How to check String in response body with mockMvc

You can call andReturn() and use the returned MvcResult object to get the content as a String.

See below:

MvcResult result = mockMvc.perform(post("/api/users").header("Authorization", base64ForTestUser).contentType(MediaType.APPLICATION_JSON)            .content("{\"userName\":\"testUserDetails\",\"firstName\":\"xxx\",\"lastName\":\"xxx\",\"password\":\"xxx\"}"))            .andDo(MockMvcResultHandlers.print())            .andExpect(status().isBadRequest())            .andReturn();String content = result.getResponse().getContentAsString();// do what you will 

@Sotirios Delimanolis answer do the job however I was looking for comparing strings within this mockMvc assertion

So here it is

.andExpect(content().string("\"Username already taken - please try with different username\""));

Of course my assertion fail:

java.lang.AssertionError: Response content expected:<"Username already taken - please try with different username"> but was:<"Something gone wrong">

because:

  MockHttpServletResponse:            Body = "Something gone wrong"

So this is proof that it works!

Spring MockMvc now has direct support for JSON. So you just say:

.andExpect(content().json("{'message':'ok'}"));

and unlike string comparison, it will say something like "missing field xyz" or "message Expected 'ok' got 'nok'.

This method was introduced in Spring 4.1.