References

• Adding Header Information to an existing HTTP Request
• How to modify request headers in a J2EE web application
• Modifying HTTP headers using Java

Problem

Simply, we can’t add or modify request headers on given HttpServletRequest instances.

Solution

The only solution, at least mentioned in above links, is using HttpServletRequestWrapper class. I wrote, for my own, a class which wraps additional headers around the actual request instance.

public class RequestHeaderWrapper extends HttpServletRequestWrapper {

    public RequestHeaderWrapper(
        final HttpServletRequest request,
        final Map<String, List<String>> precedingHeaders,
        final Map<String, List<String>> succeedingHeaders) {

        super(request);

        headers = new HashMap<>();

        if (precedingHeaders != null) {
            for (final String name : precedingHeaders.keySet()) {
                List<String> values = headers.get(name);
                if (values == null) {
                    values = new ArrayList<>();
                    headers.put(name, values);
                }
                values.addAll(precedingHeaders.get(name));
            }
        }

        for (final Enumeration<String> names = request.getHeaderNames();
             names.hasMoreElements();) {
            final String name = names.nextElement();
            List<String> value = headers.get(name);
            if (value == null) {
                value = new ArrayList<>();
                headers.put(name, value);
            }
            value.addAll(Collections.list(request.getHeaders(name)));
        }

        if (succeedingHeaders != null) {
            for (final String name : succeedingHeaders.keySet()) {
                List<String> values = headers.get(name);
                if (values == null) {
                    values = new ArrayList<>();
                    headers.put(name, values);
                }
                values.addAll(succeedingHeaders.get(name));
            }
        }
    }

    @Override
    public String getHeader(final String name) {
        final List<String> values = headers.get(name);
        if (values != null && !values.isEmpty()) {
            return values.get(0);
        }
        return null;
    }

    @Override
    public Enumeration<String> getHeaders(final String name) {
        List<String> values = headers.get(name);
        if (values == null) {
            return Collections.emptyEnumeration();
        }
        return Collections.enumeration(values);
    }

    @Override
    public Enumeration<String> getHeaderNames() {
        return Collections.enumeration(headers.keySet());
    }

    private final Map<String, List<String>> headers;
}

Full and latest source code is here and the apidocs is here.

Apache Maven

Please check the central if you’re using Apache Maven.

<dependency>
  <groupId>com.googlecode.jinahya</groupId>
  <artifactId>jinahya-ee</artifactId>
  <version>@@?</version>
</dependency>

Usage

There are some factory methods for simple use.

public class MyFilter implements Filter {

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

        final ServletRequest wrapper =
            RequestHeaderWrapper.newPrecedingInstance(
                requerst, "Accept", "application/xml");
        chain.doFilter(wrapper, response);
}