Spring MVC - Why not able to use RequestBody and RequestParam together

Question

Using HTTP dev client with Post request and Content-Type application x-www-form-urlencoded 1  Only  RequestBody URL  localhost 8080 SpringMVC welcome Body  name abc  RequestMapping method   RequestMethod POST  public String printWelcome  RequestBody String body  Model model        model addAttribute  quot message quot   body       return  quot hello quot        Gives body as  name abc  as expected  2  Only  RequestParam URL  localhost 8080 SpringMVC welcome In Body - name abc  RequestMapping method   RequestMethod POST  public String printWelcome  RequestParam String name  Model model        model addAttribute  quot name quot   name       return  quot hello quot        Gives name as  abc  as expected  3  Both together URL  localhost 8080 SpringMVC welcome Body  name abc  RequestMapping method   RequestMethod POST  public String printWelcome       RequestBody String body        RequestParam String name  Model model         model addAttribute  quot name quot   name       model addAttribute  quot message quot   body       return  quot hello quot        HTTP Error Code 400 - The request sent by the client was syntactically incorrect   4  Above with params position changed URL  localhost 8080 SpringMVC welcome Body  name abc  RequestMapping method   RequestMethod POST  public String printWelcome       RequestParam String name        RequestBody String body  Model model         model addAttribute  quot name quot   name       model addAttribute  quot message quot   body       return  quot hello quot        No Error  Name  is  abc   body is empty  5  Together but get type url parameters URL  localhost 8080 SpringMVC welcome name xyz Body  name abc  RequestMapping method   RequestMethod POST  public String printWelcome       RequestBody String body        RequestParam String name  Model model         model addAttribute  quot name quot   name       model addAttribute  quot message quot   body       return  quot hello quot        name is  xyz  and body is  name abc   6  Same as 5  but with parameters position changed  RequestMapping method   RequestMethod POST  public String printWelcome       RequestParam String name        RequestBody String body  Model model         model addAttribute  quot name quot   name       model addAttribute  quot message quot   body       return  quot hello quot        name    xyz abc  body is empty  Can someone explain this behaviour

User · Accepted Answer

The  RequestBody javadoc states     Annotation indicating a method parameter should be bound to the body   of the web request    It uses registered instances of HttpMessageConverter to deserialize the request body into an object of the annotated parameter type   And the  RequestParam javadoc states     Annotation which indicates that a method parameter should be bound to   a web request parameter     Spring binds the body of the request to the parameter annotated with  RequestBody  Spring binds request parameters from the request body  url-encoded parameters  to your method parameter  Spring will use the name of the parameter  ie  name  to map the parameter  Parameters are resolved in order  The  RequestBody is processed first  Spring will consume all the HttpServletRequest InputStream  When it then tries to resolve the  RequestParam  which is by default required  there is no request parameter in the query string or what remains of the request body  ie  nothing  So it fails with 400 because the request can t be correctly handled by the handler method  The handler for  RequestParam acts first  reading what it can of the HttpServletRequest InputStream to map the request parameter  ie  the whole query string url-encoded parameters  It does so and gets the value abc mapped to the parameter name  When the handler for  RequestBody runs  there s nothing left in the request body  so the argument used is the empty string  The handler for  RequestBody reads the body and binds it to the parameter  The handler for  RequestParam can then get the request parameter from the URL query string   The handler for  RequestParam reads from both the body and the URL query String  It would usually put them in a Map  but since the parameter is of type String  Spring will serialize the Map as comma separated values  The handler for  RequestBody then  again  has nothing left to read from the body

User · Answer

You could also just change the  RequestParam default required status to false so that HTTP response status code 400 is not generated  This will allow you to place the Annotations in any order you feel like    RequestParam required   false String name

User · Answer

It s too late to answer this question  but it could help for new readers  It seems version issues  I ran all these tests with spring 4 1 4 and found that the order of  RequestBody and  RequestParam doesn t matter     same as your result  same as your result  gave body   name abc   and name    abc  Same as 3  body   name abc   name    xyz abc  same as 5

User · Answer

It happens because of not very straight forward Servlet specification  If you are working with a native HttpServletRequest implementation you cannot get both the URL encode body and the parameters  Spring does some workarounds  which make it even more strange and nontransparent   In such cases Spring  version 3 2 4  re-renders a body for you using data from the getParameterMap   method  It mixes GET and POST parameters and breaks the parameter order  The class  which is responsible for the chaos is ServletServerHttpRequest  Unfortunately it cannot be replaced  but the class StringHttpMessageConverter can be   The clean solution is unfortunately not simple    Replacing StringHttpMessageConverter  Copy Overwrite the original class adjusting method readInternal    Wrapping HttpServletRequest overwriting getInputStream    getReader   and getParameter    methods    In the method StringHttpMessageConverter readInternal following code must be used       if  inputMessage instanceof ServletServerHttpRequest            ServletServerHttpRequest oo    ServletServerHttpRequest inputMessage          input   oo getServletRequest   getInputStream          else           input   inputMessage getBody            Then the converter must be registered in the context    lt mvc annotation-driven gt       lt mvc message-converters register-defaults  true false  gt           lt bean class  my-new-converter-class   gt      lt  mvc message-converters gt   lt  mvc annotation-driven gt    The step two is described here  Http Servlet request lose params from POST body after read it once

[spring] Spring MVC - Why not able to use @RequestBody and @RequestParam together

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