Google Gson：TypeAdapter

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;
}

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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 + "]";
    }

}

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(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();
    }

}

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(3) 测试代码

@Test
public 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));
}

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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 + "]";
    }

}

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测试代码：

@Test
public 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：