Get the Response Body in Spring Boot Filter

package com.gfg.springbootresponsefilter;

import jakarta.servlet.ServletOutputStream;
import jakarta.servlet.WriteListener;
import jakarta.servlet.http.HttpServletResponse;
import jakarta.servlet.http.HttpServletResponseWrapper;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.PrintWriter;

/**
 * Custom wrapper for HttpServletResponse to capture response body.
 */
public class CustomHttpResponseWrapper extends HttpServletResponseWrapper {

    private final ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    private final PrintWriter printWriter = new PrintWriter(outputStream);

    public CustomHttpResponseWrapper(HttpServletResponse response) {
        super(response);
    }

    @Override
    public ServletOutputStream getOutputStream() throws IOException {
        return new ServletOutputStream() {
            @Override
            public boolean isReady() {
                // Indicate whether the stream is ready to be written to.
                return true; // Changed to true for better compatibility
            }

            @Override
            public void setWriteListener(WriteListener writeListener) {
                // No-op for synchronous processing
            }

            @Override
            public void write(int b) throws IOException {
                outputStream.write(b); // Write data to buffer
            }
        };
    }

    @Override
    public PrintWriter getWriter() throws IOException {
        return printWriter; // Use PrintWriter to capture text data
    }

    public byte[] getResponseData() throws IOException {
        printWriter.flush(); // Ensure all data is written to the buffer
        return outputStream.toByteArray(); // Return buffered response data
    }
}

package com.gfg.springbootresponsefilter;

import jakarta.servlet.*;
import jakarta.servlet.http.HttpServletResponse;
import org.springframework.stereotype.Component;

import java.io.IOException;

/**
 * Filter to capture and log the response body.
 */
@Component
public class ResponseBodyLoggingFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // No initialization required
    }

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

        // Cast response to HttpServletResponse
        HttpServletResponse httpResponse = (HttpServletResponse) response;

        // Wrap the response to capture the body
        CustomHttpResponseWrapper responseWrapper = new CustomHttpResponseWrapper(httpResponse);

        // Continue with the filter chain
        chain.doFilter(request, responseWrapper);

        // Get the response body data from the wrapper
        byte[] responseData = responseWrapper.getResponseData();
        String responseBody = new String(responseData, httpResponse.getCharacterEncoding());

        // Log the response body
        System.out.println("Response Body: " + responseBody);

        // Write the response body back to the client
        response.getOutputStream().write(responseData);
    }

    @Override
    public void destroy() {
        // No cleanup required
    }
}

package com.gfg.springbootresponsefilter;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * REST controller for testing response body capture.
 */
@RestController
public class TestController {

    @GetMapping("/hello")
    public String hello() {
        return "Hello, World!"; // Response message
    }
}

package com.gfg.springbootresponsefilter;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SpringBootResponseFilterApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringBootResponseFilterApplication.class, args);
    }

}