Jackson - Exemples de modèle d'arbre
Dans Jackson, nous pouvons utiliserTree Model pour représenter la structure JSON et effectuer les opérations CRUD viaJsonNode, similaire à l'arborescence DOM XML. Ce JacksonTree Model est utile, en particulier dans les cas où une structure JSON ne correspond pas bien aux classes Java.
pom.xml
com.fasterxml.jackson.core jackson-databind 2.9.8
P.S Tested with Jackson 2.9.8
1. Traverser JSON
1.1 Jackson TreeModel example to traversing below JSON file:
C:\projects\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 Process JsonNode one by one.
JacksonTreeModelExample1.java
package com.example;
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 java.io.File;
import java.io.IOException;
public class JacksonTreeModelExample1 {
private static final ObjectMapper mapper = new ObjectMapper();
public static void main(String[] args) {
try {
JsonNode root = mapper.readTree(new File("c:\\projects\\user.json"));
// Get id
long id = root.path("id").asLong();
System.out.println("id : " + id);
// Get Name
JsonNode nameNode = root.path("name");
if (!nameNode.isMissingNode()) { // if "name" node is exist
System.out.println("firstName : " + nameNode.path("first").asText());
System.out.println("middleName : " + nameNode.path("middle").asText());
System.out.println("lastName : " + nameNode.path("last").asText());
}
// Get Contact
JsonNode contactNode = root.path("contact");
if (contactNode.isArray()) {
System.out.println("Is this node an Array? " + contactNode.isArray());
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();
}
}
}
Sortie
id : 1 firstName : Yong middleName : lastName : Mook Kim Is this node an Array? true type : phone/home ref : 111-111-1234 type : phone/work ref : 222-222-2222
2. Traversée du tableau JSON
2.1 JSON file, top level represents an Array.
c:\projects\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 The concept is same, just loop the JSON array :
JsonNode rootArray = mapper.readTree(new File("c:\\projects\\user2.json"));
for (JsonNode root : rootArray) {
// get node like the above example 1
}
JacksonTreeModelExample2.java
package com.example;
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 java.io.File;
import java.io.IOException;
public class JacksonTreeModelExample2 {
private static final ObjectMapper mapper = new ObjectMapper();
public static void main(String[] args) {
try {
JsonNode rootArray = mapper.readTree(new File("c:\\projects\\user2.json"));
for (JsonNode root : rootArray) {
// Get id
long id = root.path("id").asLong();
System.out.println("id : " + id);
// Get Name
JsonNode nameNode = root.path("name");
if (!nameNode.isMissingNode()) { // if "name" node is exist
System.out.println("firstName : " + nameNode.path("first").asText());
System.out.println("middleName : " + nameNode.path("middle").asText());
System.out.println("lastName : " + nameNode.path("last").asText());
}
// Get Contact
JsonNode contactNode = root.path("contact");
if (contactNode.isArray()) {
System.out.println("Is this node an Array? " + contactNode.isArray());
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();
}
}
}
Sortie
id : 1 firstName : Yong middleName : lastName : Mook Kim Is this node an Array? true type : phone/home ref : 111-111-1234 type : phone/work ref : 222-222-2222 id : 2 firstName : Yong middleName : lastName : Zi Lap Is this node an Array? true type : phone/home ref : 333-333-1234 type : phone/work ref : 444-444-4444
3. Exemple de modèle d'arbre CRUD
3.1 This example, show you how to create, update and remove JSON nodes, to modify JSON node, we need to convert it to ObjectNode. Lisez les commentaires pour s'expliquer d'eux-mêmes.
JacksonTreeModelExample3.java
package com.example;
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;
import java.io.File;
import java.io.IOException;
public class JacksonTreeModelExample3 {
private static final ObjectMapper mapper = new ObjectMapper();
public static void main(String[] args) {
try {
JsonNode root = mapper.readTree(new File("c:\\projects\\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
ObjectNode nameNode = (ObjectNode) root.path("name");
if ("".equals(nameNode.path("middle").asText())) {
nameNode.put("middle", "M");
}
// 3. Create a new field in nameNode
nameNode.put("nickname", "example");
// 4. Remove last field in nameNode
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().objectNode();
game1.put("name", "Fall Out 4");
game1.put("price", 49.9);
ObjectNode game2 = mapper.createObjectNode().objectNode();
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();
}
}
}
Sortie
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" : "example"
},
"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
} ]
}