json-lib反序列化时(JSONObject.toBean)，时间类型为空的处理

需求：

在我们的项目里希望JsonString传入日期类型值为空时，JSONObject.toBean时可以将Java对象的该日期属性设为null。

解决过程：

json-lib反序列化Json字符串为Java对象，可以通过以下代码处理日期字段：

 public static <T> T JsonToBean(Class<T> clazz, String JsonString) {
         JSONUtils.getMorpherRegistry().registerMorpher(
                 new DateMorpher(new String[] { "yyyy-MM-dd HH:mm:ss",
                         "yyyy-MM-dd", "yyyy-MM-dd't'HH:mm:ss" }));
         JSONObject jsonObject = JSONObject.fromObject(JsonString);
         T entity = (T) JSONObject.toBean(jsonObject, clazz);
         return entity;
     }

但如果JsonString传入{"createDate":""}时,则会在“T entity = (T) JSONObject.toBean(jsonObject, clazz)”时报以下错误：

net.sf.json.JSONException: Error while setting property=createDate type class java.lang.String

查看net.sf.ezmorph.object.DateMorpher方法的源码，关于字符串转时间的代码如下：

       public Object morph(Object value)
        {
          if (value == null) {
            return null;
          }

          if (Date.class.isAssignableFrom(value.getClass())) {
            return (Date)value;
          }

          if (!supports(value.getClass())) {
            throw new MorphException(value.getClass() + " is not supported");
          }

          String strValue = (String)value;
          SimpleDateFormat dateParser = null;

          for (int i = 0; i < this.formats.length; ++i) {
            if (dateParser == null)
              dateParser = new SimpleDateFormat(this.formats[i], this.locale);
            else {
              dateParser.applyPattern(this.formats[i]);
            }
            dateParser.setLenient(this.lenient);
            try {
              return dateParser.parse(strValue.toLowerCase());
            }
            catch (ParseException localParseException)
            {
            }
          }

          if (super.isUseDefault()) {
            return this.defaultValue;
          }
          throw new MorphException("Unable to parse the date " + value);
        }

可以看到，在18~32行会使用我们传入的formats循环进行字符串转换，如果转换成功则返回Date，如果全部失败则在37行处抛出异常，最后导致toBean方法失败。

可以看到DateMorpher类有这个构造函数可以传入Date defaultValue，在morph方法的第34行如果之前的转换均失败即返回defaultValue。但使用(Date)null作为defaultValue，在初始化DateMorpher对象时会报空指针异常，原因是DateMorpher类中有如下方法：

   public void setDefaultValue(Date defaultValue)
       {
           this.defaultValue = ((Date)defaultValue.clone());
       }

       public Date getDefaultValue()
       {
           return (Date)this.defaultValue.clone();
       }

“this.defaultValue.clone();”中defaultValue 为null所以报异常。

解决方法：

重新实现DateMorpher方法，修改setDefaultValue(Date defaultValue)和getDefaultValue()方法，对null进行处理

（当然也可是修改net.sf.ezmorph.object.DateMorpher方法，重新打包ezmorph-1.0.6.jar）。

以下是重新实现的DateMorpherEx方法：

 import net.sf.ezmorph.object.AbstractObjectMorpher;
 import java.text.DateFormat;
 import java.text.ParseException;
 import java.text.SimpleDateFormat;
 import java.util.Date;
 import java.util.Locale;
 import net.sf.ezmorph.MorphException;
 import org.apache.commons.lang.builder.EqualsBuilder;
 import org.apache.commons.lang.builder.HashCodeBuilder;

 public class DateMorpherEx extends AbstractObjectMorpher {

     private Date defaultValue;
       private String[] formats;
       private boolean lenient;
       private Locale locale;

       public DateMorpherEx(String[] formats)
       {
         this(formats, Locale.getDefault(), false);
       }

       public DateMorpherEx(String[] formats, boolean lenient)
       {
         this(formats, Locale.getDefault(), lenient);
       }

       public DateMorpherEx(String[] formats, Date defaultValue)
       {
         this(formats, defaultValue, Locale.getDefault(), false);
       }

       public DateMorpherEx(String[] formats, Date defaultValue, Locale locale, boolean lenient)
       {
         super(true);
         if ((formats == null) || (formats.length == 0)) {
           throw new MorphException("invalid array of formats");
         }

         this.formats = formats;

         if (locale == null)
           this.locale = Locale.getDefault();
         else {
           this.locale = locale;
         }

         this.lenient = lenient;
         setDefaultValue(defaultValue);
       }

       public DateMorpherEx(String[] formats, Locale locale)
       {
         this(formats, locale, false);
       }

       public DateMorpherEx(String[] formats, Locale locale, boolean lenient)
       {
         if ((formats == null) || (formats.length == 0)) {
           throw new MorphException("invalid array of formats");
         }

         this.formats = formats;

         if (locale == null)
           this.locale = Locale.getDefault();
         else {
           this.locale = locale;
         }

         this.lenient = lenient;
       }

       public boolean equals(Object obj)
       {
         if (this == obj) {
           return true;
         }
         if (obj == null) {
           return false;
         }

         if (!(obj instanceof DateMorpherEx)) {
           return false;
         }

         DateMorpherEx other = (DateMorpherEx)obj;
         EqualsBuilder builder = new EqualsBuilder();
         builder.append(this.formats, other.formats);
         builder.append(this.locale, other.locale);
         builder.append(this.lenient, other.lenient);
         if ((super.isUseDefault()) && (other.isUseDefault())) {
           builder.append(getDefaultValue(), other.getDefaultValue());
           return builder.isEquals();
         }if ((!super.isUseDefault()) && (!other.isUseDefault())) {
           return builder.isEquals();
         }
         return false;
       }

       public Date getDefaultValue()
       {
           if(this.defaultValue!=null)
               return (Date)this.defaultValue.clone();
           else
               return this.defaultValue;
       }

       public int hashCode()
       {
         HashCodeBuilder builder = new HashCodeBuilder();
         builder.append(this.formats);
         builder.append(this.locale);
         builder.append(this.lenient);
         if (super.isUseDefault()) {
           builder.append(getDefaultValue());
         }
         return builder.toHashCode();
       }

       public Object morph(Object value)
       {
         if (value == null) {
           return null;
         }

         if (Date.class.isAssignableFrom(value.getClass())) {
           return (Date)value;
         }

         if (!supports(value.getClass())) {
           throw new MorphException(value.getClass() + " is not supported");
         }

         String strValue = (String)value;
         SimpleDateFormat dateParser = null;

         for (int i = 0; i < this.formats.length; ++i) {
           if (dateParser == null)
             dateParser = new SimpleDateFormat(this.formats[i], this.locale);
           else {
             dateParser.applyPattern(this.formats[i]);
           }
           dateParser.setLenient(this.lenient);
           try {
             return dateParser.parse(strValue.toLowerCase());
           }
           catch (ParseException localParseException)
           {
           }

         }

         if (super.isUseDefault()) {
           return this.defaultValue;
         }
         throw new MorphException("Unable to parse the date " + value);
       }

       public Class morphsTo()
       {
         return Date.class;
       }

       public void setDefaultValue(Date defaultValue)
       {
           if(defaultValue!=null)
               this.defaultValue = ((Date)defaultValue.clone());
           else
               this.defaultValue = null;
       }

       public boolean supports(Class clazz)
       {
         return String.class.isAssignableFrom(clazz);
       }
 }

修改原 JsonToBean 方法，调用DateMorpherEx：

 public static <T> T JsonToBean(Class<T> clazz, String JsonString) {
         JSONUtils.getMorpherRegistry().registerMorpher(
                 new DateMorpherEx(new String[] { "yyyy-MM-dd HH:mm:ss",
                         "yyyy-MM-dd", "yyyy-MM-dd't'HH:mm:ss" }, (Date) null));//调用DateMorpherEx，defaultValue为null
         JSONObject jsonObject = JSONObject.fromObject(JsonString);
         T entity = (T) JSONObject.toBean(jsonObject, clazz);
         return entity;
     }