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https://www.mkyong.com/java/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 an XML DOM tree.
P.S Tested with Jackson 2.6.3
1.1 JSON file, top level represents an object.
{ "id" : 1, "name" : { "first" : "Yong", "last" : "Mook Kim" }, "contact" : [ { "type" : "phone/home", "ref" : "111-111-1234"}, { "type" : "phone/work", "ref" : "222-222-2222"} ]} 1.2 Using Jackson TreeModel (JsonNode) to parse and traversal above JSON file. Read comments for self-explanatory.
package com.mkyong.json;import java.io.File;import java.io.IOException;import com.fasterxml.jackson.core.JsonGenerationException;import com.fasterxml.jackson.databind.JsonMappingException;import com.fasterxml.jackson.databind.JsonNode;import com.fasterxml.jackson.databind.ObjectMapper;public class JacksonTreeModel { public static void main(String[] args) { try { long id; String firstName = ""; String middleName = ""; String lastName = ""; ObjectMapper mapper = new ObjectMapper(); JsonNode root = mapper.readTree(new File("c:\\user.json")); // Get id id = root.path("id").asLong(); System.out.println("id : " + id); // Get Name JsonNode nameNode = root.path("name"); if (nameNode.isMissingNode()) { // if "name" node is missing } else { firstName = nameNode.path("first").asText(); // missing node, just return empty string middleName = nameNode.path("middle").asText(); lastName = nameNode.path("last").asText(); System.out.println("firstName : " + firstName); System.out.println("middleName : " + middleName); System.out.println("lastName : " + lastName); } // Get Contact JsonNode contactNode = root.path("contact"); if (contactNode.isArray()) { // If this node an Arrray? } for (JsonNode node : contactNode) { String type = node.path("type").asText(); String ref = node.path("ref").asText(); System.out.println("type : " + type); System.out.println("ref : " + ref); } } catch (JsonGenerationException e) { e.printStackTrace(); } catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } }} Output
id : 1firstName : YongmiddleName :lastName : Mook Kimtype : phone/homeref : 111-111-1234type : phone/workref : 222-222-2222
2.1 JSON file, top level represents an Array.
[ { "id" : 1, "name" : { "first" : "Yong", "last" : "Mook Kim" }, "contact" : [ { "type" : "phone/home", "ref" : "111-111-1234"}, { "type" : "phone/work", "ref" : "222-222-2222"} ]},{ "id" : 2, "name" : { "first" : "Yong", "last" : "Zi Lap" }, "contact" : [ { "type" : "phone/home", "ref" : "333-333-1234"}, { "type" : "phone/work", "ref" : "444-444-4444"} ]}] 2.2 The concept is same, just loops the first node.
ObjectMapper mapper = new ObjectMapper();JsonNode rootArray = mapper.readTree(new File("c:\\user2.json"));for(JsonNode root : rootArray){ //refer example 1.2 above, same ways to process nodes} 3.1 This example, show you how to create, update and remove nodes (ObjectNode and ArrayNode). Read the comments for self-explanatory.
package com.mkyong.json;import java.io.File;import java.io.IOException;import com.fasterxml.jackson.core.JsonGenerationException;import com.fasterxml.jackson.databind.JsonMappingException;import com.fasterxml.jackson.databind.JsonNode;import com.fasterxml.jackson.databind.ObjectMapper;import com.fasterxml.jackson.databind.node.ArrayNode;import com.fasterxml.jackson.databind.node.ObjectNode;public class JacksonTreeModel { public static void main(String[] args) { try { ObjectMapper mapper = new ObjectMapper(); JsonNode root = mapper.readTree(new File("c:\\user.json")); String resultOriginal = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(root); System.out.println("Before Update " + resultOriginal); // 1. Update id to 1000 ((ObjectNode) root).put("id", 1000L); // 2. If middle name is empty , update to M JsonNode nameNode = root.path("name"); if ("".equals(nameNode.path("middle").asText())) { ((ObjectNode) nameNode).put("middle", "M"); } // 3. Create a new field in nameNode ((ObjectNode) nameNode).put("nickname", "mkyong"); // 4. Remove last field in nameNode ((ObjectNode) nameNode).remove("last"); // 5. Create a new ObjectNode and add to root ObjectNode positionNode = mapper.createObjectNode(); positionNode.put("name", "Developer"); positionNode.put("years", 10); ((ObjectNode) root).set("position", positionNode); // 6. Create a new ArrayNode and add to root ArrayNode gamesNode = mapper.createArrayNode(); ObjectNode game1 = mapper.createObjectNode(); game1.put("name", "Fall Out 4"); game1.put("price", 49.9); ObjectNode game2 = mapper.createObjectNode(); game2.put("name", "Dark Soul 3"); game2.put("price", 59.9); gamesNode.add(game1); gamesNode.add(game2); ((ObjectNode) root).set("games", gamesNode); // 7. Append a new Node to ArrayNode ObjectNode email = mapper.createObjectNode(); email.put("type", "email"); email.put("ref", "abc@mkyong.com"); JsonNode contactNode = root.path("contact"); ((ArrayNode) contactNode).add(email); String resultUpdate = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(root); System.out.println("After Update " + resultUpdate); } catch (JsonGenerationException e) { e.printStackTrace(); } catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } }} Output
Before Update { "id" : 1, "name" : { "first" : "Yong", "last" : "Mook Kim" }, "contact" : [ { "type" : "phone/home", "ref" : "111-111-1234" }, { "type" : "phone/work", "ref" : "222-222-2222" } ]}After Update { "id" : 1000, "name" : { "first" : "Yong", "middle" : "M", "nickname" : "mkyong" }, "contact" : [ { "type" : "phone/home", "ref" : "111-111-1234" }, { "type" : "phone/work", "ref" : "222-222-2222" }, { "type" : "email", "ref" : "abc@mkyong.com" } ], "position" : { "name" : "Developer", "years" : 10 }, "games" : [ { "name" : "Fall Out 4", "price" : 49.9 }, { "name" : "Dark Soul 3", "price" : 59.9 } ]} 转载地址：http://ejbsi.baihongyu.com/