fastjson反序列化失败autoType is not support

骑猪看日落 2022-03-31 13:09 816阅读 0赞

## 描述 ##

通过fastjson反序列化某javabean时失败，并抛出以下异常：

Could not deserialize: autoType is not support. com.xxx.Shop; nested exception is com.alibaba.fastjson.JSONException: autoType is not support. com.xxx.Shop
    	at com.alibaba.fastjson.support.spring.GenericFastJsonRedisSerializer.deserialize(GenericFastJsonRedisSerializer.java:37)

然而只有项目第一次反序列化该javabean时会抛异常失败，复现方式只有重启项目后的第一次反序列化操作。

## 过程 ##

查询官方文档，开启AutoType的方法  
[enable\_autotype][enable_autotype]。

但是文档中的方法均测试无效，无奈debug源码，发现抛出异常的代码为  
`com.alibaba.fastjson.parser.ParserConfig`的1125行代码：

JavaBeanInfo beanInfo = JavaBeanInfo.build(clazz, clazz, propertyNamingStrategy);
    if (beanInfo.creatorConstructor != null && autoTypeSupport) { 
        throw new JSONException("autoType is not support. " + typeName);
    }

经与正常反序列化的javabean比较后，发现反序列化失败的javabean在如上代码执行时，`beanInfo.creatorConstructor`的值不为null，最后抛出`autoType is not support`的异常。

继续追踪，在`com.alibaba.fastjson.util.JavaBeanInfo`283行代码判断反序列化失败的javabean为接口或抽象类：

boolean isInterfaceOrAbstract = clazz.isInterface() || Modifier.isAbstract(clazz.getModifiers());

再于`com.alibaba.fastjson.util.JavaBeanInfo`381行代码的if判断分支下给`beanInfo.creatorConstructor`赋值：

else if (!isInterfaceOrAbstract){ 
        ...
        for (Constructor constructor : constructors) { 
            Class<?>[] parameterTypes = constructor.getParameterTypes();
        
            if (className.equals("org.springframework.security.web.authentication.WebAuthenticationDetails")) { 
                if (parameterTypes.length == 2 && parameterTypes[0] == String.class && parameterTypes[1] == String.class) { 
                    creatorConstructor = constructor;
                    creatorConstructor.setAccessible(true);
                    paramNames = ASMUtils.lookupParameterNames(constructor);
                    break;
                }
            }
        
            if (className.equals("org.springframework.security.web.authentication.preauth.PreAuthenticatedAuthenticationToken")) { 
                if (parameterTypes.length == 3
                        && parameterTypes[0] == Object.class
                        && parameterTypes[1] == Object.class
                        && parameterTypes[2] == Collection.class) { 
                    creatorConstructor = constructor;
                    creatorConstructor.setAccessible(true);
                    paramNames = new String[] { "principal", "credentials", "authorities"};
                    break;
                }
            }
        
            if (className.equals("org.springframework.security.core.authority.SimpleGrantedAuthority")) { 
                if (parameterTypes.length == 1
                        && parameterTypes[0] == String.class) { 
                    creatorConstructor = constructor;
                    paramNames = new String[] { "authority"};
                    break;
                }
            }
        
            boolean is_public = (constructor.getModifiers() & Modifier.PUBLIC) != 0;
            if (!is_public) { 
                continue;
            }
            String[] lookupParameterNames = ASMUtils.lookupParameterNames(constructor);
            if (lookupParameterNames == null || lookupParameterNames.length == 0) { 
                continue;
            }
        
            if (creatorConstructor != null
                    && paramNames != null && lookupParameterNames.length <= paramNames.length) { 
                continue;
            }
        
            paramNames = lookupParameterNames;
            // 有参数构造方法给beanInfo.creatorConstructor赋值
            creatorConstructor = constructor;
        }
    }

最终定位项目中通过fastjson反序列化失败，是因为该javabean没有无参构造方法，被fastjson判断为接口或抽象类，最终抛出`autoType is not support`的异常。

## 解决 ##

给javabean添加无参构造方法。

[enable_autotype]: https://github.com/alibaba/fastjson/wiki/enable_autotype