結合使用ImageIO.read和重定向URL

Question

我正在嘗試使用ImageIO從網絡讀取圖像：

URL url = new URL(location);
bi = ImageIO.read(url);

如果location是以實際圖像結尾的URL（例如http://www.lol.net/1.jpg ），則上面的代碼有效。 但是，當URL是重定向時（例如， http : //www.lol.net/redirection導致http://www.lol.net/1.jpg ），上述代碼在bi中返回null 。

兩個問題。 一，為什么會這樣？ 是因為ImageIO庫試圖根據URL字符串找到合適的ImageReader嗎？ 第二，什么是解決此限制的最佳方法？ 請注意，我需要BufferedImage輸出而不是Image輸出。

編輯 ：對於想測試它的人，我嘗試讀取的URL是http://graph.facebook.com/804672289/picture ，該URL轉換為http://profile.ak.fbcdn.net/hprofile- ak-snc4 / hs351.snc4 / 41632_804672289_6662_q.jpg 。

編輯2 ：我在上一次編輯中不正確。 URL是https://graph.facebook.com/804672289/picture 。 如果我將https替換為http，則上面的代碼可以正常工作。 因此，我的新問題是如何使其與HTTPS一起使用，因此我不需要進行替換。

Answer 1

我在使用https圖片鏈接時遇到了同樣的問題。 問題是，當我在代碼中讀取https鏈接時，它將返回200。但實際上，它是301。為解決此問題，我使用了“ curl”用戶代理，以便獲得301並進行迭代，直到找到最終鏈接。 請參見下面的代碼：

希望這對@ Eldad-Mor有幫助。

private InputStream getInputStream(String url) throws IOException {
        InputStream stream = null;
        try {
            stream = handleRedirects(url);
            byte[] bytes = IOUtils.toByteArray(stream);
            return new ByteArrayInputStream(bytes);
        } finally {
            if (stream != null)
                stream.close();
        }
    }

    /**
     * Handle redirects in the URL Manually. Method calls itself if redirects are found until there re no more redirects.
     * 
     * @param url URL
     * @return input stream
     * @throws IOException
     */
    private InputStream handleRedirects(String url) throws IOException {
        HttpURLConnection.setFollowRedirects(false);
        URL obj = new URL(url);
        HttpURLConnection conn = (HttpURLConnection) obj.openConnection();
        conn.setRequestProperty("User-Agent", "curl/7.30.0");
        conn.connect();
        boolean redirect = false;
        LOG.info(conn.getURL().toString());

        int status = conn.getResponseCode();
        if (status != HttpURLConnection.HTTP_OK) {
            if (status == HttpURLConnection.HTTP_MOVED_TEMP
                    || status == HttpURLConnection.HTTP_MOVED_PERM
                    || status == HttpURLConnection.HTTP_SEE_OTHER)
                redirect = true;
        }
        if (redirect) {
            String newUrl =conn.getHeaderField("Location");
            conn.getInputStream().close();
            conn.disconnect();
            return handleRedirects(newUrl);
        }
        return conn.getInputStream();
    }

Answer 2

在我看來， http：//www.lol.net/1.jpg似乎並不直接指向圖像。

正如@Bozho所指出的，ImageIO使用默認的URL.openConnection （由於地址以“ http”開頭）返回一個HttpURLConnection ，該默認情況下具有setFollowRedirects(true) 。

關於您的編輯 ，此代碼對我來說似乎很好：

URL url = new URL("http://graph.facebook.com/804672289/picture");
BufferedImage bi = ImageIO.read(url);

System.out.println(bi);
// Prints: BufferedImage@43b09468: type = 5 ColorModel: #pixelBits = 24 numComponents = 3 color space = java.awt.color.ICC_ColorSpace@7ddf5a8f transparency = 1 has alpha = false isAlphaPre = false ByteInterleavedRaster: width = 50 height = 50 #numDataElements 3 dataOff[0] = 2

我懷疑您的錯誤在其他地方。

Answer 3

關於您的編輯2：

ImageIo.read（url），不必理會url類型。 即http或https。

您可以簡單地將url傳遞給此方法，但是如果要傳遞https url，則需要執行某些步驟來驗證SSL證書。 請找到以下示例。

1）對於http和https：

import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.security.cert.X509Certificate;
import javax.imageio.ImageIO;
import javax.net.ssl.HttpsURLConnection;
import javax.net.ssl.SSLContext;
import javax.net.ssl.TrustManager;
import javax.net.ssl.X509TrustManager;


/**
 * @author Syed CBE
 *
 */
public class Main {


    public static void main(String[] args) {

                int height = 0,width = 0;
                String imagePath="https://www.sampledomain.com/sampleimage.jpg";
                System.out.println("URL=="+imagePath);
                InputStream connection;
                try {
                    URL url = new URL(imagePath);  
                    if(imagePath.indexOf("https://")!=-1){
                        final SSLContext sc = SSLContext.getInstance("SSL");
                        sc.init(null, getTrustingManager(), new java.security.SecureRandom());                                 
                        HttpsURLConnection.setDefaultSSLSocketFactory(sc.getSocketFactory());
                        connection = url.openStream();
                     }
                    else{
                        connection = url.openStream();
                    }
                    BufferedImage bufferedimage = ImageIO.read(connection);
                    width          = bufferedimage.getWidth();
                    height         = bufferedimage.getHeight();
                    System.out.println("width="+width);
                    System.out.println("height="+height);
                } catch (MalformedURLException e) {

                    System.out.println("URL is not correct : " + imagePath);
                } catch (IOException e) {

                    System.out.println("IOException Occurred : "+e);
                }
                catch (Exception e) {

                    System.out.println("Exception Occurred  : "+e);
                }


    }

     private static TrustManager[] getTrustingManager() {
            TrustManager[] trustAllCerts = new TrustManager[] { new X509TrustManager() {

                   @Override
                   public java.security.cert.X509Certificate[] getAcceptedIssuers() {
                         return null;
                   }

                   @Override
                   public void checkClientTrusted(X509Certificate[] certs, String authType) {
                   }

                   @Override
                   public void checkServerTrusted(X509Certificate[] certs, String authType) {
                   }
            } };
            return trustAllCerts;
     }

}

2）僅針對http：

// This Code will work only for http, you can make it work for https but you need additional code to add SSL certificate using keystore
    public static void getImage(String testUrl) {

            String testUrl="https://sampleurl.com/image.jpg";

        HttpGet httpGet = new HttpGet(testUrl);
                 System.out.println("HttpGet is  ---->"+httpGet.getURI());
                HttpResponse httpResponse = null;
                HttpClient httpClient=new DefaultHttpClient();

                try {

                    httpResponse = httpClient.execute(httpGet);
                    InputStream stream=httpResponse.getEntity().getContent();
                     BufferedImage sourceImg = ImageIO.read(stream);
                    System.out.println("------ source -----"+sourceImg.getHeight());
                     sourceImg.getWidth();
                        System.out.println(sourceImg);
                }catch (MalformedURLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    System.out.println("------ MalformedURLException -----"+e);
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                System.out.println("------  IOEXCEPTION -----"+e);
                }
    }

Answer 4

可以使用Apache HttpClient，對我來說它工作正常。

http://hc.apache.org/

    public static void main(String args[]) throws Exception{
    String url = "http://graph.facebook.com/804672289/picture?width=800";

    HttpClient client = HttpClients.createDefault();
    HttpResponse response = client.execute(new HttpGet(url));
    BufferedImage image = ImageIO.read(input);

    if(image == null){
        throw new RuntimeException("Ooops");
    } else{
        System.out.println(image.getHeight());
    }
}