三种方式解决SpringBoot拦截器不能注入bean的问题

小灰灰 2022-12-30 13:43 265阅读 0赞

一.原因

*  这两天在写代码的时候遇到一个问题,为什么使用SpringBoot的时候,拦截器中使用@Autowired注入bean会报空指针.如下面代码所示,我们知道,Spring管理的bean发现有这个注解时候，它会直接注入相应的另一个Spring管理的bean.当 Spring 容器启动时，AutowiredAnnotationBeanPostProcessor (继承InstantiationAwareBeanPostProcessorAdapter)将扫描 Spring 容器中所有 Bean，当发现 Bean 中拥有@Autowired 注解时就找到和其匹配（默认按类型匹配）的 Bean，并注入到对应的地方中去。那为什么这里的注解没有生效呢?
 *  网上传说:了解SpringBoot的都知道SpringBoot的目录格式有着明确的规定,它减轻编程人员负担的同时,更加要求了编程的规范化,SpringBoot初始化的时候,会加载com.boot.app下的bean,一层一层加载,当注册LoggerInterceptor的时候,发现LoggerInterceptor中有@Autowired注解,就会去另外一个spring管理器中索取另外一个LoggerJpa,而这时候LoggerJpa根本没有初始化.所以就无法注入LoggerJpa的bean类完成相应的操作.
 *  自我理解:注册拦截器时直接通过new LoggerInterceptor(),并没有触发Spring去管理bean,所以@Autowired没有生效.
 *      /**
         * ========================
         *
         * @author 小龙虾
         * Created with IntelliJ IDEA.
         * Date：2018/1/22
         * Time：20:02
         * ========================
         */
        public class LoggerInterceptor implements HandlerInterceptor {
            public static final String SEND_TIME = "send_time";
            public static final String DATA = "param_data";
            //问题:无法注入loggerDao
            @Autowired
            private LoggerJpa loggerDao;
            /**
            * 进入springMVC的controller之前开始记录日志实体
             * @param httpServletRequest request
             * @param httpServletResponse response
             * @param o 实体类
             * @return  boolean
             * @throws Exception
             */
            @Override
            public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse         httpServletResponse, Object o) throws Exception {
                //创建日记实体类
                LoggerEntity entity = new LoggerEntity();
                //获得sessionId
                String sessionId = httpServletRequest.getRequestedSessionId();
                //请求地址信息
                String requestURI = httpServletRequest.getRequestURI();
                //请求参数信息(利用fastJson转换参数)
                String params = JSON.toJSONString(httpServletRequest.getParameterMap(),
                    SerializerFeature.DisableCircularReferenceDetect,
                    SerializerFeature.WriteMapNullValue);
                //设置客户端ip
                entity.setClientIp(LoggerUtil.getCliectIp(httpServletRequest));
                //设置请求方法
                entity.setMethod(httpServletRequest.getMethod());
                //设置请求类型
                entity.setType(LoggerUtil.getRequestType(httpServletRequest));
                //设置请求参数
                entity.setParamData(params);
                //设置请求地址
                entity.setUri(requestURI);
                //设置sessionId
                entity.setSessionId(sessionId);
                //设置请求开始时间
                httpServletRequest.setAttribute(SEND_TIME, System.currentTimeMillis());
                //设置请求实体到request内,方便afterCompletion调用
                httpServletRequest.setAttribute(DATA, entity);
                return true;
              }
            @Override
            public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
            }
        
            @Override
            public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {
                //请求状态
                int status = httpServletResponse.getStatus();
                //当前时间
                long time = System.currentTimeMillis();
                //上次请求时间
                Long requestTime = Long.valueOf(httpServletRequest.getAttribute(SEND_TIME).toString());
                //获取请求日记的实体
                LoggerEntity entity = (LoggerEntity) httpServletRequest.getAttribute(DATA);
                //设置时间差
                entity.setConsuming(Long.valueOf(time-requestTime).toString());
                //设置错误码
                entity.setStatusCode(status+"");
                //设置返回值
                entity.setReturnData(JSON.toJSONString(httpServletRequest.getAttribute(LoggerUtil.LOGGER_RETURN),
                    SerializerFeature.DisableCircularReferenceDetect,
                    SerializerFeature.WriteMapNullValue));
                //通过WebApplicationContextUtils获取loggerDao
               //LoggerJpa loggerDao = getDao(LoggerJpa.class,httpServletRequest);
                //将日记写入数据库
                loggerDao.save(entity);
            }
        }

二.解决方法

*  了解到原因之后,那么如何解决呢?在这里,有两种常见的解决方法.

①.利用WebApplicationContextUtils去获取WebApplicationContext,然后在通过WebApplicationContext去获取相应的bean.

*      public <T> T getDao(Class<T> clazz,HttpServletRequest request){
            //通过该方法获得的applicationContext 已经是初始化之后的applicationContext 容器
            WebApplicationContext applicationContext = WebApplicationContextUtils.getRequiredWebApplicationContext(request.getServletContext());
            return applicationContext.getBean(clazz);
        }

②.在初始化LoggerInterceptor 之前就初始化LoggerJpa

*      /**
         * ========================
         *
         * @author 小龙虾
         * Created with IntelliJ IDEA.
         * Date：2018/1/23
         * Time：11:51
         * ========================
         */
        @Configuration
        public class LoggerConfiguration extends WebMvcConfigurerAdapter {
        
            @Bean
            public LoggerInterceptor loggerInterceptor(){
                System.out.println("嘻嘻嘻嘻");
                return new LoggerInterceptor();
            }
            /**
             * LoggerInterceptor,形成拦截链
             * @param registry 拦截器注册类
             */
            @Override
            public void addInterceptors(InterceptorRegistry registry){
                //在放入拦截器之前调用loggerInterceptor(),触发LocalContainerEntityManagerFactoryBean使得拦截器的在注册之前所有的bean都持久化
                registry.addInterceptor(loggerInterceptor()).addPathPatterns("/**");
                System.out.println("呵呵呵呵");
            }
        }

③.构造器

*      public class LoggerInterceptor implements HandlerInterceptor {
            private static final String SEND_TIME = "send_time";
            private static final String DATA = "param_data";
            private LoggerJpa loggerDao;
            public LoggerInterceptor(LoggerJpa loggerDao){
                this.loggerDao = loggerDao;
            }
        //拦截器三个方法略...
        }
 *      /**
         * ========================
         *
         * @author 小龙虾
         * Created with IntelliJ IDEA.
         * Date：2018/1/23
         * Time：11:51
         * ========================
         */
        @Configuration
        public class LoggerConfiguration extends WebMvcConfigurerAdapter {
        
            //@Bean
            //public LoggerInterceptor loggerInterceptor(){
            //    System.out.println("嘻嘻嘻嘻")
            //    return new LoggerInterceptor(loggerDao);
            //}
            @Autowired
            private LoggerJpa loggerDao;
            /**
             * LoggerInterceptor,形成拦截链
             * @param registry 拦截器注册类
             */
            @Override
            public void addInterceptors(InterceptorRegistry registry){
                //利用构造方法注入
               registry.addInterceptor(new LoggerInterceptor(loggerDao)).addPathPatterns("/**");
                System.out.println("呵呵呵呵");
            }
        }