Jackson - Tree 树到 JSON

在此示例中，我们使用 JsonNode 创建了一棵树，并将其写入 json 文件并读回。

在C:\>Jackson_WORKSPACE中创建一个名为JacksonTester的java类文件。

File: JacksonTester.java

import java.io.File;
import java.io.IOException;
import java.util.Iterator;

import com.fasterxml.jackson.core.JsonParseException;
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 JacksonTester {
   public static void main(String args[]){
      JacksonTester tester = new JacksonTester();
      try {
         ObjectMapper mapper = new ObjectMapper();

         JsonNode rootNode = mapper.createObjectNode();
         JsonNode marksNode = mapper.createArrayNode();
         ((ArrayNode)marksNode).add(100);
         ((ArrayNode)marksNode).add(90);
         ((ArrayNode)marksNode).add(85);
         ((ObjectNode) rootNode).put("name", "Mahesh Kumar");
         ((ObjectNode) rootNode).put("age", 21);
         ((ObjectNode) rootNode).put("verified", false);
         ((ObjectNode) rootNode).put("marks",marksNode);

         mapper.writeValue(new File("student.json"), rootNode);

         rootNode = mapper.readTree(new File("student.json"));

         JsonNode nameNode = rootNode.path("name");
         System.out.println("Name: "+ nameNode.textValue());

         JsonNode ageNode = rootNode.path("age");
         System.out.println("Age: " + ageNode.intValue());

         JsonNode verifiedNode = rootNode.path("verified");
         System.out.println("Verified: " + (verifiedNode.booleanValue() ? "Yes":"No"));

         JsonNode marksNode1 = rootNode.path("marks");
         Iterator<JsonNode> iterator = marksNode1.elements();
         System.out.print("Marks: [ ");
         while (iterator.hasNext()) {
            JsonNode marks = iterator.next();
            System.out.print(marks.intValue() + " "); 
         }
         System.out.println("]");
      } catch (JsonParseException e) {
         e.printStackTrace();
      } catch (JsonMappingException e) {
         e.printStackTrace();
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

验证结果

使用javac编译器编译类，如下所示:

C:\Jackson_WORKSPACE>javac JacksonTester.java

现在运行 jacksonTester 查看结果:

C:\Jackson_WORKSPACE>java JacksonTester

验证输出

Name: Mahesh Kumar
Age: 21
Verified: No
Marks: [ 100 90 85 ]