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
下面是用Java代码从网上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);
}
其他回答
简单使用有一个问题:
org.apache.commons.io.FileUtils.copyURLToFile(URL, File)
如果你需要下载和保存非常大的文件,或者在一般情况下,如果你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();
}
下载一个文件需要你阅读它。无论哪种方式,您都必须以某种方式查看该文件。而不是逐行,你可以从流中逐字节读取:
BufferedInputStream in = new BufferedInputStream(new URL("http://www.website.com/information.asp").openStream())
byte data[] = new byte[1024];
int count;
while((count = in.read(data, 0, 1024)) != -1)
{
out.write(data, 0, count);
}
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
这里有许多优雅而有效的答案。但是简洁会让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异常,并且可能希望以不同的方式处理某些与网络相关的错误—例如,决定是否应该重试下载。
下面是一个方法,它不会为网络错误抛出异常(仅用于真正异常的问题,如url格式错误或写入文件的问题)
/**
* 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;
}
这可以读取互联网上的文件,并将其写入文件。
import java.net.URL;
import java.io.FileOutputStream;
import java.io.File;
public class Download {
public static void main(String[] args) throws Exception {
URL url = new URL("https://www.google.com/images/branding/googlelogo/1x/googlelogo_color_272x92dp.png"); // Input URL
FileOutputStream out = new FileOutputStream(new File("out.png")); // Output file
out.write(url.openStream().readAllBytes());
out.close();
}
}
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