Spring中使用Mockito模拟WebClient返回JSON响应的实现问题

首先明确你现有代码的两个核心问题：

• 测试方法中手动给webClient重新赋值为真实构建的实例，覆盖了@Mock生成的代理对象，导致@InjectMocks注入失效，且无服务配置的真实WebClient调用必然报错
• WebClient是链式调用结构，需要逐层模拟每一步调用的返回对象，不能直接模拟单一方法

完整实现步骤 #

1. 基础依赖确认 #

Spring Boot项目引入spring-boot-starter-test即可自带Mockito、Reactor测试相关依赖，无需额外引入。

2. 测试代码示例 #

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;
import org.springframework.web.reactive.function.client.WebClient;
import reactor.core.publisher.Mono;
import static org.mockito.ArgumentMatchers.eq;
import static org.mockito.Mockito.when;
import static org.junit.jupiter.api.Assertions.assertEquals;

// JUnit4版本替换为 @RunWith(MockitoJUnitRunner.class)
@ExtendWith(MockitoExtension.class)
public class TranslateDaoTest {

    @Mock
    private WebClient webClient;
    @Mock
    private WebClient.RequestHeadersUriSpec requestHeadersUriSpec;
    @Mock
    private WebClient.RequestHeadersSpec requestHeadersSpec;
    @Mock
    private WebClient.ResponseSpec responseSpec;

    @InjectMocks
    private TranslateDao translateDao;

    @Test
    void getTestReturnExpectedResult() {
        // 构造期望返回的模拟数据，对应你要返回的JSON结构字段
        Test expectedResult = new Test();
        expectedResult.setId(123);
        expectedResult.setName("测试返回值");

        // 逐层模拟WebClient链式调用
        when(webClient.get()).thenReturn(requestHeadersUriSpec);
        // 用eq精确匹配你业务代码中写死的uri地址，也可以用anyString()模糊匹配
        when(requestHeadersUriSpec.uri(eq("url"))).thenReturn(requestHeadersSpec);
        when(requestHeadersSpec.retrieve()).thenReturn(responseSpec);
        when(responseSpec.bodyToMono(Test.class)).thenReturn(Mono.just(expectedResult));

        // 执行测试方法
        Test actualResult = translateDao.getTest("qw");

        // 结果断言
        assertEquals(expectedResult.getId(), actualResult.getId());
        assertEquals(expectedResult.getName(), actualResult.getName());
    }
}

简化写法（无需提前声明逐层Mock对象） #

@Test
void getTestShorterVersion() {
    Test expectedResult = new Test();
    expectedResult.setId(123);
    
    when(webClient.get()).thenReturn(mock(WebClient.RequestHeadersUriSpec.class));
    when(webClient.get().uri(eq("url"))).thenReturn(mock(WebClient.RequestHeadersSpec.class));
    when(webClient.get().uri(eq("url")).retrieve()).thenReturn(mock(WebClient.ResponseSpec.class));
    when(webClient.get().uri(eq("url")).retrieve().bodyToMono(Test.class)).thenReturn(Mono.just(expectedResult));

    Test actual = translateDao.getTest("test");
    assertEquals(expectedResult.getId(), actual.getId());
}

扩展场景 #

如果需要模拟调用失败的异常场景，只需把bodyToMono的返回值替换为错误Mono即可：

when(responseSpec.bodyToMono(Test.class)).thenReturn(Mono.error(new RuntimeException("调用远端服务失败")));

内容的提问来源于stack exchange，提问作者Arczi