Spring MVC 框架学习笔记之BaseCommandController和AbstractCommandController
Spring的BaseCommandController继承自AbstractController。在看BaseCommandController之前先看他的继承类AbstractCommandController是如何实现
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);}<style type="text/css">.csharpcode, .csharpcode pre{font-size: small;color: black;font-family: Consolas, "Courier New", Courier, Monospace;background-color: #ffffff;/*white-space: pre;*/}.csharpcode pre { margin: 0em; }.csharpcode .rem { color: #008000; }.csharpcode .kwrd { color: #0000ff; }.csharpcode .str { color: #006080; }.csharpcode .op { color: #0000c0; }.csharpcode .preproc { color: #cc6633; }.csharpcode .asp { background-color: #ffff00; }.csharpcode .html { color: #800000; }.csharpcode .attr { color: #ff0000; }.csharpcode .alt{background-color: #f4f4f4;width: 100%;margin: 0em;}.csharpcode .lnum { color: #606060; }</style>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);}<style type="text/css">.csharpcode, .csharpcode pre{font-size: small;color: black;font-family: Consolas, "Courier New", Courier, Monospace;background-color: #ffffff;/*white-space: pre;*/}.csharpcode pre { margin: 0em; }.csharpcode .rem { color: #008000; }.csharpcode .kwrd { color: #0000ff; }.csharpcode .str { color: #006080; }.csharpcode .op { color: #0000c0; }.csharpcode .preproc { color: #cc6633; }.csharpcode .asp { background-color: #ffff00; }.csharpcode .html { color: #800000; }.csharpcode .attr { color: #ff0000; }.csharpcode .alt{background-color: #f4f4f4;width: 100%;margin: 0em;}.csharpcode .lnum { color: #606060; }</style>createCommand创建了一个CommandClass的对象。
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, command, errors);}}onBindAndValidate(request, command, errors);}return binder;}<style type="text/css">.csharpcode, .csharpcode pre{font-size: small;color: black;font-family: Consolas, "Courier New", Courier, Monospace;background-color: #ffffff;/*white-space: pre;*/}.csharpcode pre { margin: 0em; }.csharpcode .rem { color: #008000; }.csharpcode .kwrd { color: #0000ff; }.csharpcode .str { color: #006080; }.csharpcode .op { color: #0000c0; }.csharpcode .preproc { color: #cc6633; }.csharpcode .asp { background-color: #ffff00; }.csharpcode .html { color: #800000; }.csharpcode .attr { color: #ff0000; }.csharpcode .alt{background-color: #f4f4f4;width: 100%;margin: 0em;}.csharpcode .lnum { color: #606060; }</style>这个方法首先创建了DataBinder对象，然后，获取创建绑定对象时发生的错误。报错在errors。接下来绑定对象，调用onBind处理绑定事件；接下来应用Validator。然后调用onBindAndValidate来处理绑定和验证事件。最后返回binder。
处理完之后调用handle方法进行处理。
综上所述，AbstractCommandController具有两个功能:
1、将请求参数转换为Command对象。在该Controller中，我们设置一个object对象。然后BaseCommandController将请求的参数进行转换。如果请求参数有value值，就会调用object的的setValue对象来设置对象里的值。如果请求参数中有address.city.就会调用object中getAddress().setCity()方法来赋值。这个object可以是任意的object，唯一的要求就是这个object类没有参数。
2、对数据进行验证。在转换和验证时发生错误时，需要在handle(request, response, command,errors)中进行处理。
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