使用LinkedHashMaps从对象获取和修改值

Question

Object valueArray = x.getFieldData().getData().getAdditionalProperties().get("items");

Object value = x.getFieldData().getData().getAdditionalProperties().get("value");
    if(value != null){
        Double result = (Double) value * Double.parseDouble(rule.values.get(0));
        x.getFieldData().getData().getAdditionalProperties().put("value", result);
    }

有什么想法可以解决这个问题吗？谢谢。

Answer 1

这在某种程度上取决于您的数据是如何记录的。您必须对所有保持安全的东西进行类型化，为此您需要做出一些假设：

if (valueArray instanceof List) {
    @SuppressWarnings("unchecked") // <- need a type in List declaration rather than '?' to allow for List.set, 'Object' being safe
    List<Object> valueList = (List<Object>) valueArray;
    for (int i = 0; i < valueList.size(); i++) {
        Object val = valueList.get(i);
        if (val instanceof Map) {
            @SuppressWarnings("unchecked") // <- you need to be sure that all keys are strings to do that, otherwise use <Object, Object> and typecast again as needed
            Map<String, Object> mVal = (Map<String, Object>) val;
            //Do something with you map, e.g. change some value:
            mVal.put("myprop", "a-value");
        }
        //Or change the value entirely, e.g.:
        valueList.set(i, new LinkedHashMap<String, Object>());
    }
}

注意，instanceof检查还检查null。

现在，如果100%保证读取对象始终是java.util.list的java.util.map(linkedHashmap是map的子类）(string类型的键）的java.util.list(arraylist（正如arraylist一样），则可以简化为：

if (valueArray instanceof List) {
    @SuppressWarnings("unchecked") // <- need to be 100% sure of all types involved every time: UNSAFE operation!
    List<Map<String, Object>> valueList = (List<Map<String, Object>>) valueArray;
    for (int i = 0; i < valueList.size(); i++) {
        Map<String, Object> val = valueList.get(i);
        if (val != null) {
            //Do something with you map, e.g. change some value:
            val.put("myprop", "a-value");
        }
        //Or change the value entirely, e.g.:
        valueList.set(i, new LinkedHashMap<String, Object>());
    }
}