RestTemplate Mock throws NullPointerException

问题

I have a rest template that makes a call in a method in a service class like so:

public CustomerResponse someMethod() {
CustomerResponse response = restTemplate.exchange(url, HttpMethod.GET, null,  CustomerRes.class).getBody();
return response;
}

When trying to mock the restTemplate in my test class, it keeps throwing a NullPointerException on the line where the mock restTemplate is called:

public void checkResponseIsNotNull() {
CustomerResponse customerResponseMock = mock(CustomerResponse.class);
when(restTemplate.exchange(url, HttpMethod.GET, null, CustomerResponse.class).getBody()).thenReturn(customerResponseMock);
CustomerResponse cr = service.someMethod();
Assert.assertNotNull(cr);
}

Why is NullPointer being thrown? I have mocked a RestTemplate before, just without the getBody() method which leads be to believe its that which is causing the null pointer.

回答1:

You should add one more level of mocking:

CustomerResponse customerResponseMock = mock(CustomerResponse.class);
ResponseEntity reMock = mock(ResponseEntity.class);

when(reMock.getBody()).thenReturn(customerResponseMock);
when(restTemplate.exchange(url, HttpMethod.GET, null, CustomerResponse.class)).thenReturn(reMock);

CustomerResponse cr = service.someMethod();

Originally you were setting-up the ResponseEntity only and the RestTemplate still remained with the defaults.. thus returning null when exchange has been called.

来源：https://stackoverflow.com/questions/53284914/resttemplate-mock-throws-nullpointerexception