dubbo自定义序列化扩展，解决hessian序列化时Persistent相关对象序列化错误

dubbo自定义序列化扩展，解决hessian序列化时Persistent相关对象序列化错误

dubbo进行PRC调用，例如消费者请求提供者的数据，使用hessian序列化时，对于Set，Map，List集合，PersistentSet，PersistentMap，PersistentCollection等对象无法识别，所以会报错。
例如，实体类中包含Set，Map等数据：

    @ManyToMany(fetch = FetchType.EAGER)
    @JoinTable(name = "person", joinColumns = {@JoinColumn(name = "company_id")},
            inverseJoinColumns = {@JoinColumn(name = "person_id")})
    private Set<Person> personSet;

消费者调用时，错误如下：

com.alibaba.com.caucho.hessian.io.HessianFieldException: com.test.core.entity.Company.personSet: java.util.Set cannot be assigned from null
	at com.alibaba.com.caucho.hessian.io.JavaDeserializer.logDeserializeError(JavaDeserializer.java:173)
	at com.alibaba.com.caucho.hessian.io.JavaDeserializer$ObjectFieldDeserializer.deserialize(JavaDeserializer.java:410)
	at com.alibaba.com.caucho.hessian.io.JavaDeserializer.readObject(JavaDeserializer.java:276)
	at com.alibaba.com.caucho.hessian.io.JavaDeserializer.readObject(JavaDeserializer.java:203)
	at com.alibaba.com.caucho.hessian.io.Hessian2Input.readObjectInstance(Hessian2Input.java:2818)
	at com.alibaba.com.caucho.hessian.io.Hessian2Input.readObject(Hessian2Input.java:2145)
	at com.alibaba.com.caucho.hessian.io.Hessian2Input.readObject(Hessian2Input.java:2074)
	at com.alibaba.com.caucho.hessian.io.Hessian2Input.readObject(Hessian2Input.java:2118)
	at com.alibaba.com.caucho.hessian.io.Hessian2Input.readObject(Hessian2Input.java:2074)
	at org.apache.dubbo.common.serialize.hessian2.Hessian2ObjectInput.readObject(Hessian2ObjectInput.java:92)
	at org.apache.dubbo.common.serialize.hessian2.Hessian2ObjectInput.readObject(Hessian2ObjectInput.java:97)
	at org.apache.dubbo.rpc.protocol.dubbo.DecodeableRpcResult.handleValue(DecodeableRpcResult.java:134)
	at org.apache.dubbo.rpc.protocol.dubbo.DecodeableRpcResult.decode(DecodeableRpcResult.java:92)
	at org.apache.dubbo.rpc.protocol.dubbo.DecodeableRpcResult.decode(DecodeableRpcResult.java:112)
	at org.apache.dubbo.rpc.protocol.dubbo.DubboCodec.decodeBody(DubboCodec.java:92)
	at org.apache.dubbo.remoting.exchange.codec.ExchangeCodec.decode(ExchangeCodec.java:122)
	at org.apache.dubbo.remoting.exchange.codec.ExchangeCodec.decode(ExchangeCodec.java:82)
	at org.apache.dubbo.rpc.protocol.dubbo.DubboCountCodec.decode(DubboCountCodec.java:48)
	at org.apache.dubbo.remoting.transport.netty4.NettyCodecAdapter$InternalDecoder.decode(NettyCodecAdapter.java:90)

解决

使用dubbo序列化扩展，自定义序列化，增加对持久化对象的识别判断，具体配置可查看dubbo官网 序列化扩展

1. 编写自己的PersistentSerializerFactory，继承SerializerFactory。

import com.alibaba.com.caucho.hessian.io.*;
import org.hibernate.Hibernate;
import org.hibernate.collection.internal.AbstractPersistentCollection;
import org.hibernate.collection.internal.PersistentMap;
import org.hibernate.collection.internal.PersistentSet;

import java.io.IOException;
import java.util.*;

public class PersistentSerializerFactory extends SerializerFactory{
    public static final SerializerFactory TESTSERIALIZER_FACTORY = new PersistentSerializerFactory();

    public PersistentSerializerFactory() {
    }

    public ClassLoader getClassLoader() {
        return Thread.currentThread().getContextClassLoader();
    }
    private HibernateListSerializer listSerializer = new HibernateListSerializer();
    private HibernateMapSerializer mapSerializer = new HibernateMapSerializer();
    private HibernateBeanSerializer hibernateBeanSerializer = new HibernateBeanSerializer();
    private HibernateSetSerializer setSerializer = new HibernateSetSerializer();

    @SuppressWarnings("rawtypes")
    //序列化时，判断persistent相关类型，添加持久化对象的序列化方式，如果不是，则走父类的序列化方法
    public Serializer getSerializer(Class cl) throws HessianProtocolException {
        if (PersistentMap.class.isAssignableFrom(cl)) {
            return mapSerializer;
        } else if(PersistentSet.class.isAssignableFrom(cl)){
            return setSerializer;
        } else if (AbstractPersistentCollection.class.isAssignableFrom(cl)) {
            return listSerializer;
        } else if (cl.getSimpleName().contains("_$$_javassist_")) {
            return hibernateBeanSerializer;
        }
        return super.getSerializer(cl);
    }

    private static class HibernateBeanSerializer implements Serializer {
        @Override
        public void writeObject(Object obj, AbstractHessianOutput out) throws IOException {
            boolean init = Hibernate.isInitialized(obj);

            out.writeObject(init ? obj : null);
            out.flush();
            return;
        }
    }

    private static class HibernateSetSerializer implements Serializer{
        private CollectionSerializer delegate = new CollectionSerializer();

        @SuppressWarnings({"unchecked", "rawtypes"})
        public void writeObject(Object obj, AbstractHessianOutput out) throws IOException {
            if (Hibernate.isInitialized(obj)) {
                delegate.writeObject(new ArrayList((Set) obj), out);
            } else {
                delegate.writeObject(new ArrayList(), out);
            }
        }

    }

    private static class HibernateListSerializer implements Serializer {
        private CollectionSerializer delegate = new CollectionSerializer();

        @SuppressWarnings({"unchecked", "rawtypes"})
        public void writeObject(Object obj, AbstractHessianOutput out) throws IOException {
            if (Hibernate.isInitialized(obj)) {
                delegate.writeObject(new ArrayList((Collection) obj), out);
            } else {
                delegate.writeObject(new ArrayList(), out);
            }
        }

    }

    private static class HibernateMapSerializer implements Serializer {
        private MapSerializer delegate = new MapSerializer();

        @SuppressWarnings({"unchecked", "rawtypes"})
        public void writeObject(Object obj, AbstractHessianOutput out) throws IOException {
            if (Hibernate.isInitialized(obj)) {
                delegate.writeObject(new HashMap((Map) obj), out);
            } else {
                delegate.writeObject(new HashMap(), out);
            }
        }

    }
}

2. 新建PersistentSerialization，实现Serialization：

import org.apache.dubbo.common.URL;
import org.apache.dubbo.common.serialize.ObjectInput;
import org.apache.dubbo.common.serialize.ObjectOutput;
import org.apache.dubbo.common.serialize.Serialization;
import org.apache.dubbo.common.serialize.hessian2.Hessian2ObjectInput;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class PersistentSerialization implements Serialization {
    @Override
    //注意，由于dubbo有很多序列化方式的扩展，每种方式有自己的id,自定义id时注意冲突，重复时会有ERROR提示
    public byte getContentTypeId() {
        return 22;
    }
    @Override
    public String getContentType() {
        return "persistent";
    }
    @Override
    public ObjectOutput serialize(URL url, OutputStream out) throws IOException {
        return new PersistentObjectOutput(out);
    }
    @Override
    public ObjectInput deserialize(URL url, InputStream is) throws IOException {
        return new Hessian2ObjectInput(is);
    }
}

3. 新建PersistentObjectOutput(实现ObjectOutput接口)：

import com.alibaba.com.caucho.hessian.io.Hessian2Output;
import org.apache.dubbo.common.serialize.ObjectOutput;

import java.io.IOException;
import java.io.OutputStream;

public class PersistentObjectOutput implements ObjectOutput{
    private final Hessian2Output mH2o;
	//注意：设置Output的Factory为上面自己定义的序列化工厂类
    public PersistentObjectOutput(OutputStream os) {
        this.mH2o = new Hessian2Output(os);
        this.mH2o.setSerializerFactory(PersistentSerializerFactory.TESTSERIALIZER_FACTORY);
    }

    public void writeBool(boolean v) throws IOException {
        this.mH2o.writeBoolean(v);
    }

    public void writeByte(byte v) throws IOException {
        this.mH2o.writeInt(v);
    }

    public void writeShort(short v) throws IOException {
        this.mH2o.writeInt(v);
    }

    public void writeInt(int v) throws IOException {
        this.mH2o.writeInt(v);
    }

    public void writeLong(long v) throws IOException {
        this.mH2o.writeLong(v);
    }

    public void writeFloat(float v) throws IOException {
        this.mH2o.writeDouble((double)v);
    }

    public void writeDouble(double v) throws IOException {
        this.mH2o.writeDouble(v);
    }

    public void writeBytes(byte[] b) throws IOException {
        this.mH2o.writeBytes(b);
    }

    public void writeBytes(byte[] b, int off, int len) throws IOException {
        this.mH2o.writeBytes(b, off, len);
    }

    public void writeUTF(String v) throws IOException {
        this.mH2o.writeString(v);
    }

    public void writeObject(Object obj) throws IOException {
        this.mH2o.writeObject(obj);
    }

    public void flushBuffer() throws IOException {
        this.mH2o.flushBuffer();
    }
}

4. 新建ObjectInput类(实现ObjectInput接口)：
   反序列化时可以直接使用hessian的类，在deserialize方法中，直接使用Hessian2ObjectInput。
5. 按照官网示例的maven项目结构部署代码和配置文件：

src
 |-main
    |-java
        |-com
            |-xxx
                |-XxxSerialization.java (实现Serialization接口)
                |-XxxObjectInput.java (实现ObjectInput接口)
                |-XxxObjectOutput.java (实现ObjectOutput接口)
    |-resources
        |-META-INF
            |-dubbo
                |-org.apache.dubbo.common.serialize.Serialization (纯文本文件，内容为：xxx=com.xxx.XxxSerialization)

META-INF/dubbo/org.apache.dubbo.common.serialize.Serialization文件内容：
persistent=com.xxx.persistentSerialization

6. 最后，在application配置文件中配置dubbo的序列化方式：
   

dubbo:
  protocol:
    serialization: persistent

最后

消费者进行调用时，会进入自定义的序列化工厂方法中，判断是否为持久化对象，如果是，则通过自定义序列化返回相应对象，如果不是，则进入父类的原生方法中进行序列化。