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

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;
    }