如何读取和复制 HTTP servlet 响应输出流内容以进行日志记录

java logging servlets servlet-filters

2022-08-31 17:07:23

我已经在我的java Web服务器（实际上是appengine）中创建了一个过滤器，用于记录传入请求的参数。我还想记录我的Web服务器写入的结果响应。虽然我可以访问响应对象，但我不确定如何从中获取实际的字符串/内容响应。

有什么想法吗？

答案 1

您需要创建一个过滤器，其中使用自定义的HttpServletResponseWrapper实现包装参数，其中您可以覆盖并返回自定义ServletOutputStream实现，其中您复制基本抽象的ProstoutStream#write（int b）方法中的写入字节。然后，将包装的自定义传递给调用，最后您应该能够在调用后获得复制的响应。ServletResponsegetOutputStream()getWriter()HttpServletResponseWrapperFilterChain#doFilter()

换句话说，：Filter

@WebFilter("/*")
public class ResponseLogger implements Filter {

    @Override
    public void init(FilterConfig config) throws ServletException {
        // NOOP.
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException, IOException {
        if (response.getCharacterEncoding() == null) {
            response.setCharacterEncoding("UTF-8"); // Or whatever default. UTF-8 is good for World Domination.
        }

        HttpServletResponseCopier responseCopier = new HttpServletResponseCopier((HttpServletResponse) response);

        try {
            chain.doFilter(request, responseCopier);
            responseCopier.flushBuffer();
        } finally {
            byte[] copy = responseCopier.getCopy();
            System.out.println(new String(copy, response.getCharacterEncoding())); // Do your logging job here. This is just a basic example.
        }
    }

    @Override
    public void destroy() {
        // NOOP.
    }

}

定制：HttpServletResponseWrapper

public class HttpServletResponseCopier extends HttpServletResponseWrapper {

    private ServletOutputStream outputStream;
    private PrintWriter writer;
    private ServletOutputStreamCopier copier;

    public HttpServletResponseCopier(HttpServletResponse response) throws IOException {
        super(response);
    }

    @Override
    public ServletOutputStream getOutputStream() throws IOException {
        if (writer != null) {
            throw new IllegalStateException("getWriter() has already been called on this response.");
        }

        if (outputStream == null) {
            outputStream = getResponse().getOutputStream();
            copier = new ServletOutputStreamCopier(outputStream);
        }

        return copier;
    }

    @Override
    public PrintWriter getWriter() throws IOException {
        if (outputStream != null) {
            throw new IllegalStateException("getOutputStream() has already been called on this response.");
        }

        if (writer == null) {
            copier = new ServletOutputStreamCopier(getResponse().getOutputStream());
            writer = new PrintWriter(new OutputStreamWriter(copier, getResponse().getCharacterEncoding()), true);
        }

        return writer;
    }

    @Override
    public void flushBuffer() throws IOException {
        if (writer != null) {
            writer.flush();
        } else if (outputStream != null) {
            copier.flush();
        }
    }

    public byte[] getCopy() {
        if (copier != null) {
            return copier.getCopy();
        } else {
            return new byte[0];
        }
    }

}

定制：ServletOutputStream

public class ServletOutputStreamCopier extends ServletOutputStream {

    private OutputStream outputStream;
    private ByteArrayOutputStream copy;

    public ServletOutputStreamCopier(OutputStream outputStream) {
        this.outputStream = outputStream;
        this.copy = new ByteArrayOutputStream(1024);
    }

    @Override
    public void write(int b) throws IOException {
        outputStream.write(b);
        copy.write(b);
    }

    public byte[] getCopy() {
        return copy.toByteArray();
    }

}

答案 2

BalusC解决方案还可以，但有点过时。春天现在有它的功能。您需要做的就是使用，它具有方法。[ContentCachingResponseWrapper]public byte[] getContentAsByteArray()

我建议制作WrapprFactory，这将允许它可配置，无论是使用默认的RecertWrapper还是ContentCachingResponseWrapper。