Python自定义实现JSON解码器的完整指南

import json
json_str = '{"name": "张三", "age": 25}'
data = json.loads(json_str)
print(type(data))   # <class 'dict'>

# 自动还原为 Person 对象
person = json.loads(json_str, cls=PersonDecoder)
print(person.name)   # 张三

import json
from datetime import datetime
from typing import Any

class Person:
    def __init__(self, name: str, age: int, created_at: datetime = None):
        self.name = name
        self.age = age
        self.created_at = created_at or datetime.now()
    
    def __repr__(self):
        return f"Person(name={self.name}, age={self.age}, created_at={self.created_at})"


class PersonEncoder(json.JSONEncoder):
    """序列化编码器"""
    def default(self, obj):
        if isinstance(obj, Person):
            return {
                "__type__": "Person",
                "name": obj.name,
                "age": obj.age,
                "created_at": obj.created_at.isoformat()
            }
        if isinstance(obj, datetime):
            return {"__type__": "datetime", "value": obj.isoformat()}
        return super().default(obj)


class PersonDecoder(json.JSONDecoder):
    """自定义解码器：重写 decode 方法"""
    
    def decode(self, s: str) -> Any:
        """解析 JSON 字符串，还原为 Person 对象"""
        # 先调用父类方法解析为 Python 字典
        data = super().decode(s)
        return self._convert(data)
    
    def _convert(self, data):
        """递归转换数据"""
        if isinstance(data, dict):
            # 检查类型标识
            if data.get("__type__") == "Person":
                created_at = data.get("created_at")
                if created_at:
                    created_at = datetime.fromisoformat(created_at)
                return Person(
                    name=data["name"],
                    age=data["age"],
                    created_at=created_at
                )
            if data.get("__type__") == "datetime":
                return datetime.fromisoformat(data["value"])
            # 递归处理字典中的每个值
            return {k: self._convert(v) for k, v in data.items()}
        
        elif isinstance(data, list):
            # 递归处理列表中的每个元素
            return [self._convert(item) for item in data]
        
        return data


# 测试
p = Person("张三", 25)
json_str = json.dumps(p, cls=PersonEncoder, ensure_ascii=False)
print("序列化:", json_str)

restored = json.loads(json_str, cls=PersonDecoder)
print("还原:", restored)
print("类型:", type(restored))
print("姓名:", restored.name)
print("创建时间类型:", type(restored.created_at))

class Address:
    def __init__(self, city: str, district: str):
        self.city = city
        self.district = district
    
    def __repr__(self):
        return f"Address(city={self.city}, district={self.district})"

class Student:
    def __init__(self, name: str, age: int, address: Address = None):
        self.name = name
        self.age = age
        self.address = address
    
    def __repr__(self):
        return f"Student(name={self.name}, age={self.age}, address={self.address})"


class MultiDecoder(json.JSONDecoder):
    """支持多种类型的解码器"""
    
    def decode(self, s: str) -> Any:
        data = super().decode(s)
        return self._convert(data)
    
    def _convert(self, data):
        if isinstance(data, dict):
            obj_type = data.get("__type__")
            
            if obj_type == "Person":
                return Person(
                    name=data["name"],
                    age=data["age"],
                    created_at=self._convert(data.get("created_at"))
                )
            
            if obj_type == "Student":
                return Student(
                    name=data["name"],
                    age=data["age"],
                    address=self._convert(data.get("address"))
                )
            
            if obj_type == "Address":
                return Address(
                    city=data["city"],
                    district=data["district"]
                )
            
            if obj_type == "datetime":
                return datetime.fromisoformat(data["value"])
            
            # 递归处理
            return {k: self._convert(v) for k, v in data.items()}
        
        elif isinstance(data, list):
            return [self._convert(item) for item in data]
        
        return data


class MultiEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, Person):
            return {"__type__": "Person", "name": obj.name, "age": obj.age, "created_at": obj.created_at}
        if isinstance(obj, Student):
            return {"__type__": "Student", "name": obj.name, "age": obj.age, "address": obj.address}
        if isinstance(obj, Address):
            return {"__type__": "Address", "city": obj.city, "district": obj.district}
        if isinstance(obj, datetime):
            return {"__type__": "datetime", "value": obj.isoformat()}
        return super().default(obj)


# 测试
addr = Address("北京", "朝阳区")
student = Student("李四", 20, addr)
json_str = json.dumps(student, cls=MultiEncoder, ensure_ascii=False, indent=2)
print("序列化:")
print(json_str)

restored = json.loads(json_str, cls=MultiDecoder)
print("\n还原:")
print(restored)
print(restored.address.city)

class Life:
    def __init__(self,name,age):
        self.name = name
        self.age = age

    def __str__(self):
        return f"name:{self.name},age:{self.age}"

class Animal(Life):
    def __init__(self,name,age,speed):
        super().__init__(name,age)
        self.speed = speed

    def __str__(self):
        return f"{super().__str__()},speed:{self.speed}"

class Flyable:
    def fly(self):
        return f"{self.name}正在飞行,速度为{self.speed}"

class SwimAble:
    def swim(self):
        return f"{self.name}正在游泳,速度为{self.speed}"
class AttackAble:
    def attack(self):
        return f"{self.name}会攻击,破坏力强大"

class Bird(Flyable,Animal,Life,AttackAble):
    def __init__(self,name,age,speed):
        super().__init__(name,age,speed)

    def speek(self):
        return f"{self.name}正在喳喳喳"

class Dog(Animal,Life,SwimAble,AttackAble):
    def __init__(self,name,age,speed):
        super().__init__(name,age,speed)

    def speek(self):
        return f"{self.name}正在汪汪汪"

class BigSwan(Animal,Life,SwimAble,Flyable,AttackAble):
    def __init__(self,name,age,speed):
        super().__init__(name,age,speed)

    def speek(self):
        return f"{self.name}发出鹅鹅鹅的声音"

l0 = Life("张飞",18)
print(l0)
a0 = Animal("陈军",18,30)
print(a0)
b1 = Bird("刘振阳",18,100)
print(b1,b1.speek(),b1.fly(),b1.attack())
d1 = Dog("陈军",18,30)
print(d1,d1.speek(),d1.swim(),d1.attack())
bs = BigSwan("张怡飞",20,50)
print(bs,bs.speek(),bs.swim(),bs.fly(),bs.attack())