🌱 @JsonProperty, @JsonNaming

public class TestDto {
    private Long testId;

    public TestDto() {
    }

    public TestDto(Long testId) {
        this.testId = testId;
    }

    public Long getTestId() {
        return testId;
    }

    public void setTestId(Long testId) {
        this.testId = testId;
    }
}

public class Test2Dto {
    private Long test_id;

    public Test2Dto() {
    }

    public Test2Dto(Long test_id) {
        this.test_id = test_id;
    }

    public Long getTest_id() {
        return test_id;
    }

    public void setTest_id(Long test_id) {
        this.test_id = test_id;
    }
}

@RestController
public class TestController {
    @GetMapping("/test")
    public ResponseEntity<TestDto> test() {
        return ResponseEntity.ok().body(new TestDto(10L));
    }

    @PostMapping("/test")
    public ResponseEntity<TestDto> test(@RequestBody TestDto testDto) {
        System.out.println(testDto.getTestId());
        return ResponseEntity.ok().body(new TestDto(10L));
    }

    @GetMapping("/test2")
    public ResponseEntity<Test2Dto> test2() {
        return ResponseEntity.ok().body(new Test2Dto(10L));
    }

    @PostMapping("/test2")
    public ResponseEntity<Test2Dto> test2(@RequestBody Test2Dto testDto) {
        System.out.println(testDto.getTest_id());
        return ResponseEntity.ok().body(new Test2Dto(10L));
    }
}

@Test
void postTest() throws Exception {
    // given
    Test2Dto testDto = new Test2Dto(10L);
    String json = new ObjectMapper().writeValueAsString(testDto);
    System.out.println(json);

    // then
    mockMvc.perform(MockMvcRequestBuilders
            .post("/test")
            .content(json)
            .header("Content-Type", "application/json"))
            .andDo(print())
            .andExpect(status().isOk())
            .andExpect(jsonPath("$.test_id").value(10L));
}

public class TestDto {
    @JsonProperty("test_id")
    private Long testId;

    public TestDto() {
    }

    public TestDto(Long testId) {
        this.testId = testId;
    }

    public Long getTestId() {
        return testId;
    }

    public void setTestId(Long testId) {
        this.testId = testId;
    }
}

import com.fasterxml.jackson.databind.PropertyNamingStrategy;
import com.fasterxml.jackson.databind.annotation.JsonNaming;

@JsonNaming(value = PropertyNamingStrategy.SnakeCaseStrategy.class)
public class TestDto {
    private Long testId;

    public TestDto() {
    }

    public TestDto(Long testId) {
        this.testId = testId;
    }

    public Long getTestId() {
        return testId;
    }

    public void setTestId(Long testId) {
        this.testId = testId;
    }
}

spring.jackson.property-naming-strategy=SNAKE_CASE