springBoot @Autowired注入对象为空原因总结

深藏阁楼爱情的钟 2022-04-23 11:10 765阅读 0赞

BankDAO类内容如下：  
package com.wiseco.engine.dao;  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N1bmppbmp1YW4_size_16_color_FFFFFF_t_70]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N1bmppbmp1YW4_size_16_color_FFFFFF_t_70 1]

Controller中内容：  
cacheTableMap.get(tableName)值为：com.wiseco.engine.dao.BankDAO  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N1bmppbmp1YW4_size_16_color_FFFFFF_t_70 2]  
结果调用controller执行refreshCache函数时报空指针异常，通过debug模式跟踪发现以下地方cacheJob对象是null。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N1bmppbmp1YW4_size_16_color_FFFFFF_t_70 3]  
分析后原因如下：controller中的对象是通过反射创建的新对象，不是spring容器中的对象，而cacheJob是通过autoWired注入到spring容器中的对象中的。因此对于新创建的对象cacheJob对象就是空值。

解决办法一：conroller中还是使用springboot自己的对象  
写的工具类为SpringUtil，实现ApplicationContextAware接口，并加入Component注解，让spring扫描到该bean

@Component
    public class SpringUtil implements ApplicationContextAware {
    
        private static Logger logger = LoggerFactory.getLogger(SpringUtil.class);
    
        private static ApplicationContext applicationContext;   
    
        @Override
    
        public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
    
            if(SpringUtil.applicationContext == null) {
    
                SpringUtil.applicationContext = applicationContext;
    
            }
    
            logger.info("ApplicationContext配置成功,applicationContext对象："+SpringUtil.applicationContext);
    
        }
    
        public static ApplicationContext getApplicationContext() {
    
            return applicationContext;
    
        }
    
        public static Object getBean(String name) {
    
            return getApplicationContext().getBean(name);
    
        }
    
        public static <T> T getBean(Class<T> clazz) {
    
            return getApplicationContext().getBean(clazz);
    
        }
    
        public static <T> T getBean(String name,Class<T> clazz) {
    
            return getApplicationContext().getBean(name,clazz);
    
        }
    
    
    }

修改代码如下，controller调用成功，不再有空指针异常  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N1bmppbmp1YW4_size_16_color_FFFFFF_t_70 4]

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N1bmppbmp1YW4_size_16_color_FFFFFF_t_70 1]: /images/20220320/f637b9a9816648949f304c054b71ad83.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N1bmppbmp1YW4_size_16_color_FFFFFF_t_70 2]: /images/20220320/8650ea0a2cf04585afa0df33d612145a.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N1bmppbmp1YW4_size_16_color_FFFFFF_t_70 3]: /images/20220320/67cbdee0b2a445d79880e4140c90f9cb.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3N1bmppbmp1YW4_size_16_color_FFFFFF_t_70 4]: /images/20220320/1e894739687d4f7c9925bc89f2c62eda.png