追求無(wú)止境

Spring的BaseCommandController繼承自AbstractController。在看BaseCommandController之前先看他的繼承類(lèi)AbstractCommandController是如何實(shí)現(xiàn)

AbstractController的handleInternalRequest方法的：

protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
throws Exception {
Object command = getCommand(request);
ServletRequestDataBinder binder = bindAndValidate(request, command);
BindException errors = new BindException(binder.getBindingResult());
return handle(request, response, command, errors);
}

getCommand就是BaseCommandController中的方法。

protected Object getCommand(HttpServletRequest request) throws Exception {
return createCommand();
}
protected final Object createCommand() throws Exception {
if (this.commandClass == null) {
throw new IllegalStateException("Cannot create command without commandClass being set - " +
"either set commandClass or (in a form controller) override formBackingObject");
}
if (logger.isDebugEnabled()) {
logger.debug("Creating new command of class [" + this.commandClass.getName() + "]");
}
return BeanUtils.instantiateClass(this.commandClass);
}

createCommand創(chuàng)建了一個(gè)CommandClass的對(duì)象。

然后再看bindAndValidate方法：

protected final ServletRequestDataBinder bindAndValidate(HttpServletRequest request, Object command)
throws Exception {
ServletRequestDataBinder binder = createBinder(request, command);
BindException errors = new BindException(binder.getBindingResult());
if (!suppressBinding(request)) {
binder.bind(request);
onBind(request, command, errors);
if (this.validators != null && isValidateOnBinding() && !suppressValidation(request, command, errors)) {
for (int i = 0; i < this.validators.length; i++) {
ValidationUtils.invokeValidator(this.validators[i], command, errors);
}
}
onBindAndValidate(request, command, errors);
}
return binder;
}

這個(gè)方法首先創(chuàng)建了 DataBinder對(duì)象，然后，獲取創(chuàng)建綁定對(duì)象時(shí)發(fā)生的錯(cuò)誤。報(bào)錯(cuò)在errors。接下來(lái)綁定對(duì)象，調(diào)用onBind處理綁定事件；接下來(lái)應(yīng)用Validator。然后調(diào)用onBindAndValidate來(lái)處理綁定和驗(yàn)證事件。最后返回binder。

處理完之后調(diào)用handle方法進(jìn)行處理。

綜上所述，AbstractCommandController具有兩個(gè)功能:

1、將請(qǐng)求參數(shù)轉(zhuǎn)換為Command對(duì)象。在該Controller中，我們?cè)O(shè)置一個(gè)object對(duì)象。然后BaseCommandController將請(qǐng)求的參數(shù)進(jìn)行轉(zhuǎn)換。如果請(qǐng)求參數(shù)有value值，就會(huì)調(diào)用object的的setValue對(duì)象來(lái)設(shè)置對(duì)象里的值。如果請(qǐng)求參數(shù)中有address.city.就會(huì)調(diào)用object中g(shù)etAddress().setCity()方法來(lái)賦值。這個(gè)object可以是任意的object，唯一的要求就是這個(gè)object類(lèi)沒(méi)有參數(shù)。

2、對(duì)數(shù)據(jù)進(jìn)行驗(yàn)證。在轉(zhuǎn)換和驗(yàn)證時(shí)發(fā)生錯(cuò)誤時(shí)，需要在handle(request, response, command, errors)中進(jìn)行處理。