ackson框架 json字串、map、java物件的轉換例子

先下載框架jar包:

下面是一些例子：

package jackson;

import java.io.File;
import java.io.FileInputStream;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import org.codehaus.jackson.JsonEncoding;
import org.codehaus.jackson.JsonFactory;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.JsonNode;
import org.codehaus.jackson.JsonParser;
import org.codehaus.jackson.JsonToken;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.node.ArrayNode;
import org.codehaus.jackson.node.ObjectNode;
import org.junit.Test;

public class Testjackson {
   
//@Test
public void test1(){
try{

ObjectMapper mapper = new ObjectMapper();
    String jsonString = "{\"name\":\"Mahesh\", \"age\":21}";

     //json字串轉物件
     Student student = mapper.readValue(jsonString, Student.class);
     System.out.println(student);
        
     //物件轉json字串
     jsonString = mapper.writeValueAsString(student);
     System.out.println(jsonString);
     
     //json字串轉為Map物件
     Map map=mapper.readValue(jsonString, Map.class);
     System.out.println(map);
     
}catch(Exception e) {
e.printStackTrace();
}
}

//@Test
public void test2(){
try{

Student student = new Student();
        student.setAge(10);
        student.setName("Mahesh");
        ObjectMapper mapper = new ObjectMapper(); 
        //將Java物件序列化到一個JSON檔案
        mapper.writeValue(new File("d:/student.json"), student);
        System.out.println("d:/student.json檔案生成結束");
        
        //讀取JSON檔案轉換為物件
        Student student2 = mapper.readValue(new File("student.json"), Student.class);
        System.out.println(student2);
}catch(Exception e) {
e.printStackTrace();
}
}

//@Test
public void test3(){
try {
   ObjectMapper mapper = new ObjectMapper();
           Map<String,Object> studentDataMap = new HashMap<String,Object>(); 
           int[] marks = {1,2,3};

           Student student = new Student();
           student.setAge(10);
           student.setName("Mahesh");
           
           studentDataMap.put("student", student);
           studentDataMap.put("name", "Mahesh Kumar");   
           studentDataMap.put("verified", Boolean.FALSE);
           studentDataMap.put("marks", marks);
                
           //Map轉換為joson檔案
           mapper.writeValue(new File("d:/student2.json"), studentDataMap);
           //result student.json
//{ 
           //   "student":{"name":"Mahesh","age":10},
           //   "marks":[1,2,3],
           //   "verified":false,
           //   "name":"Mahesh Kumar"
           //}
           //json檔案轉換為map
           studentDataMap = mapper.readValue(new File("d:/student2.json"), Map.class);

           System.out.println(studentDataMap.get("student"));
           System.out.println(studentDataMap.get("name"));
           System.out.println(studentDataMap.get("verified"));
           System.out.println(studentDataMap.get("marks"));
           
} catch (Exception e) {
e.printStackTrace();
}
}
//@Test//樹遍歷
public void test4(){
try {
    ObjectMapper mapper = new ObjectMapper();
        String jsonString = "{\"name\":\"Mahesh Kumar\", \"age\":21,\"verified\":false,\"marks\": [100,90,85]}";
        JsonNode rootNode = mapper.readTree(jsonString);

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

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

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

        JsonNode marksNode = rootNode.path("marks");
        Iterator<JsonNode> iterator = marksNode.getElements();
        System.out.print("Marks: [ ");
        while (iterator.hasNext()) {
           JsonNode marks = iterator.next();
           System.out.print(marks.getIntValue() + " "); 
        }
        System.out.println("]");
} catch (Exception e) {
e.printStackTrace();
}
}
//@Test//樹到JSON轉換
public void test5(){
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("d:/student3.json"), rootNode);
            
        rootNode = mapper.readTree(new FileInputStream("student.json"));
       
        JsonNode nameNode = rootNode.path("name");
        System.out.println("Name: "+ nameNode.getTextValue());

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

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

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

//@Test//樹到java物件
public void test6(){
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 FileInputStream("student.json"));

        Student2 student = mapper.treeToValue(rootNode, Student2.class);

        System.out.println("Name: "+ student.getName());
        System.out.println("Age: " + student.getAge());
        System.out.println("Verified: " + (student.isVerified() ? "Yes":"No"));
        System.out.println("Marks: "+Arrays.toString(student.getMarks()));
} catch (Exception e) {
e.printStackTrace();
}
}

@Test//Jackson流式API
public void test7(){
try {
JsonFactory jasonFactory = new JsonFactory();

        JsonGenerator jsonGenerator = jasonFactory.createJsonGenerator(new File("d:/student7.json"),
        JsonEncoding.UTF8);
        jsonGenerator.writeStartObject();
        jsonGenerator.writeStringField("name", "Mahesh Kumar"); 
        jsonGenerator.writeNumberField("age", 21);
        jsonGenerator.writeBooleanField("verified", false); 
        jsonGenerator.writeFieldName("marks"); 
        jsonGenerator.writeStartArray(); 
        jsonGenerator.writeNumber(100); 
        jsonGenerator.writeNumber(90); 
        jsonGenerator.writeNumber(85); 
        jsonGenerator.writeEndArray(); 
        jsonGenerator.writeEndObject(); 
        jsonGenerator.close();        

        //result student.json
        //{ 
        //   "name":"Mahesh Kumar",
        //   "age":21,
        //   "verified":false,
        //   "marks":[100,90,85]
        //}
        ObjectMapper mapper = new ObjectMapper();
        Map<String,Object> dataMap = mapper.readValue(new File("d:/student7.json"), Map.class);

        System.out.println(dataMap.get("name"));
        System.out.println(dataMap.get("age"));
        System.out.println(dataMap.get("verified"));
        System.out.println(dataMap.get("marks"));
} catch (Exception e) {
e.printStackTrace();
}
}

@Test//使用JsonParser 讀取JSON
public void test8(){
try {

JsonFactory jasonFactory = new JsonFactory();

        JsonGenerator jsonGenerator = jasonFactory.createJsonGenerator(new File(
           "student.json"), JsonEncoding.UTF8);
        jsonGenerator.writeStartObject();
        jsonGenerator.writeStringField("name", "Mahesh Kumar"); 
        jsonGenerator.writeNumberField("age", 21);
        jsonGenerator.writeBooleanField("verified", false); 
        jsonGenerator.writeFieldName("marks"); 
        jsonGenerator.writeStartArray(); 
        jsonGenerator.writeNumber(100); 
        jsonGenerator.writeNumber(90); 
        jsonGenerator.writeNumber(85); 
        jsonGenerator.writeEndArray(); 
        jsonGenerator.writeEndObject(); 
        jsonGenerator.close();        

        //result student.json
        //{ 
        //   "name":"Mahesh Kumar",
        //   "age":21,
        //   "verified":false,
        //   "marks":[100,90,85]
        //}

        JsonParser jsonParser = jasonFactory.createJsonParser(new File("d:/student7.json"));
        while (jsonParser.nextToken() != JsonToken.END_OBJECT) {
           //get the current token
           String fieldname = jsonParser.getCurrentName();
           if ("name".equals(fieldname)) {
              //move to next token
              jsonParser.nextToken();
              System.out.println(jsonParser.getText());          
           }
           if("age".equals(fieldname)){
              //move to next token
              jsonParser.nextToken();
              System.out.println(jsonParser.getNumberValue());          
           }
           if("verified".equals(fieldname)){
              //move to next token
              jsonParser.nextToken();
              System.out.println(jsonParser.getBooleanValue());          
           }
           if("marks".equals(fieldname)){
              //move to [ 
              jsonParser.nextToken();
              // loop till token equal to "]"
              while (jsonParser.nextToken() != JsonToken.END_ARRAY) {
                 System.out.println(jsonParser.getNumberValue()); 
              }
           }
        }
} catch (Exception e) {
e.printStackTrace();
}
}
}

class Student2 {
  String name;
  int age;
  boolean verified;
  int[] marks;
  public String getName() {
     return name;
  }
  public void setName(String name) {
     this.name = name;
  }
  public int getAge() {
     return age;
  }
  public void setAge(int age) {
     this.age = age;
  }
  public boolean isVerified() {
     return verified;
  }
  public void setVerified(boolean verified) {
     this.verified = verified;
  }
  public int[] getMarks() {
     return marks;
  }
  public void setMarks(int[] marks) {
     this.marks = marks;
  }
}
--------------------- 
作者：GavinYCF 
來源：CSDN 
轉自原文：https://blog.csdn.net/yucaifu1989/article/details/46637005