java静态工具类注入service出现NullPointerException异常处理

2024-04-02 19:04:59 770人浏览安东尼

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摘要

目录一般我们在controller层调用service时，只需要使用@Autowired注解即可，例如如下代码我们经常看到： @RestController @RequestMa


@RestController
@RequestMapping("business")
public class BizResourceController {
    @Autowired
    private BusinessService businessService;
    @RequestMapping(path = "/queryYearList", method = RequestMethod.POST)
    public List<String> queryYearList(@RequestParam("cityCode") String cityCode) {
        return businessService.queryYearList(cityCode);
    }
}

以上代码的含义就是通过在controller中注入业务层类（BusinessService）调用业务层方法queryYearList。但是如果我们要在我们自己封装的Utils工具类中或者非controller普通类中使用@Autowired注解注入Service或者Mapper接口，直接注入是报错的，因为Utils使用了静态的方法，我们是无法直接使用非静态接口的，当我们遇到这样的问题，我们就要想办法解决了。例如：


public class RedisHelper {
    private static final Logger logger = LoggerFactory.getLogger(RedisHelper.class);
    @Autowired
    private static StringRedisTemplate redisTemplate;

    
    public static void scan(String pattern, Consumer<byte[]> consumer) {
        redisTemplate.execute((RedisConnection connection) -> {
            try (Cursor<byte[]> cursor = connection.scan(ScanOptions.scanOptions().count(Long.MAX_VALUE).match(pattern).build())) {
                cursor.forEachRemaining(consumer);
                return null;
            } catch (IOException e) {
                e.printStackTrace();
                throw new RuntimeException(e);
            }
        });
    }

    
    public static List<String> keys(String pattern) {
        List<String> keys = new ArrayList<>();
        scan(pattern, item -> {
            //符合条件的key
            String key = new String(item, StandardCharsets.UTF_8);
            keys.add(key);
        });
        return keys;
    }

    public static void delete(List<String> lisTKEy) {
        try {
            logger.info("需要删除key：" + listKey);
            Long delete1 = redisTemplate.delete(listKey);
            logger.info("清除redis-key结果：{}",delete1);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

如上代码在redis工具类中想要注入StringRedisTemplate但是我们使用的时候会发现，这个StringRedisTemplate对象时null。所以当我们需要有类似需求进行注入的时候要调整注入方式和写法，如下代码：


@Component
public class RedisHelper {
    private static final Logger logger = LoggerFactory.getLogger(RedisHelper.class);
    private static StringRedisTemplate redisTemplate;

    @Autowired
    public void setRedisTemplate(StringRedisTemplate redisTemplate) {
        RedisHelper.redisTemplate = redisTemplate;
    }

    
    public static void scan(String pattern, Consumer<byte[]> consumer) {
        redisTemplate.execute((RedisConnection connection) -> {
            try (Cursor<byte[]> cursor = connection.scan(ScanOptions.scanOptions().count(Long.MAX_VALUE).match(pattern).build())) {
                cursor.forEachRemaining(consumer);
                return null;
            } catch (IOException e) {
                e.printStackTrace();
                throw new RuntimeException(e);
            }
        });
    }

    
    public static List<String> keys(String pattern) {
        List<String> keys = new ArrayList<>();
        scan(pattern, item -> {
            //符合条件的key
            String key = new String(item, StandardCharsets.UTF_8);
            keys.add(key);
        });
        return keys;
    }

    public static void delete(List<String> listKey) {
        try {
            logger.info("需要删除key：" + listKey);
            Long delete1 = redisTemplate.delete(listKey);
            logger.info("清除redis-key结果：{}",delete1);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

其修改的核心是：