在拦截器 spring 引导上添加自定义 header

Question

I have an interceptor I need to add a custom header which is required for other parts of the code

public class KeyTaskInterceptor implements HandlerInterceptor {

@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {

    if (// a custom condition) {
        request.  // set custom header key ... `KeyCode`
    }
    return true;
} 

The problem is the frontend doesn't send this custom header named " KeyCode " and I can't change the implementation for the controllers that expect this header so I have to find a way to add a custom header on request on preHandle method before sending the request to the controller. Can someone help me, please?

Answer 1

HttpServletRequest object is read-only and you cannot modify its headers in the HandlerInterceptor . The only thing that you can do with it - is to set attributes and read them later in your controller.

But as in your case you can't change the implementation of the controllers to read attributes, you need actually modify request headers.

There is a way of how to do it - is to use a Filter in which you will substitute the incoming request object with your own request wrapper implementation. By using a request wrapper, you can modify its headers list as you need.

There is a good tutorial that explains how to do it.

Below is an example based on this tutorial, slightly adapted for your use case:

@Component
public class CustomHeaderFilter implements Filter {
  @Override
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
      throws IOException, ServletException {
    MutableHttpServletRequest mutableRequest = new MutableHttpServletRequest((HttpServletRequest) request);
    mutableRequest.putHeader("KeyCode", "custom value");
    chain.doFilter(mutableRequest, response);
  }
}

And the implementation of the MutableHttpServletRequest from the tutorial :

class MutableHttpServletRequest extends HttpServletRequestWrapper {
    // holds custom header and value mapping
    private final Map<String, String> customHeaders;
 
    public MutableHttpServletRequest(HttpServletRequest request){
        super(request);
        this.customHeaders = new HashMap<String, String>();
    }
    
    public void putHeader(String name, String value){
        this.customHeaders.put(name, value);
    }
 
    public String getHeader(String name) {
        // check the custom headers first
        String headerValue = customHeaders.get(name);
        
        if (headerValue != null){
            return headerValue;
        }
        // else return from into the original wrapped object
        return ((HttpServletRequest) getRequest()).getHeader(name);
    }
 
    public Enumeration<String> getHeaderNames() {
        // create a set of the custom header names
        Set<String> set = new HashSet<String>(customHeaders.keySet());
        
        // now add the headers from the wrapped request object
        @SuppressWarnings("unchecked")
        Enumeration<String> e = ((HttpServletRequest) getRequest()).getHeaderNames();
        while (e.hasMoreElements()) {
            // add the names of the request headers into the list
            String n = e.nextElement();
            set.add(n);
        }
 
        // create an enumeration from the set and return
        return Collections.enumeration(set);
    }
}