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！