捕获并记录响应正文 [英] Capture and log the response body

问题描述

我有一个处理某些HTTP请求和响应的servlet。我想在发送回客户端之前记录响应正文。有没有什么方法可以在从servlet作为 HttpServletResponse 对象发送之前捕获响应主体？

I have a servlet that handle certain HTTP requests and responses. I want to log the response body before sending back to the client. Is there any way that I can capture the response body before it is send as a HttpServletResponse object from the servlet?

推荐答案

如果我理解正确，您想记录响应正文？这是一项相当昂贵的任务，但如果这是业务需求...

If I understand you correctly, you want to log the response body? That's a pretty expensive task, but if that's the business requirement...

正如@duffymo指出的那样，过滤器是一个合适的地方。您可以通过使用 ServletResponse 来捕获响应正文/servlet/http/HttpServletRequestWrapper.html\"rel =noreferrer> HttpServletResponseWrapper 实现取代 HttpServletResponse #getWriter（）具有自己的实现，将响应主体复制到某个缓冲区。在使用替换后的响应继续过滤器链后，只需记录副本。

As @duffymo pointed, a Filter is a suitable place for this. You can capture the response body by replacing the passed-in ServletResponse with a HttpServletResponseWrapper implementation which replaces the HttpServletResponse#getWriter() with an own implementation which copies the response body into some buffer. After continuing the filter chain with the replaced response, just log the copy.

以下是 doFilter（）方法可以如下所示：

Here's a kickoff example how the doFilter() method can look like:

public void doFilter(ServletRequest request, final ServletResponse response, FilterChain chain) throws IOException, ServletException {
    final CopyPrintWriter writer = new CopyPrintWriter(response.getWriter());
    chain.doFilter(request, new HttpServletResponseWrapper((HttpServletResponse) response) {
        @Override public PrintWriter getWriter() {
            return writer;
        }
    });
    logger.log(writer.getCopy());
}

以下是 CopyPrintWriter 看起来像：

public class CopyPrintWriter extends PrintWriter {

    private StringBuilder copy = new StringBuilder();

    public CopyPrintWriter(Writer writer) {
        super(writer);
    }

    @Override
    public void write(int c) {
        copy.append((char) c); // It is actually a char, not an int.
        super.write(c);
    }

    @Override
    public void write(char[] chars, int offset, int length) {
        copy.append(chars, offset, length);
        super.write(chars, offset, length);
    }

    @Override
    public void write(String string, int offset, int length) {
        copy.append(string, offset, length);
        super.write(string, offset, length);
    }

    public String getCopy() {
        return copy.toString();
    }

}

将此过滤器映射到 url-pattern 您要为其记录回复。请记住，二进制/静态内容（如图像，CSS，JS文件等）不会以这种方式记录。您希望使用足够的 url-pattern 来排除它们，例如 * .jsp 或仅在有问题的servlet的 servlet-name 上。如果你想要记录二进制/静态内容（我没有看到任何好处），那么你需要以与以下相同的方式替换 HttpServletResponse＃getOutputStream（）好吧。

Map this filter on an url-pattern for which you'd like to log responses for. Keep in mind that binary/static content like images, CSS, JS files and so on won't be logged this way. You'd like to exclude them by using a specific enough url-pattern, e.g. *.jsp or just on the servlet-name of the servlet in question. If you want to log binary/static content anyway (for which I don't see any benefit), then you need to replace the HttpServletResponse#getOutputStream() the same way as well.

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