json-lib json反序列化——日期转换

将json格式的字符串转为对象，其中key-value有将String的日期转为Date类型，怪现象就是，转出来的Date类型的值是当前的系统时间。

网上有许多答案，在反序列化之前需要注册Date解析类型，也就是这段代码：

JSONUtils.getMorpherRegistry().registerMorpher(new DateMorpher(new String[]{"yyyy-MM-dd"}));

发现并没啥用，最后发现一切的原因都是因为这个方法用错了。

仔细看源码，原来在json-lib中一个MorpherRegistry类，所有的转化类型都存在Map morphers中。

在第一次使用JSONObject静态方法时，就会自动注册默认的类型，JSONObject.java中调用了JSONUtils.java，JSONUtils.java源码中有这么一段：

static {
    MorphUtils.registerStandardMorphers(morpherRegistry);
}

在MorphUtils.java代码是：

 public class MorphUtils {
     public static final BigDecimal BIGDECIMAL_ONE = new BigDecimal("1");
     public static final BigDecimal BIGDECIMAL_ZERO = new BigDecimal("0");

     public static void registerStandardMorphers(MorpherRegistry morpherRegistry) {
         morpherRegistry.clear();
         registerStandardPrimitiveMorphers(morpherRegistry);
         registerStandardPrimitiveArrayMorphers(morpherRegistry);
         registerStandardObjectMorphers(morpherRegistry);
         registerStandardObjectArrayMorphers(morpherRegistry);
     }

     public static void registerStandardObjectArrayMorphers(MorpherRegistry morpherRegistry) {
         morpherRegistry.registerMorpher(new ObjectArrayMorpher(new BooleanObjectMorpher(Boolean.FALSE)));
         morpherRegistry.registerMorpher(new ObjectArrayMorpher(new CharacterObjectMorpher(new Character('\u0000'))));
         morpherRegistry.registerMorpher(new ObjectArrayMorpher(StringMorpher.getInstance()));
         morpherRegistry.registerMorpher(new ObjectArrayMorpher(new NumberMorpher(Byte.class, new Byte((byte)0))));
         morpherRegistry.registerMorpher(new ObjectArrayMorpher(new NumberMorpher(Short.class, new Short((short)0))));
         morpherRegistry.registerMorpher(new ObjectArrayMorpher(new NumberMorpher(Integer.class, new Integer(0))));
         morpherRegistry.registerMorpher(new ObjectArrayMorpher(new NumberMorpher(Long.class, new Long(0L))));
         morpherRegistry.registerMorpher(new ObjectArrayMorpher(new NumberMorpher(Float.class, new Float(0.0F))));
         morpherRegistry.registerMorpher(new ObjectArrayMorpher(new NumberMorpher(Double.class, new Double(0.0D))));
         morpherRegistry.registerMorpher(new ObjectArrayMorpher(new NumberMorpher(BigInteger.class, BigInteger.ZERO)));
         morpherRegistry.registerMorpher(new ObjectArrayMorpher(new NumberMorpher(BigDecimal.class, BIGDECIMAL_ZERO)));
         morpherRegistry.registerMorpher(new ObjectArrayMorpher(ClassMorpher.getInstance()));
     }

     public static void registerStandardObjectMorphers(MorpherRegistry morpherRegistry) {
         morpherRegistry.registerMorpher(new BooleanObjectMorpher(Boolean.FALSE));
         morpherRegistry.registerMorpher(new CharacterObjectMorpher(new Character('\u0000')));
         morpherRegistry.registerMorpher(StringMorpher.getInstance());
         morpherRegistry.registerMorpher(new NumberMorpher(Byte.class, new Byte((byte)0)));
         morpherRegistry.registerMorpher(new NumberMorpher(Short.class, new Short((short)0)));
         morpherRegistry.registerMorpher(new NumberMorpher(Integer.class, new Integer(0)));
         morpherRegistry.registerMorpher(new NumberMorpher(Long.class, new Long(0L)));
         morpherRegistry.registerMorpher(new NumberMorpher(Float.class, new Float(0.0F)));
         morpherRegistry.registerMorpher(new NumberMorpher(Double.class, new Double(0.0D)));
         morpherRegistry.registerMorpher(new NumberMorpher(BigInteger.class, BigInteger.ZERO));
         morpherRegistry.registerMorpher(new NumberMorpher(BigDecimal.class, BIGDECIMAL_ZERO));
         morpherRegistry.registerMorpher(ClassMorpher.getInstance());
     }

     public static void registerStandardPrimitiveArrayMorphers(MorpherRegistry morpherRegistry) {
         morpherRegistry.registerMorpher(new BooleanArrayMorpher(false));
         morpherRegistry.registerMorpher(new CharArrayMorpher('\u0000'));
         morpherRegistry.registerMorpher(new ByteArrayMorpher((byte)0));
         morpherRegistry.registerMorpher(new ShortArrayMorpher((short)0));
         morpherRegistry.registerMorpher(new IntArrayMorpher(0));
         morpherRegistry.registerMorpher(new LongArrayMorpher(0L));
         morpherRegistry.registerMorpher(new FloatArrayMorpher(0.0F));
         morpherRegistry.registerMorpher(new DoubleArrayMorpher(0.0D));
     }

     public static void registerStandardPrimitiveMorphers(MorpherRegistry morpherRegistry) {
         morpherRegistry.registerMorpher(new BooleanMorpher(false));
         morpherRegistry.registerMorpher(new CharMorpher('\u0000'));
         morpherRegistry.registerMorpher(new ByteMorpher((byte)0));
         morpherRegistry.registerMorpher(new ShortMorpher((short)0));
         morpherRegistry.registerMorpher(new IntMorpher(0));
         morpherRegistry.registerMorpher(new LongMorpher(0L));
         morpherRegistry.registerMorpher(new FloatMorpher(0.0F));
         morpherRegistry.registerMorpher(new DoubleMorpher(0.0D));
     }

     private MorphUtils() {
     }
 }

因此，在JSONUtils初始化的时候，就将默认类型放在了MorpherRegistry的morphs中。从上面的代码可以看出来，Date不属于默认的类型。因此，这里可以看出来，在做json反序列化时，如果有需要转成Date类型的String，就需要自己手动注册一个DateMorpher。

怎么加是一个问题了。其实在文章最前面提到的网上的解决方案也并没有错，看下源码就知道了，为啥这个方法却在我使用的时候不起作用了。

在MorpherRegistry.java中Morpher注册源码：

 public class MorpherRegistry implements Serializable {
     private static final long serialVersionUID = -3894767123320768419L;
     private Map morphers = new HashMap();

     public MorpherRegistry() {
     }

     public synchronized Morpher[] getMorphersFor(Class clazz) {
         List registered = (List)this.morphers.get(clazz);
         if(registered != null && !registered.isEmpty()) {
             Morpher[] morphs = new Morpher[registered.size()];
             int k = 0;

             for(Iterator i = registered.iterator(); i.hasNext(); morphs[k++] = (Morpher)i.next()) {
                 ;
             }

             return morphs;
         } else {
             return new Morpher[]{IdentityObjectMorpher.getInstance()};
         }
     }

     public Object morph(Class target, Object value) {
         if(value == null) {
             Morpher var9 = this.getMorpherFor(target);
             if(var9 instanceof ObjectMorpher) {
                 return ((ObjectMorpher)var9).morph(value);
             } else {
                 try {
                     Method var10 = var9.getClass().getDeclaredMethod("morph", new Class[]{class$java$lang$Object == null?(class$java$lang$Object = class$("java.lang.Object")):class$java$lang$Object});
                     return var10.invoke(var9, new Object[]{value});
                 } catch (Exception var7) {
                     throw new MorphException(var7);
                 }
             }
         } else {
             Morpher[] morphers = this.getMorphersFor(target);

             for(int i = 0; i < morphers.length; ++i) {
                 Morpher morpher = morphers[i];
                 if(morpher.supports(value.getClass())) {
                     if(morpher instanceof ObjectMorpher) {
                         return ((ObjectMorpher)morpher).morph(value);
                     }

                     try {
                         Method e = morpher.getClass().getDeclaredMethod("morph", new Class[]{class$java$lang$Object == null?(class$java$lang$Object = class$("java.lang.Object")):class$java$lang$Object});
                         return e.invoke(morpher, new Object[]{value});
                     } catch (Exception var8) {
                         throw new MorphException(var8);
                     }
                 }
             }

             return value;
         }
     }

     public synchronized void registerMorpher(Morpher morpher, boolean override) {
         Object registered = (List)this.morphers.get(morpher.morphsTo());
         if(override || registered == null) {
             registered = new ArrayList();
             this.morphers.put(morpher.morphsTo(), registered);
         }

         if(!((List)registered).contains(morpher)) {
             ((List)registered).add(morpher);
         }

     }
 }

在registerMorpher()中，可以看出来morpher事实上是一个Map<Object.class, List<Morpher>>的结构，而在使用morph()将String转为对象时取得是最先符合的类型。因此，前文中提到提到的网络解决方法，在morpher.get(Object.class)不为空时，只是对List<Morpher> registered进行add操作。由此，在进行转化操作时，就不一定获取到正确的对应类型。因此从registerMorpher()方法中可以看出，我们只需要override设置为false，这个问题也就解决了。

假如我们在调试的时候，需要修改这个注册类型，且又不想重启服务的时候，这样写就很方便了。

JSONUtils.getMorpherRegistry().registerMorpher(new DateMorpher(new String[]{"yyyy-MM-dd"}), true);

这样就能获取到正确的转化类型。

前文还提到一个问题，就是时间转化，变成了当前系统的时间。在MorpherRegistry进行反序列时，morph()中

((ObjectMorpher)morpher).morph(value)

调用的方法是BeanMorpher.morph方法，在BeanMorpher.morp()方法中

 public Object morph(Object sourceBean) {
         if(sourceBean == null) {
             return null;
         } else if(!this.supports(sourceBean.getClass())) {
             throw new MorphException("unsupported class: " + sourceBean.getClass().getName());
         } else {
             Object targetBean = null;

             try {
                 targetBean = this.beanClass.newInstance();
                 PropertyDescriptor[] e = PropertyUtils.getPropertyDescriptors(this.beanClass);

                 for(int i = 0; i < e.length; ++i) {
                     PropertyDescriptor targetPd = e[i];
                     String name = targetPd.getName();
                     if(targetPd.getWriteMethod() == null) {
                         log.info("Property \'" + this.beanClass.getName() + "." + name + "\' has no write method. SKIPPED.");
                     } else {
                         Class sourceType = null;
                         if(sourceBean instanceof DynaBean) {
                             DynaBean targetType = (DynaBean)sourceBean;
                             DynaProperty value = targetType.getDynaClass().getDynaProperty(name);
                             if(value == null) {
                                 log.warn("DynaProperty \'" + name + "\' does not exist. SKIPPED.");
                                 continue;
                             }

                             sourceType = value.getType();
                         } else {
                             PropertyDescriptor var12 = PropertyUtils.getPropertyDescriptor(sourceBean, name);
                             if(var12 == null) {
                                 log.warn("Property \'" + sourceBean.getClass().getName() + "." + name + "\' does not exist. SKIPPED.");
                                 continue;
                             }

                             if(var12.getReadMethod() == null) {
                                 log.warn("Property \'" + sourceBean.getClass().getName() + "." + name + "\' has no read method. SKIPPED.");
                                 continue;
                             }

                             sourceType = var12.getPropertyType();
                         }

                         Class var13 = targetPd.getPropertyType();
                         Object var14 = PropertyUtils.getProperty(sourceBean, name);
                         this.setProperty(targetBean, name, sourceType, var13, var14);
                     }
                 }

                 return targetBean;
             } catch (MorphException var10) {
                 throw var10;
             } catch (Exception var11) {
                 throw new MorphException(var11);
             }
         }
     }

　sourceBean不属于DynaBean，且var12的值也为null，因此返回的值就是targetBean，时间的一个实例，即当前时间。