set content range in spring - spring

Question

I have many resting api in my spring boot application.
#GetMapping("lc/all")
List<LC> getAll()
{
return lcRepository.findAll();
}
Mainly they are sending list.
Now for some reason, I have to receive the length of the response. Changing for each and every method would be tedious.
How can I set Content-Range for each method automatically.
I have modified the CORS:
#Bean
public WebMvcConfigurer corsConfigurer() {
return new WebMvcConfigurer() {
#Override
public void addCorsMappings(CorsRegistry registry) {
registry
.addMapping("/**")
.allowedOrigins("http://localhost:5000")
.exposedHeaders("Content-Range");
}
};
}

Answer 1

First you need a filter that writes only the requested range part as a response when range header is present.
package com.example.contentrange;
import static java.nio.charset.StandardCharsets.UTF_8;
import static javax.servlet.http.HttpServletResponse.SC_PARTIAL_CONTENT;
import static javax.servlet.http.HttpServletResponse.SC_REQUESTED_RANGE_NOT_SATISFIABLE;
import java.io.IOException;
import java.util.Arrays;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.http.HttpRange;
import org.springframework.web.util.ContentCachingResponseWrapper;
#WebFilter("/*")
public class AddResponseHeaderFilter implements Filter {
#Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
HttpServletRequest httpServletRequest = (HttpServletRequest) request;
var rangeHeader = httpServletRequest.getHeader("Range");
// if there is no range request in the header than do the "normal" filtering
if (rangeHeader == null) {
chain.doFilter(request, response);
return;
}
HttpRange range = HttpRange.parseRanges(rangeHeader).get(0);
ContentCachingResponseWrapper responseWrapper =
new ContentCachingResponseWrapper((HttpServletResponse) response);
try {
chain.doFilter(request, responseWrapper);
} finally {
byte[] copy = responseWrapper.getContentAsByteArray();
int size = responseWrapper.getContentSize();
int lower = (int) range.getRangeStart(size);
int upper = (int) range.getRangeEnd(size);
if (lower <= size) {
responseWrapper.setStatus(SC_PARTIAL_CONTENT);
byte[] subArray = Arrays.copyOfRange(copy, lower, upper + 1);
String newContent = new String(subArray, UTF_8);
responseWrapper.reset();
responseWrapper.setHeader(
"Content-Range", String.format("bytes %d-%d/%d", lower, upper, size));
responseWrapper.setContentLength(newContent.length());
responseWrapper.getWriter().write(newContent);
responseWrapper.getWriter().flush();
responseWrapper.flushBuffer();
responseWrapper.copyBodyToResponse();
} else {
responseWrapper.setStatus(SC_REQUESTED_RANGE_NOT_SATISFIABLE);
}
}
}
}
Second you need to add org.springframework.boot.web.servlet.ServletComponentScan annotation to your application class.
#ServletComponentScan
#SpringBootApplication
public class ContentRangeApplication {
public static void main(String[] args) {
SpringApplication.run(ContentRangeApplication.class, args);
}
}
For more info on Range: https://developer.mozilla.org/en-US/docs/Web/HTTP/Range_requests