spring3mvc如何把checkbox的值绑定到model对象的int数据类型

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model对象：User.java:

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public class User {
private int id;
private String name;
//0:男，1:女，页面上表现为radiobutton
private int gender;
private int age;
//0:没毕业，1：已经毕业，页面上表现为checkbox
private int graduted;
//0:没结婚，1：已经结婚，页面上表现为checkbox
private int married;
}

form表单：
<form:form id="user" modelAttribute="user" action="save.do">
<table>
<tr><td>用户名：</td><td><form:input path="name" /></td></tr>
<tr><td>性别：</td><td>男:<form:radiobutton path="gender" value="0"/>
女:<form:radiobutton path="gender" value="1"/></td>
</tr>
<tr><td>年龄：</td><td><form:input path="age" /></td></tr>
<!-- Attribute 'value' is required when binding to non-boolean values -->
<tr><td>其他：</td><td>毕业：<form:checkbox path="graduted" value="1"/>婚否：<form:checkbox path="married" value="1"/></td>
</tr>
<tr><td colspan="2"><input type="submit" value="提交"></td></tr>
</table>
</form:form>

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UserController：
@Controller
@RequestMapping("/user")
public class UserController{
private static class IntEditor extends CustomNumberEditor{
public IntEditor(){
super(Integer.class,true);
}
public void setAsText(String text) throws IllegalArgumentException {
if (text==null || text.trim().equals("")) {
// Treat empty String as null value.
setValue(0);
} else {
// Use default valueOf methods for parsing text.
setValue(Integer.parseInt(text));
}
}
}
@InitBinder
public void initBinder(WebDataBinder binder){
binder.registerCustomEditor(int.class, null, new IntEditor());
}
@RequestMapping(value="/add")
public ModelAndView add(HttpServletRequest request){
ModelAndView mav = new ModelAndView("useradd");
//Neither BindingResult nor plain target object for bean name 'user' available as request attribute
mav.addObject("user", new User());
return mav;
}
@RequestMapping(value="/save")
public ModelAndView save(HttpServletRequest request,
@ModelAttribute("user") User user){
ModelAndView mav = new ModelAndView("redirect:list.do");
System.out.println(user);
return mav;
}
}

浏览器输入：http://localhost:8080/sp3form/user/add.do，会弹出输入页面，如果，两个checkbox都不选中，然后，提交的时候，会报错：

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.validation.BindException: org.springframework.validation.BeanPropertyBindingResult: 2 errors
Field error in object 'user' on field 'graduted': rejected value [null]; codes [typeMismatch.user.graduted,typeMismatch.graduted,typeMismatch.int,typeMismatch]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [user.graduted,graduted]; arguments []; default message [graduted]]; default message [Failed to convert property value of type 'null' to required type 'int' for property 'graduted'; nested exception is java.lang.IllegalArgumentException: Cannot convert value of type [null] to required type [int] for property 'graduted': PropertyEditor [org.springframework.beans.propertyeditors.CustomNumberEditor] returned inappropriate value]
Field error in object 'user' on field 'married': rejected value [null]; codes [typeMismatch.user.married,typeMismatch.married,typeMismatch.int,typeMismatch]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [user.married,married]; arguments []; default message [married]]; default message [Failed to convert property value of type 'null' to required type 'int' for property 'married'; nested exception is java.lang.IllegalArgumentException: Cannot convert value of type [null] to required type [int] for property 'married': PropertyEditor [org.springframework.beans.propertyeditors.CustomNumberEditor] returned inappropriate value]
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:863)

具体的来说就是：null无法转化成int。

然后，上网一通google，基本上是两种解决办法：
（1）使用Integer，而不是int，null不能转化成int，但是可以转化成为Integer。这么做转化虽然没问题，但是，如果把model对象插入到数据库的时候还得把null改成0，麻烦！
（2）添加一个InitBinder，重写setAsText()方法，如同上面的代码那样，可仍然报错！一开始怀疑是setAsText方法没被调用，但是debug的时候发现，有两个值确实调用了setAsText，但是checkbox却并没有调用。也就是说，在setAsText之前就已经出错了！

大家都是你抄我来我抄你，没有一个能解决问题，所谓靠墙墙倒，靠人人跑，本来想偷点懒的，关键时候还得靠自己啊！

然后，就开始debug，看看源码里面是如何处理的。最开始找到的解决办法是重写WebDataBinder里面的getEmptyValue方法：

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protected Object getEmptyValue(String field, Class fieldType) {
if (fieldType != null && boolean.class.equals(fieldType) || Boolean.class.equals(fieldType)) {
// Special handling of boolean property.
return Boolean.FALSE;
}
else if (fieldType != null && fieldType.isArray()) {
// Special handling of array property.
return Array.newInstance(fieldType.getComponentType(), 0);
}else if(fieldType == int.class || fieldType == long.class){
return 0;
}
else {
// Default value: try null.
return null;
}
}

这样从源头上，就把问题给解决了，但是，这还要修改spring的源代码，貌似不太理想。

继续debug：
TypeConverterDelegate:

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/**
* Convert the given text value using the given property editor.
* @param oldValue the previous value, if available (may be <code>null</code>)
* @param newTextValue the proposed text value
* @param editor the PropertyEditor to use
* @return the converted value
*/
protected Object doConvertTextValue(Object oldValue, String newTextValue, PropertyEditor editor) {
try {
editor.setValue(oldValue);
}
catch (Exception ex) {
if (logger.isDebugEnabled()) {
logger.debug("PropertyEditor [" + editor.getClass().getName() + "] does not support setValue call", ex);
}
// Swallow and proceed.
}
editor.setAsText(newTextValue);
return editor.getValue();
}

到这里才发现，spring首先调用的是自定义的editor的setValue然后才调用的setAsText，因此：

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public void setAsText(String text) throws IllegalArgumentException {
if (text==null || text.trim().equals("")) {
// Treat empty String as null value.
setValue(0);
} else {
// Use default valueOf methods for parsing text.
setValue(Integer.parseInt(text));
}
}

这种方式根本就是行不通的！
既然找到了原因，那么，也就找到了解决办法，我们需要重写setValue，而不是setAsText：

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private static class IntEditor extends CustomNumberEditor{
public IntEditor(){
super(Integer.class,true);
}
@Override
public void setValue(Object value) {
if(value == null){
super.setValue(0);
}else{
super.setValue(value);
}
}
}
@InitBinder
public void initBinder(WebDataBinder binder){
binder.registerCustomEditor(int.class, "graduted", new IntEditor());
binder.registerCustomEditor(int.class, "married", new IntEditor());
}

世界从此清净了！