使用 Apache HttpClient 下载文件

Question

what im trying to do is to download a file with httpclient. At the moment my code is the following.

    HttpClient client = HttpClientBuilder.create().build();
    HttpGet request = new HttpGet(downloadURL);     


    HttpResponse response = client.execute(request);

    HttpEntity entity = response.getEntity();
    if (entity != null) {
        FileOutputStream fos = new FileOutputStream("C:\\file");
        entity.writeTo(fos);
        fos.close();
    }

My download URL is something like that: http://example.com/file/afz938f348dfa3

As you can see there is no extension to the file (in the url at least) however, when i go to the url with a normal browser, it does download the file "asdasdaasda.txt" or "asdasdasdsd.pdf" (the name is different from the url and the extenstion is not always the same, depends on what im trying to download).

My http response looks like this:

Date: Mon, 29 May 2017 14:57:14 GMT Server: Apache/2.4.10 Content-Disposition: attachment; filename="149606814324_testfile.txt" Accept-Ranges: bytes Cache-Control: public, max-age=0 Last-Modified: Mon, 29 May 2017 14:29:06 GMT Etag: W/"ead-15c549c4678-gzip" Content-Type: text/plain; charset=UTF-8 Vary: Accept-Encoding Content-Encoding: gzip Content-Length: 2554 Keep-Alive: timeout=5, max=100 Connection: Keep-Alive

How can i do so my java code automatically download the file with the good name and extension in a specific folder ?

Answer 1

You can get the file name and extension from your response's content-disposition header

First get the header then parse it for the filename as explained here , ie:

HttpEntity entity = response.getEntity();
if (entity != null) {
    String name = response.getFirstHeader('Content-Disposition').getValue();
    String fileName = disposition.replaceFirst("(?i)^.*filename=\"([^\"]+)\".*$", "$1");
    FileOutputStream fos = new FileOutputStream("C:\\" + fileName);
    entity.writeTo(fos);
    fos.close();
}

Answer 2

More formal way would be to use HeaderElements API:

    Optional<String> resolveFileName(HttpResponse response) {
        return Arrays.stream(response.getFirstHeader("Content-Disposition").getElements())
                .map(element -> element.getParameterByName("filename"))
                .filter(Objects::nonNull)
                .map(NameValuePair::getValue)
                .findFirst();
    }

Answer 3

Java 11 code to download file using java.net.http.HttpClient

import java.io.IOException;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;

...

public static void downloadFile(String productId) throws IOException, InterruptedException {
        String url = "https://sameer-platform.com/v1/products/" + productId + "/download/model";

        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest.newBuilder().uri(URI.create(url)).build();

        // Creates new File at provided location user.dir and copies the filename from Content-Disposition
        HttpResponse<Path> response = client.send(request,
                HttpResponse.BodyHandlers.ofFileDownload(Path.of(System.getProperty("user.dir")),
                        StandardOpenOption.CREATE, StandardOpenOption.WRITE));

        System.out.println(response.statusCode());
        System.out.println(response.headers());
        Path path = response.body();
        System.out.println("Path=" + path); // Absolute Path of downloaded file
    }