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;
}