JUnit 5无法Mock Java.net.http.HttpClient.send问题排查求助

在Java Maven非SpringBoot项目中编写JUnit 5测试代码时，尝试Mock API调用，但执行测试时仍会调用真实API，不符合预期。以下是业务代码和测试代码：

实际业务代码 #

public class MyService {

    public void create(String apiHost, String firstPage) {
        HttpClient httpClient = HttpClient.newBuilder()
                .version(HttpClient.Version.HTTP_2)
                .connectTimeout(Duration.ofSeconds(30))
                .build();
        HttpRequest httpRequest = getHttpRequest(apiHost, firstPage);
 
        MyResponse myResponse = invokeApi(httpClient, httpRequest);
        List<ResponseData> responseDataList = new ArrayList<>(myResponse.getData());
        while (null != myResponse.getLinks().getNext()) {

            myResponse = invokeApi(httpClient, getHttpRequest(apiHost, myResponse.getLinks().getNext()));
            responseDataList.addAll(myResponse.getData());
        }

        createFile(fileName, responseDataList);
    }

    private HttpRequest getHttpRequest(String apiHost, String pageUri) {
        return HttpRequest.newBuilder()
                .header("Content-Type", "application/json")
                .GET()
                .uri(URI.create(apiHost + pageUri))
                .build();
    }

    @SneakyThrows
    MyResponse invokeApi(HttpClient httpClient, HttpRequest httpRequest) {
        HttpResponse<Supplier<MyResponse>> result = httpClient.send(httpRequest, new JsonBodyHandler<>(MyResponse.class));
        return result.body().get();
    }

    @SneakyThrows
    void createFile(String fileName, List<ResponseData> responseDataList) {
        Path filePath = Paths.get("test/path" + fileName);
        Files.createFile(filePath);
        Files.writeString(filePath, header + System.lineSeparator(), StandardOpenOption.APPEND);
        for (ResponseData responseData : responseDataList) {
            Files.writeString(filePath, responseData + System.lineSeparator(), StandardOpenOption.APPEND);
        }
    }
}

JUnit 5测试代码 #

@ExtendWith(MockitoExtension.class)
class MyServiceTests {

    @InjectMocks
    private MyService myService;

    @Mock
    private HttpClient httpClient;
    @Mock
    HttpResponse<Object> httpResponse;

    @Mock
    private HttpRequest request;

    @Mock
    Supplier<MyResponse> myResponseSupplier;


    @Test
    void testSendMessage() throws Exception {

        when(httpClient.send(any(),any())).thenReturn(httpResponse);
        when(httpResponse.body()).thenReturn(myResponseSupplier);
        when(myResponseSupplier.get()).thenReturn(getMyResponse());
        myService.create("https://www.google.com", "/v1/test?page_size=100");
        verify(httpClient).send(request, HttpResponse.BodyHandlers.ofString());
    }
}

问题原因及修复方案 #

核心问题 #

业务代码的create方法中直接在内部创建了HttpClient实例（HttpClient httpClient = HttpClient.newBuilder().build()），导致测试类中@Mock的HttpClient和业务代码使用的HttpClient完全是两个独立对象，Mockito无法对局部创建的对象进行Mock，因此测试时会走真实API调用。

修复步骤 #

1. 重构业务代码，将HttpClient改为依赖注入

修改MyService，通过构造方法注入HttpClient，同时保留无参构造用于生产环境：

public class MyService {
    private final HttpClient httpClient;

    // 构造注入，用于测试时传入Mock实例
    public MyService(HttpClient httpClient) {
        this.httpClient = httpClient;
    }

    // 无参构造，生产环境默认创建HttpClient
    public MyService() {
        this.httpClient = HttpClient.newBuilder()
                .version(HttpClient.Version.HTTP_2)
                .connectTimeout(Duration.ofSeconds(30))
                .build();
    }

    public void create(String apiHost, String firstPage) {
        // 不再创建局部HttpClient，直接使用成员变量
        HttpRequest httpRequest = getHttpRequest(apiHost, firstPage);
        // 后续业务逻辑保持不变...
    }

    // 其他方法（getHttpRequest、invokeApi、createFile）保持不变
}

2. 调整测试代码，修正Mock和验证逻辑

• 修正HttpResponse的泛型，匹配业务代码中使用的HttpResponse<Supplier<MyResponse>>
• 修正verify的参数匹配，业务代码中使用的是自定义JsonBodyHandler，不能用HttpResponse.BodyHandlers.ofString()
• 处理分页场景的多次调用返回：

@ExtendWith(MockitoExtension.class)
class MyServiceTests {

    @InjectMocks
    private MyService myService;

    @Mock
    private HttpClient httpClient;
    @Mock
    private HttpResponse<Supplier<MyResponse>> httpResponse;
    @Mock
    private Supplier<MyResponse> myResponseSupplier;

    @Test
    void testCreate() throws Exception {
        // 构造第一页响应（带下一页链接）
        MyResponse firstPageResponse = new MyResponse();
        firstPageResponse.setData(Arrays.asList(new ResponseData()));
        Links firstPageLinks = new Links();
        firstPageLinks.setNext("/v1/test?page_size=100&page=2");
        firstPageResponse.setLinks(firstPageLinks);

        // 构造第二页响应（无下一页链接）
        MyResponse secondPageResponse = new MyResponse();
        secondPageResponse.setData(Arrays.asList(new ResponseData()));
        Links secondPageLinks = new Links();
        secondPageLinks.setNext(null);
        secondPageResponse.setLinks(secondPageLinks);

        // Mock HttpClient.send方法，返回预设响应
        when(httpClient.send(any(HttpRequest.class), any(HttpResponse.BodyHandler.class)))
                .thenReturn(httpResponse);
        when(httpResponse.body()).thenReturn(myResponseSupplier);
        // 模拟两次调用返回不同结果（对应分页）
        when(myResponseSupplier.get())
                .thenReturn(firstPageResponse)
                .thenReturn(secondPageResponse);

        // 执行测试方法
        myService.create("https://www.google.com", "/v1/test?page_size=100");

        // 验证HttpClient.send被调用两次（两次分页请求）
        verify(httpClient, times(2)).send(any(HttpRequest.class), any(HttpResponse.BodyHandler.class));
    }

    // 辅助方法：构造测试用MyResponse（按需填充数据）
    private MyResponse getMyResponse() {
        return new MyResponse();
    }
}

3. 额外注意事项

• 业务代码中invokeApi使用了自定义JsonBodyHandler，测试时HttpResponse的泛型必须和业务代码一致，否则会因类型不匹配导致Mock失效。
• 测试中的verify不能用预先Mock的request对象，因为业务代码中的HttpRequest是动态生成的，需用any(HttpRequest.class)这类匹配器来匹配。
• 若无法修改业务代码的构造方式，可通过反射替换局部HttpClient，但这种方式会增加测试复杂度，不推荐。

内容的提问来源于stack exchange，提问作者springenthusiast