最近工作问题总结——反射&volatile等

╰+哭是因爲堅強的太久メ 2024-04-17 05:29 62阅读 0赞

> 根据业务需求，需要每天从服务器拿数据，数据格式以“|”分割，类似zhang san|18，这样的。然后需要读取文件，将其转成Object。因为数据格式不是json或者xml等，所以无法使用fastjson等直接转换成Object。但是数据是有序的，因此可以使用反射或者setter方法进行构建Object。

## 一、反射 ##

@Slf4j
    public class EBBSDataMapper {
        private static volatile Field[] fields;
    
        public static CustomerInfo convertToCustomer(String line) throws Exception {
            String[] strings = line.split("\\|", -1);
            return arrayToJson(strings);
        }
    
        public static CustomerInfo arrayToJson(String[] array) throws Exception {
            String[] trimArray = Arrays.stream(array).map(s -> StringUtils.trimToNull(s)).toArray(String[]::new);
            CustomerInfo customerInfo = CustomerInfo.class.newInstance();
            fields = CustomerInfo.class.getDeclaredFields();
    
            for (int i = 0; i < fields.length; i++) {
                Field field = fields[i];
                // bypass $jacocoData
                // Maven integrates jacoco to count the code coverage of unit tests
                // Jacoco weaves an additional field named $jacocoData into the compiled classes
                // So using java reflect will find this boolean[] field
                if (field.isSynthetic()) {
                    continue;
                }
    
                String fieldName = field.getName();
                field.setAccessible(true);
                String fieldClassName = field.getType().getSimpleName();
                log.debug(fieldName + " [" + fieldClassName + "," + trimArray[i] + "]");
    
                TargetExecutorFactory.getTargetExecutor(fieldClassName).setData(field, trimArray[i], customerInfo);
            }
    
            return customerInfo;
        }
    }

这里，首先通过String的split将字段分割出来，然后将空字符串“”转成null，接着通过反射将数据存入对象中。

有关反射的知识：[Java高级特性——反射][Java]

值得注意的是，这里利用多态和简单工厂模式将反射的set重构了，这样以后有利于扩展，而且代码没有if、else if，看起来干净整洁。

public interface TargetExecutor {
        void setData(Field field, String data, CustomerInfo output) throws Exception;
    }

@Slf4j
    public class LocalDateTargetExecutor implements TargetExecutor {
    
        @Override
        public void setData(Field field, String data, CustomerInfo output) throws Exception {
            try {
                LocalDate localDate = StringUtils.isEmpty(data) ? null :
                        LocalDate.parse(data, DateTimeFormatter.ofPattern("yyyy-MM-dd"));
                field.set(output, localDate);
            } catch (IllegalAccessException | DateTimeParseException e) {
                log.error(e.getMessage());
                throw e;
            }
        }
    }

public class TargetExecutorFactory {
        public static TargetExecutor getTargetExecutor(String fieldClassName) {
            TargetExecutor targetExecutor;
            switch (fieldClassName) {
                case "LocalDate":
                    targetExecutor = new LocalDateTargetExecutor();
                    break;
                case "String":
                    targetExecutor = new StringTargetExecutor();
                    break;
                case "BigDecimal":
                    targetExecutor = new BigDecimalTargetExecutor();
                    break;
                case "EBBSRelStatusEnum":
                    targetExecutor = new EBBSRelStatusEnumTargetExecutor();
                    break;
                case "GenderEnum":
                    targetExecutor = new GenderEnumTargetExecutor();
                    break;
                case "RiskLevelEnum":
                    targetExecutor = new RiskLevelEnumTargetExecutor();
                    break;
                default:
                    throw new BatchProcessingException("No TargetExecutor for [" + fieldClassName + "]");
            }
            return targetExecutor;
        }
    }

## 二、Jacoco导致的反射错误 ##

问题描述：当时在本地直接跑测试，是一切正常的。然后上传到Jenkins上面，发现Unit Test Step build失败了。经过打断点，查log，最后才发现是Maven test有问题。Maven test集成了Jacoco做代码覆盖率，而Jacoco在编译时会动态织入一个boolean\[\] $jacocoData字段，因此在DataMapper中无法找到该boolean数组如何set数据，导致错误。

解决办法：只要把该字段跳过就好。

if (field.isSynthetic()) {
        continue;
    }

## 三、多线程下反射资源冲突 ##

问题描述：因为数据量比较多，因此采用Java的线程池去多线程处理数据转换。但是，实际运行时发现，有些数据无法set进去。

解决办法：采用volatile

private static volatile Field[] fields;

volatile学习：[Java中Volatile关键字详解][Java_Volatile]

[Java]: https://www.jianshu.com/p/9be58ee20dee
[Java_Volatile]: https://www.cnblogs.com/zhengbin/p/5654805.html