jackson使用

配置ObjectMapper

參考鏈接

ObjectMapper mapper = new ObjectMapper();

• 配置要檢測序列化的字段

  • 自動檢測所有成員字段 auto-detect all member fields

  mapper.setVisibility(PropertyAccessor.FIELD, Visibility.ANY);

  • 只有get方法的成員 but only public getters

  mapper.setVisibility(PropertyAccessor.GETTER, Visibility.NONE);

  • 1 沒有set或者is方法 and none of “is-setters”

  setVisibility(PropertyAccessor.IS_GETTER, Visibility.NONE);

• 禁止拋出異常

  • 返回的JSON字符串中含有我們並不需要的字段，那麼當對應的實體類中不含有該字段時，會拋出一個異常

  objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES,false);

• 對於數字轉換，是數字的標識符但不是數字的轉換

mapper.configure(Feature.ALLOW_NON_NUMERIC_NUMBERS, true);

• 該特性決定是否接受強制非數組（JSON）值到Java集合類型。如果允許，集合反序列化將嘗試處理非數組值。

mapper.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);

• 空JSON字符串可以等價於JSON null

mapper.configure(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT, true);

---

轉換成指定的集合對象

public static <T> T readJson(String jsonStr, Class<?> collectionClass, Class<?>... elementClasses) throws Exception {
   ObjectMapper mapper = new ObjectMapper();
   JavaType javaType = mapper.getTypeFactory().constructParametricType(collectionClass, elementClasses);
   return mapper.readValue(jsonStr, javaType);
}

---

1. 
/**
* 該特性允許parser可以識別"Not-a-Number" (NaN)標識集合作爲一個合法的浮點數。 例如： allows (tokens are quoted contents, not including
* quotes):
* <ul>
* <li>"INF" (for positive infinity), as well as alias of "Infinity"
* <li>"-INF" (for negative infinity), alias "-Infinity"
* <li>"NaN" (for other not-a-numbers, like result of division by zero)
* </ul>
*/
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