如何使用Spock框架Mock java.net.http.HttpClient？

问题背景 #

现有静态方法提供HttpClient实例：

@CompileStatic
private static HttpClient getClient() {
    return HttpClient.newBuilder()
            .version(HttpClient.Version.HTTP_2)
            .connectTimeout(Duration.ofSeconds(5))
            .build()
}

业务代码中通过该实例调用第三方API：

final HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString())

无法重构代码，尝试GroovySpy(global: true)、GroovyMock(global: true)（包括针对HttpClientImpl）均无效，且因依赖过多无法重写getClient()方法，需要Mock指定返回值。

可行方案：使用PowerMock + Mockito 静态Mock #

由于目标是Mock静态方法HttpClient.newBuilder()的链式调用，从而控制返回的HttpClient实例，进而Mock其send方法，步骤如下：

1. 引入依赖
   确保测试依赖中包含PowerMock和Mockito的适配包（以Gradle为例）：

testImplementation "org.powermock:powermock-module-junit4:2.0.9"
testImplementation "org.powermock:powermock-api-mockito2:2.0.9"
testImplementation "org.mockito:mockito-core:3.12.4"

2. 编写测试代码

import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mock;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import static org.mockito.ArgumentMatchers.any;
import static org.mockito.Mockito.when;
import static org.powermock.api.mockito.PowerMockito.mockStatic;

@RunWith(PowerMockRunner.class)
@PrepareForTest(HttpClient.class) // 标记需要Mock的静态类
public class YourServiceTest {

    @Mock
    private HttpClient mockHttpClient;
    @Mock
    private HttpClient.Builder mockBuilder;
    @Mock
    private HttpResponse<String> mockResponse;

    @Test
    public void testApiCall() throws Exception {
        // 1. Mock HttpClient.newBuilder() 返回我们的mockBuilder
        mockStatic(HttpClient.class);
        when(HttpClient.newBuilder()).thenReturn(mockBuilder);

        // 2. 链式Mock Builder的配置方法，最终返回mockHttpClient
        when(mockBuilder.version(any(HttpClient.Version.class))).thenReturn(mockBuilder);
        when(mockBuilder.connectTimeout(any())).thenReturn(mockBuilder);
        when(mockBuilder.build()).thenReturn(mockHttpClient);

        // 3. Mock send方法的返回值
        when(mockResponse.body()).thenReturn("Mocked API Response");
        when(mockHttpClient.send(any(HttpRequest.class), any(HttpResponse.BodyHandler.class)))
                .thenReturn(mockResponse);

        // 执行你的业务方法，此时会使用我们Mock的HttpClient
        YourService.yourBusinessMethod();

        // 验证逻辑（可选）
        // verify(mockHttpClient).send(any(HttpRequest.class), any(HttpResponse.BodyHandler.class));
    }
}

关键说明 #

• PowerMock允许Mock静态方法、私有方法等Mockito无法覆盖的场景，正好适配HttpClient.newBuilder()这种静态创建实例的场景。
• 通过链式Mock Builder的每一步调用，确保最终返回我们创建的Mock HttpClient实例，这样后续的send调用就能被我们控制。
• 无需修改原有业务代码，完全通过测试框架实现Mock。

内容的提问来源于stack exchange，提问作者john