多个动态包含一个JSF标签

每个JSF开发人员都知道ui：include和ui：param标签。您可以包括一个facelet（XHTML文件）并传递一个对象，该对象将在包含的facelet中可用，如下所示：

<ui:include src="/sections/columns.xhtml"><ui:param name="columns" value="#{bean.columns}"/>
</ui:include>

因此，您可以在带有dynamich列的PrimeFaces DataTable中使用它（p：columns）

<p:dataTable value="#{bean.entries}" var="data" rowKey="#{data.id}" ...>...<ui:include src="/sections/columns.xhtml"><ui:param name="data" value="#{data}"/><ui:param name="columns" value="#{bean.columns}"/></ui:include></p:dataTable>

其中包含的facelet可能包含此代码

<ui:composition xmlns="http://www.w3.org/1999/xhtml"xmlns:p="http://primefaces.org/ui"xmlns:ui="http://java.sun.com/jsf/facelets"...><p:columns value="#{columns}" var="column"><f:facet name="header"><h:outputText value="#{msgs[column.header]}"/></f:facet>// place some input / select or complex composite component for multiple data types here.// a simple example for demonstration purpose:<p:inputText value="#{data[column.property]}"/></p:columns>
</ui:composition>

＃{bean.columns}表示描述这些列的特殊对象的列表。我将此类对象命名为ColumnModel。所以，这是一个
列出<ColumnModel>。 ColumnModel具有例如属性标头和属性。

继续。现在，如果要添加对排序/过滤的支持，我们可以使用动态路径，该路径引用包含排序或/和过滤功能的特定facelet文件。简单地将src属性绑定到bean属性。

<ui:include src="#{bean.columnsIncludeSrc}"><ui:param name="data" value="#{data}"/><ui:param name="columns" value="#{bean.columns}"/>
</ui:include>

豆有类似的东西

private boolean isFilterRight;
private boolean isSortRight// setter / getterpublic String getColumnsIncludeSrc() {if (isFilterRight && isSortRight) {return "/include/columnsTableFilterSort.xhtml";} else if (isFilterRight && !isSortRight) {return "/include/columnsTableFilter.xhtml";} else if (!isFilterRight && isSortRight) {return "/include/columnsTableSort.xhtml";} else {return "/include/columnsTable.xhtml";}
}

根据所设置的布尔权限，包含了不同的方面。因此，将要包含的文件的决定放在Bean中。为了更加灵活，我们可以将表封装在一个复合组件中，并将决策逻辑移至组件类。

<cc:interface componentType="xxx.component.DataTable"><cc:attribute name="id" required="false" type="java.lang.String"shortDescription="Unique identifier of the component in a NamingContainer"/><cc:attribute name="entries" required="true"shortDescription="The data which are shown in the datatable. This is a list of object representing one row."/><cc:attribute name="columns" required="true" type="java.util.List"shortDescription="The columns which are shown in the datatable. This is a list of instances of type ColumnModel."/>...
</cc:interface>
<cc:implementation><p:dataTable value="#{cc.attrs.entries}" var="data" rowKey="#{data.id}" ...>...<ui:include src="#{cc.columnsIncludeSrc}"><ui:param name="data" value="#{data}"/><ui:param name="columns" value="#{cc.attrs.columns}"/></ui:include></p:dataTable>
</cc:implementation>

ui：include如何工作？这是在构建视图时应用的标记处理程序。在JSF 2中，组件树根据POST请求构建两次，一次在RESTORE_VIEW阶段，一次在RENDER_RESPONSE阶段。在GET上，它在RENDER_RESPONSE阶段构建一次。此行为在JSF 2规范中指定，并且在Mojarra和MyFaces中相同。如果页面作者使用条件包含或条件模板，则必须在RENDER_RESPONSE中建立视图。因此，您可以确保ui：include的src属性在呈现阶段之前不久就得到了评估。

但是到了重点！到目前为止，我所写的内容只是介绍了扩展ui：include的动机。最近，我有一项任务要使用带有动态列的ap：dataTable和p：rowEditor。在PrimeFaces展示柜中就是这样的。问题只是–这种编辑功能不支持p：columns。我的想法是动态地多次添加p：column标签，但是具有不同的上下文参数。您可以将其想象为ui：include和ui：param在循环中。在上面的示例中，我们打算遍历List <ColumnModel>。每次循环迭代都应在所包含的facelet中提供ColumnModel类型的实例。因此，我编写了一个自定义标签处理程序以多次包含任何facelet。

package xxx.taghandler;import xxx.util.VariableMapperWrapper;
import java.io.IOException;
import java.util.List;
import java.util.UUID;
import javax.el.ExpressionFactory;
import javax.el.ValueExpression;
import javax.el.VariableMapper;
import javax.faces.component.UIComponent;
import javax.faces.view.facelets.FaceletContext;
import javax.faces.view.facelets.TagAttribute;
import javax.faces.view.facelets.TagAttributeException;
import javax.faces.view.facelets.TagConfig;
import javax.faces.view.facelets.TagHandler;/*** Tag handler to include a facelet multiple times with different contextes (objects from "value").* The attribute "value" can be either of type java.util.List or array.* If the "value" is null, the tag handler works as a standard ui:include.*/
public class InlcudesTagHandler extends TagHandler {private final TagAttribute src;private final TagAttribute value;private final TagAttribute name;public InlcudesTagHandler(TagConfig config) {super(config);this.src = this.getRequiredAttribute("src");this.value = this.getAttribute("value");this.name = this.getAttribute("name");}@Overridepublic void apply(FaceletContext ctx, UIComponent parent) throws IOException {String path = this.src.getValue(ctx);if ((path == null) || (path.length() == 0)) {return;}// wrap the original mapper - this is important when some objects passed into include via ui:param// because ui:param invokes setVariable(...) on the set variable mappper instanceVariableMapper origVarMapper = ctx.getVariableMapper();ctx.setVariableMapper(new VariableMapperWrapper(origVarMapper));try {this.nextHandler.apply(ctx, null);ValueExpression ve = (this.value != null) ? this.value.getValueExpression(ctx, Object.class) : null;Object objValue = (ve != null) ? ve.getValue(ctx) : null;if (objValue == null) {// include facelet only oncectx.includeFacelet(parent, path);} else {int size = 0;if (objValue instanceof List) {size = ((List) objValue).size();} else if (objValue.getClass().isArray()) {size = ((Object[]) objValue).length;}final ExpressionFactory exprFactory = ctx.getFacesContext().getApplication().getExpressionFactory();final String strName = this.name.getValue(ctx);// generate unique Id as a valid Java identifier and use it as variable for the provided value expressionfinal String uniqueId = "a" + UUID.randomUUID().toString().replaceAll("-", "");ctx.getVariableMapper().setVariable(uniqueId, ve);// include facelet multiple timesStringBuilder sb = new StringBuilder();for (int i = 0; i < size; i++) {if ((strName != null) && (strName.length() != 0)) {// create a new value expression in the array notation and bind it to the variable "name"sb.append("#{");sb.append(uniqueId);sb.append("[");sb.append(i);sb.append("]}");ctx.getVariableMapper().setVariable(strName,exprFactory.createValueExpression(ctx, sb.toString(), Object.class));}// included facelet can access the created above value expressionctx.includeFacelet(parent, path);// reset for next iterationsb.setLength(0);}}} catch (IOException e) {throw new TagAttributeException(this.tag, this.src, "Invalid path : " + path);} finally {// restore original mapperctx.setVariableMapper(origVarMapper);}}
}

最重要的调用是ctx.includeFacelet（parent，path）。 JSF API中的 includeFacelet（…）方法在相对于当前标记的某个路径上包含了facelet标记。类VariableMapperWrapper用于通过ui：param从名称到值的映射。对于带有列的示例，在每次调用includeFacelet（...）之前，变量列还将映射到表达式＃{columns [0]}，＃{columns [1]}等。好吧，不完全是这些表达式，在列的位置应该是一个唯一的名称，该名称再次映射到columns对象（以避免可能的名称冲突）。映射器类如下所示

package xxx.util;import java.util.HashMap;
import java.util.Map;
import javax.el.ELException;
import javax.el.ValueExpression;
import javax.el.VariableMapper;/*** Utility class for wrapping a VariableMapper. Modifications occur to the internal Map instance.* The resolving occurs first against the internal Map instance and then against the wrapped VariableMapper* if the Map doesn't contain the requested ValueExpression.*/
public class VariableMapperWrapper extends VariableMapper {private final VariableMapper wrapped;private Map<String, ValueExpression> vars;public VariableMapperWrapper(VariableMapper orig) {super();this.wrapped = orig;}@Overridepublic ValueExpression resolveVariable(String variable) {ValueExpression ve = null;try {if (this.vars != null) {// try to resolve against the internal mapve = this.vars.get(variable);}if (ve == null) {// look in the wrapped variable mapperreturn this.wrapped.resolveVariable(variable);}return ve;} catch (Throwable e) {throw new ELException("Could not resolve variable: " + variable, e);}}@Overridepublic ValueExpression setVariable(String variable, ValueExpression expression) {if (this.vars == null) {this.vars = new HashMap<String, ValueExpression>();}return this.vars.put(variable, expression);}
}

在taglib XML文件中注册标签处理程序，您就可以完成。

<tag><tag-name>includes</tag-name><handler-class>xxx.taghandler.InlcudesTagHandler</handler-class><attribute><description><![CDATA[The relative path to a XHTML file to be include one or multiple times.]]></description><name>src</name><required>true</required><type>java.lang.String</type></attribute><attribute><description><![CDATA[Objects which should be available in the included XHTML files. This attribute can be eitherof type java.util.List or array. If it is null, the tag handler works as a standard ui:include.]]></description><name>value</name><required>false</required><type>java.lang.Object</type></attribute><attribute><description><![CDATA[The name of the parameter which points to an object of each iteration over the given value.]]></description><name>name</name><required>false</required><type>java.lang.String</type></attribute>
</tag>

现在我可以在复合组件中使用它了

<p:dataTable value="#{cc.attrs.entries}" var="data" rowKey="#{data.id}" ...>...<custom:includes src="#{cc.columnsIncludeSrc}" value="#{cc.attrs.columns}" name="column"><ui:param name="data" value="#{data}"/></custom:includes> </p:dataTable>

典型的facelet文件（和组件树）包含一个非常规则的p：column标记，这意味着我们能够使用DataTable的所有功能！

<ui:composition xmlns="http://www.w3.org/1999/xhtml"xmlns:p="http://primefaces.org/ui"xmlns:ui="http://java.sun.com/jsf/facelets"...><p:column headerText="#{msgs[column.header]}"><p:cellEditor><f:facet name="output"><custom:typedOutput outputType="#{column.outputTypeName}"typedData="#{column.typedData}"value="#{data[column.property]}"timeZone="#{cc.timeZone}"calendarPattern="#{cc.calendarPattern}"       locale="#{cc.locale}"/></f:facet><f:facet name="input"><custom:typedInput inputType="#{column.inputTypeName}"typedData="#{column.typedData}"label="#{column.inputTypeName}"value="#{data[column.property]}"onchange="highlightEditedRow(this)"timeZone="#{cc.timeZone}"calendarPattern="#{cc.calendarPattern}"locale="#{cc.locale}"/></f:facet></p:cellEditor></p:column>
</ui:composition>