GSON使用总结

一、引入gson版本

com.google.code.gson gson 2.8.5

二、两种使用方式

2.1基本使用

Gson gson = new Gson();

2.2自定义

Gson gson = new GsonBuilder() .xxxx() .create();

常用使用如下替换xxxx()方法:

2.1.FieldNamingPolicy.IDENTITY 默认属性，不改变字段的属性 2.2.FieldNamingPolicy.LOWER_CASE_WITH_DASHES 是字段属性小写，并加上-为分割 2.3.FieldNamingPolicy.LOWER_CASE_WITH_DOTS 是字段属性小写，并加上.为分割 2.4. FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES 是字段属性小写，并 加上_为分割 2.5.FieldNamingPolicy.UPPER_CAMEL_CASE 每个单词首字母大写 2.6.FieldNamingPolicy.UPPER_CAMEL_CASE_WITH_SPACES 每个首字母大写并以空格隔开

注：这些策略不会影响标记@SerializedName注解的字段

3. serializeNulls()，作用序列化空字段

4.setExclusionStrategies(new ExclusionStrategy())，作用设置字段是否需要序列化，如果shouldSkipClass(Class) 或shouldSkipField(attribute)方法返回true，将不会序列化和反序列化该类型（字段）

5.excludeFieldsWithoutExposeAnnotation()，需要配合@Expose注解来使用 ，忽略某个字段进行初始化

6.
excludeFieldsWithModifiers(Modifier.STATIC) Modifier.STATIC， 不序列化被 static修饰的字段Modifier.TRANSIENT,不序列化被transient修饰的字段，Modifier.VOLATILE 不序列化被volatile修饰的字段

7.registerTypeAdapter(Type, Object)自定义序列化和反序列化方法

三、常用注解

3.1 @since 指定该字段在序列化和反序列化时在哪个版本显示

public class Employee{ private Integer id; @Since(1.0) private String firstName; @Since(1.1) private String lastName; @Since(1.2) private String email; } Employee employeeObj = new Employee(1, "Lokesh", "Gupta", "howtogoinjava@gmail.com"); Gson gson = new GsonBuilder() .setVersion(1.1) .create(); System.out.println(gson.toJson(employeeObj)); 只序列化1.1及之前的版本的字段 { "id": 1, "firstName": "Lokesh", "lastName": "Gupta" }

3.2.@SerializedName按照指定的字段名进行序列化和反序列化 序列化时email以emailId输出，反序列化的时候以emailAddress输入 代码如下

public class Employee { private Integer id; private String firstName; private String lastName; @SerializedName(value = "emailId", alternate = "emailAddress") private String email; } //序列化代码 Employee emp = new Employee(1001, "Lokesh", "Gupta", "howtodoinjava@gmail.com"); Gson gson = new GsonBuilder().setPrettyPrinting().create(); System.out.println(gson.toJson(emp)); //序列化输出 { "id": 1001, "firstName": "Lokesh", "lastName": "Gupta", "emailId": "howtodoinjava@gmail.com" } //反序列化 String json = "{'id': 1001," + "'firstName': 'Lokesh'," + "'lastName': 'Gupta'," + "'email': 'howtodoinjava@gmail.com'," + "'emailAddress': 'admin@gmail.com'}"; Gson gson = new GsonBuilder().setPrettyPrinting().create(); Employee emp = gson.fromJson(json, Employee.class); System.out.println(emp); //反序列化输出 Employee [id=1001, firstName=Lokesh, lastName=Gupta, email=admin@gmail.com]

3.3.@Expose序列化和反序列化是否忽略该字段 @Expose(serialize = false)

private String lastName; @Expose (serialize = false, deserialize = false) private String emailAddress; Gson gson = new GsonBuilder() .excludeFieldsWithoutExposeAnnotation() .create(); 注使用new Gson()来执行 toJson() and fromJson() 方法时不生效的， transient 与 @Expose (serialize = false, deserialize = false)有相同的效果

四、自定义序列化和反序列化

4.1实现JsonSerializer接口

import com.google.gson.JsonElement; import com.google.gson.JsonPrimitive; import com.google.gson.JsonSerializationContext; import com.google.gson.JsonSerializer; public class BooleanSerializer implements JsonSerializer { public JsonElement serialize(Boolean aBoolean, Type type, JsonSerializationContext jsonSerializationContext) { if(aBoolean){ return new JsonPrimitive(1); } return new JsonPrimitive(0); } } import com.google.gson.Gson; import com.google.gson.GsonBuilder; public class Main { public static void main(String[] args) throws Exception { Employee emp = new Employee(1, "Lokesh", "Gupta", "howtodoinjava@gmail.com", true); Gson gson = new GsonBuilder() .registerTypeAdapter(Boolean.class, new BooleanSerializer()) .setPrettyPrinting() .create(); String json = gson.toJson(emp); System.out.println(json); } } //输出 { "id": 1, "firstName": "Lokesh", "lastName": "Gupta", "email": "howtodoinjava@gmail.com", "active": 1 }

4.2JsonDeserializer反序列化接口

//Employee.java public class Employee { private Integer id; private String firstName; private String lastName; private String email; private LocalDate dob; } //EmployeeDeserializer.java public class EmployeeDeserializer implements JsonDeserializer { @Override public Employee deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException { JsonObject jsonObject = json.getAsJsonObject(); LocalDate localDate = LocalDate.of( jsonObject.get("year").getAsInt(), jsonObject.get("month").getAsInt(), jsonObject.get("day").getAsInt() ); return new Employee( jsonObject.get("id").getAsInt(), jsonObject.get("firstName").getAsString(), jsonObject.get("lastName").getAsString(), jsonObject.get("email").getAsString(), localDate); } } public class Main{ public static void main(String[] args) throws Exception { String json = "{'id': 1001," + "'firstName': 'Lokesh'," + "'lastName': 'Gupta'," + "'email': 'howtodoinjava@gmail.com', " + "'day': 11, " + "'month': 8, " + "'year': 2019}"; Gson gson = new GsonBuilder() .registerTypeAdapter(Employee.class, new EmployeeDeserializer()) .create(); Employee employee = gson.fromJson(json, Employee.class); System.out.println(employee); } }

五、gson反序列化数组，List，Set，Map，如果这些类型作为成员属性和序列化时无须特殊处理

import java.lang.reflect.Type; import com.google.gson.Gson; import com.google.gson.reflect.TypeToken; 1.数组 String userJson = "[{'name': 'Alex','id': 1}, " + "{'name': 'Brian','id':2}, " + "{'name': 'Charles','id': 3}]"; Gson gson = new Gson(); User[] userArray = gson.fromJson(userJson, User[].class); //2.List String userJson = "[{'name': 'Alex','id': 1}, " + "{'name': 'Brian','id':2}, " + "{'name': 'Charles','id': 3}]"; Gson gson = new Gson(); Type userListType = new TypeToken>(){}.getType(); ArrayList userArray = gson.fromJson(userJson, userListType); //3.Set Gson gson = new Gson(); Type setType = new TypeToken>(){}.getType(); Set userSet = gson.fromJson(jsonString, setType); //4.Map HashMap employeeMap = new HashMap<>(); employeeMap.put(1, new Employee(1l, "Alex", LocalDate.of(1990, 01, 01))); employeeMap.put(2, new Employee(2l, "Bob", LocalDate.of(1990, 02, 01))); //Deep clone Gson gson = new Gson(); String jsonString = gson.toJson(employeeMap); Type type = new TypeToken>(){}.getType(); HashMap clonedMap = gson.fromJson(jsonString, type);

参考学习：
https://howtodoinjava.com/learningpaths/gson/