Downloading an image in java

Question

I have to download an image from the nasa website. Problem is, that my code sometimes works, sucessfully downloading an image, while sometimes saves only 186B (don't know why exactly 186).

Problems is for sure connected with the way nasa sahres those photos. For instance, an image from that link https://mars.jpl.nasa.gov/msl-raw-images/msss/00001/mcam/0001ML0000001000I1_DXXX.jpg is saved sucessfully, while from that link https://mars.nasa.gov/mer/gallery/all/2/f/001/2F126468064EDN0000P1001L0M1-BR.JPG fails.

Here is my code

public static void saveImage(String imageUrl, String destinationFile){
    URL url;
    try {
        url = new URL(imageUrl);
        System.out.println(url);
        InputStream is = url.openStream();
        OutputStream os = new FileOutputStream(destinationFile);

        byte[] b = new byte[2048];
        int length;

        while ((length = is.read(b)) != -1) {
            os.write(b, 0, length);
        }

        is.close();
        os.close();
    } catch (MalformedURLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

Does someone have an idea, why is doesn't work?

---

public boolean downloadPhotosSol(int i) throws JSONException, IOException {
    String url0 =  "https://api.nasa.gov/mars-photos/api/v1/rovers/spirit/photos?sol=" + this.chosenMarsDate + "&camera=" + this.chosenCamera + "&page=" + i + "&api_key=###";
    JSONObject json = JsonReader.readJsonFromUrl(url0);
    if(json.getJSONArray("photos").length() == 0) return true;
    String workspace = new File(".").getCanonicalPath();
    String pathToFolder = workspace+File.separator+this.getManifest().getName() + this.chosenMarsDate + this.chosenCamera +"Strona"+i;
    new File(pathToFolder).mkdirs();
    for(int j = 0;j<json.getJSONArray("photos").length();j++) {
        String url = ((JSONObject) json.getJSONArray("photos").get(j)).getString("img_src");
        SaveImage.saveImage(url, pathToFolder+File.separator+"img"+j+".jpg");
    }
    return false;
}

Answer 1

When you get a 186 byte file, open it with a text editor and see what is inside. It could contain an HTTP error message in HTML format. If instead you see the first 186 bytes of your image file, then something is not working right with your program.

EDIT: From your comments it looks like you are getting an HTTP 301 response, which is a redirect to another location. A web browser handles this automatically without you noticing. However, your Java program is not following the redirect to the new location. You need to use an HTTP Java library that handles redirects.

Answer 2

Best and short way of doing it:

try(InputStream in = new URL("http://example.com/image.jpg").openStream()){
    Files.copy(in, Paths.get("C:/File/To/Save/To/image.jpg"));
}