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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。
1 public abstract class AbstractBean implements Serializable { 2 protected HashMapWrapper internalHashMapData = null; 3 4 public HashMapWrapper getInternalHashMapData() { 5 return internalHashMapData; 6 } 7 8 public void setInternalHashMapData(HashMapWrapper internalHashMapData) { 9 this.internalHashMapData = internalHashMapData;10 }11 } 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。
1 public class FirstJavaBean extends AbstractBean {2 public String getName(){3 return this.internalHashMapData.getString("name");4 }5 public void setName(String name){6 this.internalHashMapData.setString("name",name);7 }8 } 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。
1 public class HashMapWrapper implements Serializable { 2 private HashMap internalHashMap; 3 public HashMapWrapper(){ 4 internalHashMap = new HashMap (0); 5 } 6 public void setInternalHashMap(HashMap hashMap){ 7 this.internalHashMap = hashMap; 8 } 9 public HashMap getInternalHashMap(){ 10 return this.internalHashMap; 11 } 12 13 public BigDecimal getBigDecimal(String key){ 14 return getBigDecimalOr(key,null); 15 } 16 public BigDecimal getBigDecimalOr(String key,BigDecimal defaultValue){ 17 Object value = internalHashMap.get(key); 18 if(value instanceof BigDecimal){ 19 return (BigDecimal)value; 20 }else 21 return defaultValue; 22 } 23 24 public void setBigDecimal(String key,BigDecimal value){ 25 internalHashMap.put(key,value); 26 } 27 28 public BigInteger getBigInteger(String key){ 29 return getBigIntegerOr(key,null); 30 } 31 public BigInteger getBigIntegerOr(String key,BigInteger defaultValue){ 32 Object value = internalHashMap.get(key); 33 if(value instanceof BigInteger){ 34 return (BigInteger)value; 35 }else 36 return defaultValue; 37 } 38 public void setBigInteger(String key,BigInteger value){ 39 internalHashMap.put(key,value); 40 } 41 public Boolean getBooleanOr(String key,Boolean defaultValue){ 42 Object value = internalHashMap.get(key); 43 if(value instanceof Boolean){ 44 return (Boolean)value; 45 }else 46 return defaultValue; 47 } 48 public Boolean getBoolean(String key){ 49 return getBooleanOr(key,null); 50 } 51 52 public void setBoolean(String key,Boolean value){ 53 internalHashMap.put(key,value); 54 } 55 public Byte getByte(String key){ 56 return getByteOr(key,null); 57 } 58 public Byte getByteOr(String key,Byte defaultValue){ 59 Object value = internalHashMap.get(key); 60 if(value instanceof Byte){ 61 return (Byte)value; 62 }else 63 return defaultValue; 64 } 65 66 public void setByte(String key,Byte value){ 67 internalHashMap.put(key,value); 68 } 69 public Character getCharacterOr(String key,Character defaultValue){ 70 Object value = internalHashMap.get(key); 71 if(value instanceof Character){ 72 return (Character)value; 73 }else 74 return defaultValue; 75 } 76 public Character getCharacter(String key){ 77 return getCharacterOr(key,null); 78 } 79 public void setCharacter(String key,Character value){ 80 internalHashMap.put(key,value); 81 } 82 public Date getDateOr(String key, Date defaultValue){ 83 Object value = internalHashMap.get(key); 84 if(value instanceof Date){ 85 return (Date)value; 86 }else 87 return defaultValue; 88 } 89 public Date getDate(String key){ 90 return getDateOr(key,null); 91 } 92 public void setDate(String key,Date value){ 93 internalHashMap.put(key,value); 94 } 95 96 public Double getDouble(String key){ 97 return getDoubleOr(key,null); 98 } 99 public Double getDoubleOr(String key,Double defaultValue){100 Object value = internalHashMap.get(key);101 if(value instanceof Double){102 return (Double)value;103 }else104 return defaultValue;105 }106 public void setDouble(String key,Double value){107 internalHashMap.put(key,value);108 }109 public Float getFloatOr(String key,Float defaultValue){110 Object value = internalHashMap.get(key);111 if(value instanceof Float){112 return (Float)value;113 }else114 return defaultValue;115 }116 public Float getFloat(String key){117 return getFloatOr(key,null);118 }119 public void setFloat(String key,Float value){120 internalHashMap.put(key,value);121 }122 public Integer getIntegerOr(String key,Integer defaultValue){123 Object value = internalHashMap.get(key);124 if(value instanceof Integer){125 return (Integer)value;126 }else127 return defaultValue;128 }129 public Integer getInteger(String key){130 return getIntegerOr(key,null);131 }132 public void setInteger(String key,Integer value){133 internalHashMap.put(key,value);134 }135 public Long getLongOr(String key,Long defaultValue){136 Object value = internalHashMap.get(key);137 if(value instanceof Long){138 return (Long)value;139 }else140 return defaultValue;141 }142 public Long getLong(String key){143 return getLongOr(key,null);144 }145 public void setLong(String key,Long value){146 internalHashMap.put(key,value);147 }148 public Short getShortOr(String key,Short defaultValue){149 Object value = internalHashMap.get(key);150 if(value instanceof Short){151 return (Short)value;152 }else153 return defaultValue;154 }155 public Short getShort(String key){156 return getShortOr(key,null);157 }158 public void setShort(String key,Short value){159 internalHashMap.put(key,value);160 }161 public String getStringOr(String key,String defaultValue){162 Object value = internalHashMap.get(key);163 if(value instanceof String){164 return (String)value;165 }else166 return defaultValue;167 }168 public String getString(String key){169 return getStringOr(key,null);170 }171 public void setString(String key,String value){172 internalHashMap.put(key,value);173 }174 public boolean getBooleanValueOr(String key,boolean defaultValue){175 Object value = internalHashMap.get(key);176 if(value instanceof Boolean){177 return (Boolean)value;178 }else179 return defaultValue;180 }181 public boolean getBooleanValue(String key){182 return getBooleanValueOr(key,false);183 }184 public void setBooleanValue(String key,boolean value){185 internalHashMap.put(key,value);186 }187 public byte getByteValueOr(String key,byte defaultValue){188 Object value = internalHashMap.get(key);189 if(value instanceof Byte){190 return (Byte)value;191 }else192 return defaultValue;193 }194 public byte getByteValue(String key){195 return getByteValueOr(key,(byte)0);196 }197 public void setByteValue(String key,byte value){198 internalHashMap.put(key,value);199 }200 public char getCharValueOr(String key,char defaultValue){201 Object value = internalHashMap.get(key);202 if(value instanceof Character){203 return (Character)value;204 }else205 return defaultValue;206 }207 public char getCharValue(String key){208 return getCharValueOr(key,(char)0);209 }210 public void setCharValue(String key,char value){211 internalHashMap.put(key,value);212 }213 public double getDoubleValueOr(String key,double defaultValue){214 Object value = internalHashMap.get(key);215 if(value instanceof Double){216 return (Double)value;217 }else218 return defaultValue;219 }220 public double getDoubleValue(String key){221 return getDoubleValueOr(key,0.0d);222 }223 public void setDoubleValue(String key,double value){224 internalHashMap.put(key,value);225 }226 public float getFloatValueOr(String key,float defaultValue){227 Object value = internalHashMap.get(key);228 if(value instanceof Float){229 return (Float)value;230 }else231 return defaultValue;232 }233 public float getFloatValue(String key){234 return getFloatValueOr(key,0.0f);235 }236 public void setFloatValue(String key,float value){237 internalHashMap.put(key,value);238 }239 public int getIntValueOr(String key,int defaultValue){240 Object value = internalHashMap.get(key);241 if(value instanceof Integer){242 return (Integer)value;243 }else244 return defaultValue;245 }246 public int getIntValue(String key){247 return getIntValueOr(key,0);248 }249 public void setIntValue(String key,int value){250 internalHashMap.put(key,value);251 }252 public long getLongValueOr(String key,long defaultValue){253 Object value = internalHashMap.get(key);254 if(value instanceof Long){255 return (Long)value;256 }else257 return defaultValue;258 }259 public long getLongValue(String key){260 return getLongValueOr(key,0L);261 }262 public void setLongValue(String key,long value){263 internalHashMap.put(key,value);264 }265 public short getShortValueOr(String key,short defaultValue){266 Object value = internalHashMap.get(key);267 if(value instanceof Short){268 return (Short)value;269 }else270 return defaultValue;271 }272 public short getShortValue(String key){273 return getShortValueOr(key,(short)0);274 }275 public void setShortValue(String key,short value){276 internalHashMap.put(key,value);277 }278 public Object getObjectOr(String key,Object defaultValue){279 Object value = internalHashMap.get(key);280 if( value == null ){281 return defaultValue;282 }else {283 return internalHashMap.get(key);284 }285 }286 public Object getObject(String key){287 return internalHashMap.get(key);288 }289 public void setObject(String key,Object value){290 internalHashMap.put(key,value);291 }292 public T getAsResultOr(String key,T defaultValue){293 T value = (T) internalHashMap.get(key);294 if(value == null){295 return defaultValue;296 }else {297 return value;298 }299 }300 public T getAsResult(String key){301 return (T) internalHashMap.get(key);302 }303 public void setAsValue(String key,T value){304 internalHashMap.put(key,value);305 }306 307 public boolean getboolean(String key) {308 return getBooleanValue(key);309 }310 public void setboolean(String key,boolean value){311 setBooleanValue(key,value);312 }313 public byte getbyte(String key) {314 return getByteValue(key);315 }316 public void setbyte(String key,byte value){317 setByteValue(key,value);318 }319 public char getchar(String key) {320 return getCharValue(key);321 }322 public void setchar(String key,char value){323 setCharValue(key,value);324 }325 public double getdouble(String key) {326 return getDoubleValue(key);327 }328 public void setdouble(String key,double value){329 setDoubleValue(key,value);330 }331 public float getfloat(String key) {332 return getFloatValue(key);333 }334 public void setfloat(String key,float value){335 setFloatValue(key,value);336 }337 public int getint(String key) {338 return getIntValue(key);339 }340 public void setint(String key,int value){341 setIntValue(key,value);342 }343 public long getlong(String key) {344 return getLongValue(key);345 }346 public void setlong(String key,long value){347 setLongValue(key,value);348 }349 public short getshort(String key) {350 return getShortValue(key);351 }352 public void setshort(String key,short value){353 setShortValue(key,value);354 }355 }
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