Java中的ImageIcon更新(来自互联网)？

2023年4月9日 156次阅读

我有一些带有图像的URL.此图像在每个请求期间更新(即,对(相同)URL的每个请求都返回一个新图像).比如说,这个URL指向CAPTCHA.

我的目标是在我的程序中加载和显示几个这样的图像.

以下代码将这些图像加载到我的本地文件系统并且工作正常(即,所有图像都不同,唯一)：

String filePath;
String urlPath;
int numOfFilesToDownload;

//Here filePath and urlPath are initialized.
//filePath points to the directory, where to save images
//urlPath is the url from where to download images
//numOfFilesToDownload is the number of files to download

for(int i = 0; i < numOfFilesToDownload; i++){
    //Initializing connection
    URL url = new URL(urlPath);
    HttpURLConnection conn = (HttpURLConnection) url.openConnection();

    //Downloading image
    try(InputStream is = conn.getInputStream();
        FileOutputStream os = new FileOutputStream(filePath + "img" + i + ".jpg")){
        int b;
        while((b = is.read()) != -1)
            os.write(b);
    }
}

但是当我尝试以下事情时,会发生一些奇怪的事情：

for(int i = 0; i < numOfFilesToDownload; i++){
    //Initializing image from the url
    URL url = new URL(urlPath);
    javax.swing.ImageIcon ico = new javax.swing.ImageIcon(url);

    //Showing the graphical dialog window with the image
    javax.swing.JOptionPane.showMessageDialog(null, ico);
}

在后一种情况下,每个对话框包含在第一次迭代期间下载的相同图像,即一个图像.

此外,实验表明,如果你将“？r =”连接到urlPath(即一个简单的GET请求参数),那么url仍然有效.
以下代码似乎是有效的,并且完全符合它的要求(即显示的每个图像与前一个不同)：

for(int i = 0; i < numOfFilesToDownload; i++){
    //Initializing image from the url
    URL url = new URL(urlPath + "?r=" + i);
    javax.swing.ImageIcon ico = new javax.swing.ImageIcon(url);

    //Showing the graphical dialog window with the image
    javax.swing.JOptionPane.showMessageDialog(null, ico);
}

因此,我可以得出结论,ImageIcon以某种方式记住它处理的URL,并且根本不打算两次执行相同的工作……为什么以及如何？关于它的javadocs什么也没有.

最佳答案 当我尝试更改代码时,它运行正常.我的
SSCCE：

import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;

import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JOptionPane;
import javax.swing.SwingUtilities;

public class TestUrls {
   public static final String BASE_URL_PATH = "http://static.ed.edmunds-media.com/" +
        "unversioned/adunit/homepage_showcase/";
   public static final String[] URL_PATHS = {
      "honda-odyssey-2013.png",
      "chevrolet-impala-2013.png",
      "mazda-cx9-2013.png",
      "toyota-rav4-2013-2.png"
   };

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            for (String urlPath : URL_PATHS) {
               String fullUrlPath = BASE_URL_PATH + urlPath;
               try {
                  URL url = new URL(fullUrlPath);
                  BufferedImage img = ImageIO.read(url);
                  ImageIcon icon = new ImageIcon(img);
                  JOptionPane.showMessageDialog(null, icon);
               } catch (MalformedURLException e) {
                  e.printStackTrace();
               } catch (IOException e) {
                  e.printStackTrace();
               } 
            }
         }
      });
   }
}
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