ImmutableList hessian2序列化失败问题分析_java.util.list cannot be assigned from null

问题描述

A服务提供了个RPC接口给B服务使用，入参里有个参数是List类型，B服务在传参时使用Guava里的 ImmutableList，结果发生报错。
其中，B服务即consumer端的异常为：「com.alibaba.dubbo.remoting.RemotingException: Fail to decode request due to: RpcInvocation [methodName=…」 。consumer端异常截图：

A服务即provider端的异常为：「com.alibaba.com.caucho.hessian.io.HessianFieldException: com.pdd.service.smart.contract.request.agreement.QueryCarrierAgreementEffectiveWarehouseInfoRequest.agreementTypeList: java.util.List cannot be assigned from null」。provider端异常截图:

然而，当将 ImmutableList 改成 ArrayList 时报错消失，接口恢复正常。

环境说明

已知我司使用的RPC框架是dubbo，其中的序列化协议是dubbo默认的hessian2，对应版本是：hessian-lite:3.2.1-fixed-2。

< 上图出自：https://cn.dubbo.apache.org/zh/docs3-v2/java-sdk/reference-manual/protocol/dubbo/ >

问题复现

从第一部分【问题描述】中的异常堆栈信息可知，问题主要出在hessian2序列化的过程中，更准确一点是consumer反序列化时解析出错，导致异常。因此问题定位为dubbo的Serialize 数据序列化层，仅从hessian2序列化和反序列化来复现和分析问题。
< dubbo代码架构 https://cn.dubbo.apache.org/zh/docs3-v2/java-sdk/concepts-and-architecture/code-architecture/ >

public class HessianLiteUtils {
   
    /**
     * 序列化
     */
    public static byte[] serialize(Object object) {
   
        Hessian2Output h2o = null;
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();

        try {
   
            h2o = new Hessian2Output(outputStream);
            h2o.writeObject(object);
            h2o.flush();
            return outputStream.toByteArray();
        } catch (Exception e) {
   
            System.out.println("HessianUtils.serialize exception " + e.getMessage());
            throw new RuntimeException("HessianUtils.serialize 异常", e);
        } finally {
   
            if (h2o != null) {
   
                try {
   
                    h2o.close();
                } catch (IOException e) {
   
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * 反序列化.
     */
    public static Object deserialize(byte[] bytes) {
   
        Hessian2Input h2i = null;
        try {
   
            ByteArrayInputStream inputStream = new ByteArrayInputStream(bytes);
            h2i = new Hessian2Input(inputStream);
            return h2i.readObject();
        } catch (Exception e) {
   
            System.out.println("HessianUtils.deserialize exception " + e.getMessage());
            throw new RuntimeException("HessianUtils.deserialize 异常", e);
        } finally {
   
            if (h2i != null) {
   
                try {
   
                    h2i.close();
                } catch (IOException e) {
   
                    e.printStackTrace();
                }
            }
        }
    }

    public static String hex(byte[] bytes) {
   
        StringBuilder result = new StringBuilder();
        for (byte b : bytes) {
   
            result.append(String.format("%02x", b));
            // upper case
            // result.append(String.format("%02X", aByte));
        }
        return result.toString();
    }
    
    public static void main(String[] args) {
   
        Person person = new Person();
        person.setName("胖嘟嘟");
        person.setMale(true);
        person.setAge(10);
        person.setList(Lists.newArrayList(1, 2));

        // Person 可正常序列化和反序列化
        byte[] bytes = serialize(person);
        System.out.println("serialized hex bytes: " + hex(bytes));
        Object object = deserialize(bytes);
        System.out.println("deserialized object: " + object.toString());

        // Request 序列化成功，反序列化失败
        Request request = new Request();
        request.setList(ImmutableList.of(1, 2));
        byte[] bytesRequest = serialize(request);
        System.out.println("serialized hex bytes: " + hex(bytesRequest));
        Object objectReq = deserialize(bytesRequest);
        System.out.println("deserialized object: " + objectReq.toString());
    }
}

// 其中Person和Request的定义为
public class Person implements Serializable {
   
    private static final long serialVersionUID = 7242674494415301661L;

    private String name;
    private boolean isMale;
    private int age;
    private List<Integer> list;
	// 此处省略getter、setter和toString
}

public class Request implements Serializable {
   
    private static final long serialVersionUID = 408723925489378046L;

    private List<Integer> list;

    public List<Integer> getList() {
   
        return list;
    }

    public void setList(List<Integer> list) {
   
        this.list = list;
    }
}
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在上述代码中Person可正常序列化，输出结果为：

serialized hex bytes: 4306506572736f6e94046c697374036167650669734d616c65046e616d65607a91929a5403e88396e5989fe5989f
deserialized object: Person{
   name='胖嘟嘟', isMale=true, age=10, list=[1, 2]}
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Request中List参数传ImmutableList会导致反序列化异常，表现和rpc接口异常一样，问题复现。

serialized hex bytes: 43075265717565737491046c69737460433036636f6d2e676f6f676c652e636f6d6d6f6e2e636f6c6c6563742e496d6d757461626c654c6973742453657269616c697a6564466f726d9108656c656d656e74736172075b6f626a6563749192
HessianUtils.deserialize exception Request.list: com.google.common.collect.ImmutableList cannot be assigned from null
Exception in thread "main" java.lang.RuntimeException: HessianUtils.deserialize 异常
	at HessianLiteUtils.deserialize(HessianLiteUtils.java:59)
	at HessianLiteUtils.main(HessianLiteUtils.java:99)
Caused by: com.alibaba.com.caucho.hessian.io.HessianFieldException: Request.list: com.google.common.collect.ImmutableList cannot be assigned from null
	at com.alibaba.com.caucho.hessian.io.JavaDeserializer.logDeserializeError(JavaDeserializer.java:171)
	at com.alibaba.com.caucho.hessian.io.JavaDeserializer$ObjectFieldDeserializer.deserialize(JavaDeserializer.java:414)
	at com.alibaba.com.caucho.hessian.io.JavaDeserializer.readObject(JavaDeserializer.java:275)
	at com.alibaba.com.caucho.hessian.io.JavaDeserializer.readObject(JavaDeserializer.java:199)
	at com.alibaba.com.caucho.hessian.io.SerializerFactory.readObject(SerializerFactory.java:529)
	at com.alibaba.com.caucho.hessian.io.Hessian2Input.readObjectInstance(Hessian2Input.java:2803)
	at com.alibaba.com.caucho.hessian.io.Hessian2Input.readObject(Hessian2Input.java:2743)
	at com.alibaba.com.caucho.hessian.io.Hessian2Input
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