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的执行流程之核心方法，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，这是一个很重要的用来操作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，假设用到上传功能的能够细致阅读下面前边部分的代码。我们这里不做解释，能够往下看。

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

        }

　　这是用来获取到表单全部的名称。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);
            }

　　遍历表单全部的名称，并通过parameterValue = request.getParameterValues(name);获得名称相应的value值。之后就是通过properties.put(stripped, parameterValue);将名称作为key。名称相应的值作为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。这种方法会遍历ActionForm的值的类型。而且讲Map中的值的类型改为和ActionForm相应的类型。

到这里processPopulate的方法就实现完成。BeanUtils的populate方法是将从form表单取到的名称和值映射到相应的ActionForm中，源代码例如以下

    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);运行完，至此，完毕了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。