如何使用Java从Internet下载和保存文件?

时间:2009-05-28 14:53:59

标签: java download

我需要抓取并保存到目录中的在线文件(例如http://www.example.com/information.asp)。我知道有几种方法可以逐行获取和读取在线文件(URL),但有没有办法只使用Java下载和保存文件?

23 个答案:

答案 0 :(得分:541)

尝试Java NIO

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() 可能比从源通道读取并写入此通道的简单循环更有效。许多操作系统可以直接从源通道将字节传输到文件系统缓存中,而无需实际复制它们。

查看有关here的更多信息。

注意:transferFrom中的第三个参数是要传输的最大字节数。 Integer.MAX_VALUE最多会传输2 ^ 31个字节,Long.MAX_VALUE最多允许2 ^ 63个字节(大于现有的任何文件)。

答案 1 :(得分:471)

使用apache commons-io,只需一行代码:

FileUtils.copyURLToFile(URL, File)

答案 2 :(得分:116)

更简单的nio用法:

URL website = new URL("http://www.website.com/information.asp");
try (InputStream in = website.openStream()) {
    Files.copy(in, target, StandardCopyOption.REPLACE_EXISTING);
}

答案 3 :(得分:85)

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();
        }
    }
}

您需要处理异常,可能在此方法外部。

答案 4 :(得分:23)

下载文件需要您阅读它,无论哪种方式,您都必须以某种方式浏览文件。您可以直接从流中读取字节,而不是逐行读取:

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);
    }

答案 5 :(得分:18)

这是一个老问题,但这是一个简洁,可读,仅限JDK的解决方案,资源封闭:

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。

答案 6 :(得分:17)

使用Java 7+时,请使用以下方法从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here

答案 7 :(得分:15)

这个答案几乎与选择的答案完全相同,但有两个增强功能: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();
        }
    }

答案 8 :(得分:10)

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]);
        }
    }
}

答案 9 :(得分:8)

就我个人而言,我发现Apache's HttpClient能够满足我对此需要做的所有事情。 Here是一个关于使用HttpClient

的精彩教程

答案 10 :(得分:6)

这是另一个基于Brian Risk's answer的java7变体,使用了try-with语句:

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);
      }

  }

答案 11 :(得分:2)

这里有许多优雅而有效的答案。但简洁可能会让我们失去一些有用的信息。特别是,一个通常不希望将连接错误视为异常,并且可能希望区别对待某种与网络相关的错误 - 例如,决定是否应该重试下载。

这是一种不会针对网络错误抛出异常的方法(仅针对真正异常的问题,如格式错误的网址或写入文件的问题)

/**
 * 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;
}

答案 12 :(得分:1)

可以使用Apache HttpComponents而不是Commons-IO下载该文件。此代码允许您根据URL下载Java文件并将其保存在特定目标位置。

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;
}

与单行代码形成对比:

FileUtils.copyURLToFile(fileURL, new File(fileSavePath),
                        URLS_FETCH_TIMEOUT, URLS_FETCH_TIMEOUT);

此代码可让您更好地控制流程,并且不仅可以指定超时,还可以指定User-AgentReferer值,这对许多网站都至关重要。

答案 13 :(得分:1)

总结(以某种方式抛光和更新)以前的答案。以下三种方法实际上是等同的。 (我添加了显式超时,因为我认为它们是必须的,当连接丢失时,没有人希望下载永远冻结。)

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,对我来说似乎都是正确的。它们安全有效。 (速度上的差异似乎很难相关 - 我在本地服务器上写入180Mb到SSD磁盘的时间波动在1.2到1.5左右)。他们不需要外部库。所有工作都具有任意大小和(根据我的经验)HTTP重定向。

此外,如果找不到资源,则全部抛出FileNotFoundException(通常是错误404),如果DNS解析失败,则抛出java.net.UnknownHostException;其他IOException对应于传输过程中的错误。

(标记为社区维基,随时添加信息或更正)

答案 14 :(得分:1)

underscore-java库中有方法U.fetch(url)。

的pom.xml:

  <groupId>com.github.javadev</groupId>
  <artifactId>underscore</artifactId>
  <version>1.40</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();
    }
}

答案 15 :(得分:1)

简单使用的问题是:

org.apache.commons.io.FileUtils.copyURLToFile(URL, File) 

如果您需要下载并保存非常大的文件,或者一般情况下如果您需要自动重试,以防连接断开。

我建议在这种情况下使用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();
}

答案 16 :(得分:0)

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;
    }
}

答案 17 :(得分:0)

您可以使用netloader for Java在一行中执行此操作:

new NetFile(new File("my/zips/1.zip"), "https://example.com/example.zip", -1).load(); //returns true if succeed, otherwise false.

答案 18 :(得分:0)

如果您在代理后面,可以在java程序中设置代理如下:

        Properties systemSettings = System.getProperties();
        systemSettings.put("proxySet", "true");
        systemSettings.put("https.proxyHost", "https proxy of your org");
        systemSettings.put("https.proxyPort", "8080");

如果您不在代理之后,请不要在代码中包含上述行。当您在代理服务器后面时,可以使用完整的代码来下载文件。

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();
        }
    }

答案 19 :(得分:0)

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);
    }

答案 20 :(得分:0)

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"));

使用

的第三种方法
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。

答案 21 :(得分:0)

这个可以在网络上读取文件并写入文件,希望对你也有帮助。

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();
    }
}

答案 22 :(得分:0)

java.net.http.HttpClient 使用授权的解决方案:

    HttpClient client = HttpClient.newHttpClient();
    
    HttpRequest request = HttpRequest.newBuilder()
            .GET()
            .header("Accept", "application/json")
            //.header("Authorization", "Basic ci5raG9kemhhZXY6NDdiYdfjlmNUM=") if you need
            .uri(URI.create("https://jira.google.ru/secure/attachment/234096/screenshot-1.png"))
            .build();

    HttpResponse<InputStream> response = client.send(request, HttpResponse.BodyHandlers.ofInputStream());

    try (InputStream in = response.body()) {
        Files.copy(in, Paths.get(target + "screenshot-1.png""), StandardCopyOption.REPLACE_EXISTING);
    }