无法在HandlerInterceptorAdapter中自动装配服务

  • Z时代
  • 2024-01-10
  • 分类：问答

我得到一个NullPointerException想要的时候@Autowire我@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：

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)

回答：

那是因为Spring不在管理您的PagePopulationInterceptor实例。您在以下代码中自行创建

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

更改为

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

这样，由于PagePopulationInterceptor实例是从@Bean方法生成的，因此Spring将管理实例的生命周期。Spring将扫描它以寻找@Autowired目标并注入它们。

假设它PagePopulationInterceptor在要@ComponentScan编辑的包中。

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