Java中如何控制资源的缓存？
我正在构建一个 Java 小程序，它涉及从 URL 下载图像和其他资源。我发现图像正在被缓存，并且可以在 Java 控制面板中的临时 Internet 文件/查看.../资源下查看它们。不幸的是，我需要能够更新图像并让这些更新出现在小程序的执行之间，但缓存导致了问题。
我找不到任何有关控制此类资源缓存的信息。什么进程正在缓存资源以及如何控制它？特别是如何设置图像甚至特定图像的到期时间？
如果相关，我将使用如下代码下载图像：（mt 是 MediaTracker 对象）。
public BufferedImage getImageFromUrl(String url)
{
Image img = null;
try {
URL u = new URL(url);
img = java.awt.Toolkit.getDefaultToolkit().createImage(u);
mt.addImage(img, numImages++);
mt.waitForAll();
...
感谢您的任何帮助。
I am building a Java applet that involves downloading images among other resources from a URL. I have discovered that the images are being cached, and can view them in the Java Control Panel under Temporary Internet Files / View... / Resources. Unfortunately I need to be able to update the images and have these updates appear between executions of the applet but the cache is causing problems.
I can't find any information about what controls the caching of these kinds of resources. What process is caching the resources and how do I control it? In particular how do I set the expiry time for images, or perhaps even specific images?
In case it is relevant, I am downloading the images using code like this: (mt is a MediaTracker object).
public BufferedImage getImageFromUrl(String url)
{
Image img = null;
try {
URL u = new URL(url);
img = java.awt.Toolkit.getDefaultToolkit().createImage(u);
mt.addImage(img, numImages++);
mt.waitForAll();
...
Thanks for any help.
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使用它可以避免来自服务器的缓存图像：
如果您想控制过期时间，您可以通过添加以下行来专门设置
Cache-Control或Expires标头：Use this to avoid cached images from the server:
If you want control over the expiry time you can specifically set the
Cache-ControlorExpiresheaders by adding lines like:使用
URLConnection将图像下载到byte数组中。将此byte数组传递给createImage()。您可能还想通过在URLConnection对象上调用setUseCaches(false)来关闭缓存。Use a
URLConnectionto download the image into abytearray. Pass thisbytearray tocreateImage(). You may also want to turn off caching by callingsetUseCaches(false)on theURLConnectionobject.