Jackson - 树到 JSON

  • 简述

    在此示例中,我们使用 JsonNode 创建了一个树,并将其写入 json 文件并回读。
    C:\>Jackson_WORKSPACE 中创建一个名为“JacksonTester”的 Java 类文件。
    文件: 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 以查看结果:
    
    C:\Jackson_WORKSPACE>java JacksonTester
    
    验证输出
    
    Name: Mahesh Kumar
    Age: 21
    Verified: No
    Marks: [ 100 90 85 ]