Using Spring's #RequestBody and reading HttpServletRequest.getInputStream() afterwards - json

Question

I'm mapping my request's JSON POST data into an object using Spring's #RequestBody annotation and MappingJacksonHttpMessageConverter. However after that I'd like to read the data in String form to do some additional authentication. But when the marshalling has happened, the InputStream in HttpServletRequest is empty. Once I remove the #RequestBody parameter from the method the reading of POST data into a String works as expected.
Do I have to compromise by giving up the #RequestBody and doing the binding somehow manually or is there a more elegant solution?

Answer 1

So, basically you need to compute a hash of the request body. The elegant way to do it is to apply a decorator to the InputStream.
For example, inside a handler method (in this case you can't use #RequestBody and need to create HttpMessageConverter manually):
#RequestMapping(...)
public void handle(HttpServletRequest request) throws IOException {
final HashingInputStreamDecorator d =
new HashingInputStreamDecorator(request.getInputStream(), secretKey);
HttpServletRequest wrapper = new HttpServletRequestWrapper(request) {
#Override
public ServletInputStream getInputStream() throws IOException {
return d;
}
};
HttpMessageConverter conv = ...;
Foo requestBody = (Foo) conv.read(Foo.class, new ServletServerHttpRequest(wrapper));
String hash = d.getHash();
...
}
where hash is computed incrementally in overriden read methods of HashingInputStreamDecorator.
You can also use #RequestBody if you create a Filter to apply the decorator. In this case decorator can pass the computed hash to the handler method as a request attribute. However, you need to map this filter carefully to apply it only to the requests to specific handler method.

Answer 2

In your urlMapping bean you can declare list of additional interceptors:
<bean id="urlMapping" class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping">
<property name="interceptors">
<list>
<bean class="org.foo.MyAuthInterceptor"/>
</list>
</property>
</bean>
Those interceptors have access to HttpServletRequest, though if you read from the stream the chances are that parameter mapper won't be able to read it.
public class AuthInterceptor extends HandlerInterceptorAdapter {
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
...
}
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView mav) {
...
}
}

Answer 3

If I understand this correctly, one common way used with JAX-RS (which is somewhat similar to Spring MVC with respect to binding requests) is to first "bind" into some intermediate raw type (usually byte[], but String also works), and manually bind from that to object, using underlying data binder (Jackson). I often do this to be able to fully customize error handling of data binding.