JUnit 5中使用MockMvcBuilders.standaloneSetup()遇NoClassDefFoundError问题

测试代码 #

public class MyControllerTest {
    @InjectMocks
    private MyController myController;

    @Mock
    private MyCommonService myCommonService;

    private MockMvc mockMvc;

    @BeforeEach
    public void setup() {
        MockitoAnnotations.openMocks(this);
        mockMvc = MockMvcBuilders.standaloneSetup
                (new MyCommonServiceController()).build();
    }

    @Test
    public void testDataReturnsOk() throws Exception {
        when(myCommonService.getData())
                .thenReturn(Collections.singletonList(new myDto()));

        mockMvc.perform(get("/data"))
                .andExpect(status().isOk());
    }
}

报错信息 #

java.lang.NoClassDefFoundError: jakarta/servlet/ServletException

    at org.springframework.test.web.servlet.setup.MockMvcBuilders.standaloneSetup(MockMvcBuilders.java:76)
    at com.markitclear.cui.cp.rest.controller.CPCommonServiceControllerTest.setup(CPCommonServiceControllerTest.java:36)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)

问题分析 #

1. 依赖缺失：报错提示找不到jakarta/servlet/ServletException类，说明测试环境缺少Jakarta Servlet API相关依赖，MockMvc运行需要该依赖支持。
2. 测试逻辑错误：setup方法初始化MockMvc时，新建了MyCommonServiceController实例，而非使用@InjectMocks注解注入的myController，导致@Mock标记的myCommonService未被注入到控制器中，测试逻辑会失效。
3. 代码规范问题：myDto类名不符合Java大驼峰命名规范，应改为MyDto。

修复步骤 #

1. 补充依赖 #

如果是Spring Boot项目，确保构建文件中包含spring-boot-starter-test依赖，它已包含所需的Servlet API测试依赖：
Maven（pom.xml）：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
</dependency>

Gradle（build.gradle）：

testImplementation 'org.springframework.boot:spring-boot-starter-test'

如果是非Spring Boot项目，需单独添加Jakarta Servlet API测试依赖：
Maven：

<dependency>
    <groupId>jakarta.servlet</groupId>
    <artifactId>jakarta.servlet-api</artifactId>
    <version>5.0.0</version>
    <scope>test</scope>
</dependency>

2. 修正MockMvc初始化逻辑 #

将setup方法中的new MyCommonServiceController()替换为myController，确保Mock服务被正确注入：

@BeforeEach
public void setup() {
    MockitoAnnotations.openMocks(this);
    mockMvc = MockMvcBuilders.standaloneSetup(myController).build();
}

3. 修正Dto类名 #

把new myDto()改为new MyDto()，遵循Java命名规范。

修正后的完整测试代码：

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.request.MockMvcRequestBuilders;
import org.springframework.test.web.servlet.result.MockMvcResultMatchers;
import java.util.Collections;
import static org.mockito.Mockito.when;

public class MyControllerTest {
    @InjectMocks
    private MyController myController;

    @Mock
    private MyCommonService myCommonService;

    private MockMvc mockMvc;

    @BeforeEach
    public void setup() {
        MockitoAnnotations.openMocks(this);
        mockMvc = MockMvcBuilders.standaloneSetup(myController).build();
    }

    @Test
    public void testDataReturnsOk() throws Exception {
        when(myCommonService.getData())
                .thenReturn(Collections.singletonList(new MyDto()));

        mockMvc.perform(MockMvcRequestBuilders.get("/data"))
                .andExpect(MockMvcResultMatchers.status().isOk());
    }
}

内容的提问来源于stack exchange，提问作者Nidhi257