是否可以通过编程方式调用方法签名中定义的方法?

时间:2016-01-15 19:40:45

标签: jsf jsf-2 primefaces composite-component

假设我有一个复合组件

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
        "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:composite="http://java.sun.com/jsf/composite"
  `enter code here`    xmlns:h="http://java.sun.com/jsf/html"
      xmlns:p="http://primefaces.org/ui">

<h:head></h:head>
<h:body>
    <composite:interface componentType="editableLabel">
        <composite:attribute name="value" required="true" type="java.lang.String"/>
        <composite:attribute name="oldValue" type="java.lang.String"/>
        <composite:attribute name="editMode" required="false" default="#{false}" type="java.lang.Boolean"/>
        <composite:attribute name="updateListener" required="false" method-signature="void actionListener()"/>
        <composite:attribute name="cancelListener" required="false" method-signature="void actionListener()"/>
    </composite:interface>
    <composite:implementation>
        <h:panelGroup id="editableLabelComponent">
            <h:panelGroup rendered="#{cc.attrs.editMode}">
                <p:inputText value="#{cc.attrs.value}"/>

                <p:commandButton value="Update" actionListener="#{cc.update}" update="editableLabelComponent"/>

                <p:commandButton value="Cancel" actionListener="#{cc.cancel}" update="editableLabelComponent"/>
            </h:panelGroup>

            <p:commandLink>
                <p:outputLabel id="display" value="#{cc.attrs.value}" rendered="#{!cc.attrs.editMode}"/>
                <p:ajax event="click" listener="#{cc.toggleEditMode}" update="editableLabelComponent"/>
            </p:commandLink>
        </h:panelGroup>
    </composite:implementation>
</h:body>

</html>

使用FacesComponent

import org.apache.commons.lang3.StringUtils;

import javax.el.ELContext;
import javax.el.ValueExpression;
import javax.faces.component.FacesComponent;
import javax.faces.component.NamingContainer;
import javax.faces.component.UIComponentBase;
import javax.faces.component.UINamingContainer;
import javax.faces.context.FacesContext;
import java.io.Serializable;

/**
 * Created by labraham on 1/14/16.
 */
@FacesComponent(value = "editableLabel")
public class EditableLabel extends UIComponentBase implements Serializable, NamingContainer {
  private static final long serialVersionUID = 108467781935083432L;

  public static final String VALUE_ATTRIBUTE = "#{cc.attrs.value}";
  public static final String OLD_VALUE_ATTRIBUTE = "#{cc.attrs.oldValue}";
  public static final String EDIT_MODE_ATTRIBUTE = "#{cc.attrs.editMode}";

  private FacesContext context;
  private ELContext elContext;

  @Override
  public String getFamily() {
    return UINamingContainer.COMPONENT_FAMILY;
  }

  /**
   *
   */
  public void update() {

    ValueExpression oldValue = getAttr(OLD_VALUE_ATTRIBUTE, String.class);

    String value = (String) getAttr(VALUE_ATTRIBUTE, String.class).getValue(getElContext());

    oldValue.setValue(getElContext(), value);

    toggleEditMode();
  }

  /**
   *
   */
  public void cancel() {
    ValueExpression value = getAttr(VALUE_ATTRIBUTE, String.class);

    String oldValue = (String) getAttr(OLD_VALUE_ATTRIBUTE, String.class).getValue(getElContext());

    value.setValue(getElContext(), oldValue);

    toggleEditMode();
  }

  /**
   *
   */
  public void toggleEditMode() {
    if (StringUtils.isEmpty((String) getAttr(OLD_VALUE_ATTRIBUTE, String.class).getValue(getElContext()))) {
     getAttr(OLD_VALUE_ATTRIBUTE, String.class).setValue(getElContext(),
         getAttr(VALUE_ATTRIBUTE, String.class).getValue(getElContext())
     );
    }

    ValueExpression editmode = getAttr(EDIT_MODE_ATTRIBUTE, Boolean.class);
    editmode.setValue(getElContext(), !((Boolean) editmode.getValue(getElContext())));

  }

  /**Get value expression for a given attr.*/
  private ValueExpression getAttr(final String attribute, final Class<?> attributeType) {
    return getContext().getApplication().getExpressionFactory()
           .createValueExpression(getElContext(), attribute, attributeType);
  }

  /**Get ElContext.*/
  public ELContext getElContext() {
    if (this.elContext == null) {
      elContext = getContext().getELContext();
    }
    return elContext;
  }

  public void setElContext(final ELContext elContext) {
    this.elContext = elContext;
  }

  /**Get faces context*/
  public FacesContext getContext() {
    if (this.context == null) {
      context = FacesContext.getCurrentInstance();
    }
    return context;
  }

  public void setContext(final FacesContext context) {
    this.context = context;
  }
}

现在,此小部件的所有实例都将具有取消和更新的基线功能,如cancel()和update()函数所定义。然而,除了这个基本功能之外,用户可能还需要一些额外的功能(例如,在更新时调用web服务),这些功能将通过updateListener和/或cancelListener属性中的某种辅助bean方法添加。

我的问题是是否可以从FacesComponent内部以编程方式调用用户附加到侦听器属性的方法,或者我是否采用了错误的方法?

1 个答案:

答案 0 :(得分:3)

是的,它可用作MethodExpression类型的属性。继承的UIComponent#getAttributes()映射以通常的方式提供所有复合属性。另请参阅How to access Composite Component attribute values in the backing UIComponent?

,例如,获取#{cc.attrs.updateListener}并调用没有参数:

MethodExpression updateListener = (MethodExpression) getAttributes().get("updateListener");
updateListener.invoke(getFacesContext().getELContext(), null);
对具体问题

无关,处理ValueExpression属性的方式很笨拙。要获得#{cc.attrs.oldvalue},请执行以下操作:

String oldvalue = (String) getAttributes().get("oldvalue");

要设置#{cc.attrs.value},只需执行以下操作:

getAttributes().put("value", oldvalue);

FacesContextELContext作为实例变量在技术上幸运地在这个特定的构造中没有坏处,但这很可疑,你最好在方法局部范围内获得它们。 FacesContext仅由继承的UIComponent#getFacesContext()提供。

另见: