How to download and save a file from Internet usin

2018-12-31 00:22发布

There is an online file (such as http://www.example.com/information.asp) I need to grab and save to a directory. I know there are several methods for grabbing and reading online files (URLs) line-by-line, but is there a way to just download and save the file using Java?

标签: java download
20条回答
千与千寻千般痛.
2楼-- · 2018-12-31 00:59

There is an issue with simple usage of:

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

if you need to download and save very large files, or in general if you need automatic retries in case connection is dropped.

What I suggest in such cases is Apache HttpClient along with org.apache.commons.io.FileUtils. For example:

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();
}
查看更多
其实,你不懂
3楼-- · 2018-12-31 01:01

Downloading a file requires you to read it, either way you will have to go through the file in some way. Instead of line by line, you can just read it by bytes from the stream:

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);
    }
查看更多
看淡一切
4楼-- · 2018-12-31 01:01

This answer is almost exactly like selected answer but with two enhancements: it's a method and it closes out the FileOutputStream object:

    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();
        }
    }
查看更多
公子世无双
5楼-- · 2018-12-31 01:01

If you are behind a proxy, you can set the proxies in java program as below:

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

If you are not behind a proxy, don't include the lines above in your code. Full working code to download a file when you are behind a proxy.

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();
        }
    }
查看更多
深知你不懂我心
6楼-- · 2018-12-31 01:02

It's an old question but here's an elegant JDK-only solution:

public static void download(String url, String fileName) throws Exception {
    try (InputStream in = URI.create(url).toURL().openStream()) {
        Files.copy(in, Paths.get(fileName));
    }
}

Concise, readable, properly closed resources leveraging nothing but the core JDK and language features.

查看更多
梦醉为红颜
7楼-- · 2018-12-31 01:06

Simpler nio usage:

URL website = new URL("http://www.website.com/information.asp");
try (InputStream in = website.openStream()) {
    Files.copy(in, target, StandardCopyOption.REPLACE_EXISTING);
}
查看更多
登录 后发表回答