捕获并记录响应正文

java servlets

2022-09-01 07:37:43

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。有没有办法在响应正文作为对象从 servlet 发送之前捕获它？HttpServletResponse

答案 1

如果我正确理解您，您要记录响应正文吗？这是一项非常昂贵的任务，但如果这是业务需求...

正如@duffymo指出的那样，a是一个适合这样的地方。您可以通过将传入的响应体替换为 HttpServletResponseWrapper 实现来捕获响应正文，该实现将响应正文替换为将响应正文复制到某个缓冲区中。使用替换的响应继续筛选器链后，只需记录副本即可。FilterServletResponseHttpServletResponse#getWriter()

下面是一个启动示例，该方法的外观如何：doFilter()

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());
}

以下是可以的外观：CopyPrintWriter

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();
    }

}

将此筛选器映射到要为其记录响应的上。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。您希望通过使用足够具体的来排除它们，例如或者只是在有问题的servlet上。如果你想记录二进制/静态内容（我没有看到任何好处），那么你也需要以同样的方式替换。url-patternurl-pattern*.jspservlet-nameHttpServletResponse#getOutputStream()

答案 2

BalusC 应答的替代方法使用 TeeOutputStream 一次写入两个输出流。

public void doFilterInternal(HttpServletRequest req, HttpServletResponse res, FilterChain chain) throws IOException, ServletException {
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    final PrintStream ps = new PrintStream(baos);

    chain.doFilter(req,new HttpServletResponseWrapper(res) {
         @Override
         public ServletOutputStream getOutputStream() throws IOException {
            return new DelegatingServletOutputStream(new TeeOutputStream(super.getOutputStream(), ps)
            );
         }
         @Override
         public  PrintWriter getWriter() throws IOException {
            return new PrintWriter(new DelegatingServletOutputStream (new TeeOutputStream(super.getOutputStream(), ps))
            );
         }
      });

    //Get Response body calling baos.toString();
}