如何根据Content-type添加响应头；在提交响应之前获取内容类型 [英] How to add response headers based on Content-type; getting Content-type before the response is committed

问题描述

我想为所有 image/* 和 text/css 设置 Expires 标头.我在 Filter 中执行此操作.然而:

I want to set the Expires header for all image/* and text/css. I'm doing this in a Filter. However:

• 在调用 chain.doFilter(..) 之前，Content-type 还没有实现"
• 在调用 chain.doFilter(..) 之后，Content-type 被设置，但 content-length 也是如此，它禁止添加新的 headers(至少在 Tomcat 实现中)

• before calling chain.doFilter(..) the Content-type is not yet "realized"
• after calling chain.doFilter(..) the Content-type is set, but so is content-length, which forbids adding new headers (at least in Tomcat implementation)

我可以使用请求资源的扩展名，但是由于一些 css 文件是由 Richfaces 通过从 jar 文件中获取它们生成的，因此文件名不是 x.css，但是是/xx/yy/zz.xcss/DATB/....

I can use the extensions of the requested resource, but since some of the css files are generated by richfaces by taking them from inside jar-files, the name of the file isn't x.css, but is /xx/yy/zz.xcss/DATB/....

那么，有没有办法在提交响应之前获取 Content-type.

So, is there a way to get the Content-type before the response is committed.

推荐答案

是的，实现 HttpServletResponseWrapper 并覆盖 setContentType().

class AddExpiresHeader extends HttpServletResponseWrapper {
    private static final long ONE_WEEK_IN_MILLIS = 604800000L;

    public AddExpiresHeader(HttpServletResponse response) {
        super(response);
    }

    public void setContentType(String type) {
        if (type.startsWith("text") || type.startsWith("image")) {
            super.setDateHeader("Expires", System.currentTimeMillis() + ONE_WEEK_IN_MILLIS);
        }
        super.setContentType(type);
    }
}

并按如下方式使用它:

chain.doFilter(request, new AddExpiresHeader((HttpServletResponse) response));

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