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[英]Parse JSON object containing multiple nested objects without making class for each nested object
[英]Parse Json to object containing objects
我有以下代码与json,我从accuweather得到
{
"Headline":{
"EffectiveDate":"2019-07-29T07:00:00+06:00",
"EffectiveEpochDate":1564362000,
"Severity":3,
"Text":"The heat wave will continue through Friday",
"Category":"heat",
"EndDate":"2019-08-02T19:00:00+06:00",
"EndEpochDate":1564750800
},
"DailyForecasts":[
{
"Date":"2019-07-29T07:00:00+06:00",
"EpochDate":1564362000,
"Temperature":{
"Minimum":{
"Value":19.1,
"Unit":"C",
"UnitType":17
},
"Maximum":{
"Value":36.7,
"Unit":"C",
"UnitType":17
}
},
"Day":{
"Icon":30,
"IconPhrase":"Hot",
"HasPrecipitation":false
},
"Night":{
"Icon":35,
"IconPhrase":"Partly cloudy",
"HasPrecipitation":false
},
"Sources":[
"AccuWeather"
]
}
]
}
我尝试通过jackson将这个对象解析为POJO
public static void main( String[] args )
{
String x = "{\"Headline\":{\"EffectiveDate\":\"2019-07-29T07:00:00+06:00\",\"EffectiveEpochDate\":1564362000,\"Severity\":3,\"Text\":\"The heat wave will continue through Friday\",\"Category\":\"heat\",\"EndDate\":\"2019-08-02T19:00:00+06:00\",\"EndEpochDate\":1564750800},\"DailyForecasts\":[{\"Date\":\"2019-07-29T07:00:00+06:00\",\"EpochDate\":1564362000,\"Temperature\":{\"Minimum\":{\"Value\":19.1,\"Unit\":\"C\",\"UnitType\":17},\"Maximum\":{\"Value\":36.7,\"Unit\":\"C\",\"UnitType\":17}},\"Day\":{\"Icon\":30,\"IconPhrase\":\"Hot\",\"HasPrecipitation\":false},\"Night\":{\"Icon\":35,\"IconPhrase\":\"Partly cloudy\",\"HasPrecipitation\":false},\"Sources\":[\"AccuWeather\"]}]}";
ObjectMapper objectMapper = new ObjectMapper();
try {
Weather weather = objectMapper.readValue(x, Weather.class);
System.out.println(weather);
} catch (IOException e) {
e.printStackTrace();
}
}
我有json中指定的所有模型,如Headline
, DailyForecasts
数组, Temperature
包含TemperatureItems
(在json中命名为minimum和maximum)等等,所有模型都有私有字段和公共构造函数,getter和setter。 但是我没有一些字段,因为我想省略它们(Day,Night,EpochDate,Source)。
当我运行程序时,我收到错误
com.fasterxml.jackson.databind.exc.InvalidDefinitionException:无法构造
test.models.weather.Weather
实例(没有test.models.weather.Weather
,如默认构造,存在):无法从Object值反序列化(没有基于委托或属性的Creator)
我也尝试过Gson
但它返回Null值的对象
难道我做错了什么? 还有另一种方法吗?
编辑 :这些是模型,@ LazerBass是对的,因为我首先没有包含默认构造函数,现在错误已经改变:
com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException:无法识别的字段“标题”(类test.models.weather.Weather),未标记为可忽略(2个已知属性:“标题”,“dailyForecasts”])
public class TemperatureItem {
public double value;
public String unit;
public String unitType;
public TemperatureItem() {
}
//Getters and setters
}
public class Temperature {
private TemperatureItem maximum;
private TemperatureItem minimum;
public Temperature(TemperatureItem maximum, TemperatureItem minimum) {
this.maximum = maximum;
this.minimum = minimum;
}
public Temperature() {
}
//Getters and setters
}
public class DailyForecasts {
private LocalDateTime date;
private Temperature temperature;
public DailyForecasts(LocalDateTime date, Temperature temperature) {
this.date = date;
this.temperature = temperature;
}
public DailyForecasts() {
}
//Getters and setters
}
public class Headline {
private LocalDateTime effectiveDate;
private int severity;
private String text;
private String category;
private LocalDateTime endDate;
public Headline() {
}
public Headline(LocalDateTime effectiveDate, Integer severity, String text, String category, LocalDateTime endDate) {
this.effectiveDate = effectiveDate;
this.severity = severity;
this.text = text;
this.category = category;
this.endDate = endDate;
}
//Getters and setters
}
public class Weather {
private Headline headline;
private DailyForecasts[] dailyForecasts;
public Weather() {
}
public Weather(Headline headline, DailyForecasts[] dailyForecasts) {
this.headline = headline;
this.dailyForecasts = dailyForecasts;
}
//Getters and setters
}
我发现,如果我将json字符串转换为小写,我可以得到一些值,虽然没有解析Array
和LocalDateTime
从异常消息判断我猜你的Weather
类正在使用无参数构造函数。 尝试添加一个。 例如
public class Weather {
public Weather() {
// no arg constructor needed for jackson
}
}
要生成Weather类及其对应的类,请使用以下链接并选择源类型为json。 它将根据json字符串生成所需的类。
http://www.jsonschema2pojo.org/
生成类后,可以使用@JsonIgnore注释不需要的字段。
当Jackson
失败时会出现“ 没有创建者,就像默认构造,存在 ”这样的消息,它需要你模型中每个POJO
类的默认的public
no-argument
构造函数。
当它失败并显示“ 无法识别的字段...未标记为可忽略的... ”之类的消息时,您需要禁用FAIL_ON_UNKNOWN_PROPERTIES功能。
也可以看看:
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