一种高兼容性的JavaBean序列化方案

　　在对JavaBean做序列化时，我们可能在某些场景希望前后兼容性好一些。比如所有的javaBean都序列化后保存在数据库，用的时候需要反序列化创建。随着业务的发展，数据模型可能会进行变更，那么原来的数据进行反序列化时可能会遇到版本不一致的问题。作者在对drools的Fact建模时就遇到了类似问题。那么有没有一种兼容性比较好的序列化方案同时又不失javaBean的基础特性（getter和setter函数）呢？答案是肯定的。

　　其实，简单来说，HashMap的序列化时兼容性应该是最好的，因为它就是简单的键值对，不需要版本的概念。但毕竟不是JavaBean对象，那么能不能融合着两者呢？哈哈，当然可以，废话不多说，先上代码。

 public abstract class AbstractBean implements Serializable {
     protected HashMapWrapper internalHashMapData = null;

     public HashMapWrapper getInternalHashMapData() {
         return internalHashMapData;
     }

     public void setInternalHashMapData(HashMapWrapper internalHashMapData) {
         this.internalHashMapData = internalHashMapData;
     }
 }

　　AbstractBean这个抽象类，保护一个HashMapWrapper的字段，用来存储所有字段的数据。

 public class FirstJavaBean extends AbstractBean {
     public String getName(){
         return this.internalHashMapData.getString("name");
     }
     public void setName(String name){
         this.internalHashMapData.setString("name",name);
     }
 }

　　继承AbstractBean时，包含了一个name字段，要特别注意getter和setter的实现方式。都是通过internalHashMapData存取数据的。这样做可以把数据的存储和数据的接口解耦了。如果FirstJavaBean接口变更了，对数据存取没有任何影响，序列化时就可以消除版本不一致带来的问题了！这个方法还是非常巧妙的有没有。

　　下面是对hashMap的简单封装，由于该封装后期不再变化，对序列化也不会有任何影响。

 public class HashMapWrapper implements Serializable {
     private HashMap<String,Object> internalHashMap;
     public HashMapWrapper(){
         internalHashMap = new HashMap<String,Object>(0);
     }
     public void setInternalHashMap(HashMap<String,Object> hashMap){
         this.internalHashMap = hashMap;
     }
     public HashMap<String,Object> getInternalHashMap(){
         return this.internalHashMap;
     }

     public BigDecimal getBigDecimal(String key){
         return getBigDecimalOr(key,null);
     }
     public BigDecimal getBigDecimalOr(String key,BigDecimal defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof BigDecimal){
             return (BigDecimal)value;
         }else
             return defaultValue;
     }

     public void setBigDecimal(String key,BigDecimal value){
         internalHashMap.put(key,value);
     }

     public BigInteger getBigInteger(String key){
         return getBigIntegerOr(key,null);
     }
     public BigInteger getBigIntegerOr(String key,BigInteger defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof BigInteger){
             return (BigInteger)value;
         }else
             return defaultValue;
     }
     public void setBigInteger(String key,BigInteger value){
         internalHashMap.put(key,value);
     }
     public Boolean getBooleanOr(String key,Boolean defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Boolean){
             return (Boolean)value;
         }else
             return defaultValue;
     }
     public Boolean getBoolean(String key){
         return getBooleanOr(key,null);
     }

     public void setBoolean(String key,Boolean value){
         internalHashMap.put(key,value);
     }
     public Byte getByte(String key){
         return getByteOr(key,null);
     }
     public Byte getByteOr(String key,Byte defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Byte){
             return (Byte)value;
         }else
             return defaultValue;
     }

     public void setByte(String key,Byte value){
         internalHashMap.put(key,value);
     }
     public Character getCharacterOr(String key,Character defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Character){
             return (Character)value;
         }else
             return defaultValue;
     }
     public Character getCharacter(String key){
         return getCharacterOr(key,null);
     }
     public void setCharacter(String key,Character value){
         internalHashMap.put(key,value);
     }
     public Date getDateOr(String key, Date defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Date){
             return (Date)value;
         }else
             return defaultValue;
     }
     public Date getDate(String key){
         return getDateOr(key,null);
     }
     public void setDate(String key,Date value){
         internalHashMap.put(key,value);
     }

     public Double getDouble(String key){
         return getDoubleOr(key,null);
     }
     public Double getDoubleOr(String key,Double defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Double){
             return (Double)value;
         }else
             return defaultValue;
     }
     public void setDouble(String key,Double value){
         internalHashMap.put(key,value);
     }
     public Float getFloatOr(String key,Float defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Float){
             return (Float)value;
         }else
             return defaultValue;
     }
     public Float getFloat(String key){
         return getFloatOr(key,null);
     }
     public void setFloat(String key,Float value){
         internalHashMap.put(key,value);
     }
     public Integer getIntegerOr(String key,Integer defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Integer){
             return (Integer)value;
         }else
             return defaultValue;
     }
     public Integer getInteger(String key){
         return getIntegerOr(key,null);
     }
     public void setInteger(String key,Integer value){
         internalHashMap.put(key,value);
     }
     public Long getLongOr(String key,Long defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Long){
             return (Long)value;
         }else
             return defaultValue;
     }
     public Long getLong(String key){
         return getLongOr(key,null);
     }
     public void setLong(String key,Long value){
         internalHashMap.put(key,value);
     }
     public Short getShortOr(String key,Short defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Short){
             return (Short)value;
         }else
             return defaultValue;
     }
     public Short getShort(String key){
         return getShortOr(key,null);
     }
     public void setShort(String key,Short value){
         internalHashMap.put(key,value);
     }
     public String getStringOr(String key,String defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof String){
             return (String)value;
         }else
             return defaultValue;
     }
     public String getString(String key){
         return getStringOr(key,null);
     }
     public void setString(String key,String value){
         internalHashMap.put(key,value);
     }
     public boolean getBooleanValueOr(String key,boolean defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Boolean){
             return (Boolean)value;
         }else
             return defaultValue;
     }
     public boolean getBooleanValue(String key){
         return getBooleanValueOr(key,false);
     }
     public void setBooleanValue(String key,boolean value){
         internalHashMap.put(key,value);
     }
     public byte getByteValueOr(String key,byte defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Byte){
             return (Byte)value;
         }else
             return defaultValue;
     }
     public byte getByteValue(String key){
         return getByteValueOr(key,(byte)0);
     }
     public void setByteValue(String key,byte value){
         internalHashMap.put(key,value);
     }
     public char getCharValueOr(String key,char defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Character){
             return (Character)value;
         }else
             return defaultValue;
     }
     public char getCharValue(String key){
         return getCharValueOr(key,(char)0);
     }
     public void setCharValue(String key,char value){
         internalHashMap.put(key,value);
     }
     public double getDoubleValueOr(String key,double defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Double){
             return (Double)value;
         }else
             return defaultValue;
     }
     public double getDoubleValue(String key){
         return getDoubleValueOr(key,0.0d);
     }
     public void setDoubleValue(String key,double value){
         internalHashMap.put(key,value);
     }
     public float getFloatValueOr(String key,float defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Float){
             return (Float)value;
         }else
             return defaultValue;
     }
     public float getFloatValue(String key){
         return getFloatValueOr(key,0.0f);
     }
     public void setFloatValue(String key,float value){
         internalHashMap.put(key,value);
     }
     public int getIntValueOr(String key,int defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Integer){
             return (Integer)value;
         }else
             return defaultValue;
     }
     public int getIntValue(String key){
         return getIntValueOr(key,0);
     }
     public void setIntValue(String key,int value){
         internalHashMap.put(key,value);
     }
     public long getLongValueOr(String key,long defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Long){
             return (Long)value;
         }else
             return defaultValue;
     }
     public long getLongValue(String key){
         return getLongValueOr(key,0L);
     }
     public void setLongValue(String key,long value){
         internalHashMap.put(key,value);
     }
     public short getShortValueOr(String key,short defaultValue){
         Object value = internalHashMap.get(key);
         if(value instanceof Short){
             return (Short)value;
         }else
             return defaultValue;
     }
     public short getShortValue(String key){
         return getShortValueOr(key,(short)0);
     }
     public void setShortValue(String key,short value){
         internalHashMap.put(key,value);
     }
     public Object getObjectOr(String key,Object defaultValue){
         Object value = internalHashMap.get(key);
         if( value == null ){
             return defaultValue;
         }else {
             return internalHashMap.get(key);
         }
     }
     public Object getObject(String key){
         return internalHashMap.get(key);
     }
     public void setObject(String key,Object value){
         internalHashMap.put(key,value);
     }
     public <T> T getAsResultOr(String key,T defaultValue){
         T value = (T) internalHashMap.get(key);
         if(value == null){
             return defaultValue;
         }else {
             return value;
         }
     }
     public <T> T getAsResult(String key){
         return (T) internalHashMap.get(key);
     }
     public <T> void setAsValue(String key,T value){
         internalHashMap.put(key,value);
     }

     public boolean getboolean(String key) {
         return getBooleanValue(key);
     }
     public void setboolean(String key,boolean value){
         setBooleanValue(key,value);
     }
     public byte getbyte(String key) {
         return getByteValue(key);
     }
     public void setbyte(String key,byte value){
         setByteValue(key,value);
     }
     public char getchar(String key) {
         return getCharValue(key);
     }
     public void setchar(String key,char value){
         setCharValue(key,value);
     }
     public double getdouble(String key) {
         return getDoubleValue(key);
     }
     public void setdouble(String key,double value){
         setDoubleValue(key,value);
     }
     public float getfloat(String key) {
         return getFloatValue(key);
     }
     public void setfloat(String key,float value){
         setFloatValue(key,value);
     }
     public int getint(String key) {
         return getIntValue(key);
     }
     public void setint(String key,int value){
         setIntValue(key,value);
     }
     public long getlong(String key) {
         return getLongValue(key);
     }
     public void setlong(String key,long value){
         setLongValue(key,value);
     }
     public short getshort(String key) {
         return getShortValue(key);
     }
     public void setshort(String key,short value){
         setShortValue(key,value);
     }
 }