深入浅出学习Struts框架（十二）-分析Struts框架实例7

上一篇博客主要是讲解ActionServlet中的一个方法processActionForm，当我们在截取字符串，再根据字符串取得ActionMapping之后，我们就要用利用ActionMapping来创建ActionForm，并且把ActionForm放到request或session中管理。获得ActionForm之后，我们就要将ActionForm中的数据放到Mapping中，以便实例化Action。在Struts中有一个方法是专门把ActionForm的数据放到Mapping的，这个方法就是processPopulate。今天我们就来详细来看看这个方法。

首先这个方法主要的功能是将表单数据放到Map中，并且将Map的值根据ActionForm类型转换好后设置到ActionForm中。

这个方法具体的流程是首先执行ActionForm中的reset方法进行重置，然后得到表单中所有输入域的name名称，再调用request.getParameterValues(),根据name名称得到相应的值，最后将表单中的数据全部放到一个map中，map的key为表单输入域的名称，map的value为表单输入域的值（字符串数组），接下来调用一个第三方组件BeanUtils，将Map中的值，根据ActionForm中的类型先转换好，再调用ActionForm中的setter方法设置到ActionForm上。

下面咱们来跟随源代码来看看这个方法的实现过程.首先还是和以前博客一样设置断点，进入process方法，找到processPopulate方法：

进入这个方法，看到这个方法的实现源代码：

protectedvoid processPopulate(HttpServletRequest request,

                                   HttpServletResponse response,

                                   ActionForm form,

                                   ActionMapping mapping)

        throws ServletException {

        if (form == null) {

            return;

        }
        // Populate the bean properties of this ActionForm instance

        if (log.isDebugEnabled()) {

            log.debug(" Populating bean properties from this request");

        }
        form.setServlet(this.servlet);

        form.reset(mapping, request);
        if (mapping.getMultipartClass() != null) {

            request.setAttribute(Globals.MULTIPART_KEY,

                                 mapping.getMultipartClass());

        }

        RequestUtils.populate(form, mapping.getPrefix(), mapping.getSuffix(),

                              request);
        // Set the cancellation request attribute if appropriate

        if ((request.getParameter(Constants.CANCEL_PROPERTY) != null) ||

            (request.getParameter(Constants.CANCEL_PROPERTY_X) != null)) {       
            request.setAttribute(Globals.CANCEL_KEY, Boolean.TRUE);

        } 
}

其中，form.reset(mapping, request);这个方法就是讲form重置，作用是使ActionForm中的值恢复初始状态。

下面RequestUtils.populate(form, mapping.getPrefix(), mapping.getSuffix()这个方法就是要完成填充map和转换类型等操作的，具体实现：

publicstaticvoid populate(

            Object bean,

            String prefix,

            String suffix,

            HttpServletRequest request)

            throws ServletException {

        // Build a list of relevant request parameters from this request
        HashMap properties = new HashMap();
        // Iterator of parameter names
        Enumeration names = null;

        // Map for multipart parameters

        Map multipartParameters = null;

         String contentType = request.getContentType();

        String method = request.getMethod();

        boolean isMultipart = false;

         if (bean instanceof ActionForm) {

            ((ActionForm) bean).setMultipartRequestHandler(null);

        }

 	MultipartRequestHandler multipartHandler = null;

        if ((contentType != null)

                && (contentType.startsWith("multipart/form-data"))

                && (method.equalsIgnoreCase("POST"))) {

            // Get the ActionServletWrapper from the form bean

            ActionServletWrapper servlet;

            if (bean instanceof ActionForm) {

                servlet = ((ActionForm) bean).getServletWrapper();

            } else {

                thrownew ServletException(

                        "bean that's supposed to be "

                        + "populated from a multipart request is not of type "

                        + "\"org.apache.struts.action.ActionForm\", but type "

                        + "\""

                        + bean.getClass().getName()

                        + "\"");

            }

             // Obtain a MultipartRequestHandler

            multipartHandler = getMultipartHandler(request);

             if (multipartHandler != null) {

                isMultipart = true;

                // Set servlet and mapping info

                servlet.setServletFor(multipartHandler);

                multipartHandler.setMapping(

                        (ActionMapping) request.getAttribute(Globals.MAPPING_KEY));

                // Initialize multipart request class handler

                multipartHandler.handleRequest(request);

                //stop here if the maximum length has been exceeded

                Boolean maxLengthExceeded =

                        (Boolean) request.getAttribute(

                                MultipartRequestHandler.ATTRIBUTE_MAX_LENGTH_EXCEEDED);

                if ((maxLengthExceeded != null) && (maxLengthExceeded.booleanValue())) {

                    ((ActionForm) bean).setMultipartRequestHandler(multipartHandler);

                    return;

                }

                //retrieve form values and put into properties

                multipartParameters = getAllParametersForMultipartRequest(

                        request, multipartHandler);

                names = Collections.enumeration(multipartParameters.keySet());

            }

        }

        if (!isMultipart) {

            names = request.getParameterNames();

        }
        while (names.hasMoreElements()) {

            String name = (String) names.nextElement();

            String stripped = name;

            if (prefix != null) {

                if (!stripped.startsWith(prefix)) {

                    continue;

                }

                stripped = stripped.substring(prefix.length());

            }

            if (suffix != null) {

                if (!stripped.endsWith(suffix)) {

                    continue;

                }

                stripped = stripped.substring(0, stripped.length() - suffix.length());

            }

            Object parameterValue = null;

            if (isMultipart) {

                parameterValue = multipartParameters.get(name);

            } else {

                parameterValue = request.getParameterValues(name);

            }
            // Populate parameters, except "standard" struts attributes

            // such as 'org.apache.struts.action.CANCEL'

            if (!(stripped.startsWith("org.apache.struts."))) {

                properties.put(stripped, parameterValue);

            }

        }

        // Set the corresponding properties of our bean

        try {

            BeanUtils.populate(bean, properties);

        } catch(Exception e) {

            thrownew ServletException("BeanUtils.populate", e);

        } finally {

            if (multipartHandler != null) {

                // Set the multipart request handler for our ActionForm.

                // If the bean isn't an ActionForm, an exception would have been

                // thrown earlier, so it's safe to assume that our bean is

                // in fact an ActionForm.

                ((ActionForm) bean).setMultipartRequestHandler(multipartHandler);

            }

        }
    }

这段实现的前半部分是关于上传的代码，因为咱们这个实例不和上传有关，所以直接忽略，直接到

if (!isMultipart) {

            names = request.getParameterNames();

        }

这段代码，这段代码主要是获得表单的所有名称，之后通过下面这段代码：

while (names.hasMoreElements()) {

            String name = (String) names.nextElement();

            String stripped = name;

            if (prefix != null) {

                if (!stripped.startsWith(prefix)) {

                    continue;

                }

                stripped = stripped.substring(prefix.length());

            }

            if (suffix != null) {

                if (!stripped.endsWith(suffix)) {

                    continue;

                }

                stripped = stripped.substring(0, stripped.length() - suffix.length());

            }

            Object parameterValue = null;

            if (isMultipart) {

                parameterValue = multipartParameters.get(name);

            } else {

                parameterValue = request.getParameterValues(name);

            }

             // Populate parameters, except "standard" struts attributes

            // such as 'org.apache.struts.action.CANCEL'

            if (!(stripped.startsWith("org.apache.struts."))) {

                properties.put(stripped, parameterValue);

            }

        }

遍历名称，并且通过parameterValue = request.getParameterValues(name);获得名称对应的value值，之后通过

if (!(stripped.startsWith("org.apache.struts."))) {

                properties.put(stripped, parameterValue);

            }

将名称作为key值，讲名称的value值作为value值添加到map中，到此为止，我们就讲表单数据添加到了map中。

随后，调用第三方的组件来实现类型转换：

try {

            BeanUtils.populate(bean, properties);

        } catch(Exception e) {

            thrownew ServletException("BeanUtils.populate", e);

        } finally {

            if (multipartHandler != null) {

                // Set the multipart request handler for our ActionForm.

                // If the bean isn't an ActionForm, an exception would have been

                // thrown earlier, so it's safe to assume that our bean is

                // in fact an ActionForm.

                ((ActionForm) bean).setMultipartRequestHandler(multipartHandler);

            }

        }

这个方法会遍历ActionForm的值的类型，并且讲Map中的值的类型改为和ActionForm对应的类型。

到这里processPopulate的方法就实现完毕，实现了这个方法有什么用处呢？敬请等待下一篇博文！