How to test my servlet using JUnit

Question

I have created a web system using Java Servlets and now want to make JUnit testing  My dataManager is just a basic piece of code that submits it to the database  How would you test a Servlet with JUnit   My code example that allows a user to register sign up  which is submitted from my main page via AJAX   public void doPost HttpServletRequest request  HttpServletResponse response            throws ServletException  IOException          Get parameters     String userName   request getParameter  username        String password   request getParameter  password        String name   request getParameter  name         try               Load the database driver         Class forName  com mysql jdbc Driver               pass reg details to datamanager                dataManager   new DataManager              store result as string         String result   dataManager register userName  password  name              set response to html   no cache         response setContentType  text html            response setHeader  Cache-Control    no-cache              send response with register result         response getWriter   write result          catch Exception e           System out println  Exception is      e

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public class WishServletTest    WishServlet wishServlet   HttpServletRequest mockhttpServletRequest   HttpServletResponse mockhttpServletResponse    Before public void setUp        wishServlet new WishServlet        mockhttpServletRequest createNiceMock HttpServletRequest class       mockhttpServletResponse createNiceMock HttpServletResponse class       Test public void testService  throws Exception      File file  new File  Sample txt        File createTempFile  ashok   txt        expect mockhttpServletRequest getParameter  username    andReturn  ashok        expect mockhttpServletResponse getWriter    andReturn new PrintWriter file        replay mockhttpServletRequest       replay mockhttpServletResponse       wishServlet doGet mockhttpServletRequest  mockhttpServletResponse       FileReader fileReader new FileReader file       int count   0      String str           while    count fileReader read     -1           str str  char count             Assert assertTrue str trim   equals  Helloashok         verify mockhttpServletRequest       verify mockhttpServletResponse

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You can do this using Mockito to have the mock return the correct params  verify they were indeed called  optionally specify number of times   write the  result  and verify it s correct   import static org junit Assert    import static org mockito Mockito    import java io    import javax servlet http    import org apache commons io FileUtils  import org junit Test   public class TestMyServlet extends Mockito        Test     public void testServlet   throws Exception           HttpServletRequest request   mock HttpServletRequest class                  HttpServletResponse response   mock HttpServletResponse class                when request getParameter  username    thenReturn  me            when request getParameter  password    thenReturn  secret             StringWriter stringWriter   new StringWriter            PrintWriter writer   new PrintWriter stringWriter           when response getWriter    thenReturn writer            new MyServlet   doPost request  response            verify request  atLeast 1   getParameter  username       only if you want to verify username was called            writer flush       it may not have been flushed yet            assertTrue stringWriter toString   contains  My expected string

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I find Selenium tests more useful with integration or functional  end-to-end  testing   I am working with trying to use org springframework mock web  but I am not very far along   I am attaching a sample controller with a jMock test suite   First  the Controller   package com company admin web   import javax validation Valid   import org springframework beans factory annotation Autowired  import org springframework stereotype Controller  import org springframework ui Model  import org springframework validation BindingResult  import org springframework validation ObjectError  import org springframework web bind annotation ModelAttribute  import org springframework web bind annotation RequestMapping  import org springframework web bind annotation RequestMethod  import org springframework web bind annotation SessionAttributes  import org springframework web bind support SessionStatus   import com company admin domain PaymentDetail  import com company admin service PaymentSearchService  import com company admin service UserRequestAuditTrail  import com company admin web form SearchCriteria          Controls the interactions regarding to the refunds          author slgelma         Controller  SessionAttributes   user    authorization    public class SearchTransactionController        public static final String SEARCH TRANSACTION PAGE    searchtransaction        private PaymentSearchService searchService        private Validator searchCriteriaValidator      private UserRequestAuditTrail notifications        Autowired     public void setSearchService PaymentSearchService searchService            this searchService   searchService              Autowired     public void setNotifications UserRequestAuditTrail notifications            this notifications   notifications              RequestMapping value       SEARCH TRANSACTION PAGE      public String setUpTransactionSearch Model model            SearchCriteria searchCriteria   new SearchCriteria            model addAttribute  searchCriteria   searchCriteria           notifications transferTo SEARCH TRANSACTION PAGE           return SEARCH TRANSACTION PAGE              RequestMapping value       SEARCH TRANSACTION PAGE  method RequestMethod POST  params  cancel       public String cancelSearch             notifications redirectTo HomeController HOME PAGE           return  redirect      HomeController HOME PAGE              RequestMapping value       SEARCH TRANSACTION PAGE  method RequestMethod POST  params  execute       public String executeSearch               ModelAttribute  searchCriteria    Valid SearchCriteria searchCriteria              BindingResult result  Model model              SessionStatus status              searchCriteriaValidator validate criteria  result           if  result hasErrors                  notifications transferTo SEARCH TRANSACTION PAGE               return SEARCH TRANSACTION PAGE            else               PaymentDetail payment                    searchService getAuthorizationFor searchCriteria geteWiseTransactionId                 if  payment    null                    ObjectError error   new ObjectError                           eWiseTransactionId    Transaction not found                    result addError error                   model addAttribute  searchCriteria   searchCriteria                   notifications transferTo SEARCH TRANSACTION PAGE                   return SEARCH TRANSACTION PAGE                else                   model addAttribute  authorization   payment                   notifications redirectTo PaymentDetailController PAYMENT DETAIL PAGE                   return  redirect      PaymentDetailController PAYMENT DETAIL PAGE                                     Next  the test       package test unit com company admin web       import static org hamcrest Matchers containsString      import static org hamcrest Matchers equalTo      import static org junit Assert assertThat       import org jmock Expectations      import org jmock Mockery      import org jmock integration junit4 JMock      import org jmock integration junit4 JUnit4Mockery      import org junit Before      import org junit Test      import org junit runner RunWith      import org springframework ui Model      import org springframework validation BindingResult      import org springframework validation ObjectError      import org springframework web bind support SessionStatus       import com company admin domain PaymentDetail      import com company admin service PaymentSearchService      import com company admin service UserRequestAuditTrail      import com company admin web HomeController      import com company admin web PaymentDetailController      import com company admin web SearchTransactionController      import com company admin web form SearchCriteria                  Tests the behavior of the SearchTransactionController          author slgelma                     RunWith JMock class      public class SearchTransactionControllerTest            private final Mockery context   new JUnit4Mockery             private final SearchTransactionController controller   new SearchTransactionController            private final PaymentSearchService searchService   context mock PaymentSearchService class           private final UserRequestAuditTrail notifications   context mock UserRequestAuditTrail class           private final Model model   context mock Model class                             throws java lang Exception                      Before         public void setUp   throws Exception               controller setSearchService searchService               controller setNotifications notifications                       Test         public void setUpTheSearchForm                  final String target   SearchTransactionController SEARCH TRANSACTION PAGE               context checking new Expectations                      oneOf model  addAttribute                          with any String class    with any Object class                     oneOf notifications  transferTo with any String class                                   String nextPage   controller setUpTransactionSearch model               assertThat  Controller is not requesting the correct form                        target  equalTo nextPage                        Test         public void cancelSearchTest                  final String target   HomeController HOME PAGE               context checking new Expectations                     never model  addAttribute with any String class    with any Object class                     oneOf notifications  redirectTo with any String class                                   String nextPage   controller cancelSearch                assertThat  Controller is not requesting the correct form                        nextPage  containsString target                        Test         public void executeSearchWithNullTransaction                  final String target   SearchTransactionController SEARCH TRANSACTION PAGE               final SearchCriteria searchCriteria   new SearchCriteria                searchCriteria seteWiseTransactionId null                final BindingResult result   context mock BindingResult class               final SessionStatus status   context mock SessionStatus class                context checking new Expectations                      allowing result  hasErrors    will returnValue true                    never model  addAttribute with any String class    with any Object class                     never searchService  getAuthorizationFor searchCriteria geteWiseTransactionId                     oneOf notifications  transferTo with any String class                                   String nextPage   controller executeSearch searchCriteria  result  model  status               assertThat  Controller is not requesting the correct form                        target  equalTo nextPage                        Test         public void executeSearchWithEmptyTransaction                  final String target   SearchTransactionController SEARCH TRANSACTION PAGE               final SearchCriteria searchCriteria   new SearchCriteria                searchCriteria seteWiseTransactionId                   final BindingResult result   context mock BindingResult class               final SessionStatus status   context mock SessionStatus class                context checking new Expectations                      allowing result  hasErrors    will returnValue true                    never model  addAttribute with any String class    with any Object class                     never searchService  getAuthorizationFor searchCriteria geteWiseTransactionId                     oneOf notifications  transferTo with any String class                                   String nextPage   controller executeSearch searchCriteria  result  model  status               assertThat  Controller is not requesting the correct form                        target  equalTo nextPage                        Test         public void executeSearchWithTransactionNotFound                  final String target   SearchTransactionController SEARCH TRANSACTION PAGE              final String badTransactionId    badboy                final PaymentDetail transactionNotFound   null               final SearchCriteria searchCriteria   new SearchCriteria                searchCriteria seteWiseTransactionId badTransactionId                final BindingResult result   context mock BindingResult class               final SessionStatus status   context mock SessionStatus class                context checking new Expectations                      allowing result  hasErrors    will returnValue false                    atLeast 1  of model  addAttribute with any String class    with any Object class                     oneOf searchService  getAuthorizationFor with any String class                         will returnValue transactionNotFound                    oneOf result  addError with any ObjectError class                     oneOf notifications  transferTo with any String class                                   String nextPage   controller executeSearch searchCriteria  result  model  status               assertThat  Controller is not requesting the correct form                        target  equalTo nextPage                        Test         public void executeSearchWithTransactionFound                  final String target   PaymentDetailController PAYMENT DETAIL PAGE              final String goodTransactionId    100000010               final PaymentDetail transactionFound   context mock PaymentDetail class                final SearchCriteria searchCriteria   new SearchCriteria                searchCriteria seteWiseTransactionId goodTransactionId                final BindingResult result   context mock BindingResult class               final SessionStatus status   context mock SessionStatus class                context checking new Expectations                      allowing result  hasErrors    will returnValue false                    atLeast 1  of model  addAttribute with any String class    with any Object class                     oneOf searchService  getAuthorizationFor with any String class                         will returnValue transactionFound                    oneOf notifications  redirectTo with any String class                                   String nextPage   controller executeSearch searchCriteria  result  model  status               assertThat  Controller is not requesting the correct form                        nextPage  containsString target                       I hope this might help

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First you should probably refactor this a bit so that the DataManager is not created in the doPost code   you should try Dependency Injection to get an instance   See the Guice video for a nice intro to DI     If you re being told to start unit testing everything  then DI is a must-have   Once your dependencies are injected you can test your class in isolation   To actually test the servlet  there are other older threads that have discussed this   try here and here

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Updated Feb 2018  OpenBrace Limited has closed down  and its ObMimic product is no longer supported   Here s another alternative  using OpenBrace s ObMimic library of Servlet API test-doubles  disclosure  I m its developer    package com openbrace experiments examplecode stackoverflow5434419   import static org junit Assert    import com openbrace experiments examplecode stackoverflow5434419 YourServlet  import com openbrace obmimic mimic servlet ServletConfigMimic  import com openbrace obmimic mimic servlet http HttpServletRequestMimic  import com openbrace obmimic mimic servlet http HttpServletResponseMimic  import com openbrace obmimic substate servlet RequestParameters  import org junit Before  import org junit Test  import javax servlet ServletException  import javax servlet http HttpServletRequest  import javax servlet http HttpServletResponse  import java io IOException          Example tests for   link YourServlet doPost HttpServletRequest     HttpServletResponse           author Mike Kaufman  OpenBrace Limited     public class YourServletTest            The servlet to be tested by this instance s test         private YourServlet servlet           The  mimic  request to be used in this instance s test         private HttpServletRequestMimic request           The  mimic  response to be used in this instance s test         private HttpServletResponseMimic response                  Create an initialized servlet and a request and response for this        instance s test                 throws ServletException if the servlet s init method throws such an            exception               Before     public void setUp   throws ServletException                         Note that for the simple servlet and tests involved             - We don t need anything particular in the servlet s ServletConfig             - The ServletContext isn t relevant  so ObMimic can be left to use              its default ServletContext for everything                      servlet   new YourServlet            servlet init new ServletConfigMimic             request   new HttpServletRequestMimic            response   new HttpServletResponseMimic                          Test the doPost method with example argument values                 throws ServletException if the servlet throws such an exception          throws IOException if the servlet throws such an exception               Test     public void testYourServletDoPostWithExampleArguments               throws ServletException  IOException               Configure the request  In this case  all we need are the three            request parameters          RequestParameters parameters               request getMimicState   getRequestParameters            parameters set  username    mike            parameters set  password    xyz zyx            parameters set  name    Mike                Run the  doPost           servlet doPost request  response               Check the response s Content-Type  Cache-Control header and            body content          assertEquals  text html  charset ISO-8859-1               response getMimicState   getContentType             assertArrayEquals new String      no-cache                 response getMimicState   getHeaders   getValues  Cache-Control             assertEquals     expected result from dataManager register                  response getMimicState   getBodyContentAsString                 Notes    Each  mimic  has a  mimicState  object for its logical state  This provides a clear distinction between the Servlet API methods and the configuration and inspection of the mimic s internal state  You might be surprised that the check of Content-Type includes  charset ISO-8859-1   However  for the given  doPost  code this is as per the Servlet API Javadoc  and the HttpServletResponse s own getContentType method  and the actual Content-Type header produced on e g  Glassfish 3  You might not realise this if using normal mock objects and your own expectations of the API s behaviour  In this case it probably doesn t matter  but in more complex cases this is the sort of unanticipated API behaviour that can make a bit of a mockery of mocks  I ve used response getMimicState   getContentType   as the simplest way to check Content-Type and illustrate the above point  but you could indeed check for  text html  on its own if you wanted  using response getMimicState   getContentTypeMimeType     Checking the Content-Type header the same way as for the Cache-Control header also works  For this example the response content is checked as character data  with this using the Writer s encoding   We could also check that the response s Writer was used rather than its OutputStream  using response getMimicState   isWritingCharacterContent     but I ve taken it that we re only concerned with the resulting output  and don t care what API calls produced it  though that could be checked too      It s also possible to retrieve the response s body content as bytes  examine the detailed state of the Writer OutputStream etc    There are full details of ObMimic and a free download at the OpenBrace website  Or you can contact me if you have any questions  contact details are on the website

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First off  in a real application  you would never get database connection info in a servlet  you would configure it in your app server   There are ways  however  of testing Servlets without having a container running  One is to use mock objects  Spring provides a set of very useful mocks for things like HttpServletRequest  HttpServletResponse  HttpServletSession  etc   http   static springsource org spring docs 3 0 x api org springframework mock web package-summary html  Using these mocks  you could test things like  What happens if username is not in the request   What happens if username is in the request   etc  You could then do stuff like   import static org junit Assert assertEquals   import java io IOException   import javax servlet ServletException  import javax servlet http HttpServlet  import javax servlet http HttpServletRequest  import javax servlet http HttpServletResponse   import org junit Before  import org junit Test  import org springframework mock web MockHttpServletRequest  import org springframework mock web MockHttpServletResponse   public class MyServletTest       private MyServlet servlet      private MockHttpServletRequest request      private MockHttpServletResponse response        Before     public void setUp             servlet   new MyServlet            request   new MockHttpServletRequest            response   new MockHttpServletResponse                Test     public void correctUsernameInRequest   throws ServletException  IOException           request addParameter  username    scott            request addParameter  password    tiger             servlet doPost request  response            assertEquals  text html   response getContentType                     etc

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Another approach would be to create an embedded server to  host  your servlet  allowing you to write calls against it with libraries meant to make calls to actual servers  the usefulness of this approach somewhat depends on how easily you can make  legitimate  programatic calls to the server - I was testing a JMS  Java Messaging Service  access point  for which clients abound    There are a couple of different routes you can go - the usual two are tomcat and jetty    Warning  something to be mindful of when choosing the server to embed is the version of servlet-api you are using  the library which provides classes like HttpServletRequest   If you are using 2 5  I found Jetty 6 x to work well  which is the example I ll give below   If you re using servlet-api 3 0  the tomcat-7 embedded stuff seems to be a good option  however I had to abandon my attempt to use it  as the application I was testing used servlet-api 2 5  Trying to mix the two will result in NoSuchMethod and other such exceptions when attempting to configure or start the server   You can set up such a server like this  Jetty 6 1 26  servlet-api 2 5    public void startServer int port  Servlet yourServletInstance       Server server   new Server port       Context root   new Context server       Context SESSIONS        root addServlet new ServletHolder yourServletInstance     servlet context path           If you need the servlet context for anything  such as spring wiring  you coudl get it like this       ServletContext servletContext   root getServletContext         server start

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EDIT  Cactus is now a dead project  http   attic apache org projects jakarta-cactus html  You may want to look at cactus  http   jakarta apache org cactus   Project Description Cactus is a simple test framework for unit testing server-side java code  Servlets  EJBs  Tag Libs  Filters        The intent of Cactus is to lower the cost of writing tests for server-side code  It uses JUnit and extends it  Cactus implements an in-container strategy  meaning that tests are executed inside the container

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Use Selenium for webbased unit tests  There s a Firefox plugin called Selenium IDE which can record actions on the webpage and export to JUnit testcases which uses Selenium RC to run the test server

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