Google Gson 使用简介

原文：http://www.cnblogs.com/haippy/archive/2012/05/20/2509329.html

一、如何将数组转化为 json 串？

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

二、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;
}
}

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<String> names = new ArrayList<String>();
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<Student> students = new ArrayList<Student>();
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<List<Student>>(){}.getType();
List<Student> 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() = Alice
student.getName() = Bob
student.getName() = Carol
student.getName() = Mallory

三、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<String, String> colours = new HashMap<String, String>();
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<Map<String, String>>(){}.getType();
Map<String, String> 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 = #FFFFFF
map.get = #0000FF
map.get = #FFFF00
map.get = #008000
map.get = #000000
map.get = #FF0000

四、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);
}
}

以下是输出结果：

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

五、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()        = Duke
student.getAddress()     = Menlo Park
student.getDateOfBirth() = Tue Feb 01 00:00:00 CST 2000

六、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);
}
}

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"}