/*
 * 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 javax.servlet.jsp.tagext;

import java.io.IOException;
import java.io.Writer;

import javax.servlet.jsp.JspContext;
import javax.servlet.jsp.JspException;

/**
 * Encapsulates a portion of JSP code in an object that
 * can be invoked as many times as needed.  JSP Fragments are defined
 * using JSP syntax as the body of a tag for an invocation to a SimpleTag
 * handler, or as the body of a &lt;jsp:attribute&gt; standard action
 * specifying the value of an attribute that is declared as a fragment,
 * or to be of type JspFragment in the TLD.
 * <p>
 * The definition of the JSP fragment must only contain template
 * text and JSP action elements.  In other words, it must not contain
 * scriptlets or scriptlet expressions.  At translation time, the
 * container generates an implementation of the JspFragment abstract class
 * capable of executing the defined fragment.
 * <p>
 * A tag handler can invoke the fragment zero or more times, or
 * pass it along to other tags, before returning.  To communicate values
 * to/from a JSP fragment, tag handlers store/retrieve values in
 * the JspContext associated with the fragment.
 * <p>
 * Note that tag library developers and page authors should not generate
 * JspFragment implementations manually.
 * <p>
 * <i>Implementation Note</i>: It is not necessary to generate a
 * separate class for each fragment.  One possible implementation is
 * to generate a single helper class for each page that implements
 * JspFragment. Upon construction, a discriminator can be passed to
 * select which fragment that instance will execute.
 *
 * @since JSP 2.0
 */
public abstract class JspFragment {

    /**
     * Default constructor.
     */
    public JspFragment() {
        // NO-OP by default
    }

    /**
     * Executes the fragment and directs all output to the given Writer,
     * or the JspWriter returned by the getOut() method of the JspContext
     * associated with the fragment if out is null.
     *
     * @param out The Writer to output the fragment to, or null if
     *     output should be sent to JspContext.getOut().
     * @throws javax.servlet.jsp.JspException Thrown if an error occurred
     *     while invoking this fragment.
     * @throws javax.servlet.jsp.SkipPageException Thrown if the page
     *     that (either directly or indirectly) invoked the tag handler that
     *     invoked this fragment is to cease evaluation.  The container
     *     must throw this exception if a Classic Tag Handler returned
     *     Tag.SKIP_PAGE or if a Simple Tag Handler threw SkipPageException.
     * @throws java.io.IOException If there was an error writing to the
     *     stream.
     */
    public abstract void invoke( Writer out )
        throws JspException, IOException;

    /**
     * Returns the JspContext that is bound to this JspFragment.
     *
     * @return The JspContext used by this fragment at invocation time.
     */
    public abstract JspContext getJspContext();

}
