Jackson Treeモデルの例

ジャクソンでは、 "Tree Model"を使ってJSONを表現し、 "JsonNode"を使って読み書き操作を実行できます。これはXML DOMツリーに似ています。

P.S Jackson 2.6.3 でテスト済み

1. TreeModelのトラバースの例

1.1 JSONファイル、トップレベルはオブジェクトを表します。

c:\\ user.json

{
  "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 Jackson TreeModel( JsonNode )を使用して、JSONファイルを解析して走査します。コメントは読んでください。

JacksonTreeModel.java

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();
        }
    }

}

出力

id : 1
firstName : Yong
middleName :
lastName : Mook Kim
type : phone/home
ref : 111-111-1234
type : phone/work
ref : 222-222-2222

2. TreeModelのトラバースの例 - 第2部

2.1 JSONファイル、トップレベルは配列を表します。

c:\\ user2.json

…​.[ { "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概念は同じで、最初のノードをループするだけです。

    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. TreeModelのCRUDの例

3.1この例題では、ノード( ObjectNode`と ArrayNode`)を作成、更新、削除する方法を示します。コメントを読み、自明です。

JacksonTreeModel.java

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", "[email protected]");

            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();
        }
    }

}

出力

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" : "[email protected]"
  }],
  "position" : {
    "name" : "Developer",
    "years" : 10
  },
  "games" :[{
    "name" : "Fall Out 4",
    "price" : 49.9
  }, {
    "name" : "Dark Soul 3",
    "price" : 59.9
  }]}

参考文献

ジャクソンによる処理:方法#3/3:ツリートラバーサル]。 http://stackoverflow.com/questions/23271699/adding-property-to-json-using-jackson [StackOverflow

: Adding property to JSON using Jackson]. link://java/jackson-2-convert-java-object-to-from-json/[Jackson 2 –

JSONとオブジェクトの変換]

jackson json リンク://タグ/ツリーモデル/[ツリーモデル]

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