将JSON记录转换为LinkedHashMap< String,String>使用Jackson API [英] Convert JSON record to LinkedHashMap<String,String> using Jackson API
问题描述
我有一个JSON文件(它包含JSON对象数组.)
我试图逐个对象地阅读它.
我需要将每个对象都转换为键和值均为字符串的LinkedHashMap<String,String>
.请注意,即使JSON对象包含非字符串值(Integer/Boolean
),我也希望我的LinkedHashMap
包含字符串.
I have a JSON file(it contains an array of JSON objects.)
I am trying to read it object by object.
Each object I need to convert it to a LinkedHashMap<String,String>
where both the key and value are strings. Note that even if the JSON objects contain a non-string value(Integer/Boolean
), I want my LinkedHashMap
to contain a string.
这是我的JSON文件(films.json
):
This is my JSON file (films.json
):
[
{
"name": "Fight Club",
"year": 1999,
}
]
现在,它有1个对象.我想将其转换为LinkedHashMap<String,String>
.
Now, this has 1 object. I want to convert it to a LinkedHashMap<String,String>
.
因此对于上面的示例,我的LinkedHashMap
应该包含(对于第一个JSON对象):
So for the above example, my LinkedHashMap
should contain(for the 1st JSON object) :
名称"; :"Fight CLub"
"name" : "Fight CLub"
年" :"1999"
"year" : "1999"
请注意年份在LinkedHashMap
中而不是Integer
中是String
.
Notice how the year is String
in the LinkedHashMap
and not Integer
.
这是我尝试过的.
Map<String, Object> myLinkedHashMap;
JsonParser jsonParser = new JsonFactory().createParser(new File("films.json"));
jsonParser = new JsonFactory().createParser(new File(filePath));
jsonParser.nextToken();
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new JavaTimeModule());
mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
while(jsonParser.nextToken() != JsonToken.END_ARRAY){
myLinkedHashMap = mapper.readValue(jsonParser, LinkedHashMap.class);
}
变量myLinkedHashMap
将包含我的JSON文件中对象的键/值对.
The variable myLinkedHashMap
will contain a key/value pair for an object in my JSON file.
但是问题在于,对于JSON文件的年份",我在LinkedHashMap中获取了Integer,因为JSON文件还包含Integer.
But the problem is that for 'year' of the JSON file, I am getting Integer in the LinkedHashMap as the JSON file also contains Integer.
相反,我希望将Integer
用作LinkedHashMap
中的String
.
Instead, I want the Integer
as String
in the LinkedHashMap
.
请帮助我在LinkedHashMap
中获取String
,而不是Integer
.
Please help me get String
in the LinkedHashMap
instead of Integer
.
注意:该解决方案也应该对其他数据类型通用.
Note: The solution should be generic to other data types also.
因此,如果JSON对象包含布尔值true
,则我的LinkedHashMap
应该包含"true"
.
So if the JSON object contains boolean true
, then my LinkedHashMap
should contain "true"
.
推荐答案
您可以使用TypeFactory
和constructMapType
方法构造地图类型,以确切地说明readValue
方法中您需要什么.参见以下示例:
You can construct map type using TypeFactory
and constructMapType
method to tell exactly what do you need from readValue
method. See below example:
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.type.MapType;
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
import org.springframework.util.Assert;
import java.io.File;
import java.util.LinkedHashMap;
public class JsonMapApp {
public static void main(String[] args) throws Exception {
File jsonFile = new File("./resource/test.json").getAbsoluteFile();
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new JavaTimeModule());
mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
JsonParser jsonParser = mapper.getFactory().createParser(jsonFile);
jsonParser.nextToken();
MapType mapType = mapper.getTypeFactory().constructMapType(LinkedHashMap.class, String.class, String.class);
while (jsonParser.nextToken() != JsonToken.END_ARRAY) {
LinkedHashMap<String, String> map = mapper.readValue(jsonParser, mapType);
map.forEach((k, v) -> {
Assert.isInstanceOf(String.class, v);
System.out.println(k + " -> " + v + " (" + v.getClass().getName() + ")");
});
}
}
}
上面的代码显示:
name -> Fight Club (java.lang.String)
year -> 1999 (java.lang.String)
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