Spring Returning empty HTTP Responses with ResponseEntity Void doesn t work

Question

We are implementing a REST API with Spring  4 1 1    For certain HTTP requests  we would like to return a head with no body as a response  However  using ResponseEntity lt Void gt  doesn t seem to work  When called with a MockMvc test  a 406  Not acceptable  is returned  Using ResponseEntity lt String gt  without a parameter value  new  ResponseEntity lt String gt   HttpStatus NOT FOUND    works fine    Method    RequestMapping  method   RequestMethod HEAD  value   Constants KEY   public ResponseEntity lt Void gt  taxonomyPackageExists   PathVariable final String key          LOG debug   taxonomyPackageExists queried with key   0    key       NON-NLS-1       final TaxonomyKey taxonomyKey   TaxonomyKey fromString  key         LOG debug   Taxonomy key created   0    taxonomyKey       NON-NLS-1       if   this xbrlInstanceValidator taxonomyPackageExists  taxonomyKey                LOG debug   Taxonomy package with key   0  exists    taxonomyKey       NON-NLS-1           return new ResponseEntity lt Void gt   HttpStatus OK           else            LOG debug   Taxonomy package with key   0  does NOT exist    taxonomyKey       NON-NLS-1           return new ResponseEntity lt Void gt   HttpStatus NOT FOUND               Test case  TestNG    public class TaxonomyQueryControllerTest    private XbrlInstanceValidator   xbrlInstanceValidatorMock  private TaxonomyQueryController underTest  private MockMvc                 mockMvc    BeforeMethod public void setUp         this xbrlInstanceValidatorMock   createMock  XbrlInstanceValidator class        this underTest   new TaxonomyQueryController  this xbrlInstanceValidatorMock        this mockMvc   MockMvcBuilders standaloneSetup  this underTest   build        Test public void taxonomyPackageDoesNotExist   throws Exception          record     expect  this xbrlInstanceValidatorMock taxonomyPackageExists  anyObject  TaxonomyKey class       andStubReturn              false            replay     replay  this xbrlInstanceValidatorMock            do the test     final String taxonomyKey   RestDataFixture taxonomyKeyString       this mockMvc perform  head    taxonomypackages  key    taxonomyKey   accept     NON-NLS-1              MediaType APPLICATION XML     andExpect  status   isNotFound              Fails with this stack trace    FAILED  taxonomyPackageDoesNotExist java lang AssertionError  Status expected  lt 404 gt  but was  lt 406 gt  at org springframework test util AssertionErrors fail AssertionErrors java 60  at org springframework test util AssertionErrors assertEquals AssertionErrors java 89  at org springframework test web servlet result StatusResultMatchers 10 match StatusResultMatchers java 652  at org springframework test web servlet MockMvc 1 andExpect MockMvc java 153  at de zeb control application xbrlstandalonevalidator restservice TaxonomyQueryControllerTest taxonomyPackageDoesNotExist TaxonomyQueryControllerTest java 54  at sun reflect NativeMethodAccessorImpl invoke0 Native Method  at sun reflect NativeMethodAccessorImpl invoke NativeMethodAccessorImpl java 57  at sun reflect DelegatingMethodAccessorImpl invoke DelegatingMethodAccessorImpl java 43  at java lang reflect Method invoke Method java 606  at org testng internal MethodInvocationHelper invokeMethod MethodInvocationHelper java 84  at org testng internal Invoker invokeMethod Invoker java 714  at org testng internal Invoker invokeTestMethod Invoker java 901  at org testng internal Invoker invokeTestMethods Invoker java 1231  at org testng internal TestMethodWorker invokeTestMethods TestMethodWorker java 127  at org testng internal TestMethodWorker run TestMethodWorker java 111  at org testng TestRunner privateRun TestRunner java 767  at org testng TestRunner run TestRunner java 617  at org testng SuiteRunner runTest SuiteRunner java 334  at org testng SuiteRunner runSequentially SuiteRunner java 329  at org testng SuiteRunner privateRun SuiteRunner java 291  at org testng SuiteRunner run SuiteRunner java 240  at org testng SuiteRunnerWorker runSuite SuiteRunnerWorker java 52  at org testng SuiteRunnerWorker run SuiteRunnerWorker java 86  at org testng TestNG runSuitesSequentially TestNG java 1224  at org testng TestNG runSuitesLocally TestNG java 1149  at org testng TestNG run TestNG java 1057  at org testng remote RemoteTestNG run RemoteTestNG java 111  at org testng remote RemoteTestNG initAndRun RemoteTestNG java 204  at org testng remote RemoteTestNG main RemoteTestNG java 175

User · Answer

For Spring 5 2  this works for me    PostMapping   foo   ResponseEntity lt Void gt  foo  PathVariable UUID fooId        return fooService findExam fooId               map uri - gt  ResponseEntity noContent    lt Void gt build                 orElse ResponseEntity notFound   build

User · Answer

You can also not specify the type parameter which seems a bit cleaner and what Spring intended when looking at the docs    RequestMapping method   RequestMethod HEAD  value   Constants KEY   public ResponseEntity taxonomyPackageExists   PathVariable final String key                   return new ResponseEntity HttpStatus NO CONTENT

User · Answer

NOTE  This is true for the version mentioned in the question  4 1 1 RELEASE   Spring MVC handles a ResponseEntity return value through HttpEntityMethodProcessor    When the ResponseEntity value doesn t have a body set  as is the case in your snippet  HttpEntityMethodProcessor tries to determine a content type for the response body from the parameterization of the ResponseEntity return type in the signature of the  RequestMapping handler method   So for  public ResponseEntity lt Void gt  taxonomyPackageExists   PathVariable final String key       that type will be Void  HttpEntityMethodProcessor will then loop through all its registered HttpMessageConverter instances and find one that can write a body for a Void type  Depending on your configuration  it may or may not find any   If it does find any  it still needs to make sure that the corresponding body will be written with a Content-Type that matches the type s  provided in the request s Accept header  application xml in your case   If after all these checks  no such HttpMessageConverter exists  Spring MVC  will decide that it cannot produce an acceptable response and therefore return a 406 Not Acceptable HTTP response   With ResponseEntity lt String gt   Spring will use String as the response body and find StringHttpMessageConverter as a handler  And since StringHttpMessageHandler can produce content for any media type  provided in the Accept header   it will be able to handle the application xml that your client is requesting   Spring MVC has since been changed to only return 406 if the body in the ResponseEntity is NOT null  You won t see the behavior in the original question if you re using a more recent version of Spring MVC     In iddy85 s solution  which seems to suggest ResponseEntity lt   gt   the type for the body will be inferred as Object  If you have the correct libraries in your classpath  ie  Jackson  version   2 5 0  and its XML extension  Spring MVC will have access to MappingJackson2XmlHttpMessageConverter which it can use to produce application xml for the type Object  Their solution only works under these conditions  Otherwise  it will fail for the same reason I ve described above

User · Answer

According Spring 4 MVC ResponseEntity BodyBuilder and ResponseEntity Enhancements Example it could be written as           return ResponseEntity ok   build            return ResponseEntity noContent   build      UPDATE   If returned value is Optional there are convinient method  returned ok   or notFound     return ResponseEntity of optional

User · Answer

Your method implementation is ambiguous  try the following   edited your code  a little bit and used HttpStatus NO CONTENT i e 204 No Content as in place of HttpStatus OK     The server has fulfilled the request but does not need to return an   entity-body  and might want to return updated metainformation  The   response MAY include new or updated metainformation in the form of   entity-headers  which if present SHOULD be associated with the   requested variant    Any value of T will be ignored for 204   but not for 404    public ResponseEntity lt   gt  taxonomyPackageExists   PathVariable final String key                 LOG debug   taxonomyPackageExists queried with key   0    key       NON-NLS-1              final TaxonomyKey taxonomyKey   TaxonomyKey fromString  key                LOG debug   Taxonomy key created   0    taxonomyKey       NON-NLS-1               if   this xbrlInstanceValidator taxonomyPackageExists  taxonomyKey                       LOG debug   Taxonomy package with key   0  exists    taxonomyKey       NON-NLS-1                   return new ResponseEntity lt T gt  HttpStatus NO CONTENT                 else                  LOG debug   Taxonomy package with key   0  does NOT exist    taxonomyKey       NON-NLS-1                  return new ResponseEntity lt T gt   HttpStatus NOT FOUND

User · Answer

Personally  to deal with empty responses  I use in my Integration Tests the MockMvcResponse object like this     MockMvcResponse response   RestAssuredMockMvc given                    webAppContextSetup webApplicationContext                   when                    get   v1 ticket         assertThat response mockHttpServletResponse   getStatus    isEqualTo HttpStatus NO CONTENT value       and in my controller I return empty response in a specific case like this     return ResponseEntity noContent   build

[java] Spring: Returning empty HTTP Responses with ResponseEntity<Void> doesn't work

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