如何使用Java从Internet下载和保存文件？

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中。我知道有几种方法可以一行一行地抓取和读取在线文件（URL），但是有没有一种方法可以使用Java下载和保存文件？

下载文件需要您阅读，无论哪种方法，您都必须以某种方式浏览文件。您可以从流中按字节读取，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);
    }

试一试：

使用

transferFrom（）

可能比从源通道读取并写入此通道的简单循环效率更高。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，而无需实际复制它们

多看看

注意：transferFrom中的第三个参数是要传输的最大字节数

Integer.MAX_VALUE

最多传输2^31个字节，

Long.MAX_VALUE

最多允许传输2^63个字节（大于现有的任何文件）

您将需要处理异常，可能是此方法之外的异常。

就我个人而言，我发现自己完全有能力处理与此相关的所有事情。是一个关于使用HttpClient的很好的教程

使用apache，只有一行代码：

FileUtils.copyURLToFile(URL, File)

import java.io.*；
导入java.net。*；
公共类归档{
公共静态void下载（字符串地址、字符串localFileName）{
OutputStream out=null；
URLConnection conn=null；
InputStream in=null；
试一试{
URL=新的URL（地址）；
out=new BufferedOutputStream（new FileOutputStream（localFileName））；
conn=url.openConnection（）；
in=conn.getInputStream（）；
字节[]缓冲区=新字节[1024]；
国际货币联盟；
长numwrited=0；
while（（numRead=in.read（buffer））！=-1）{
out.write（缓冲区，0，numRead）；
numwrited+=numRead；
}
System.out.println（localFileName+“\t”+numwrited）；
} 
捕获（异常）{
异常。printStackTrace（）；
} 
最后{
试一试{
if（in！=null）{
in.close（）；
}
if（out！=null）{
out.close（）；
}
} 
捕获（ioe异常ioe）{
}
}
}
公共静态无效下载（字符串地址）{
int lastSlashIndex=地址.lastIndexOf（'/'）；
如果（lastSlashIndex>=0&&
lastSlashIndex

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);
}

---

在简单使用时存在以下问题：

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

若您需要下载并保存非常大的文件，或者通常若您需要在连接断开时自动重试

在这种情况下，我建议使用ApacheHttpClient和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();
}

java -jar so-downloader.jar https://github.com/JanStureNielsen/so-downloader/archive/main.zip so-downloader-source.zip

---

此答案几乎与“选定答案”完全相同，但有两个增强：它是一个方法，并关闭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();
        }
    }

---

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。

这是另一个基于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);
      }

  }

---

可以使用Apache的

HttpComponents

而不是

Commons IO

下载该文件。此代码允许您根据文件的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;
}

与单行代码相比：

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

此代码将为您提供对流程的更多控制，让您不仅可以指定超时，还可以指定

用户代理

和

Referer

值，这对许多网站都很重要。

库中有方法U.fetch（url）

pom.xml：

  <groupId>com.github.javadev</groupId>
  <artifactId>underscore</artifactId>
  <version>1.45</version>

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下载永远冻结。）

我没有发现明显的差异，对我来说都是正确的。它们既安全又高效。（速度上的差异似乎并不相关——我从本地服务器向SSD磁盘写入180Mb数据的时间在1.2到1.5段之间波动）。它们不需要外部库。根据我的经验，所有这些都可以使用任意大小的HTTP重定向

此外，如果未找到资源（通常为错误404），则所有抛出

FileNotFoundException

，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，请随意添加信息或更正）

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，一个“强”经常不想考虑连接错误（异常）<强>，并且可能希望不同地处理一些与网络相关的错误-例如，决定是否重试下载。 这里有一个方法，它不会对网络错误抛出异常（仅适用于真正的异常问题，如错误的url或写入文件的问题）

/**
*从（http/https）URL下载并保存到文件。
*不考虑连接错误是一个例外。相反，它返回：
*  
*0=正常
*1=连接间
FileUtils.copyURLToFile(fileURL, new File(fileSavePath),
                        URLS_FETCH_TIMEOUT, URLS_FETCH_TIMEOUT);

  <groupId>com.github.javadev</groupId>
  <artifactId>underscore</artifactId>
  <version>1.45</version>

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();
    }
}

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();
}

/**
 * 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;
}

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;
    }
}

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

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

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();
        }
    }

static long download(String sourceUrl, String targetFileName) throws Exception {
    try (InputStream in = URI.create(sourceUrl).toURL().openStream()) {
        return Files.copy(in, Paths.get(targetFileName));
    }
}

package so.downloader;

import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URI;
import java.nio.file.Files;
import java.nio.file.Paths;

public class Application {
    public static void main(String[] args) throws MalformedURLException, IOException {
        if (2 != args.length) {
            System.out.println(String.format("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 sourceUrl, String targetFileName) throws MalformedURLException, IOException {
        try (InputStream in = URI.create(sourceUrl).toURL().openStream()) {
            return Files.copy(in, Paths.get(targetFileName));
        }
    }

}

java -jar so-downloader.jar <source-URL> <target-filename>

java -jar so-downloader.jar https://github.com/JanStureNielsen/so-downloader/archive/main.zip so-downloader-source.zip

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);
    }

ReadableByteChannel aq = Channels.newChannel(new url("https//asd/abc.txt").openStream());
FileOutputStream fileOS = new FileOutputStream("C:Users/local/abc.txt")
FileChannel writech = fileOS.getChannel();

FileUtils.copyURLToFile(new url("https//asd/abc.txt",new local file on system("C":/Users/system/abc.txt"));

InputStream xy = new ("https//asd/abc.txt").openStream();

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();
    }
}

    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);
    }