Read json file with multiple objects into a map java

Question

Note: Before posting this here, I spent a chunk of time trying to look for a solution about this here, but couldn't find any.

I have this JSON file that contains multiple json objects that I want to read into a map, each object is of the format {"key1":"value1", "key2":"value2"}, I tried

Map<String, String> map = MAPPER.readValue(fixture("fixtures/file_name.json"), new TypeReference<Map<String, String>>() {});

as that worked for reading a file into a map of map of list (Map<String, Map<String, List<String>>>). Is there something that should be different?

My .json file looks like

[
   {"key1":"value1_1", "key2":"value2_1"},
   {"key1":"value1_2", "key2":"value2_2"},
   ...
]

I have also another json file that I want to read into a map, that looks like

[
   "key1": {
       "key1_1": [
           {"key1_1_1":"value1", "key1_1_2":"value2"},
           ...
       ],
       ...
    },
    "key2":<int>,
    "key3":{
        "key3_1":[],
        ...
    },
    ...
    "key_n":<string>,
    ...
]

Can you help me map those files correctly, without writing too many lines of code?

Coder · Accepted Answer · 2017-03-03 16:00:22Z

1

As you are handling different cases of nested objects varying from Strings to JsonArrays it would be good to implement your map as Map<String, Object>.

Follow the below implementation,

ObjectMapper mapper = new ObjectMapper();
MapType type = mapper.getTypeFactory().constructMapType(
    Map.class, String.class, Object.class);
Map<String, Object> data = mapper.readValue(jsonString, type);

Here I am reading the JSON as a string. You can change your implementation to accommodate file reading as well.

answered Mar 3, 2017 at 16:00

Coder

2,2391 gold badge20 silver badges21 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

mupierrix Over a year ago

these classes you are using to create the mapper are in which import? I am using the Jackson import, but I am getting this error

com.fasterxml.jackson.databind.JsonMappingException: Can not find a (Map) Key deserializer for type [collection type; class java.util.List, contains [simple type, class java.lang.Object]]

Coder Over a year ago

These are the regular java imports. You might be doing something else wrong as there is no list implementation in my code here but you are trying to map from list. Can you share your code ?

mupierrix Over a year ago

Sorry @Coder, it's my mistake. There was a part I didn't remove. All is working fine now. Thank you.

Simon · Accepted Answer · 2017-03-03 13:28:46Z

0

I would suggest you to use the Jackson library.

Here is a mkyong tutorial

Just change the code to

Map map = mapper.readValue(new File("c:\\whatever.json"), Map.class);

edited Mar 3, 2017 at 13:28

answered Mar 3, 2017 at 13:23

Simon

6293 silver badges8 bronze badges

7 Comments

m0skit0 Over a year ago

Why are you using Windows paths in your answer?

Evgeny Veretennikov Over a year ago

@m0skit0 I guess, he did it, because mkyong did it in his tutorial

Simon Over a year ago

@m0skit0 I just changed the code in the tutorial to convert the json object to a map. The path can be any path. BTW, I am not sure why my answer got down voted.....

m0skit0 Over a year ago

Because you're using Windows paths which are really not standard and not even used in the question. I would actually remove it but I can't unless you edit your question. While you're at it, you can remove Windows paths.

Simon Over a year ago

@m0skit0 As I stated, this is just a copy of the tutorial, the reason why I left the path there is that I just want to make it more clear, which line I was modifying. To be honest, I don't think any dev would be confused by a windows path, since this is just a path and can be changed to anything.

|

Collectives™ on Stack Overflow

Read json file with multiple objects into a map java

2 Answers 2

3 Comments

7 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

7 Comments

Your Answer

Sign up or log in

Post as a guest

Related