如何确保我的图片完整？ （在java中）

Question

i using below code to get a picture from URL:

    URL url=new URL("http://www.google.com/images/logos/ps_logo2.png");
    InputStream in=url.openStream();
    ByteArrayOutputStream tmpOut = new ByteArrayOutputStream();
    byte[] buf = new byte[512];
    int len;
    while (true) {
        len = in.read(buf);
        if (len == -1) {
            break;
        }
        tmpOut.write(buf, 0, len);
    }
    tmpOut.close();

    byte[] picture=tmpOut.toByteArray();
    System.out.println(picture.length);

this code is okay,but my internet connect is very very bad,

so ,I maybe get a broken picture like this:

How can I ensure the picture file is complete ?

I think you can add this code to try and test this:

if (len == -1) { change to if (len == -1 || (int)(Math.random()*100)==1 ) {

full test code:

    URL url=new URL("http://www.google.com/images/logos/ps_logo2.png");
    InputStream in=url.openStream();
    ByteArrayOutputStream tmpOut = new ByteArrayOutputStream();
    byte[] buf = new byte[512];
    int len;
    while (true) {
        len = in.read(buf);
        if (len == -1 || (int)(Math.random()*100)==1 ) {
            break;
        }
        tmpOut.write(buf, 0, len);
    }
    tmpOut.close();
    byte[] picture =tmpOut.toByteArray();
    System.out.println(picture.length);

thanks for help :)

Answer 1

Have you looked into using the ImageIO class for loading images - it takes care of a lot of these details for you:

Image image;
try {    
  URL url = new URL("http://www.google.com/images/logos/ps_logo2.png");
  image = ImageIO.read(url);
} catch (IOException e) {
   ...
}

Answer 2

Try using URL.openConnection() instead You get an URLConnection object on which you can query the content length (if provided) ( URLConnection.getContentLength() ). That would help in most case.

In the other case you can analyze the image header to get its length, but that would require a dedicated analyzer for each format.