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。
1 import com.google.gson.Gson; 2 3 public class ArrayToJson { 4 public static void main(String[] args) { 5 int[] numbers = {1, 1, 2, 3, 5, 8, 13}; 6 String[] days = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"}; 7 8 // 9 // Create a new instance of Gson 10 // 11 Gson gson = new Gson(); 12 13 // 14 // Convert numbers array into JSON string. 15 // 16 String numbersJson = gson.toJson(numbers); 17 18 // 19 // Convert strings array into JSON string 20 // 21 String daysJson = gson.toJson(days); 22 System.out.println("numbersJson = " + numbersJson); 23 System.out.println("daysJson = " + daysJson); 24 25 // 26 // Convert from JSON string to a primitive array of int. 27 // 28 int[] fibonacci = gson.fromJson(numbersJson, int[].class); 29 for (int i = 0; i < fibonacci.length; i++) { 30 System.out.print(fibonacci[i] + " "); 31 } 32 System.out.println(""); 33 34 // 35 // Convert from JSON string to a string array. 36 // 37 String[] weekDays = gson.fromJson(daysJson, String[].class); 38 for (int i = 0; i < weekDays.length; i++) { 39 System.out.print(weekDays[i] + " "); 40 } 41 System.out.println(""); 42 43 // 44 // Converting multidimensional array into JSON 45 // 46 int[][] data = {{1, 2, 3}, {3, 4, 5}, {4, 5, 6}}; 47 String json = gson.toJson(data); 48 System.out.println("Data = " + json); 49 50 // 51 // Convert JSON string into multidimensional array of int. 52 // 53 int[][] dataMap = gson.fromJson(json, int[][].class); 54 for (int i = 0; i < data.length; i++) { 55 for (int j = 0; j < data[i].length; j++) { 56 System.out.print(data[i][j] + " "); 57 } 58 System.out.println(""); 59 } 60 } 61 }
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。
1 import java.util.Date; 2 3 public class Student { 4 private String name; 5 private String address; 6 private Date dateOfBirth; 7 8 public Student() { 9 } 10 11 public Student(String name, String address, Date dateOfBirth) { 12 this.name = name; 13 this.address = address; 14 this.dateOfBirth = dateOfBirth; 15 } 16 }
1 import com.google.gson.Gson; 2 import com.google.gson.reflect.TypeToken; 3 4 import java.lang.reflect.Type; 5 import java.util.ArrayList; 6 import java.util.Date; 7 import java.util.List; 8 9 public class CollectionToJson { 10 public static void main(String[] args) { 11 // 12 // Converts a collection of string object into JSON string. 13 // 14 List<String> names = new ArrayList<String>(); 15 names.add("Alice"); 16 names.add("Bob"); 17 names.add("Carol"); 18 names.add("Mallory"); 19 20 Gson gson = new Gson(); 21 String jsonNames = gson.toJson(names); 22 System.out.println("jsonNames = " + jsonNames); 23 24 // 25 // Converts a collection Student object into JSON string 26 // 27 Student a = new Student("Alice", "Apple St", new Date(2000, 10, 1)); 28 Student b = new Student("Bob", "Banana St", null); 29 Student c = new Student("Carol", "Grape St", new Date(2000, 5, 21)); 30 Student d = new Student("Mallory", "Mango St", null); 31 32 List<Student> students = new ArrayList<Student>(); 33 students.add(a); 34 students.add(b); 35 students.add(c); 36 students.add(d); 37 38 gson = new Gson(); 39 String jsonStudents = gson.toJson(students); 40 System.out.println("jsonStudents = " + jsonStudents); 41 42 // 43 // Converts JSON string into a collection of Student object. 44 // 45 Type type = new TypeToken<List<Student>>(){}.getType(); 46 List<Student> studentList = gson.fromJson(jsonStudents, type); 47 48 for (Student student : studentList) { 49 System.out.println("student.getName() = " + student.getName()); 50 } 51 } 52 }
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。
1 import com.google.gson.Gson; 2 import com.google.gson.reflect.TypeToken; 3 4 import java.lang.reflect.Type; 5 import java.util.HashMap; 6 import java.util.Map; 7 8 public class MapToJson { 9 public static void main(String[] args) { 10 Map<String, String> colours = new HashMap<String, String>(); 11 colours.put("BLACK", "#000000"); 12 colours.put("RED", "#FF0000"); 13 colours.put("GREEN", "#008000"); 14 colours.put("BLUE", "#0000FF"); 15 colours.put("YELLOW", "#FFFF00"); 16 colours.put("WHITE", "#FFFFFF"); 17 18 // 19 // Convert a Map into JSON string. 20 // 21 Gson gson = new Gson(); 22 String json = gson.toJson(colours); 23 System.out.println("json = " + json); 24 25 // 26 // Convert JSON string back to Map. 27 // 28 Type type = new TypeToken<Map<String, String>>(){}.getType(); 29 Map<String, String> map = gson.fromJson(json, type); 30 for (String key : map.keySet()) { 31 System.out.println("map.get = " + map.get(key)); 32 } 33 } 34 }
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。
1 import com.google.gson.Gson; 2 3 import java.util.Calendar; 4 5 public class StudentToJson { 6 public static void main(String[] args) { 7 Calendar dob = Calendar.getInstance(); 8 dob.set(2000, 1, 1, 0, 0, 0); 9 Student student = new Student("Duke", "Menlo Park", dob.getTime()); 10 11 Gson gson = new Gson(); 12 String json = gson.toJson(student); 13 System.out.println("json = " + json); 14 } 15 }
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。
1 import com.google.gson.Gson; 2 3 public class JsonToStudent { 4 public static void main(String[] args) { 5 String json = "{\"name\":\"Duke\",\"address\":\"Menlo Park\",\"dateOfBirth\":\"Feb 1, 2000 12:00:00 AM\"}"; 6 7 Gson gson = new Gson(); 8 Student student = gson.fromJson(json, Student.class); 9 10 System.out.println("student.getName() = " + student.getName()); 11 System.out.println("student.getAddress() = " + student.getAddress()); 12 System.out.println("student.getDateOfBirth() = " + student.getDateOfBirth()); 13 } 14 }
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。
1 import com.google.gson.Gson; 2 3 import java.util.Calendar; 4 5 public class GsonFieldExample { 6 public static void main(String[] args) { 7 Calendar dob = Calendar.getInstance(); 8 dob.set(1980, 10, 11); 9 People people = new People("John", "350 Banana St.", dob.getTime()); 10 people.setSecret("This is a secret!"); 11 12 Gson gson = new Gson(); 13 String json = gson.toJson(people); 14 System.out.println("json = " + json); 15 } 16 }
1 public class People { 2 private String name; 3 private String address; 4 private Date dateOfBirth; 5 private Integer age; 6 private transient String secret; 7 8 public People(String name, String address, Date dateOfBirth) { 9 this.name = name; 10 this.address = address; 11 this.dateOfBirth = dateOfBirth; 12 } 13 14 public String getSecret() { 15 return secret; 16 } 17 18 public void setSecret(String secret) { 19 this.secret = secret; 20 } 21 }
以下是输出结果：
json = {"name":"John","address":"350 Banana St.","dateOfBirth":"Nov 11, 1980 8:47:04 AM"}
