystemProxies", "true");
//code to fetch file
try {
server=new URL(url);
connection = server.openConnection();
is = connection.getInputStream();
byte[] buffer = new byte[is.available()];
is.read(buffer);
targetFile = new File("src/main/resources/targetFile.java");
outStream = new FileOutputStream(targetFile);
outStream.write(buffer);
} catch (MalformedURLException e) {
System.out.println("THE URL IS NOT CORRECT ");
e.printStackTrace();
} catch (IOException e) {
System.out.println("Io exception");
e.printStackTrace();
}
finally{
if(outStream!=null) outStream.close();
}
}
使用新频道的第一种方法
ReadableByteChannel aq = Channels.newChannel(new url("https//asd/abc.txt").openStream());
FileOutputStream fileOS = new FileOutputStream("C:Users/local/abc.txt")
FileChannel writech = fileOS.getChannel();
使用FileUtils的第二种方法
FileUtils.copyURLToFile(new url("https//asd/abc.txt",new local file on system("C":/Users/system/abc.txt"));
第三种方法使用
InputStream xy = new ("https//asd/abc.txt").openStream();
这是我们可以使用基本的Java代码和其他第三方库下载文件的方式。这些仅供快速参考。请使用上述关键字在Google上搜索以获取详细信息和其他选项。