org.apache.myfaces.custom.buffer.AbstractBuffer Maven / Gradle / Ivy

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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.myfaces.custom.buffer;

import javax.el.ValueExpression;
import javax.faces.component.UIComponentBase;
import javax.faces.context.FacesContext;

import org.apache.myfaces.buildtools.maven2.plugin.builder.annotation.JSFComponent;
import org.apache.myfaces.buildtools.maven2.plugin.builder.annotation.JSFJspProperties;
import org.apache.myfaces.buildtools.maven2.plugin.builder.annotation.JSFJspProperty;
import org.apache.myfaces.buildtools.maven2.plugin.builder.annotation.JSFProperty;

/**
 * A component that renders its child components into an in-memory buffer rather than
 * render them directly to the response stream.
 * 
 * Property "into" is an EL expression that specifies where to store a String holding
 * the results of rendering all the children of this component; this is assigned to
 * after rendering of this component (and its children) is complete.
 * 
 * 
 * Typically, an h:output tag is then used later in the same page to output the buffer
 * contents.
 * 
 * 
 * This can be useful with JSF1.1/JSP2.0 to work around the well-known problem where
 * on first render of a page, a component "A" cannot reference a component "B" which is
 * defined later in the page because it has not yet been created. A solution is to define
 * "B" before "A", but wrapped in a Buffer component. Component A can then be rendered
 * and successfully reference "B" because it now exists. And later in the page, the buffer
 * contents can then be output, preserving the original layout.
 * 
 * 
 * This can also be useful when rendering the same data block multiple times within a page.
 * For example, a datatable can be rendered with a datascroller both before and after it;
 * first render the table into a buffer B1, then render the datascroller into a buffer B2,
 * then output buffers B2,B1,B2.
 * 
 * 
 * @since 1.1.7
 * @author Sylvain Vieujot (latest modification by $Author: lu4242 $)
 * @version $Revision: 691871 $ $Date: 2008-09-04 06:32:08 +0200 (Thu, 04 Sep 2008) $
 */
@JSFComponent(
        name = "t:buffer",
        clazz = "org.apache.myfaces.custom.buffer.Buffer",
        tagClass = "org.apache.myfaces.custom.buffer.BufferTag")
@JSFJspProperties(properties={
        @JSFJspProperty(
                name = "rendered",
                returnType = "boolean", 
                tagExcluded = true),
        @JSFJspProperty(
                name = "binding",
                returnType = "java.lang.String",
                tagExcluded = true),
        @JSFJspProperty(
                name = "id",
                returnType = "java.lang.String",
                tagExcluded = true)
                })
public abstract class AbstractBuffer extends UIComponentBase{

    public static final String COMPONENT_TYPE = "org.apache.myfaces.Buffer";
    public static final String COMPONENT_FAMILY = "javax.faces.Data";
    private static final String DEFAULT_RENDERER_TYPE = "org.apache.myfaces.Buffer";

    protected abstract String getLocalInto();
    
    public abstract void setInto(String into);

    void fill(String content, FacesContext facesContext){
        ValueExpression intoVB;

        if (getLocalInto() == null) {
            intoVB = getValueExpression("into");
            setInto(intoVB.getExpressionString());
        } else {
            intoVB = facesContext.getApplication().
            getExpressionFactory().createValueExpression(
                    facesContext.getELContext(), getLocalInto(), Object.class );
        }

        intoVB.setValue(facesContext.getELContext(), content);
    }
    
    /**
     * An EL expression that specifies where to store a String holding 
     * the results of rendering all the children of this component; 
     * this is assigned to after rendering of this component (and its 
     * children) is complete.
     * 
     */
    @JSFProperty(
            required = true,
            localMethod = true)
    protected abstract String getInto(); 

}