一、概述:
Gson是Google提供的一個Java庫,它可以用來將Java對象轉(zhuǎn)換為JSON字符串。還可以用于將JSON字符串轉(zhuǎn)換為等效的Java對象。另外,其另一個特點是支持java的泛型集合和json字符串之間的轉(zhuǎn)換。
二、API介紹
1.google-gson的Gson對象的創(chuàng)建方法:
Gson gson=new Gson();
Gson gson=new GsonBuilder().create();
2.google-gson的使用非常簡單,其提供的toJson()和fromJson()方法用于Java對象和JSON格式字符串的相互轉(zhuǎn)換。
toJson():用于把java對象轉(zhuǎn)換為json格式字符串
fromJson():用于把json格式字符串轉(zhuǎn)換為java對象
三、實例
實體類User:
public class User {
private String name;
private int age;
private String address;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public User(String name, int age, String address) {
super();
this.name = name;
this.age = age;
this.address = address;
}
@Override
public String toString() {
return "User [name=" + name + ", age=" + age + ", address=" + address
+ "]";
}
}
使用google-gson的代碼片段如下:
//0. 初始化json、User數(shù)組、List<User>、Map<String,User>、google-gson對象等數(shù)據(jù):
//構建json格式的字符串
String jsonString="{'name':'tom','age':23,'address':'北京'}";
User u1=new User("艾迪森", 25, "北京");
User u2=new User("安迪", 23, "南京");
User u3=new User("托馬斯", 21, "上海");
User u4=new User("愛麗絲", 22, "鄭州");
User []us={u1,u2,u3,u4};
List<User> users=new ArrayList<User>();
users.add(u1);
users.add(u2);
users.add(u3);
users.add(u4);
Map<String,User> maps=new HashMap<String, User>();
maps.put("1001", u1);
maps.put("1002", u2);
maps.put("1003", u3);
maps.put("1004", u4);
//創(chuàng)建gson對象
Gson g=new GsonBuilder().create();
//1.json(對象)字符串和java對象間的相互轉(zhuǎn)換
//把json格式的數(shù)據(jù)轉(zhuǎn)換為java對象
User u=g.fromJson(jsonString,User.class);
System.out.println(u);
//輸出結果:User [name=tom, age=23, address=北京]
//java對象的信息轉(zhuǎn)換為json字符串
jsonString=g.toJson(u);
System.out.println(jsonString);
//輸出結果:{"name":"tom","age":23,"address":"北京"}
//2.json(數(shù)組)字符串和java對象數(shù)組間的相互轉(zhuǎn)換
//把java的數(shù)組轉(zhuǎn)為json格式字符串
jsonString=g.toJson(us);
System.out.println(jsonString);
//輸出結果:
[
{"name":"艾迪森","age":25,"address":"北京"},
{"name":"安迪","age":23,"address":"南京"},
{"name":"托馬斯","age":21,"address":"上海"},
{"name":"愛麗絲","age":22,"address":"鄭州"}
]
us=null;
//把json數(shù)組中的數(shù)據(jù)轉(zhuǎn)為java數(shù)組對象
us=g.fromJson(jsonString, User[].class);
for(User uu:us){
System.out.println(uu);
}
//輸出結果:
User [name=艾迪森, age=25, address=北京]
User [name=安迪, age=23, address=南京]
User [name=托馬斯, age=21, address=上海]
User [name=愛麗絲, age=22, address=鄭州]
//3.json(數(shù)組)字符串和java泛型集合對象List間的相互轉(zhuǎn)換
//把list中的元素轉(zhuǎn)為json格式數(shù)組
jsonString=g.toJson(users);
System.out.println(jsonString);
//輸出結果:同數(shù)組
[
{"name":"艾迪森","age":25,"address":"北京"},
{"name":"安迪","age":23,"address":"南京"},
{"name":"托馬斯","age":21,"address":"上海"},
{"name":"愛麗絲","age":22,"address":"鄭州"}
]
users.clear();
//把json數(shù)組中的數(shù)據(jù)轉(zhuǎn)為java集合對象list
TypeToken<List<User>> typeToken=new TypeToken<List<User>>(){};
Type type=typeToken.getType();
//如果使用了泛型集合就要使用type,指定泛型的具體類型。
users=g.fromJson(jsonString,type);
for(User uu:users){
System.out.println(uu);
}
//輸出結果:同數(shù)組
User [name=艾迪森, age=25, address=北京]
User [name=安迪, age=23, address=南京]
User [name=托馬斯, age=21, address=上海]
User [name=愛麗絲, age=22, address=鄭州]
//4.json(對象)字符串和java泛型集合對象Map間的相互轉(zhuǎn)換
//把map的中的數(shù)據(jù)轉(zhuǎn)為json格式
jsonString=g.toJson(maps);
System.out.println(jsonString);
//輸出結果:
{
"1003":{"name":"托馬斯","age":21,"address":"上海"},
"1004":{"name":"愛麗絲","age":22,"address":"鄭州"},
"1001":{"name":"艾迪森","age":25,"address":"北京"},
"1002":{"name":"安迪","age":23,"address":"南京"}
}
maps.clear();
//把json數(shù)組中的數(shù)據(jù)轉(zhuǎn)為java集合對象
TypeToken<Map<String,User>> typeTokenMap=new TypeToken<Map<String,User>>(){};
Type typeMap=typeTokenMap.getType();
//如果使用了泛型集合就要使用type,指定泛型的具體類型。
maps=g.fromJson(jsonString,typeMap);
for(Map.Entry<String, User> uu:maps.entrySet()){
System.out.println(uu.getValue());
}
//輸出結果:
User [name=托馬斯, age=21, address=上海]
User [name=愛麗絲, age=22, address=鄭州]
User [name=艾迪森, age=25, address=北京]
User [name=安迪, age=23, address=南京]
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