FastJson 反序列化报 default constructor not found 错误怎么绕过

1、如何可以修改相关反序列化类代码，就加上默认构造方法。

2、如果不能修改相关类代码，就利用如下工具类，给反序列化错误的那个类指定一个构造方法。

package com.me.best.mock.utils;

import com.alibaba.fastjson.parser.DefaultJSONParser;
import com.alibaba.fastjson.parser.ParserConfig;
import com.alibaba.fastjson.parser.deserializer.JavaBeanDeserializer;
import com.alibaba.fastjson.util.FieldInfo;
import com.alibaba.fastjson.util.JavaBeanInfo;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;
import java.util.function.BiFunction;

public class FastJsonStrengthen {

    public static void addTypeInstance(Class clazz, BiFunction biFunction) {
        ParserConfig parserConfig = ParserConfig.getGlobalInstance();
        List fieldList = new ArrayList<>();
        for (Class currentClass = clazz; currentClass != null; currentClass = currentClass.getSuperclass()) {
            Field[] fields = currentClass.getDeclaredFields();

            try {
                Class javaBeanInfoClass = JavaBeanInfo.class;
                String methodName = "computeFields";
                Method computeFields = getMethod(javaBeanInfoClass, methodName);

                computeFields.setAccessible(true);
                computeFields.invoke(null, clazz, clazz, parserConfig.propertyNamingStrategy, fieldList, fields);
            } catch (Exception e) {
                e.printStackTrace();
            }

        }

        JavaBeanInfo javaBeanInfo = new JavaBeanInfo(clazz, clazz, null, null, null, null, null, fieldList);

        JavaBeanDeserializer deserializer = new JavaBeanDeserializer(parserConfig, javaBeanInfo){
            @Override
            public Object createInstance(DefaultJSONParser parser, Type type) {
                return biFunction.apply(parser, type);
            }
        };
        parserConfig.putDeserializer(clazz,
                deserializer);
    }

    public static Method getMethod(Class clazz, String methodName) {
        Method[] methods = clazz.getDeclaredMethods();
        Method computeFields = null;
        for (Method method : methods) {
            if (method.getName().equals(methodName)) {
                computeFields = method;
            }
        }
        return computeFields;
    }

}

使用样例

FastJsonStrengthen.addTypeInstance(User.class, (parser, type)->{
    User user2 = User.build();
    return user2;
});