standard-examples/src/main/java/org/apache/taglibs/standard/examples/taglib/ResourceTag.java

/*
 * 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.taglibs.standard.examples.taglib;

import java.io.IOException;
import java.io.PrintWriter;
import java.io.Reader;
import java.io.Writer;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletResponseWrapper;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;

import org.apache.taglibs.standard.examples.util.IOBean;
import org.apache.taglibs.standard.examples.util.ServletResponseWrapperForWriter;

/**
 * <p>Tag handler for &lt;resource&gt;
 *
 * @author Pierre Delisle
 */
public class ResourceTag extends TagSupport {

    //*********************************************************************
    // Instance variables

    private String id;
    private String resource;

    private Reader reader;

    //*********************************************************************
    // Constructors

    public ResourceTag() {
        super();
        init();
    }

    private void init() {
        id = null;
        resource = null;
    }

    //*********************************************************************
    // Tag's properties

    /**
     * Tag's 'id' attribute
     */
    public void setId(String id) {
        this.id = id;
    }

    /**
     * Tag's 'resource' attribute
     */
    public void setResource(String resource) {
        this.resource = resource;
    }

    //*********************************************************************
    // TagSupport methods

    public int doStartTag() throws JspException {
        reader = getReaderFromResource(resource);
        exposeVariable(reader);
        return EVAL_BODY_INCLUDE;
    }

    public int doEndTag() throws JspException {
        try {
            reader.close();
        } catch (IOException ex) {
        }
        reader = null;
        return EVAL_PAGE;
    }

    /**
     * Releases any resources we may have (or inherit)
     */
    public void release() {
        super.release();
        init();
    }

    //*********************************************************************
    // Tag's scific behavior methods

    private Reader getReaderFromResource(String name) throws JspException {
        HttpServletRequest request =
                (HttpServletRequest) pageContext.getRequest();
        HttpServletResponse response =
                (HttpServletResponse) pageContext.getResponse();
        RequestDispatcher rd = null;

        // The response of the local URL becomes the reader that
        // we export. Need temporary storage.
        IOBean ioBean = new IOBean();
        Writer writer = ioBean.getWriter();
        ServletResponseWrapper responseWrapper =
                new ServletResponseWrapperForWriter(
                        response, new PrintWriter(writer));
        rd = pageContext.getServletContext().getRequestDispatcher(name);
        try {
            rd.include(request, responseWrapper);
            return ioBean.getReader();
        } catch (Exception ex) {
            throw new JspException(ex);
        }
    }

    //*********************************************************************
    // Utility methods

    private void exposeVariable(Reader reader) {
        if (id != null) {
            pageContext.setAttribute(id, reader);
        }
    }
}