用 Jackson 來處理 JSON

Jackson 是一個 Java 用來處理 JSON 格式數據的類庫，性能很是好。

首先建立一個User對象類 (User.java)

package com.sivalabs.json;



import java.util.Date;



public class User {

 private String userId;

 private UserName userName;

 private Date dob;



 @Override

 public String toString(){

  return "User [dob=" + dob + ", userId=" + userId + ", userName="+ userName + "]";
 }

 //setters and getters



}

UserName.java

package com.sivalabs.json;



public class UserName {

 private String firstname;

 private String middlename;

 private String lastname;



 @Override

 public String toString()

 {

  return "UserName [firstname=" + firstname + 

  ", lastname=" + lastname+ 

  ", middlename=" + middlename + "]";

 }

 //setters and getters

}

[Java]代碼

//接下來建立User實例，並生成JSON數據

ObjectMapper mapper = new ObjectMapper();



UserName userName = new UserName();

userName.setFirstname("Katamreddy");

userName.setMiddlename("Siva");

userName.setLastname("PrasadReddy");



User user = new User();

user.setUserId("1");

user.setUserName(userName);

user.setDob(new Date());



Writer strWriter = new StringWriter();

mapper.writeValue(strWriter, user);

String userDataJSON = strWriter.toString();

System.out.println(userDataJSON);

執行結果

{

"userId":"1",

"userName":

{

"firstname":"Katamreddy",

"middlename":"Siva",

"lastname":"PrasadReddy"

},

"dob":1300878089906

}

接下來進行JSON到Java對象的轉換

String userDataJSON = 

"{\"userId\":\"100\",\"userName\":{\"firstname\":\"K\""+

",\"middlename\":\"Siva\",\"lastname\":\"Prasad\"},\"dob\":1300878089906}";

User userFromJSON = mapper.readValue(userDataJSON, User.class);

System.out.println(userFromJSON);

時間的格式化處理

DateFormat dateFormat = new SimpleDateFormat("MM-dd-yyyy");

SerializationConfig serConfig = mapper.getSerializationConfig();

serConfig.setDateFormat(dateFormat);

DeserializationConfig deserializationConfig = mapper.getDeserializationConfig();

deserializationConfig.setDateFormat(dateFormat);

mapper.configure(SerializationConfig.Feature.WRITE_DATES_AS_TIMESTAMPS, false);

[Java]代碼

//從文件中讀取JSON數據

User user = mapper.readValue(new File("user.json"), User.class);