Spring Boot微服务JUnit测试RestTemplate空指针异常问题排查

在Spring Boot微服务中运行JUnit测试时遇到问题：已从/authenticate/login接口获取有效的Bearer Token，通过Postman可正常调用任意服务，但将Token复制到测试方法中后，测试无法正常执行。

测试代码 #

@DisplayName("Get Order - Success Scenario")
@Test
void test_When_Order_Success() {

    String bearerToken = "eyJhbGciOiJIUzUxMiJ9.eyJzdWIiOiJVc2VyIiwiaXNzIjoiUk9MRV9VU0VSICIsImlhdCI6MTY3MTQ4ODgyMiwiZXhwIjoxNjcxNDg4OTQyfQ.g83kKmFzDH539ZcpxM9D8bE_famFOevkOqNst_E8YG07b4yR4cEqcrySvz36vw8GJxTKm9gUQIM1J_G8cC5RGQ";

    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.APPLICATION_JSON);
    headers.set("Authorization", "Bearer " + bearerToken);

    HttpEntity<String> request = new HttpEntity<String>(headers);

    //Mocking
    Order order = getMockOrder();
    when(orderRepository.findById(anyLong()))
            .thenReturn(Optional.of(order));

    when(restTemplate.exchange(
            "http://PRODUCT-SERVICE/product/" + order.getProductId(),
            HttpMethod.GET, request, ProductResponse.class).getBody()).thenReturn(getMockProductResponse());

    when(restTemplate.exchange(
            "http://PAYMENT-SERVICE/payment/order/" + order.getId(),
            HttpMethod.GET, request, PaymentResponse.class).getBody()).thenReturn(getMockPaymentResponse());

    //Actual
    OrderResponse orderResponse = orderService.getOrderDetails(1,bearerToken);

    //Verification
    verify(orderRepository, times(1)).findById(anyLong());
    verify(restTemplate, times(1)).getForObject(
            "http://PRODUCT-SERVICE/product/" + order.getProductId(),
            ProductResponse.class);
    verify(restTemplate, times(1)).getForObject(
            "http://PAYMENT-SERVICE/payment/order/" + order.getId(),
            PaymentResponse.class);

    //Assert
    assertNotNull(orderResponse);
    assertEquals(order.getId(), orderResponse.getOrderId());
}

错误信息 #

java.lang.NullPointerException: Cannot invoke "org.springframework.http.ResponseEntity.getBody()" because the return value of "org.springframework.web.client.RestTemplate.exchange(String, org.springframework.http.HttpMethod, org.springframework.http.HttpEntity, java.lang.Class, Object[])" is null

项目启动步骤 #

• 运行服务注册中心（Eureka Server）
• 运行配置中心
• 通过Docker执行以下命令启动zipkin和redis：

  docker run -d -p 9411:9411 openzipkin/zipkin
  docker run -d --name redis -p 6379:6379 redis
  

• 运行API网关
• 运行其他服务

问题根源 #

1. Mock逻辑错误：直接对restTemplate.exchange(...).getBody()做Mock，会导致exchange方法本身返回null，调用getBody()时触发空指针异常。
2. 验证逻辑不匹配：测试中Mock的是restTemplate.exchange方法，但验证时检查的是restTemplate.getForObject的调用次数，两者不对应。

修复步骤 #

1. 修正RestTemplate的Mock逻辑

先Mockexchange方法返回一个非空的ResponseEntity，再指定其getBody()的返回值：

// Mock PRODUCT-SERVICE调用
ProductResponse mockProduct = getMockProductResponse();
when(restTemplate.exchange(
        "http://PRODUCT-SERVICE/product/" + order.getProductId(),
        HttpMethod.GET,
        request,
        ProductResponse.class))
        .thenReturn(new ResponseEntity<>(mockProduct, HttpStatus.OK));

// Mock PAYMENT-SERVICE调用
PaymentResponse mockPayment = getMockPaymentResponse();
when(restTemplate.exchange(
        "http://PAYMENT-SERVICE/payment/order/" + order.getId(),
        HttpMethod.GET,
        request,
        PaymentResponse.class))
        .thenReturn(new ResponseEntity<>(mockPayment, HttpStatus.OK));

2. 修正验证逻辑

确保验证的方法与实际调用一致，将验证getForObject改为验证exchange：

verify(restTemplate, times(1)).exchange(
        "http://PRODUCT-SERVICE/product/" + order.getProductId(),
        HttpMethod.GET,
        request,
        ProductResponse.class);

verify(restTemplate, times(1)).exchange(
        "http://PAYMENT-SERVICE/payment/order/" + order.getId(),
        HttpMethod.GET,
        request,
        PaymentResponse.class);

3. 确认Token传递（可选）

检查orderService.getOrderDetails内部是否正确将传入的bearerToken构造到请求头中，确保与测试中构造的request对象一致。

内容的提问来源于stack exchange，提问作者Sercan Noyan Germiyanoğlu