Hessian源码学习（三）_JAVA_编程开发_程序员俱乐部

今天我们重点来看看Hessian是如何实现序列化的（这些序列化类可以脱离hessian源码包，单独拿出来使用），参考源码版本为3.0.20

首先我们看下序列化一个对象的代码：

// 这里可以是任何形式的OutputStream，现以FileOutputStream为例
OutputStream os = new FileOutputStream("hessianOutput"); 
// 创建 HessianOutput对象
AbstractHessianOutput out = new HessianOutput(os); 
// 设置序列化工厂 
out.setSerializerFactory(new SerializerFactory()); 
// 序列化 obj对象（obj可以是一个简单对象比如Integer，String，也可以是一个自定义类，同时也可以// 是数组，枚举，集合等等）
out.writeObject(obj); 

我们来逐步分析下上面这段代码：

1.out.setSerializerFactory(new SerializerFactory());

首先SerializerFactory是什么？顾名思义 SerializerFactory是一个序列化工厂，里面包含了序列化（反序列化）各种类型的Serializer（DeSerializer）类，我们看下在创建SerializerFactory时，它做了写什么：(由于序列化工厂包含序列化与反序列化，为了表达方面的方便，我这里只说序列化）

// 静态代码快
static {

     // 创建序列化和反序列化map，至于其中的Key-Value 我想大家也能猜到，key就是某个需要序列化的class，value就是序列化该class的Serializer类

    _serializerMap = new HashMap();
    _deserializerMap = new HashMap();
    _typeMap = new HashMap();

	// 初始化序列化和反序列化map （对于“简单类型”都使用BasicSerializer作为它的序列化类）
    addBasic(void.class, "void", BasicSerializer.NULL);
    addBasic(Boolean.class, "boolean", BasicSerializer.BOOLEAN);
    addBasic(Byte.class, "byte", BasicSerializer.BYTE);
    addBasic(Short.class, "short", BasicSerializer.SHORT);
    addBasic(Integer.class, "int", BasicSerializer.INTEGER);
    addBasic(Long.class, "long", BasicSerializer.LONG);
    addBasic(Float.class, "float", BasicSerializer.FLOAT);
    addBasic(Double.class, "double", BasicSerializer.DOUBLE);
    addBasic(Character.class, "char", BasicSerializer.CHARACTER);
    addBasic(String.class, "string", BasicSerializer.STRING);
    addBasic(Object.class, "object", BasicSerializer.OBJECT);
    addBasic(java.util.Date.class, "date", BasicSerializer.DATE);

    addBasic(boolean.class, "boolean", BasicSerializer.BOOLEAN);
    addBasic(byte.class, "byte", BasicSerializer.BYTE);
    addBasic(short.class, "short", BasicSerializer.SHORT);
    addBasic(int.class, "int", BasicSerializer.INTEGER);
    addBasic(long.class, "long", BasicSerializer.LONG);
    addBasic(float.class, "float", BasicSerializer.FLOAT);
    addBasic(double.class, "double", BasicSerializer.DOUBLE);
    addBasic(char.class, "char", BasicSerializer.CHARACTER);
    
    addBasic(boolean[].class, "[boolean", BasicSerializer.BOOLEAN_ARRAY);
    addBasic(byte[].class, "[byte", BasicSerializer.BYTE_ARRAY);
    addBasic(short[].class, "[short", BasicSerializer.SHORT_ARRAY);
    addBasic(int[].class, "[int", BasicSerializer.INTEGER_ARRAY);
    addBasic(long[].class, "[long", BasicSerializer.LONG_ARRAY);
    addBasic(float[].class, "[float", BasicSerializer.FLOAT_ARRAY);
    addBasic(double[].class, "[double", BasicSerializer.DOUBLE_ARRAY);
    addBasic(char[].class, "[char", BasicSerializer.CHARACTER_ARRAY);
    addBasic(String[].class, "[string", BasicSerializer.STRING_ARRAY);
    addBasic(Object[].class, "[object", BasicSerializer.OBJECT_ARRAY);

    _serializerMap.put(Class.class, new ClassSerializer());
    _deserializerMap.put(Class.class, new ClassDeserializer());

    _deserializerMap.put(Number.class, new BasicDeserializer(BasicSerializer.NUMBER));
    
    _serializerMap.put(BigDecimal.class, new StringValueSerializer());
    try {
      _deserializerMap.put(BigDecimal.class,
			   new StringValueDeserializer(BigDecimal.class));
    } catch (Throwable e) {
    }
    
    // 后面代码省略，内容基本同上
}

addBasic 做了写什么呢？

// addBasic 做的很简单 以 addBasic(Integer.class, "int", BasicSerializer.INTEGER); 为例子实际上就是_serializerMap.put(Integer.class, new BasicSerializer(BasicSerializer.INTEGER));
private static void addBasic(Class cl, String typeName, int type)
{
	// 放入key-value
	_serializerMap.put(cl, new BasicSerializer(type));

	Deserializer deserializer = new BasicDeserializer(type);
	_deserializerMap.put(cl, deserializer);
	_typeMap.put(typeName, deserializer);
}

2.out.writeObject(obj);

HessianOutput 继承 AbstractHessianOutput 且 writeObject是 父类中的一个抽象方法，我们看下在HessianOutput中 writeObject做了写什么：

public void writeObject(Object object)
    throws IOException
{
	if (object == null) {
	  writeNull();
	  return;
	}

	Serializer serializer;
	//从序列化工厂得到能够序列化该对象的序列化类
	serializer = _serializerFactory.getSerializer(object.getClass());   
	//使用具体的序列化类序列化对象
	serializer.writeObject(object, this); 
}

我们看下 _serializerFactory.getSerializer(object.getClass());的实现

public Serializer getSerializer(Class cl)
    throws HessianProtocolException
{
    Serializer serializer;

	// 如果是简单类型，那么直接就能获取到（备注：这里能够取到的都是之前在SerializerFactory的static静态代码块中初始化的那些key）
    serializer = (Serializer) _serializerMap.get(cl);
    if (serializer != null)
      return serializer;

	// 从缓存中取 （为什么这里有个缓存的东西，看后面代码就立刻明了）
    if (_cachedSerializerMap != null) {
      serializer = (Serializer) _cachedSerializerMap.get(cl);
      
      if (serializer != null)
	return serializer;
    }
	
	// 省略部分代码....

	// 获取其他类型的序列化类
    if (serializer != null) {
    }

    else if (HessianRemoteObject.class.isAssignableFrom(cl))
      serializer = new RemoteSerializer();

    else if (BurlapRemoteObject.class.isAssignableFrom(cl))
      serializer = new RemoteSerializer();

    else if (Map.class.isAssignableFrom(cl))
      serializer = new MapSerializer();

    else if (Collection.class.isAssignableFrom(cl)) {
      if (_collectionSerializer == null) {
	_collectionSerializer = new CollectionSerializer();
      }

      serializer = _collectionSerializer;
    }

    else if (cl.isArray())
      serializer = new ArraySerializer();

    else if (Throwable.class.isAssignableFrom(cl))
      serializer = new ThrowableSerializer(cl);

    else if (InputStream.class.isAssignableFrom(cl))
      serializer = new InputStreamSerializer();

    else if (Iterator.class.isAssignableFrom(cl))
      serializer = IteratorSerializer.create();

    else if (Enumeration.class.isAssignableFrom(cl))
      serializer = EnumerationSerializer.create();
    
    else if (Calendar.class.isAssignableFrom(cl))
      serializer = CalendarSerializer.create();
    
    else if (_enumClass != null && _enumClass.isAssignableFrom(cl))
      serializer = new EnumSerializer(cl);

    if (serializer == null)
	   // 使用默认序列化类（JavaSerializer)，一般是序列化我们自定义类的
      serializer = getDefaultSerializer(cl);  

	
    if (_cachedSerializerMap == null)
      _cachedSerializerMap = new HashMap(8);

	
	// 放入缓存map中，下次获取同样的序列化类就比较方便，不需要再经过那么多判断了
    _cachedSerializerMap.put(cl, serializer);

    return serializer;
}

3.serializer.writeObject(object, this);

这里使用刚才获取到的Serializer类（可能是JavaSerializer，也可能是BasicSerializer或者其他序列化类）来序列化对象，具体实现留待下次分析

总结以下序列化的过程就是：

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