How to convert a JSON string to a Map String String with Jackson JSON

Question

I m trying to do something like this but it doesn t work   Map lt String  String gt  propertyMap   new HashMap lt String  String gt      propertyMap   JacksonUtils fromJSON properties  Map class     But the IDE says       Unchecked assignment Map to Map lt String String gt    What s the right way to do this  I m only using Jackson because that s what is already available in the project  is there a native Java way of converting to from JSON   In PHP I would simply json decode  str  and I d get back an array  I need basically the same thing here

User · Answer

Warning you get is done by compiler  not by library  or utility method    Simplest way using Jackson directly would be   HashMap lt String Object gt  props      src is a File  InputStream  String or such props   new ObjectMapper   readValue src  new TypeReference lt HashMap lt String Object gt  gt            or  props    HashMap lt String Object gt   new ObjectMapper   readValue src  HashMap class      or even just   SuppressWarnings  unchecked      suppresses typed untype mismatch warnings  which is harmless props   new ObjectMapper   readValue src  HashMap class     Utility method you call probably just does something similar to this

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JavaType javaType   objectMapper getTypeFactory   constructParameterizedType Map class  Key class  Value class   Map lt Key  Value gt  map objectMapper readValue jsonStr  javaType     i think this will solve your problem

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Converting from String to JSON Map   Map lt String String gt  map   new HashMap lt String String gt      ObjectMapper mapper   new ObjectMapper     map   mapper readValue string  HashMap class

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just wanted to give a Kotlin answer  val propertyMap   objectMapper readValue lt Map lt String String gt  gt  properties  object   TypeReference lt Map lt String  String gt  gt

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Here is the generic solution to this problem   public static  lt K extends Object  V extends Object gt  Map lt K  V gt  getJsonAsMap String json  K key  V value        try         ObjectMapper mapper   new ObjectMapper          TypeReference lt Map lt K  V gt  gt  typeRef   new TypeReference lt Map lt K  V gt  gt                     return mapper readValue json  typeRef         catch  Exception e          throw new RuntimeException  Couldnt parse json     json  e               Hope someday somebody would think to create a util method to convert to any Key value type of Map hence this answer

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Try TypeFactory   Here s the code for Jackson JSON  2 8 4    Map lt String  String gt  result  ObjectMapper mapper  TypeFactory factory  MapType type   factory   TypeFactory defaultInstance    type      factory constructMapType HashMap class  String class  String class   mapper    new ObjectMapper    result    mapper readValue data  type     Here s the code for an older version of Jackson JSON   Map lt String  String gt  result   new ObjectMapper   readValue      data  TypeFactory mapType HashMap class  String class  String class

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ObjectReader reader   new ObjectMapper   readerFor Map class    Map lt String  String gt  map   reader readValue     foo     val         Note that reader instance is Thread Safe

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Using Google s Gson  Why not use Google s Gson as mentioned in here   Very straight forward and did the job for me   HashMap lt String String gt  map   new Gson   fromJson  yourJsonString  new TypeToken lt HashMap lt String  String gt  gt      getType

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The following works for me   Map lt String  String gt  propertyMap   getJsonAsMap json     where getJsonAsMap is defined like so   public HashMap lt String  String gt  getJsonAsMap String json        try               ObjectMapper mapper   new ObjectMapper            TypeReference lt Map lt String String gt  gt  typeRef   new TypeReference lt Map lt String String gt  gt                HashMap lt String  String gt  result   mapper readValue json  typeRef            return result            catch  Exception e                throw new RuntimeException  Couldnt parse json     json  e             Note that this will fail if you have child objects in your json  because they re not a String  they re another HashMap   but will work if your json is a key value list of properties like so          client id    my super id        exp   1481918304       iat    1450382274        url    http   www example com

User · Answer

Update Sept 2020  Although my original answer here  from many years ago  seems to be helpful and is still getting upvotes  I now use the GSON library from Google  which I find to be more intuitive  I ve got the following code  public void testJackson   throws IOException         ObjectMapper mapper   new ObjectMapper         File from   new File  quot albumnList txt quot         TypeReference lt HashMap lt String Object gt  gt  typeRef                new TypeReference lt HashMap lt String Object gt  gt             HashMap lt String Object gt  o   mapper readValue from  typeRef        System out println  quot Got  quot    o          It s reading from a file  but mapper readValue   will also accept an InputStream and you can obtain an InputStream from a string by using the following  new ByteArrayInputStream astring getBytes  quot UTF-8 quot       There s a bit more explanation about the mapper on my blog

[java] How to convert a JSON string to a Map<String, String> with Jackson JSON

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