JSON.toJSONString使用異常分析

更新時間：2023年09月11日 15:36:29 作者：土豆肉絲蓋澆飯

這篇文章主要為大家介紹了JSON.toJSONString使用異常分析,有需要的朋友可以借鑒參考下,希望能夠有所幫助,祝大家多多進步,早日升職加薪

先說說坑

JSON.toString在序列化對象時，默認通過的是get*()方法來查找屬性，而不是具體某個屬性，同時回忽略transient注解的屬性。

測試案例如下

public class FastJsonTest {
    public static void main(String[] args) {
        Person person = new Person();
        person.setBirth(new Date());
        System.out.println(JSON.toJSONString(person));
    }
    public static class Person{
        private Integer age =123;
        private transient Date birth;
        public Date getBirth() {
            return birth;
        }
        public void setBirth(Date birth) {
            this.birth = birth;
        }
        public String getName(){
            return "scj";
        }
    }
}

輸出

{"name":"scj"}

問題發(fā)生

最近在迭代一個老項目，升級中間件框架版本(不升級不給打包部署)后，在項目啟動的時候居然拋出以下異常

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.masaike.yama.platform.domain.model.product.ProductServiceEntity.properties, could not initialize proxy - no Session
at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:582)
at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:201)
at org.hibernate.collection.internal.AbstractPersistentCollection.readSize(AbstractPersistentCollection.java:145)
at org.hibernate.collection.internal.PersistentBag.size(PersistentBag.java:261)
at com.masaike.yama.platform.infrastructure.converter.ProductServiceConverterImpl.productServicePropertyVOListToProductServicePropertyDTOList(ProductServiceConverterImpl.java:139)
at com.masaike.yama.platform.infrastructure.converter.ProductServiceConverterImpl.map(ProductServiceConverterImpl.java:50)
at com.masaike.yama.platform.infrastructure.converter.ProductServiceConverterImpl.entityListToDTOList(ProductServiceConverterImpl.java:32)
at com.masaike.yama.platform.query.ProductServiceQueryServiceImpl.getAllProductService(ProductServiceQueryServiceImpl.java:43)
at com.alibaba.fastjson.serializer.ASMSerializer_12_ProductServiceQueryServiceImpl.write(Unknown Source)
at com.alibaba.fastjson.serializer.JSONSerializer.writeWithFieldName(JSONSerializer.java:333)
at com.alibaba.fastjson.serializer.ASMSerializer_1_InterfaceInfo.write(Unknown Source)
at com.alibaba.fastjson.serializer.JSONSerializer.write(JSONSerializer.java:285)
at com.alibaba.fastjson.JSON.toJSONString(JSON.java:745)
at com.alibaba.fastjson.JSON.toJSONString(JSON.java:683)
at com.alibaba.fastjson.JSON.toJSONString(JSON.java:648)
at com.alibaba.dubbo.config.masaikehttp.ExportedInterfaceManager.addInterface(ExportedInterfaceManager.java:104)//關鍵點
at com.alibaba.dubbo.config.ServiceConfig.doExport(ServiceConfig.java:321)
at com.alibaba.dubbo.config.ServiceConfig.export(ServiceConfig.java:218)
at com.alibaba.dubbo.config.spring.ServiceBean.onApplicationEvent(ServiceBean.java:123)
at com.alibaba.dubbo.config.spring.ServiceBean.onApplicationEvent(ServiceBean.java:49)
at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172)
at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165)
at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139)
at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:400)
at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:354)
at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:886)
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.finishRefresh(ServletWebServerApplicationContext.java:161)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:551)
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:754)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:386)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:307)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1242)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1230)
at com.masaike.yama.bootstrap.BootStrapApplication.main(BootStrapApplication.java:36)

這個一個使用JPA時常見問題:延遲加載的時候session不存在

關于延遲加載no-session問題，可以看如何解決JPA延遲加載no Session報錯

從日志定位到拋出異常的方法為

@Override
@Transactional(rollbackFor = Exception.class)
public List<XXDTO> getAllXX() {
    List<XXEntity> result = xXQueryRepository.findAll();
    //下面的converter會觸發(fā)延遲加載
    return XXConverter.INSTANCE.entityListToDTOList(result);
}

這邊存在兩個迷惑性行為

啟動的時候怎么調用了getAllXX方法
getAllXX我加了@Transactional，理論上是有session的

問題排查

精簡上面的異常棧

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.masaike.yama.platform.domain.model.product.ProductServiceEntity.properties, could not initialize proxy - no Session
at com.masaike.yama.platform.infrastructure.converter.ProductServiceConverterImpl.productServicePropertyVOListToProductServicePropertyDTOList(ProductServiceConverterImpl.java:139)
at com.masaike.yama.platform.infrastructure.converter.ProductServiceConverterImpl.map(ProductServiceConverterImpl.java:50)
at com.masaike.yama.platform.infrastructure.converter.ProductServiceConverterImpl.entityListToDTOList(ProductServiceConverterImpl.java:32)
at com.masaike.yama.platform.query.ProductServiceQueryServiceImpl.getAllProductService(ProductServiceQueryServiceImpl.java:43)
at com.alibaba.fastjson.JSON.toJSONString(JSON.java:648)
at com.alibaba.dubbo.config.masaikehttp.ExportedInterfaceManager.addInterface(ExportedInterfaceManager.java:104)//關鍵點
at com.alibaba.dubbo.config.ServiceConfig.doExport(ServiceConfig.java:321)
at com.alibaba.dubbo.config.ServiceConfig.export(ServiceConfig.java:218)

可以復盤出問題發(fā)生的現(xiàn)場

dubbo服務進行export的時候調用了ExportedInterfaceManager.addInterface方法，而在addInterface方法中調用的JSON.toJSONString方法觸發(fā)了ProductServiceQueryServiceImpl.getAllProductService方法

在看了ExportedInterfaceManager.addInterface源碼之后，問題的起因浮出水面

ExportedInterfaceManager這個類是用來針對接口暴露http服務時收集元數(shù)據(jù)使用

public synchronized void addInterface(Class<?> interfaceCls, Object obj) {
    //如果是代理類獲取代理類對象
    obj = getObjectTarget(obj);//獲取原始對象
    //...
    InterfaceInfo interfaceInfo = new InterfaceInfo();
    interfaceInfo.setInterfaceName(interfaceName);
    interfaceInfo.setRef(obj);//致命之處
    //...
    logger.info(String.format("start to addInterface into interfaceMap,interfaceName[%s],interfaceInfo[%s]",interfaceName, JSON.toJSONString(interfaceInfo)));//致命之處
    // add interface info to map
    interfaceMap.put(interfaceName, interfaceInfo);
}

對于第一個問題，InterfaceInfo的ref指向ProductServiceQueryServiceImpl，在打印日志的時候，JSON.toJSONString觸發(fā)了ProductServiceQueryServiceImpl中的get方法

而對于第二個問題，obj = getObjectTarget(obj);這段代碼會獲取代理的原始對象，導致事務失效。