Jackson Tree Model Example

In Jackson, you can use “Tree Model” to represent JSON, and perform the read and write operations via “JsonNode“, it is similar to DOM tree for XML. See code snippet :

 ObjectMapper mapper = new ObjectMapper();
 
 BufferedReader fileReader = new BufferedReader(
  new FileReader("c:\\user.json"));
 JsonNode rootNode = mapper.readTree(fileReader);
 
 /*** read value from key "name" ***/
 JsonNode nameNode = rootNode.path("name");
 System.out.println(nameNode.getTextValue());

This time, we show you how to read the JSON string from “file.json” into a “Tree“, and also how to read and and update those values via JsonNode.

File : file.json

{
  "age" : 29,
  "messages" : [ "msg 1", "msg 2", "msg 3" ],
  "name" : "harit"
 }

See full example, it should be self-explanatory.

package com;
 
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.Iterator;
 
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonNode;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.node.ObjectNode;
 
public class JacksonTreeNodeExample {
 public static void main(String[] args) {
 
  ObjectMapper mapper = new ObjectMapper();
 
  try {
 
   BufferedReader fileReader = new BufferedReader(
    new FileReader("c:\\user.json"));
   JsonNode rootNode = mapper.readTree(fileReader);
 
   /*** read ***/
   JsonNode nameNode = rootNode.path("name");
   System.out.println(nameNode.getTextValue());
 
   JsonNode ageNode = rootNode.path("age");
   System.out.println(ageNode.getIntValue());
 
   JsonNode msgNode = rootNode.path("messages");
   Iterator<JsonNode> ite = msgNode.getElements();
 
   while (ite.hasNext()) {
    JsonNode temp = ite.next();
    System.out.println(temp.getTextValue());
 
   }
 
   /*** update ***/
   ((ObjectNode)rootNode).put("nickname", "new nickname");
   ((ObjectNode)rootNode).put("name", "updated name");
   ((ObjectNode)rootNode).remove("age");
 
   mapper.writeValue(new File("c:\\user.json"), rootNode);
 
  } catch (JsonGenerationException e) {
 
   e.printStackTrace();
 
  } catch (JsonMappingException e) {
 
   e.printStackTrace();
 
  } catch (IOException e) {
 
   e.printStackTrace();
 
  }
 
 }
 
}

Output

harit
29
msg 1
msg 2
msg 3

And the file “c:\\file.json” is updated with following new content :

{
  "messages" : [ "msg 1", "msg 2", "msg 3" ],
  "name" : "updated name",
  "nickname" : "new nickname"
}