Google Gson 使用简介
1.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 2 3 5 8 13 Sun Mon Tue Wed Thu Fri Sat Data = [[1,2,3],[3,4,5],[4,5,6]] 2 3 4 5
2.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<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
3.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
4.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"}
5.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
6.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"}
