java - 具有 Collection 字段的对象的 GSON 自定义序列化程序

Question

我有以下架构:

public class Student {
    String name;
    List<Integer> sequence;
}

我需要我的 Student 对象的 Json

{
    name : "Bruce"
    sequence : {
         index_0 : 5
         index_1 : 2
         index_2 : 7
         index_3 : 8
    }
}

The documentation没有明确说明如何为集合编写序列化程序。

Answer 1

您可以创建一个 TypeAdapter，类似于:

public static class StudentAdapter extends TypeAdapter<Student> {
    public void write(JsonWriter writer, Student student)
            throws IOException {
        if (student == null) {
            writer.nullValue();
            return;
        }
        writer.beginObject();

        writer.name("name");
        writer.value(student.name);

        writer.name("sequence");
        writeSequence(writer, student.sequence);

        writer.endObject();
    }

    private void writeSequence(JsonWriter writer, List<Integer> seq)
            throws IOException {
        writer.beginObject();
        for (int i = 0; i < seq.size(); i++) {
            writer.name("index_" + i);
            writer.value(seq.get(i));
        }
        writer.endObject();
    }

    @Override
    public Student read(JsonReader in) throws IOException {
        // This is left blank as an exercise for the reader
        return null;
    }
}

然后注册

GsonBuilder b = new GsonBuilder();
b.registerTypeAdapter(Student.class, new StudentAdapter());
Gson g = b.create();

如果您对示例学生运行此命令:

Student s = new Student();
s.name = "John Smith";
s.sequence = ImmutableList.of(1,3,4,7); // This is a guava method
System.out.println(g.toJson(s));

输出:

{"name":"John Smith","sequence":{"index_0":1,"index_1":3,"index_2":4,"index_3":7}}