您可以使用getContentAsString方法以字符串形式获取响应数据。

    String payload = "....";
    String apiToTest = "....";
    
    MvcResult mvcResult = mockMvc.
                perform(post(apiToTest).
                content(payload).
                contentType(MediaType.APPLICATION_JSON)).
                andReturn();
    
    String responseData = mvcResult.getResponse().getContentAsString();

您可以参考此链接进行测试应用。

String body = mockMvc.perform(bla... bla).andReturn().getResolvedException().getMessage()

这将为您提供响应的主体。“用户名已被占用”在你的情况下。

你可以调用andReturn()并使用返回的MvcResult对象来获取字符串形式的内容。

见下文:

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 

一种可能的方法是简单地包含gson依赖:

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
</dependency>

并解析该值来进行验证:

@RunWith(SpringRunner.class)
@WebMvcTest(HelloController.class)
public class HelloControllerTest {

    @Autowired
    private MockMvc mockMvc;

    @MockBean
    private HelloService helloService;

    @Before
    public void before() {
        Mockito.when(helloService.message()).thenReturn("hello world!");
    }

    @Test
    public void testMessage() throws Exception {
        MvcResult mvcResult = mockMvc.perform(MockMvcRequestBuilders.get("/"))
                .andExpect(status().isOk())
                .andExpect(content().contentTypeCompatibleWith(MediaType.APPLICATION_JSON_VALUE))
                .andReturn();

        String responseBody = mvcResult.getResponse().getContentAsString();
        ResponseDto responseDto
                = new Gson().fromJson(responseBody, ResponseDto.class);
        Assertions.assertThat(responseDto.message).isEqualTo("hello world!");
    }
}

@Sotirios Delimanolis回答做的工作，但我正在寻找这个mockMvc断言中的比较字符串

就在这里

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

当然，我的断言是失败的:

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

因为:

  MockHttpServletResponse:
            Body = "Something gone wrong"

所以这就是它有效的证明!

这里有一种更优雅的方式

mockMvc.perform(post("/retrieve?page=1&countReg=999999")
            .header("Authorization", "Bearer " + validToken))
            .andExpect(status().isOk())
            .andExpect(content().string(containsString("regCount")));