Google Gson：TypeAdapter

本文内容大多基于官方文档和网上前辈经验总结，经过个人实践加以整理积累，仅供参考。

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TypeAdapter 是 Gson 2.0 开始的一个抽象类，用于接管某种类型的序列化和反序列化过程

TypeAdapter 的两个主要方法

public abstract class TypeAdapter<T> {    public abstract void write(JsonWriter out, T value) throws IOException;    public abstract T read(JsonReader in) throws IOException;}

示例

(1) POJO

public class User {    private String name;    private String phoneNumber;    public User() {}    public User(String name, String phoneNumber) {        this.name = name;        this.phoneNumber = phoneNumber;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public String getPhoneNumber() {        return phoneNumber;    }    public void setPhoneNumber(String phoneNumber) {        this.phoneNumber = phoneNumber;    }    @Override    public String toString() {        return "User [name=" + name + ", phoneNumber=" + phoneNumber + "]";    }}

(2) TypeAdapter 接口类

class UserTypeAdapter extends TypeAdapter<User> {    @Override    public User read(JsonReader reader) throws IOException {        User user = new User();        reader.beginObject();        while (reader.hasNext()) {            switch (reader.nextName()) {                case "name":                case "custom-name":                case "adapter-name":                    user.setName(reader.nextString());                    break;                case "phone":                case "custom-phone":                case "adapter-phone":                    user.setPhoneNumber(reader.nextString());                    break;                default:                    break;            }        }        reader.endObject();        return user;    }    @Override    public void write(JsonWriter writer, User user) throws IOException {        writer.beginObject();        writer.name("adapter-name").value(user.getName());        writer.name("adapter-phone").value(user.getPhoneNumber());        writer.endObject();    }}

(3) 测试代码

@Testpublic void test() throws IOException {    User user = new User("UserX", "160");    Gson gson = new GsonBuilder()        .registerTypeAdapter(User.class, new UserTypeAdapter())        .create();    System.out.println(gson.toJson(user));    String userStr = "{\"name\":\"Name\",\"phone\":\"151\"}";    System.out.println(gson.fromJson(userStr, User.class));    userStr = "{\"custom-name\":\"CustomName\",\"custom-phone\":\"152\"}";    System.out.println(gson.fromJson(userStr, User.class));    userStr = "{\"adapter-name\":\"AdapterName\",\"adapter-phone\":\"153\"}";    System.out.println(gson.fromJson(userStr, User.class));    userStr = "{\"name\":\"nameX\",\"adapter-phone\":\"154\"}";    System.out.println(gson.fromJson(userStr, User.class));    userStr = "{\"adapter-name\":\"nameY\",\"phone\":\"155\"}";    System.out.println(gson.fromJson(userStr, User.class));}

测试结果：

Gson 还提供了一个类注解 @JsonAdapter，如果使用此注释则每次生成 Gson 对象时不用再注册类型适配器，即不用再调用 GsonBuilder.registerTypeAdapter

示例

更新 POJO

@JsonAdapter(UserTypeAdapter.class)public class User {    private String name;    private String phoneNumber;    public User() {}    public User(String name, String phoneNumber) {        this.name = name;        this.phoneNumber = phoneNumber;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public String getPhoneNumber() {        return phoneNumber;    }    public void setPhoneNumber(String phoneNumber) {        this.phoneNumber = phoneNumber;    }    @Override    public String toString() {        return "User [name=" + name + ", phoneNumber=" + phoneNumber + "]";    }}

测试代码：

@Testpublic void test() throws IOException {    User user = new User("UserX", "160");    Gson gson = new Gson();    System.out.println(gson.toJson(user));    String userStr = "{\"name\":\"Name\",\"phone\":\"151\"}";    System.out.println(gson.fromJson(userStr, User.class));    userStr = "{\"custom-name\":\"CustomName\",\"custom-phone\":\"152\"}";    System.out.println(gson.fromJson(userStr, User.class));    userStr = "{\"adapter-name\":\"AdapterName\",\"adapter-phone\":\"153\"}";    System.out.println(gson.fromJson(userStr, User.class));    userStr = "{\"name\":\"nameX\",\"adapter-phone\":\"154\"}";    System.out.println(gson.fromJson(userStr, User.class));    userStr = "{\"adapter-name\":\"nameY\",\"phone\":\"155\"}";    System.out.println(gson.fromJson(userStr, User.class));}

运行结果：