How to get Response Body from servletResponse in Spring Boot Filter

Question

I want to get Response Body from ServletResponse to make a hash signature from it before passing to the client. I couldn't get the way to do it. For getting the request body from ServletRequest I have implemented like the following:

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

import javax.servlet.ReadListener;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

public class RequestWrapper extends HttpServletRequestWrapper{

    private final String body;
     
    public RequestWrapper(HttpServletRequest request) throws IOException 
    {
        //So that other request method behave just like before
        super(request);
         
        StringBuilder stringBuilder = new StringBuilder();
        BufferedReader bufferedReader = null;
        try {
            InputStream inputStream = request.getInputStream();
            if (inputStream != null) {
                bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
                char[] charBuffer = new char[128];
                int bytesRead = -1;
                while ((bytesRead = bufferedReader.read(charBuffer)) > 0) {
                    stringBuilder.append(charBuffer, 0, bytesRead);
                }
            } else {
                stringBuilder.append("");
            }
        } catch (IOException ex) {
            throw ex;
        } finally {
            if (bufferedReader != null) {
                try {
                    bufferedReader.close();
                } catch (IOException ex) {
                    throw ex;
                }
            }
        }
        //Store request pody content in 'body' variable 
        body = stringBuilder.toString();
    }
 
    @Override
    public ServletInputStream getInputStream() throws IOException {
        final ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(body.getBytes());
        ServletInputStream servletInputStream = new ServletInputStream() {
            public int read() throws IOException {
                return byteArrayInputStream.read();
            }

            @Override
            public boolean isFinished() {

                return false;
            }

            @Override
            public boolean isReady() {

                return false;
            }

            @Override
            public void setReadListener(ReadListener listener) {

                
            }
        };
        return servletInputStream;
    }
 
    @Override
    public BufferedReader getReader() throws IOException {
        return new BufferedReader(new InputStreamReader(this.getInputStream()));
    }
 
    //Use this method to read the request body N times
    public String getBody() {
        return this.body;
    }
}

How can I do similar to ServletResponse?

Answer 1

I implemented the ContentCachingResponseWrapper in the Filter to get response body from ServletResponse as follow:

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        ContentCachingResponseWrapper responseCacheWrapperObject = new ContentCachingResponseWrapper((HttpServletResponse) servletResponse);
        filterChain.doFilter(servletRequest, responseCacheWrapperObject);

        byte[] responseArray = responseCacheWrapperObject.getContentAsByteArray();
        String responseStr = new String(responseArray, responseCacheWrapperObject.getCharacterEncoding());
        //....use responsestr to make the signature

        responseCacheWrapperObject.copyBodyToResponse();
    }

Answer 2

try to use something like:

public void handleException(Throwable e, HttpServletRequest request, HttpServletResponse response, int status) {
    CustomErrorResponseException errorResponse = new CustomErrorResponseException();

    errorResponse.setError(e.getClass().getSimpleName());
    errorResponse.setStatus(status);
    errorResponse.setMessage(e.getLocalizedMessage());
    errorResponse.setPath(request.getRequestURI());
    errorResponse.setTimestamp(LocalDateTime.now().toString());

    response.setStatus(status);
    response.setContentType(MediaType.APPLICATION_JSON_VALUE);
    try {
        response.getWriter().write(jsonbMapper.serialize(errorResponse));
    } catch (IOException ex) {
        throw new RuntimeException(ex);
    }
}

And in filter just pass Exception, request, response and status you want to.