Google Gson 使用简介-白红宇

Google Gson 使用简介

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发布时间：2019-06-19

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下面的例子中我们示例如何将一个数据转换成 json 串，并使用 Gson.toJson() 方法将数组序列化为 JSON，以及Gson.fromJson() 方法将 JSON 串反序列化为 java 数组。

import com.google.gson.Gson;public class ArrayToJson {    public static void main(String[] args) {        int[] numbers = {1, 1, 2, 3, 5, 8, 13};        String[] days = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};        //        // Create a new instance of Gson        //        Gson gson = new Gson();        //        // Convert numbers array into JSON string.        //        String numbersJson = gson.toJson(numbers);        //        // Convert strings array into JSON string        //        String daysJson = gson.toJson(days);        System.out.println("numbersJson = " + numbersJson);        System.out.println("daysJson = " + daysJson);        //        // Convert from JSON string to a primitive array of int.        //        int[] fibonacci = gson.fromJson(numbersJson, int[].class);        for (int i = 0; i < fibonacci.length; i++) {            System.out.print(fibonacci[i] + " ");        }        System.out.println("");        //        // Convert from JSON string to a string array.        //        String[] weekDays = gson.fromJson(daysJson, String[].class);        for (int i = 0; i < weekDays.length; i++) {            System.out.print(weekDays[i] + " ");        }        System.out.println("");        //        // Converting multidimensional array into JSON        //        int[][] data = {
   {1, 2, 3}, {3, 4, 5}, {4, 5, 6}};        String json = gson.toJson(data);        System.out.println("Data = " + json);        //        // Convert JSON string into multidimensional array of int.        //        int[][] dataMap = gson.fromJson(json, int[][].class);        for (int i = 0; i < data.length; i++) {            for (int j = 0; j < data[i].length; j++) {                System.out.print(data[i][j] + " ");            }            System.out.println("");        }    }}

以下是输出结果：

numbersJson = [1,1,2,3,5,8,13]daysJson = ["Sun","Mon","Tue","Wed","Thu","Fri","Sat"]1 1 2 3 5 8 13 Sun Mon Tue Wed Thu Fri Sat Data = [[1,2,3],[3,4,5],[4,5,6]]1 2 3 3 4 5

如何将集合转化为 json 串？

下面的例子中我们示例如何将Java集合转换为符合 json 规则的字符串。

import java.util.Date;public class Student {    private String name;    private String address;    private Date dateOfBirth;    public Student() {    }    public Student(String name, String address, Date dateOfBirth) {        this.name = name;        this.address = address;        this.dateOfBirth = dateOfBirth;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public String getAddress() {        return address;    }    public void setAddress(String address) {        this.address = address;    }    public Date getDateOfBirth() {        return dateOfBirth;    }    public void setDateOfBirth(Date dateOfBirth) {        this.dateOfBirth = dateOfBirth;    }}

import com.google.gson.Gson;import com.google.gson.reflect.TypeToken;import java.lang.reflect.Type;import java.util.ArrayList;import java.util.Date;import java.util.List;public class CollectionToJson {    public static void main(String[] args) {        //        // Converts a collection of string object into JSON string.        //        List
     
       names = new ArrayList
      
       ();        names.add("Alice");        names.add("Bob");        names.add("Carol");        names.add("Mallory");        Gson gson = new Gson();        String jsonNames = gson.toJson(names);        System.out.println("jsonNames = " + jsonNames);        //        // Converts a collection Student object into JSON string        //        Student a = new Student("Alice", "Apple St", new Date(2000, 10, 1));        Student b = new Student("Bob", "Banana St", null);        Student c = new Student("Carol", "Grape St", new Date(2000, 5, 21));        Student d = new Student("Mallory", "Mango St", null);        List
       
         students = new ArrayList
        
         ();        students.add(a);        students.add(b);        students.add(c);        students.add(d);        gson = new Gson();        String jsonStudents = gson.toJson(students);        System.out.println("jsonStudents = " + jsonStudents);        //        // Converts JSON string into a collection of Student object.        //        Type type = new TypeToken
         
          
           >(){}.getType(); List
           
             studentList = gson.fromJson(jsonStudents, type); for (Student student : studentList) { System.out.println("student.getName() = " + student.getName()); } }}

以下是输出结果：

jsonNames = ["Alice","Bob","Carol","Mallory"]jsonStudents = [{"name":"Alice","address":"Apple St","dateOfBirth":"Nov 1, 3900 12:00:00 AM"},{"name":"Bob","address":"Banana St"},{"name":"Carol","address":"Grape St","dateOfBirth":"Jun 21, 3900 12:00:00 AM"},{"name":"Mallory","address":"Mango St"}]student.getName() = Alicestudent.getName() = Bobstudent.getName() = Carolstudent.getName() = Mallory

如何将Map转化为 json 串？

下面的例子中我们示例如何将java.util.Map转化成 json 串，然后再将 json 串转换为java.util.Map。

import com.google.gson.Gson;import com.google.gson.reflect.TypeToken;import java.lang.reflect.Type;import java.util.HashMap;import java.util.Map;public class MapToJson {    public static void main(String[] args) {        Map
     
       colours = new HashMap
      
       ();        colours.put("BLACK", "#000000");        colours.put("RED", "#FF0000");        colours.put("GREEN", "#008000");        colours.put("BLUE", "#0000FF");        colours.put("YELLOW", "#FFFF00");        colours.put("WHITE", "#FFFFFF");        //        // Convert a Map into JSON string.        //        Gson gson = new Gson();        String json = gson.toJson(colours);        System.out.println("json = " + json);        //        // Convert JSON string back to Map.        //        Type type = new TypeToken
       
        
         >(){}.getType();        Map
         
           map = gson.fromJson(json, type);        for (String key : map.keySet()) {            System.out.println("map.get = " + map.get(key));        }    }}

以下是输出结果：

json = {"WHITE":"#FFFFFF","BLUE":"#0000FF","YELLOW":"#FFFF00","GREEN":"#008000","BLACK":"#000000","RED":"#FF0000"}map.get = #FFFFFFmap.get = #0000FFmap.get = #FFFF00map.get = #008000map.get = #000000map.get = #FF0000

如何将对象转换为 json 串？

下面的例子中我们示例如何将一个 Student 对象转换成 json 串，实际操作中我们也可以将任意的 Java 类转换为 json 串，并且实施起来也非常简单，你仅仅需要创建一个 Gson 实例，然后传递将被转化为 json 串的对象，并调用该实例的 toJson 方法即可。

import com.google.gson.Gson;import java.util.Calendar;public class StudentToJson {    public static void main(String[] args) {        Calendar dob = Calendar.getInstance();        dob.set(2000, 1, 1, 0, 0, 0);        Student student = new Student("Duke", "Menlo Park", dob.getTime());        Gson gson = new Gson();        String json = gson.toJson(student);        System.out.println("json = " + json);    }}

import java.util.Date;public class Student {    private String name;    private String address;    private Date dateOfBirth;    public Student() {    }    public Student(String name, String address, Date dateOfBirth) {        this.name = name;        this.address = address;        this.dateOfBirth = dateOfBirth;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public String getAddress() {        return address;    }    public void setAddress(String address) {        this.address = address;    }    public Date getDateOfBirth() {        return dateOfBirth;    }    public void setDateOfBirth(Date dateOfBirth) {        this.dateOfBirth = dateOfBirth;    }}

以下是输出结果：

json = {"name":"Duke","address":"Menlo Park","dateOfBirth":"Feb 1, 2000 12:00:00 AM"}

如何将 json 串转换为对象？

下面的例子中我们示例如何 json 串转化成 Java对象。

import com.google.gson.Gson;public class JsonToStudent {    public static void main(String[] args) {        String json = "{\"name\":\"Duke\",\"address\":\"Menlo Park\",\"dateOfBirth\":\"Feb 1, 2000 12:00:00 AM\"}";        Gson gson = new Gson();        Student student = gson.fromJson(json, Student.class);        System.out.println("student.getName()        = " + student.getName());        System.out.println("student.getAddress()     = " + student.getAddress());        System.out.println("student.getDateOfBirth() = " + student.getDateOfBirth());    }}

以下是输出结果:

student.getName()        = Dukestudent.getAddress()     = Menlo Parkstudent.getDateOfBirth() = Tue Feb 01 00:00:00 CST 2000

如何处理对象的字段？

下面的例子中我们示例如何利用Gson处理一个对象的某一字段。

import com.google.gson.Gson;import java.util.Calendar;public class GsonFieldExample {    public static void main(String[] args) {        Calendar dob = Calendar.getInstance();        dob.set(1980, 10, 11);        People people = new People("John", "350 Banana St.", dob.getTime());        people.setSecret("This is a secret!");        Gson gson = new Gson();        String json = gson.toJson(people);        System.out.println("json = " + json);    }}

import java.util.Date;public class People {    private String name;    private String address;    private Date dateOfBirth;    private Integer age;    private transient String secret;    public People(String name, String address, Date dateOfBirth) {        this.name = name;        this.address = address;        this.dateOfBirth = dateOfBirth;    }    public String getSecret() {        return secret;    }    public void setSecret(String secret) {        this.secret = secret;    }}

以下是输出结果：

json = {"name":"John","address":"350 Banana St.","dateOfBirth":"Nov 11, 1980 8:47:04 AM"}

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