扩展dubbo的序列化协议

一、在main/java下新建包，并新增一下三个文件

PersistentObjectOutput.java 实现ObjectOutput接口

package com.heytap.ad.cpd.management.serialization;

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);
    }

    @Override
    public void writeBool(boolean v) throws IOException {
        this.mH2o.writeBoolean(v);
    }
    @Override
    public void writeByte(byte v) throws IOException {
        this.mH2o.writeInt(v);
    }
    @Override
    public void writeShort(short v) throws IOException {
        this.mH2o.writeInt(v);
    }
    @Override
    public void writeInt(int v) throws IOException {
        this.mH2o.writeInt(v);
    }
    @Override
    public void writeLong(long v) throws IOException {
        this.mH2o.writeLong(v);
    }
    @Override
    public void writeFloat(float v) throws IOException {
        this.mH2o.writeDouble((double)v);
    }
    @Override
    public void writeDouble(double v) throws IOException {
        this.mH2o.writeDouble(v);
    }
    @Override
    public void writeBytes(byte[] b) throws IOException {
        this.mH2o.writeBytes(b);
    }
    @Override
    public void writeBytes(byte[] b, int off, int len) throws IOException {
        this.mH2o.writeBytes(b, off, len);
    }
    @Override
    public void writeUTF(String v) throws IOException {
        this.mH2o.writeString(v);
    }
    @Override
    public void writeObject(Object obj) throws IOException {
        this.mH2o.writeObject(obj);
    }
    @Override
    public void flushBuffer() throws IOException {
        this.mH2o.flushBuffer();
    }
}

PersistentSerialization.java

package com.heytap.ad.cpd.management.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);
    }
}

PersistentSerializerFactory .java

package com.heytap.ad.cpd.management.serialization;

import com.alibaba.com.caucho.hessian.io.*;


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

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

    public PersistentSerializerFactory() {
    }

    @Override
    public ClassLoader getClassLoader() {
        return Thread.currentThread().getContextClassLoader();
    }
    private HibernateListSerializer listSerializer = new HibernateListSerializer();

    @Override
    @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 (List.class.isAssignableFrom(cl)) {
            return listSerializer;
        }
        return super.getSerializer(cl);
    }


    private static class HibernateListSerializer implements Serializer {
        @Override
        @SuppressWarnings({"unchecked", "rawtypes"})
        public void writeObject(Object obj, AbstractHessianOutput out) throws IOException {
            if (!out.addRef(obj)) {
                Collection list = (Collection)obj;
                Class cl = obj.getClass();
                boolean hasEnd;
                Iterator iter = list.iterator();
// 如果是list或者是set则进入下面操作，默认 hessian只支持arrayList的序列化。会报java.util.List cannot be assigned from null 这个错误
                if (obj instanceof Set || obj instanceof List
                        || !Serializable.class.isAssignableFrom(cl)) {
                    hasEnd = out.writeListBegin(list.size(), null);
                } else {
                    hasEnd = out.writeListBegin(list.size(), obj.getClass().getName());
                }
                while(iter.hasNext()) {
                    Object value = iter.next();
                    out.writeObject(value);
                }

                if (hasEnd) {
                    out.writeListEnd();
                }

            }
        }

    }


}

二、在resource下新建 resources\META-INF\dubbo ，然后新建文本文件org.apache.dubbo.common.serialize.Serialization，并写入

persistent=com.heytap.ad.cpd.management.serialization.PersistentSerialization

三、更改dubbo的启动序列化协议，可以在参数上修改-Ddubbo.protocol.serialization=persistent,也可以在配置上修改 dubbo.protocol.serialization=fastjson