gson使用指南
1. 依赖包
<!-- https://mvnrepository.com/artifact/com.google.code.gson/gson -->
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.8.5</version>
</dependency>2. gson的基本用法
Gson提供了fromJson() 和toJson() 两个直接用于解析和生成的方法
2.1 基本数据类型的解析与生成
Gson gson = new Gson();
Integer fromJson = gson.fromJson("100", Integer.class);// 100
Boolean fromJson2 = gson.fromJson("true", Boolean.class);// true
String fromJson3 = gson.fromJson("100", String.class);// 100
log.info("{},{},{}", fromJson, fromJson2, fromJson3);
String jsonNumber = gson.toJson(100); // 100
String jsonBoolean = gson.toJson(false); // false
String jsonString = gson.toJson("String"); //"String"
log.info("{},{},{}",jsonNumber, jsonBoolean, jsonString);2.2 POJO类的生成与解析
import java.util.Date;
import java.util.List;
import lombok.AllArgsConstructor;
import lombok.Data;
@Data
@AllArgsConstructor
public class User {
private String username;
private Integer age;
private Date birthday;
private Boolean ifMarried;
private String[] addr;
private List<Integer> scores;
}生成json
import java.util.Arrays;
import java.util.Date;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import com.example.gsondemo.po.User;
import com.google.gson.Gson;
import lombok.extern.slf4j.Slf4j;
@RestController
@Slf4j
public class UserController {
@GetMapping("/")
public Object name() {
Gson gson = new Gson();
User user = new User("woms", 32, new Date(), true, new String[] { "bj", "sx" }, Arrays.asList(34, 45));
String json = gson.toJson(user);
log.info(json);
return json;
}
}$ curl localhost:8080 -s | jq
{
"username": "woms",
"age": 32,
"birthday": "May 5, 2019, 12:13:54 PM",
"ifMarried": true,
"addr": [
"bj",
"sx"
],
"scores": [
34,
45
]
}
$ curl localhost:8080 -s | jq -R
"{\"username\":\"woms\",\"age\":32,\"birthday\":\"May 5, 2019, 12:16:48 PM\",\"ifMarried\":true,\"addr\":[\"bj\",\"sx\"],\"scores\":[34,45]}"解析json
Gson gson = new Gson();
User user = gson.fromJson("{\"username\":\"woms\",\"age\":32,\"birthday\":\"May 5, 2019, "
+ "12:16:48 PM\",\"ifMarried\":true,\"addr\":[\"bj\",\"sx\"],\"scores\":[34,45]}", User.class);3. 属性重命名 @SerializedName 注解的使用
@SerializedName 注解的使用import java.util.Date;
import java.util.List;
import com.google.gson.annotations.SerializedName;
import lombok.AllArgsConstructor;
import lombok.Data;
@Data
@AllArgsConstructor
public class User {
private String username;
private Integer age;
private Date birthday;
@SerializedName("if_married")
private Boolean ifMarried;
private String[] addr;
private List<Integer> scores;
}$ curl localhost:8080 -s|jq
{
"username": "woms",
"age": 32,
"birthday": "May 5, 2019, 12:54:23 PM",
"if_married": true,
"addr": [
"bj",
"sx"
],
"scores": [
34,
45
]
}3.1 为POJO字段提供备选属性名
@SerializedName注解提供了两个属性，上面用到了其中一个，别外还有一个属性alternate，接收一个String数组。
注：alternate需要2.4版本
@SerializedName(value = "emailAddress", alternate = {"email", "email_address"})
public String emailAddress;当上面的三个属性(email_address、email、emailAddress)都中出现任意一个时均可以得到正确的结果。
注：当多种情况同时出时，以最后一个出现的值为准。
Gson gson = new Gson();
String json = "{\"name\":\"怪盗kidou\",\"age\":24,\"emailAddress\":\"ikidou_1@example.com\",\"email\":\"ikidou_2@example.com\",\"email_address\":\"ikidou_3@example.com\"}";
User user = gson.fromJson(json, User.class);
System.out.println(user.emailAddress); // ikidou_3@example.com4. Gson中使用泛型
JSON中的集合有两种：数组、list
如果是数组的话，没问题，因为数组本身就是一种类型，如果是list的话会有问题，因为设计到了泛型
@Data
public class Response<T> {
private Integer code;
private String message;
private T data;
}Gson gson = new Gson();
Response<List<User>> response = new Response<>();
List<User> list = new ArrayList<>();
list.add(new User("woms", 32, new Date(), true, new String[] { "bj", "sx" }, Arrays.asList(34, 45)));
response.setCode(200);
response.setMessage("success");
response.setData(list);
return gson.toJson(response);$ curl localhost:8080 -s|jq
{
"code": 200,
"message": "success",
"data": [
{
"username": "woms",
"age": 32,
"birthday": "May 5, 2019, 1:04:53 PM",
"if_married": true,
"addr": [
"bj",
"sx"
],
"scores": [
34,
45
]
}
]
}解析json使用new TypeToken<Response<List<User>>>(){}.getType()
Gson gson = new Gson();
Response<List<User>> fromJson = gson.fromJson("{\"code\":200,\"message\":\"success\",\"data\":[{\"username\":\"woms\",\"age\":32,\"birthday\":\"May 5, 2019, 1:07:02 PM\",\"if_married\":true,\"addr\":[\"bj\",\"sx\"],\"scores\":[34,45]}]}"
, new TypeToken<Response<List<User>>>(){}.getType());5. 使用GsonBuilder导出null值、格式化输出、日期时间
一般情况下Gson类提供的 API已经能满足大部分的使用场景，但我们需要更多更特殊、更强大的功能时，这时候就引入一个新的类 GsonBuilder。
GsonBuilder从名上也能知道是用于构建Gson实例的一个类，要想改变Gson默认的设置必须使用该类配置Gson。
5.1 默认null字段是不显示的
Gson gson = new Gson();
Response<List<User>> response = new Response<>();
List<User> list = new ArrayList<>();
list.add(new User("woms", null, new Date(), true, new String[] { "bj", "sx" }, Arrays.asList(34, 45)));
response.setCode(200);
response.setMessage("success");
response.setData(list);
return gson.toJson(response);age字段我们设置了null, 生成的json是没有age字段的
$ curl localhost:8080 -s|jq
{
"code": 200,
"message": "success",
"data": [
{
"username": "woms",
"birthday": "May 5, 2019, 1:37:46 PM",
"if_married": true,
"addr": [
"bj",
"sx"
],
"scores": [
34,
45
]
}
]
}如果我们这样生成一个gson
GsonBuilder gsonBuilder = new GsonBuilder();
Gson gson = gsonBuilder.serializeNulls().create();
Response<List<User>> response = new Response<>();
List<User> list = new ArrayList<>();
list.add(new User("woms", null, new Date(), true, new String[] { "bj", "sx" }, Arrays.asList(34, 45)));
response.setCode(200);
response.setMessage("success");
response.setData(list);
return gson.toJson(response);$ curl localhost:8080 -s|jq
{
"code": 200,
"message": "success",
"data": [
{
"username": "woms",
"age": null, //这里是可以看到这个key的
"birthday": "May 5, 2019, 1:42:00 PM",
"if_married": true,
"addr": [
"bj",
"sx"
],
"scores": [
34,
45
]
}
]
}5.2 格式化日期
GsonBuilder gsonBuilder = new GsonBuilder();
Gson gson = gsonBuilder.serializeNulls().setDateFormat("yyyy-MM-dd").create();$ curl localhost:8080 -s|jq
{
"code": 200,
"message": "success",
"data": [
{
"username": "woms",
"age": null,
"birthday": "2019-05-05",
"if_married": true,
"addr": [
"bj",
"sx"
],
"scores": [
34,
45
]
}
]
}6. 字段过滤的几种方法
6.1 基于@Expose注解
GsonBuilder gsonBuilder = new GsonBuilder();
Gson gson = gsonBuilder.serializeNulls()
.excludeFieldsWithoutExposeAnnotation()//启用expose注解 只有被注解的字段才会有效
.setDateFormat("yyyy-MM-dd")
.create();@Expose //
@Expose(deserialize = true,serialize = true) //序列化和反序列化都都生效
@Expose(deserialize = true,serialize = false) //反序列化时生效
@Expose(deserialize = false,serialize = true) //序列化时生效
@Expose(deserialize = false,serialize = false) // 和不写一样6.2 基于版本
Gson在对基于版本的字段导出提供了两个注解 @Since 和 @Until,和GsonBuilder.setVersion(Double)配合使用。@Since 和 @Until都接收一个Double值。
import com.google.gson.annotations.Since;
import com.google.gson.annotations.Until;
import lombok.Data;
@Data
public class Response<T> {
@Until(3.2)
private Integer code;
@Since(3.2)
private String message;
private T data;
}GsonBuilder gsonBuilder = new GsonBuilder();
Gson gson = gsonBuilder.serializeNulls()
.setVersion(3.2)//设置版本号
.setDateFormat("yyyy-MM-dd").create();6.3 基于访问修饰符
@Data
public class Response<T> {
public Integer code;
private String message;
private T data;
}import java.lang.reflect.Modifier;
GsonBuilder gsonBuilder = new GsonBuilder();
Gson gson = gsonBuilder.serializeNulls()
.excludeFieldsWithModifiers(Modifier.PUBLIC)
.setDateFormat("yyyy-MM-dd").create();7. 禁用特殊字符转移
Gson gson = new GsonBuilder().disableHtmlEscaping().create();Last updated