springmvc设计的一个很重要的原则是开闭原则:
对修改或处理流程关闭，对扩展开放
但对于自定义controller继承MultiActionController,覆盖一些方法,改变了springmvc的部分功能
如覆盖bind(HttpServletRequest request, Object command)，绑定过程完全由用户的编程能力决定。
spring版本3.2.2
绑定入口接口：
ServletRequestDataBinder
日期格式转换在哪?
binder可以注册属性编辑器-将字符串格式转成成Data格式
@InitBinder
public void initBinder(WebDataBinder binder) {
DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
CustomDateEditor dateEditor = new CustomDateEditor(df, true);
binder.registerCustomEditor(Date.class, dateEditor);
}
参数校验在什么时候?
// If last parameter isn't of HttpSession type, it's a command.
if (paramTypes.length >= 3 &&
!paramTypes[paramTypes.length - 1].equals(HttpSession.class)) {
Object command = newCommandObject(paramTypes[paramTypes.length - 1]);
params.add(command);
bind(request, command);
}
MultiActionController#bind
protected void bind(HttpServletRequest request, Object command) throws Exception {
logger.debug("Binding request parameters onto MultiActionController command");
// 1 初始化ServletRequestDataBinder
ServletRequestDataBinder binder = createBinder(request, command);
// 2 设置request参数到command
binder.bind(request);
if (this.validators != null) {
for (Validator validator : this.validators) {
if (validator.supports(command.getClass())) {
ValidationUtils.invokeValidator(validator, command, binder.getBindingResult());
}
}
}
binder.closeNoCatch();
}
自定义validators,校验参数,必填校验等
MultiActionController#createBinder
protected ServletRequestDataBinder createBinder(HttpServletRequest request, Object command) throws Exception {
// 1.1 实例化ServletRequestDataBinder
ServletRequestDataBinder binder = new ServletRequestDataBinder(command, getCommandName(command));
// 1.2 初始化binder-用户自定义-webBindingInitializer-springmvc扩展点
initBinder(request, binder);
return binder;
}
对于MultiActionController中的方法,如bind,initBinder等可被自定义的controller子类覆盖，从而定义自己的绑定逻辑.但一般也不这么做,这样项目跟springmvc耦合性加强了
@Override
protected void bind(HttpServletRequest request, Object command) throws Exception {
System.out.println("自定义绑定方法bind");
}
@Override
protected ServletRequestDataBinder createBinder(HttpServletRequest request, Object command) throws Exception {
return null;
}
@Override
protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder) throws Exception {
binder.setAutoGrowNestedPaths(true);
binder.setAutoGrowCollectionLimit(1024);
System.out.println("hi, i am initBinder");
}
ServletRequestDataBinder继承体系为：
ServletRequestDataBinder extends WebDataBinder extends DataBinder
创建ServletRequestDataBinder的对象时,用要设置值的command对象初始化binder。即将command封装到DataBinder
=============================================职责分割线
实际绑定command对象的工作交由DataBinder接口去完成,用户(开发人员)只需要将设置值request及被设置值command传给DataBinder就行
1.request->MutalbPropertyValues(dataBinder)
2.MutalbPropertyValues->command(beanWrapper)
ServletRequestDataBinder#bind
public void bind(ServletRequest request) {
// 2.1 创建MutablePropertyValues:将request值设置到ProperValues里面
// 循环request.getParameterNames()的参数放入map,并初始化MutablePropertyValues
MutablePropertyValues mpvs = new ServletRequestParameterPropertyValues(request);
MultipartRequest multipartRequest = WebUtils.getNativeRequest(request, MultipartRequest.class);
if (multipartRequest != null) {
bindMultipart(multipartRequest.getMultiFileMap(), mpvs);
}
addBindValues(mpvs, request);
// 2.2 委托父类方法,属性值mpvs设置到command对象-已经在实例化ServletRequestDataBinder时包含
doBind(mpvs);
}
WebDataBinder#doBind
@Override
protected void doBind(MutablePropertyValues mpvs) {
// 2.2.1 处理特殊属性名(以! 或者 _开头)的属性名，去掉前缀-WebDataBinder绑定前校验
// 用户(开发人员)可在自定义的controller下,覆盖createBinder方法,改变这个地方的逻辑
checkFieldDefaults(mpvs);
checkFieldMarkers(mpvs);
// 2.2.2 委托父类方法,实际绑定command对象
super.doBind(mpvs);
}
2.2.1 处理特殊属性名,去掉前缀。如果不需要这个逻辑,可覆盖createBinder，自定义自己的dataBinder extexds ServletRequestDataBinder
DataBinder#doBind
/**
* Actual implementation of the binding process, working with the
* passed-in MutablePropertyValues instance.
* @param mpvs the property values to bind,
* as MutablePropertyValues instance
* @see #checkAllowedFields
* @see #checkRequiredFields
* @see #applyPropertyValues
*/
protected void doBind(MutablePropertyValues mpvs) {
// 2.2.2.1 检查是否自定义允许解析的属性名-DataBinder绑定前校验
checkAllowedFields(mpvs);
checkRequiredFields(mpvs);
// 2.2.2.2 执行绑定
applyPropertyValues(mpvs);
}
DataBinder#doBind是绑定mpvs到command对象的地方,也许这就是将request参数封装到MutablePropertyValues的意义。ServletRequestDataBinder只是封装request到mpvs，也有其他形式的请求参数,只需要继承DataBinder，然后做相应的封装
对于检验的错误或其他信息的处理，springmvc是将其放到DataBinder的属性bindingResult中,其为类BeanPropertyBindingResult的对象
对于2.2.1与2.2.2.1绑定前校验,整合起来看，为什么不将她们的校验放在一起。应该独立来看，每个类的关注点或职责不一样,她们只需要保持各自方法的健壮性
DataBinder#applyPropertyValues
protected void applyPropertyValues(MutablePropertyValues mpvs) {
try {
// 2.2.2.2.1
// Bind request parameters onto target object.
getPropertyAccessor().setPropertyValues(mpvs, isIgnoreUnknownFields(), isIgnoreInvalidFields());
}
catch (PropertyBatchUpdateException ex) {
// Use bind error processor to create FieldErrors.
for (PropertyAccessException pae : ex.getPropertyAccessExceptions()) {
getBindingErrorProcessor().processPropertyAccessException(pae, getInternalBindingResult());
}
}
}
getBindingErrorProcessor().processPropertyAccessException(pae, getInternalBindingResult());为异常处理机制,将异常设置到bindingResult,在绑定结束时,会调用ServletRequestDataBinder#closeNoCatch判断是否有异常,有则抛出
request->mpvs
=============================================职责分割线
DataBinder最终还是将指挥棒交给了BeanWrapper
mpvs->command
AbstractPropertyAccessor#setPropertyValues
public void setPropertyValues(PropertyValues pvs, boolean ignoreUnknown, boolean ignoreInvalid)
throws BeansException {
List<PropertyAccessException> propertyAccessExceptions = null;
List<PropertyValue> propertyValues = (pvs instanceof MutablePropertyValues ?
((MutablePropertyValues) pvs).getPropertyValueList() : Arrays.asList(pvs.getPropertyValues()));
for (PropertyValue pv : propertyValues) {
try {
// This method may throw any BeansException, which won't be caught
// here, if there is a critical failure such as no matching field.
// We can attempt to deal only with less serious exceptions.
setPropertyValue(pv);
}
catch (NotWritablePropertyException ex) {
if (!ignoreUnknown) {
throw ex;
}
// Otherwise, just ignore it and continue...
}
catch (NullValueInNestedPathException ex) {
if (!ignoreInvalid) {
throw ex;
}
// Otherwise, just ignore it and continue...
}
catch (PropertyAccessException ex) {
if (propertyAccessExceptions == null) {
propertyAccessExceptions = new LinkedList<PropertyAccessException>();
}
propertyAccessExceptions.add(ex);
}
}
// If we encountered individual exceptions, throw the composite exception.
if (propertyAccessExceptions != null) {
PropertyAccessException[] paeArray =
propertyAccessExceptions.toArray(new PropertyAccessException[propertyAccessExceptions.size()]);
throw new PropertyBatchUpdateException(paeArray);
}
}
往下跟踪就是beanWrapper如何设置属性值了,离最初的主题springmvc原理越来越远了,所以不再往下了
以下为得到beanWrapper或ConfigurablePropertyAccessor的路径-可忽略
DataBinder#getPropertyAccessor
protected ConfigurablePropertyAccessor getPropertyAccessor() {
return getInternalBindingResult().getPropertyAccessor();
}
DataBinder#getInternalBindingResult
protected AbstractPropertyBindingResult getInternalBindingResult() {
if (this.bindingResult == null) {
initBeanPropertyAccess();
}
return this.bindingResult;
}
DataBinder#initBeanPropertyAccess
public void initBeanPropertyAccess() {
Assert.state(this.bindingResult == null,
"DataBinder is already initialized - call initBeanPropertyAccess before other configuration methods");
this.bindingResult = new BeanPropertyBindingResult(
getTarget(), getObjectName(), isAutoGrowNestedPaths(), getAutoGrowCollectionLimit());
if (this.conversionService != null) {
this.bindingResult.initConversion(this.conversionService);
}
}
BeanPropertyBindingResult#getPropertyAccessor
/**
* Returns the {@link BeanWrapper} that this instance uses.
* Creates a new one if none existed before.
* @see #createBeanWrapper()
*/
@Override
public final ConfigurablePropertyAccessor getPropertyAccessor() {
if (this.beanWrapper == null) {
this.beanWrapper = createBeanWrapper();
this.beanWrapper.setExtractOldValueForEditor(true);
this.beanWrapper.setAutoGrowNestedPaths(this.autoGrowNestedPaths);
this.beanWrapper.setAutoGrowCollectionLimit(this.autoGrowCollectionLimit);
}
return this.beanWrapper;
}
BeanPropertyBindingResult#createBeanWrapper
protected BeanWrapper createBeanWrapper() {
Assert.state(this.target != null, "Cannot access properties on null bean instance '" + getObjectName() + "'!");
return PropertyAccessorFactory.forBeanPropertyAccess(this.target);
}
PropertyAccessorFactory#forBeanPropertyAccess
public static BeanWrapper forBeanPropertyAccess(Object target) {
return new BeanWrapperImpl(target);
}
感想:
如果不用command绑定,正常的request.getParameter(),效率肯定比springmvc的参数绑定效率高,空间上也占用比较少的内存.
那么在时间和空间上，有哪些区别呢，对于command绑定:
创建了ServletRequestDataBinder对象
创建了MutablePropertyValues对象-用于包装request
创建了BeanPropertyBindingResult
创建了DefaultBindingErrorProcessor
创建了BeanWrapperImpl-设置command属性
参考：
Validation, Data Binding, and Type Conversion
https://docs.spring.io/spring/docs/current/spring-framework-reference/html/validation.html