无法在HandlerInterceptorAdapter中自动装配服务

问题描述

我在尝试 @Autowire 我的 @Service NullPointerException / code>：

I'm getting a NullPointerException when trying to @Autowire my @Service:

public class PagePopulationInterceptor extends HandlerInterceptorAdapter {
    private @Autowired MyService service;

    public @Override void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView mav) {
        service.savePageView(IPUtils.toLong(request.getRemoteAddr()), request.getRequestURI(), request.getHeader("User-Agent"));
        mav.addObject("counter", service.getCounter());
    }
}

@Configuration
@ComponentScan(basePackages = "com.mycompany", excludeFilters = { @ComponentScan.Filter(Configuration.class) })
@PropertySource("classpath:application.properties")
@EnableTransactionManagement
@EnableWebMvc
public class MyConfig extends WebMvcConfigurerAdapter {
    public @Override void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new PagePopulationInterceptor());
    }
}

@Service
@Transactional
public class MyService {
    private @Autowired PageViewDao pageViewDao;

    public class Counter {
        private long total;
        private long today;
        private long yesterday;
        private long now;

        // Getters and setters
    }

    public void savePageView(long ip, String visitPage, String userAgent) {
        PageView obj = new PageView();
        obj.setVisitDate(new Date());
        obj.setUserAgent(userAgent);
        obj.setPage(visitPage);
        obj.setIp(ip);

        pageViewDao.saveOrUpdate(obj);
    }

    public Counter getCounter() {
        Counter ret = new Counter();
        // populate Counter members
        return ret;
    }
}

编辑：这是Stacktrace：

Here's the Stacktrace:

java.lang.NullPointerException
    com.mycompany.util.PagePopulationInterceptor.postHandle(PagePopulationInterceptor.java:22)
    org.springframework.web.servlet.HandlerExecutionChain.applyPostHandle(HandlerExecutionChain.java:149)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:934)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:936)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:827)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:812)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)

推荐答案

这是因为Spring没有管理你的 PagePopulationInterceptor 实例。您是在下面的代码中自己创建的

That's because Spring isn't managing your PagePopulationInterceptor instance. You are creating it yourself in the below code

public @Override void addInterceptors(InterceptorRegistry registry) {
    registry.addInterceptor(new PagePopulationInterceptor());
}

将其更改为

@Bean
public PagePopulationInterceptor pagePopulationInterceptor() {
    return new PagePopulationInterceptor();
}

public @Override void addInterceptors(InterceptorRegistry registry) {
    registry.addInterceptor(pagePopulationInterceptor());
}

通过这种方式，Spring将管理 PagePopulationInterceptor 实例，因为它是从 @Bean 方法生成的。 Spring将扫描它以获取 @Autowired 目标并注入它们。

In this way, Spring will manage the lifecycle of the PagePopulationInterceptor instance since it's generated from a @Bean method. Spring will scan it for @Autowired targets and inject them.

这假定 PagePopulationInterceptor 在一个包中 @ComponentScan ed。

This assumes that PagePopulationInterceptor is in a package to be @ComponentScaned.

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