[英]Generic way to parse JSON
我有一個JSON示例
{
"data":"some string data",
"amount":200,
"amountCurrencyList":[
{"value":4000.0,"currency":"USD"},
{"value":100.0,"currency":"GBP"}
]
}
當前將其解析為基礎對象的地圖字段的方法和方法
public void buildDetailsFromJson(String details) {
if (details != null) {
TypeReference<HashMap<String, Object>> mapTypeReference = new TypeReference<HashMap<String, Object>>() {
};
ObjectMapper mapper = new ObjectMapper();
try {
mapper.enable(DeserializationConfig.Feature.ACCEPT_SINGLE_VALUE_AS_ARRAY);
mapper.disable(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES);
detailsMap = mapper.readValue(details, mapTypeReference);
} catch (IOException e) {
log.error("Exception during JSON {} parsing! {}", details, e.getMessage());
}
}
}
JSON結構可以更改。 想法是有一個單獨的方法,理想情況下可以輕松提取所需的參數,例如map.get(key_name)
例如
public void setUpFieldsFromMap() {
HashMap<String, Object> map = super.detailsMap;
this.amountCurrencyList = (ArrayList<MoneyValue>) map.get("amountCurrencyList");
if (isNull(amountCurrencyList)) {
throw new InvalidOrMissingParametersException("Exception during JSON parsing! Critical data is missing in DetailsMap - " + map.toString());
}
}
因此,通過鍵獲取List對象並將其轉換為所需的參數。 但是當我嘗試使用List<MoneyValue>
System.out.println(detailsObj.getAmountCurrencyList().get(0).getValue());
我越來越
Exception: java.util.LinkedHashMap cannot be cast to MoneyValue
實際上,無需使用諸如TypeReference<HashMap<String, List<MoneyValue>>>
類的確切參數對TypeReference進行硬編碼,實際上是否可以實現我想要的?
UPD
public class MoneyValue {
@NotNull
private BigDecimal value;
@NotNull
private String currency;
EventDetails類
public class SomeEventDetails extends BaseEventDetails implements EventDetails {
private ArrayList<MoneyValue> amountCurrencyList;
@Override
public void setUpFieldsFromMap() {
HashMap<String, Object> map = super.detailsMap;
this.amountCurrencyList = (ArrayList<MoneyValue>) map.get("amountCurrencyList");
if (isNull(amountCurrencyList)) {
throw new InvalidOrMissingParametersException("Exception during JSON parsing! Critical data is missing in DetailsMap - " + map.toString());
}
}
}
如果一組屬性(我的意思是輸入數據的結構)不可修改,我們可以將其表示為POJO類。 使其成為DetailsData
:
public class DetailsData {
private String data;
private BigDecimal amount;
private List<MoneyValue> amountCurrencyList;
/*getters, setters, constructors*/
public DetailsData() {
}
@JsonProperty("amountCurrencyList")
private void deserializeMoneyValue(List<Map<String, Object>> data) {
if (Objects.isNull(amountCurrencyList)) {
amountCurrencyList = new ArrayList<>();
} else {
amountCurrencyList.clear();
}
MoneyValue moneyValue;
for (Map<String, Object> item : data) {
moneyValue = new MoneyValue(getValue(item.get("value")),
(String) item.get("currency"));
amountCurrencyList.add(moneyValue);
}
}
private BigDecimal getValue(Object value) {
BigDecimal result = null;
if (value != null) {
if (value instanceof BigDecimal) {
result = (BigDecimal) value;
} else if (value instanceof BigInteger) {
result = new BigDecimal((BigInteger) value);
} else if (value instanceof Number) {
result = new BigDecimal(((Number) value).doubleValue());
} else {
throw new ClassCastException("Invalid value");
}
}
return result;
}
}
正如你可以看到這里有一個方法deserializeMoneyValue
標注為JSON屬性。 因此,對於ObjectMapper,它將用作自定義反序列化器。 getValue
方法是必需的,因為Jackson是以這種方式工作的,因此該值將在滿足該值大小的類中反序列化。 例如,如果value =“ 100”,則將反序列化為Integer
;如果value =“ 100.0”,則將反序列化為Double
,依此類推。 實際上,您可以使此方法static
並移入某些util類。 總結一下,您可以按以下方式更改buildDetailsFromJson
:
public void buildDetailsFromJson(String details) {
if (details != null) {
ObjectMapper mapper = new ObjectMapper();
try {
mapper.enable(DeserializationConfig.Feature.ACCEPT_SINGLE_VALUE_AS_ARRAY);
mapper.disable(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES);
// assuming the eventDetails is an instance of DetailsData
eventDetails = mapper.readValue(details, DetailsData.class);
} catch (IOException e) {
log.error("Exception during JSON {} parsing! {}", details, e.getMessage());
}
}
}
和EventDetail類:
public class SomeEventDetails extends BaseEventDetails implements EventDetails {
private List<MoneyValue> amountCurrencyList;
@Override
public void setUpFieldsFromMap() {
this.amountCurrencyList = super.eventDetails.getAmountCurrencyList();
if (isNull(amountCurrencyList)) {
throw new InvalidOrMissingParametersException("Exception during JSON parsing! Critical data is missing in DetailsMap - " + super.eventDetails.toString());
}
}
}
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