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]
