OncePerRequestFilter测试中Mockito指定的Mock类调用时为null如何解决？

问题根因 #

mock对象不生效的核心原因有两个：

1. 你的OriginFilter使用字段注入（@Autowired直接标注私有成员变量），没有提供可传入依赖的构造方法或setter方法。测试时你是手动new OriginFilter()创建的实例，脱离了Spring容器环境，没有逻辑帮你把mock好的tokenStore注入到新建的filter实例中，所以filter里的tokenStore自然为null。
2. 你当前的测试用例没有给mock请求设置Authorization请求头，即使注入成功也不会走到tokenStore的验证逻辑分支，只会触发Token is null的警告日志。

解决方案 #

方案1（推荐）：修改过滤器为构造函数注入 #

Spring官方更推荐构造函数注入的写法，既保证依赖不可变，也天然支持单元测试传参：

@Component
public class OriginFilter extends OncePerRequestFilter {

    private final CustomJdbcTokenStore tokenStore;

    // Spring 4.3+ 单构造函数可省略@Autowired注解
    public OriginFilter(CustomJdbcTokenStore tokenStore) {
        this.tokenStore = tokenStore;
    }

    @Override
    protected void doFilterInternal(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, FilterChain filterChain)
            throws ServletException, IOException {
        // 原有逻辑保持不变
        final String requestTokenHeader = httpServletRequest.getHeader("Authorization");
        
        if (requestTokenHeader != null) {
            if(tokenStore.verifyUserAgentAndHostname(requestTokenHeader.substring(7), httpServletRequest.getHeader("User-Agent"), httpServletRequest.getRemoteAddr())){
                filterChain.doFilter(httpServletRequest, httpServletResponse);
            }else {
                httpServletResponse.setStatus(HttpServletResponse.SC_UNAUTHORIZED);
            }
        } else {
            logger.warn("Token is null");
        }
    }
}

测试时直接将mock好的tokenStore传入构造函数即可：

// 测试类中创建filter实例的代码改为
OriginFilter filter = new OriginFilter(tokenStore);
// 补充添加Authorization头的逻辑，才能走到验证分支
mockRequest.addHeader("Authorization", "Bearer test_token_value");

方案2：使用Mockito的@InjectMocks注解快速注入 #

如果你不想修改原有过滤器的注入写法，可以直接修改测试代码，用Mockito的注入能力自动把mock对象塞到filter的私有字段里：

@RunWith(MockitoJUnitRunner.class)
public class OFilterTest {

    @Mock
    CustomJdbcTokenStore tokenStore;

    // 新增该注解，Mockito会自动把@Mock标注的对象注入到对应字段
    @InjectMocks
    private OriginFilter filter;

    @Before
    public void setUp() {
        MockitoAnnotations.initMocks(this);
    }

    @Test
    public void CheckIfFilterPreventsDifferentOriginAccess() throws IOException, ServletException, ParseException {
        Assert.assertNotNull(tokenStore);
        // 不需要手动new OriginFilter了，直接用上面注解注入的filter实例
        MockHttpServletRequest mockRequest = new MockHttpServletRequest();
        // 补充加请求头，才能走到验证逻辑
        mockRequest.addHeader("Authorization", "Bearer test_token_value");
        MockHttpServletResponse mockResponse = new MockHttpServletResponse();
        FilterChain mockFilterChain = Mockito.mock(FilterChain.class);

        when(tokenStore.verifyUserAgentAndHostname(any(),any(),any())).thenReturn(true);

        filter.doFilterInternal(mockRequest, mockResponse, mockFilterChain);
        filter.destroy();
    }
}

内容的提问来源于stack exchange，提问作者midi