追求無止境

Spring的BaseCommandController繼承自AbstractController。在看BaseCommandController之前先看他的繼承類AbstractCommandController是如何實現

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創建了一個CommandClass的對象。

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;
}

這個方法首先創建了 DataBinder對象，然后，獲取創建綁定對象時發生的錯誤。報錯在errors。接下來綁定對象，調用onBind處理綁定事件；接下來應用Validator。然后調用onBindAndValidate來處理綁定和驗證事件。最后返回binder。

處理完之后調用handle方法進行處理。

綜上所述，AbstractCommandController具有兩個功能:

1、將請求參數轉換為Command對象。在該Controller中，我們設置一個object對象。然后BaseCommandController將請求的參數進行轉換。如果請求參數有value值，就會調用object的的setValue對象來設置對象里的值。如果請求參數中有address.city.就會調用object中getAddress().setCity()方法來賦值。這個object可以是任意的object，唯一的要求就是這個object類沒有參數。

2、對數據進行驗證。在轉換和驗證時發生錯誤時，需要在handle(request, response, command, errors)中進行處理。