SSH框架之Struts（4）——Struts查漏补缺BeanUtils在Struts1中

　　在上篇博客SSH框架之Struts（3）——Struts的运行流程之核心方法，我们提到RequestProcessor中的processPopulate()是用来为为ActionForm 填充数据，它是怎么实现将表单数据放入到一个ActionForm中的呢？——第三方工具，BeanUtils，相对来说，这是一个非常重要的用来操作javaBean的服务。

    public static void 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 {                throw new 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) {            throw new 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，如果用到上传功能的可以仔细阅读以下前边部分的代码，我们这里不做解释，可以往下看。

　　　　if (!isMultipart) {            names = request.getParameterNames();        }

　　这是用来获取到表单所有的名称，进而为属性值的Copy和转换做准备

        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);            }

　　遍历表单所有的名称，并通过parameterValue = request.getParameterValues(name);获得名称对应的value值。之后就是通过properties.put(stripped, parameterValue);将名称作为key，名称对应的值作为value放入到map中。

                    // Set the corresponding properties of our bean        try {            BeanUtils.populate(bean, properties);        } catch(Exception e) {            throw new 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);            }        }    }

　　在这里，主要是调用第三方服务BeanUtils来实现属性值的转换和赋值。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。BeanUtils的populate方法是将从form表单取到的名称和值映射到对应的ActionForm中，源码如下

    public static void populate(Object bean, Map properties)        throws IllegalAccessException, InvocationTargetException {        // Do nothing unless both arguments have been specified        if ((bean == null) || (properties == null)) {            return;        }        if (log.isDebugEnabled()) {            log.debug("BeanUtils.populate(" + bean + ", " +                    properties + ")");        }        // Loop through the property name/value pairs to be set        Iterator names = properties.keySet().iterator();        while (names.hasNext()) {            // Identify the property name and value(s) to be assigned            String name = (String) names.next();            if (name == null) {                continue;            }            Object value = properties.get(name);            // Perform the assignment for this property            setProperty(bean, name, value);        }    }

　　BeanUtils.populate(bean, properties);执行完，至此，完成了form表单数据到ActionForm的映射。

    BeanUtils作为一个操作javaBean的第三方服务，这里引出BeanUtils，下篇通过实例来了解和学习BeanUtils。