2019独角兽企业重金招聘Python工程师标准>>> 
1. 问题描述
我发现通过dubbo调用某类接口时，若该接口的返回类型是Collection的子类并且扩展了自实现的属性， 则返回结果集会丢失自实现的属性。 比如， 我有个接口方法返回PageList（源码如下），则当客户端调用这个方法时，得到的返回对象中并没有totalCount。 
2. 问题定位
开启debug, 跟入源码，发现dubbo是依赖hessian完成序列化与反序列化的。以下是针对Collecltion对象的序列化类：
package com.alibaba.com.caucho.hessian.io;
import java.io.IOException;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
/**
* Serializing a JDK 1.2 Collection.
*/
public class CollectionSerializer extends AbstractSerializer {
private boolean _sendJavaType = true;
/**
* Set true if the java type of the collection should be sent.
*/
public void setSendJavaType(boolean sendJavaType) {
_sendJavaType = sendJavaType;
}
/**
* Return true if the java type of the collection should be sent.
*/
public boolean getSendJavaType() {
return _sendJavaType;
}
public void writeObject(Object obj, AbstractHessianOutput out)
throws IOException {
if (out.addRef(obj))
return;
Collection list = (Collection) obj;
Class cl = obj.getClass();
boolean hasEnd;
if (cl.equals(ArrayList.class)
|| !_sendJavaType
|| !Serializable.class.isAssignableFrom(cl))
hasEnd = out.writeListBegin(list.size(), null);
else
hasEnd = out.writeListBegin(list.size(), obj.getClass().getName());
Iterator iter = list.iterator();
while (iter.hasNext()) {
Object value = iter.next();
out.writeObject(value);
}
if (hasEnd)
out.writeListEnd();
}
}
以上代码，方法 writeObject(Object obj, AbstractHessianOutput out) 的入参obj，其实相当于以上的PageList对象。仔细看就发现这个方法只对聚集的成员进行了写入，而没有对聚集外的其它属性进行写入，从而导致属性丢失。
3. 问题解决
于是， 我尝试对以上序列化类CollectionSerializer进行修改，当然还要同步修改相应的反序列化类。 以下是修改后的代码， 已通过注释标出：
package com.alibaba.com.caucho.hessian.io;
import java.io.IOException;
import java.io.Serializable;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
/**
* Serializing a JDK 1.2 Collection.
*/
public class CollectionSerializer extends AbstractSerializer {
private boolean _sendJavaType = true;
/**
* Set true if the java type of the collection should be sent.
*/
public void setSendJavaType(boolean sendJavaType) {
_sendJavaType = sendJavaType;
}
/**
* Return true if the java type of the collection should be sent.
*/
public boolean getSendJavaType() {
return _sendJavaType;
}
public void writeObject(Object obj, AbstractHessianOutput out)
throws IOException {
if (out.addRef(obj))
return;
Collection list = (Collection) obj;
Class cl = obj.getClass();
boolean hasEnd;
if (cl.equals(ArrayList.class)
|| !_sendJavaType
|| !Serializable.class.isAssignableFrom(cl))
hasEnd = out.writeListBegin(list.size(), null);
else
hasEnd = out.writeListBegin(list.size(), obj.getClass().getName());
/**
* 修改序列化过程丢失属性的bug, 对继承自Collection并扩展了新属性的类，对其新增属性序列化。
*
* Added By HuQingmiao([email protected]) on 2017-03-25.
*/
/** begin **/
try {
Class clasz = list.getClass();
//记录已经写过的子类属性，以防被同名父类属性覆盖
Set fieldNameSet = new HashSet();
// 从当前自定义List子类逐层向上处理，对各层属性进行序列化
for (; !clasz.getName().startsWith("java."); clasz = clasz.getSuperclass()) {
// 如果当前类直接实现了List或Set接口，则不对其元素进行读写. 2017-08-28
boolean impListOrSet = false;
for (Class c : clasz.getInterfaces()) {
if (List.class.equals(c) | Set.class.equals(c) | SortedSet.class.equals(c) | Collection.class.equals(c)) {
impListOrSet = true;
break;
}
}
if (impListOrSet) {
continue;
}
// 如果当前类直接继承AbstractCollection/AbstractList/ABstractSet类，则不对其元素进行读写. 2017-08-29
Class sc = clasz.getSuperclass();
if (AbstractList.class.equals(sc) | AbstractSet.class.equals(sc) | AbstractCollection.class.equals(sc)) {
continue;
}
Field[] fields = clasz.getDeclaredFields();
for (Field field : fields) {
//log.debug(">> " + clasz.getSimpleName() + "." + field.getName() + " " + field.getType());
// 子类属性已被写入，不再写入同名父属性
if (fieldNameSet.contains(field.getName())) {
continue;
}
if (Modifier.isTransient(field.getModifiers()) || Modifier.isStatic(field.getModifiers())) {
continue;
}
boolean isAccessible = field.isAccessible();
if (!isAccessible) {
field.setAccessible(true);
}
Object val = field.get(list);
//log.debug(">> "+clasz.getSimpleName()+" "+field.getName()+" "+field.getType()+" "+val);
out.writeObject(val);
field.setAccessible(isAccessible);
// 记录已写过的属性
fieldNameSet.add(field.getName());
}
}// end for (; !clasz.getName()
fieldNameSet.clear();
} catch (IllegalAccessException e) {
throw new IOException(e.getMessage());
}
/** end **/
Iterator iter = list.iterator();
while (iter.hasNext()) {
Object value = iter.next();
out.writeObject(value);
}
if (hasEnd)
out.writeListEnd();
}
}
/*
* Copyright (c) 2001-2004 Caucho Technology, Inc. All rights reserved.
*
* The Apache Software License, Version 1.1
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The end-user documentation included with the redistribution, if
* any, must include the following acknowlegement:
* "This product includes software developed by the
* Caucho Technology (http://www.caucho.com/)."
* Alternately, this acknowlegement may appear in the software itself,
* if and wherever such third-party acknowlegements normally appear.
*
* 4. The names "Hessian", "Resin", and "Caucho" must not be used to
* endorse or promote products derived from this software without prior
* written permission. For written permission, please contact
* [email protected].
*
* 5. Products derived from this software may not be called "Resin"
* nor may "Resin" appear in their names without prior written
* permission of Caucho Technology.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL CAUCHO TECHNOLOGY OR ITS CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
* OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
* OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
* BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
* OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
* IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* @author Scott Ferguson
*/
package com.alibaba.com.caucho.hessian.io;
import java.io.IOException;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.*;
/**
* Deserializing a JDK 1.2 Collection.
*/
public class CollectionDeserializer extends AbstractListDeserializer {
//private Logger log = LoggerFactory.getLogger(this.getClass());
private Class _type;
public CollectionDeserializer(Class type) {
_type = type;
}
public Class getType() {
return _type;
}
public Object readList(AbstractHessianInput in, int length)
throws IOException {
Collection list = createList();
in.addRef(list);
/**
* 解决序列化过程丢失属性的bug，对继承自Collection并扩展了新属性的类，对其新增属性反序列化。
*
* Added By HuQingmiao([email protected]) on 2017-03-25.
*/
/** begin **/
try {
Class clasz = list.getClass();
//记录已经读过的子类属性，以防被同名父类属性覆盖
Set fieldNameSet = new HashSet();
// 从当前自定义List子类逐层向上处理，对各层属性进行反序列化
for (; !clasz.getName().startsWith("java."); clasz = clasz.getSuperclass()) {
// 如果当前类直接实现了List或Set接口，则不对其元素进行读写. 2017-08-28
boolean impListOrSet = false;
for (Class c : clasz.getInterfaces()) {
if (List.class.equals(c) | Set.class.equals(c) | SortedSet.class.equals(c) | Collection.class.equals(c)) {
impListOrSet = true;
break;
}
}
if (impListOrSet) {
continue;
}
// 如果当前类直接继承AbstractCollection/AbstractList/ABstractSet类，则不对其元素进行读写. 2017-08-29
Class sc = clasz.getSuperclass();
if (AbstractList.class.equals(sc) | AbstractSet.class.equals(sc) | AbstractCollection.class.equals(sc)) {
continue;
}
Field[] fields = clasz.getDeclaredFields();
for (Field field : fields) {
//log.debug(">>2 " + clasz.getSimpleName() + "." + field.getName() + " " + field.getType());
// 子类属性已被读取，不再读取同名父属性
if (fieldNameSet.contains(field.getName())) {
continue;
}
if (Modifier.isTransient(field.getModifiers()) || Modifier.isStatic(field.getModifiers())) {
continue;
}
boolean isAccessible = field.isAccessible();
if (!isAccessible) {
field.setAccessible(true);
}
Object val = in.readObject();
//log.debug(">>2 " + clasz.getSimpleName() + "." + field.getName() + " " + field.getType() + " " + val);
field.set(list, val);
field.setAccessible(isAccessible);
// 记录已记取的属性
fieldNameSet.add(field.getName());
}
}// end for (; !clasz.getName()
fieldNameSet.clear();
} catch (IllegalAccessException e) {
throw new IOException(e.getMessage());
}
/** end **/
while (!in.isEnd())
list.add(in.readObject());
in.readEnd();
return list;
}
public Object readLengthList(AbstractHessianInput in, int length)
throws IOException {
Collection list = createList();
in.addRef(list);
/**
* 解决序列化过程丢失属性的bug，对继承自Collection并扩展了新属性的类，对其新增属性反序列化。
*
* Added By HuQingmiao([email protected]) on 2017-03-25.
*/
/** begin **/
try {
Class clasz = list.getClass();
//记录已经读过的子类属性，以防被同名父类属性覆盖
Set fieldNameSet = new HashSet();
// 从当前自定义List子类逐层向上处理，对各层属性进行反序列化
for (; !clasz.getName().startsWith("java."); clasz = clasz.getSuperclass()) {
// 如果当前类直接实现了List或Set接口，则不对其元素进行读写. 2017-08-28
boolean impListOrSet = false;
for (Class c : clasz.getInterfaces()) {
if (List.class.equals(c) | Set.class.equals(c) | SortedSet.class.equals(c) | Collection.class.equals(c)) {
impListOrSet = true;
break;
}
}
if (impListOrSet) {
continue;
}
// 如果当前类直接继承AbstractCollection/AbstractList/ABstractSet类，则不对其元素进行读写. 2017-08-29
Class sc = clasz.getSuperclass();
if (AbstractList.class.equals(sc) | AbstractSet.class.equals(sc) | AbstractCollection.class.equals(sc)) {
continue;
}
Field[] fields = clasz.getDeclaredFields();
for (Field field : fields) {
//log.debug(">>2 " + clasz.getSimpleName() + "." + field.getName() + " " + field.getType());
// 子类属性已被读取，不再读取同名父属性
if (fieldNameSet.contains(field.getName())) {
continue;
}
if (Modifier.isTransient(field.getModifiers()) || Modifier.isStatic(field.getModifiers())) {
continue;
}
boolean isAccessible = field.isAccessible();
if (!isAccessible) {
field.setAccessible(true);
}
Object val = in.readObject();
//log.debug(">>2 " + clasz.getSimpleName() + "." + field.getName() + " " + field.getType() + " " + val);
field.set(list, val);
field.setAccessible(isAccessible);
// 记录已记取的属性
fieldNameSet.add(field.getName());
}
}// end for (; !clasz.getName()
fieldNameSet.clear();
} catch (IllegalAccessException e) {
throw new IOException(e.getMessage());
}
/** end **/
for (; length > 0; length--)
list.add(in.readObject());
return list;
}
private Collection createList()
throws IOException {
Collection list = null;
if (_type == null)
list = new ArrayList();
else if (!_type.isInterface()) {
try {
list = (Collection) _type.newInstance();
} catch (Exception e) {
}
}
if (list != null) {
} else if (SortedSet.class.isAssignableFrom(_type))
list = new TreeSet();
else if (Set.class.isAssignableFrom(_type))
list = new HashSet();
else if (List.class.isAssignableFrom(_type))
list = new ArrayList();
else if (Collection.class.isAssignableFrom(_type))
list = new ArrayList();
else {
try {
list = (Collection) _type.newInstance();
} catch (Exception e) {
throw new IOExceptionWrapper(e);
}
}
return list;
}
}
对以上修改后的代码进行测试，发现在反序列化时ArrayList的子类被识别成了ArrayList，为此还需要对com.alibaba.com.caucho.hessian.io.Hessian2Input 的第21270行做如下修改：
case 0x77: {
int length = tag - 0x70;
String type = readType();
Deserializer reader;
/**
* Modified by HuQingmiao on 2017-04-01
*/
// getListDeserializer(null, cl) -> getListDeserializer(type, cl);
reader = findSerializerFactory().getListDeserializer(type, cl);
Object v = reader.readLengthList(this, length);
return v;
}
至此， 修改完毕，测试通过。
4. 关于dubbo源码
关于dubbo的bug及修改内容， 见 https://github.com/HuQingmiao/dubbo 。