java - 为什么 renderer add a hidden field with form ID as name and value

Question

我正在阅读 JSF 实现 <h:form>渲染。令我惊讶的是，我看到(在 Mojarra、MyFaces + Tomahawk 中)，他们在 encodeBegin() 上添加了一个隐藏的输入字段。方法。

这是 FormRenderer 的示例代码在莫哈拉:

@Override
public void encodeBegin(FacesContext context, UIComponent component)
      throws IOException {

    rendererParamsNotNull(context, component);

    if (!shouldEncode(component)) {
        return;
    }

    ResponseWriter writer = context.getResponseWriter();
    assert(writer != null);
    String clientId = component.getClientId(context);
    // since method and action are rendered here they are not added
    // to the pass through attributes in Util class.
    writer.write('\n');
    writer.startElement("form", component);
    writer.writeAttribute("id", clientId, "clientId");
    writer.writeAttribute("name", clientId, "name");
    writer.writeAttribute("method", "post", null);
    writer.writeAttribute("action", getActionStr(context), null);
    String styleClass =
          (String) component.getAttributes().get("styleClass");
    if (styleClass != null) {
        writer.writeAttribute("class", styleClass, "styleClass");
    }
    String acceptcharset = (String)
          component.getAttributes().get("acceptcharset");
    if (acceptcharset != null) {
        writer.writeAttribute("accept-charset", acceptcharset,
                              "acceptcharset");
    }

    RenderKitUtils.renderPassThruAttributes(context,
                                            writer,
                                            component,
                                            ATTRIBUTES);
    writer.writeText("\n", component, null);

    // this hidden field will be checked in the decode method to
    // determine if this form has been submitted.         
    writer.startElement("input", component);
    writer.writeAttribute("type", "hidden", "type");
    writer.writeAttribute("name", clientId,
                          "clientId");
    writer.writeAttribute("value", clientId, "value");
    writer.endElement("input");
    writer.write('\n');

    // Write out special hhidden field for partial submits
    String viewId = context.getViewRoot().getViewId();
    String actionURL =
        context.getApplication().getViewHandler().getActionURL(context, viewId);
    ExternalContext externalContext = context.getExternalContext();
    String encodedActionURL = externalContext.encodeActionURL(actionURL);
    String encodedPartialActionURL = externalContext.encodePartialActionURL(actionURL);
    if (encodedPartialActionURL != null) {
        if (!encodedPartialActionURL.equals(encodedActionURL)) {
            writer.startElement("input", component);
            writer.writeAttribute("type", "hidden", "type");
            writer.writeAttribute("name", "javax.faces.encodedURL", null);
            writer.writeAttribute("value", encodedPartialActionURL, "value");
            writer.endElement("input");
            writer.write('\n');
        }
    }

    if (!writeStateAtEnd) {
        context.getApplication().getViewHandler().writeState(context);
        writer.write('\n');
    }
}

我的问题:

1. 为什么有一个隐藏的输入字段被分配了 id component.getClientId(context) ，即 UIForm成分？隐藏字段的用途是什么？
2. 在 Mojarra 中，您无法选择分配自己的 id <h:form> 上的属性但你可以在 MyFaces 上。 JSF如何对待UIForm在每种情况下(例如，当 MyFaces 明确提供 id 时)？
3. Mojarra 形式 enctype默认为 application/x-www-form-urlencoded .能支持multipart/form-data吗或 text/plain ？

谢谢

Answer 1

Why is there a hidden input field that gets assigned the id component.getClientId(context), i.e., a UIForm component? What's the purpose of the hidden field?

仔细观察评论(行号来自 Mojarra 2.1.19 ):

153        // this hidden field will be checked in the decode method to
154        // determine if this form has been submitted.         
155        writer.startElement("input", component);
156        writer.writeAttribute("type", "hidden", "type");
157        writer.writeAttribute("name", clientId,
158                              "clientId");
159        writer.writeAttribute("value", clientId, "value");
160        writer.endElement("input");
161        writer.write('\n');

这因此被用来确定提交了哪个表单。此确定依次发生在 FormRenderer#decode() 中当 JSF 需要在应用请求值阶段确定 HTTP 请求参数时调用:

96         // Was our form the one that was submitted?  If so, we need to set
97         // the indicator accordingly..
98         Map<String, String> requestParameterMap = context.getExternalContext()
99               .getRequestParameterMap();
100        if (requestParameterMap.containsKey(clientId)) {
101            if (logger.isLoggable(Level.FINE)) {
102                logger.log(Level.FINE,
103                           "UIForm with client ID {0}, submitted",
104                           clientId);
105            }
106            ((UIForm) component).setSubmitted(true);
107        } else {
108            ((UIForm) component).setSubmitted(false);
109        }

换句话说，它控制着 UIForm#isSubmitted() 的结果。属性(property)。它可能在以下涉及页面中多个表单的用例中很有用:

• Check which form has an error
• How can we use multiple <h:messages> tags or <h:message> tags in a single JSF page?

---

In Mojarra, you don't have the option to assign your own id attribute on <h:form> but you can on MyFaces. How does JSF treat UIForm in each cases (e.g. when MyFaces has its an explicit provided id)?

我不确定你在说什么。这，

<h:form id="formId">

在 Mojarra 中也适合我。

---

Mojarra form enctype is defaulted to application/x-www-form-urlencoded. Can it support multipart/form-data or text/plain?

这符合 JSF 规范。是的，你可以只使用 enctype以通常的方式归因。

<h:form enctype="multipart/form-data">

这种表单的提交是否被 JSF 正确识别，是其次。在 JSF 2.2 之前，JSF 没有内置支持 multipart/form-data . JSF 组件库通过提供一个 servlet 过滤器及其文件上传组件来解决这个问题，通常在幕后使用 Apache Commons FileUpload。 JSF 2.2 直接委托(delegate)给新的 Servlet 3.0 HttpServletRequest#getPart() API，无需使用第 3 方 API 的 servlet 过滤器。另见 How to upload files to server using JSP/Servlet?