I want to get the Response body during Post HandlerInterceptor but it comes up empty.

spring-boot.version: 2.7.4

CustomPostHandlerInterceptor.java

@Component
@Order(1)
public class CustomPostHandlerInterceptor implements HandlerInterceptor {

    @Override
    public final boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        return true;
    }

    @Override
    public final void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
            ModelAndView modelAndView) throws Exception {
        ContentCachingResponseWrapper resp = new ContentCachingResponseWrapper(response);
        byte[] responseBody = resp.getContentAsByteArray();
        String res = new String(responseBody, StandardCharsets.UTF_8);
    }

    @Override
    public final void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,
            Exception ex) throws Exception {
    }
}

Controller class

@RestController
@RequestMapping("/exampleRest")
public class ExampleRest {


    @RequestMapping("/getUsername")
    @GetMapping
    public String getUsername() {
        return "michael";
    }
}

I want to get response body from HttpServletResponse. I tried different methods but it comes up empty. How can I fix?

CodePudding user response：

AFAIK the response can only be read once so you need to copy it.

You need a filter as follows:

import java.io.IOException;

import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpFilter;
import javax.servlet.http.HttpServletResponse;

import org.springframework.stereotype.Component;

@Component
public class LogFilter extends HttpFilter {
    private FilterConfig filterConfigObj;

    public void init(FilterConfig config) throws ServletException {
        this.filterConfigObj = config;
    }

    public void destroy() {
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws ServletException, IOException {
        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()));
        }
    }
}

And these dependent classes to read and preserve the response.

import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.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];
        }
    }

}

and

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;

import javax.servlet.ServletOutputStream;
import javax.servlet.WriteListener;

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();
    }

    @Override
    public boolean isReady() {
        // TODO Auto-generated method stub
        return true;
    }

    @Override
    public void setWriteListener(WriteListener listener) {
        // TODO Auto-generated method stub
        
    }

}

CodePudding user response：

You will have to cache the response in the first place, you can extend the OncePerRequestFilter from spring and then cache your response, the following code registers a filter that creates a ContentCachingWrapper for your request and response, using this you should be able to get the response using the code that you have mentioned.

@Component
public class CachingFilter extends OncePerRequestFilter {

    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response,
            FilterChain filterChain) throws ServletException, IOException {
        filterChain.doFilter(new ContentCachingRequestWrapper(request), ContentCachingResponseWrapper(response));
    }