etag and its filter

本文介绍如何在Spring框架中使用自定义过滤器实现HTTP ETag缓存控制。通过ShallowEtagResponseWrapper类包装原始响应,可以生成并设置ETag头,从而实现条件GET请求的支持。此外,还展示了如何配置web.xml来启用此过滤器。

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from spring 3:

You can re-write it with your requirement

---
So I have in web.xml:

Code:
<filter>
<filter-name>pageNotFoundFilter</filter-name>
<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
</filter>

and in my context.xml I have a bean called "pageNotFoundFilter". Very nice !

---

<filter>
<filter-name>etagFilter</filter-name>
<filter-class>org.xxx.web.filter.EtagHeaderFilter</filter-class>
</filter>

<filter-mapping>
<filter-name>etagFilter</filter-name>
</filter-mapping>


ShallowEtagResponseWrapper responseWrapper = new ShallowEtagResponseWrapper(response);
filterChain.doFilter(request, responseWrapper);

byte[] body = responseWrapper.toByteArray();
String responseETag = generateETagHeaderValue(body);
response.setHeader(HEADER_ETAG, responseETag);

String requestETag = request.getHeader(HEADER_IF_NONE_MATCH);
if (responseETag.equals(requestETag)) {
if (logger.isTraceEnabled()) {
logger.trace("ETag [" + responseETag + "] equal to If-None-Match, sending 304");
}
response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
}
else {
if (logger.isTraceEnabled()) {
logger.trace("ETag [" + responseETag + "] not equal to If-None-Match [" + requestETag +
"], sending normal response");
}
response.setContentLength(body.length);
FileCopyUtils.copy(body, response.getOutputStream());
}
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