Jackson JSON get node name from json-tree

Question

How can I receive the node names from a JSON tree using Jackson  The JSON-File looks something like this           node1  value1       node2  value2       node3             node3 1  value3 1           node3 2  value3 2            I have  JsonNode rootNode   mapper readTree fileReader     and need something like   for  JsonNode node   rootNode       if  node getName   equals  foo              bar         thanks

User · Answer

JsonNode root   mapper readTree json   root at   some-node   fields   forEachRemaining e - gt                                  System out println e getKey    ---   e getValue                    In one line Jackson 2

User · Answer

For Jackson 2   com fasterxml jackson   the methods are little bit different   Iterator lt Entry lt String  JsonNode gt  gt  nodes   rootNode get  foo   fields     while  nodes hasNext        Map Entry lt String  JsonNode gt  entry    Map Entry lt String  JsonNode gt   nodes next       logger info  key -- gt      entry getKey       value-- gt     entry getValue

User · Answer

fields   and fieldNames   both were not working for me  And I had to spend quite sometime to find a way to iterate over the keys  There are two ways by which it can be done   One is by converting it into a map  takes up more space    ObjectMapper mapper   new ObjectMapper    Map lt String  Object gt  result   mapper convertValue jsonNode  Map class   for  String key   result keySet          if key equals foo                   code here           Another  by using a String iterator   Iterator lt String gt  it   jsonNode getFieldNames    while  it hasNext          String key   it next        if  key equals foo                    code here

User · Answer

This answer applies to Jackson versions prior to 2   originally written for 1 8   See  SupunSameera s answer for a version that works with newer versions of Jackson     The JSON terms for  node name  is  key   Since JsonNode iterator   does not include keys  you need to iterate differently   for  Map Entry lt String  JsonNode gt  elt   rootNode fields          if   foo  equals elt getKey                      bar           If you only need to see the keys  you can simplify things a bit with JsonNode fieldNames     for  String key   rootNode fieldNames          if   foo  equals key                    bar             And if you just want to find the node with key  foo   you can access it directly  This will yield better performance  constant-time lookup  and cleaner clearer code than using a loop   JsonNode foo   rootNode get  foo    if  foo    null           frob that widget

User · Answer

Clarification Here   While this will work    JsonNode rootNode   objectMapper readTree file    Iterator lt Map Entry lt String  JsonNode gt  gt  fields   rootNode fields     while  fields hasNext          Map Entry lt String  JsonNode gt  entry   fields next        log info entry getKey           entry getValue         This will not   JsonNode rootNode   objectMapper readTree file    while  rootNode fields   hasNext          Map Entry lt String  JsonNode gt  entry   rootNode fields   next        log info entry getKey           entry getValue        So be careful to declare the Iterator as a variable and use that   Be sure to use the fasterxml library rather than codehaus

[java] Jackson JSON: get node name from json-tree

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