src/java/org/apache/velocity/runtime/directive/Define.java

package org.apache.velocity.runtime.directive;

/*
 * 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.    
 */

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

import org.apache.commons.lang.text.StrBuilder;
import org.apache.velocity.context.InternalContextAdapter;
import org.apache.velocity.exception.TemplateInitException;
import org.apache.velocity.exception.VelocityException;
import org.apache.velocity.runtime.Renderable;
import org.apache.velocity.runtime.RuntimeConstants;
import org.apache.velocity.runtime.RuntimeServices;
import org.apache.velocity.runtime.log.Log;
import org.apache.velocity.runtime.parser.node.Node;

/**
 * Directive that puts an unrendered AST block in the context
 * under the specified key, postponing rendering until the
 * reference is used and rendered.
 *
 * @author Andrew Tetlaw
 * @author Nathan Bubna
 * @version $Id: Define.java 686842 2008-08-18 18:29:31Z nbubna $
 */
public class Define extends Directive
{
    private String key;
    private Node block;
    private Log log;
    private int maxDepth;
    private String definingTemplate;
    
    /**
     * Return name of this directive.
     */
    public String getName()
    {
        return "define";
    }

    /**
     * Return type of this directive.
     */
    public int getType()
    {
        return BLOCK;
    }

    /**
     *  simple init - get the key
     */
    public void init(RuntimeServices rs, InternalContextAdapter context, Node node)
        throws TemplateInitException
    {
        super.init(rs, context, node);

        log = rs.getLog();

        /*
         * default max depth of two is used because intentional recursion is
         * unlikely and discouraged, so make unintentional ones end fast
         */
        maxDepth = rs.getInt(RuntimeConstants.DEFINE_DIRECTIVE_MAXDEPTH, 2);

        /*
         * first token is the name of the block. We don't even check the format,
         * just assume it looks like this: $block_name. Should we check if it has
         * a '$' or not?
         */
        key = node.jjtGetChild(0).getFirstToken().image.substring(1);

        /**
         * No checking is done. We just grab the second child node and assume
         * that it's the block!
         */
        block = node.jjtGetChild(1);

        /**
         * keep tabs on the template this came from
         */
        definingTemplate = context.getCurrentTemplateName();
    }

    /**
     * directive.render() simply makes an instance of the Block inner class
     * and places it into the context as indicated.
     */
    public boolean render(InternalContextAdapter context, Writer writer, Node node)
    {
        /* put a Block instance into the context,
         * using the user-defined key, for later inline rendering.
         */
        context.put(key, new Block(context, this));
        return true;
    }

    /**
     * Creates a string identifying the source and location of the block
     * definition, and the current template being rendered if that is
     * different.
     */
    protected String id(InternalContextAdapter context)
    {
        StrBuilder str = new StrBuilder(100)
            .append("block $").append(key)
            .append(" (defined in ").append(definingTemplate)
            .append(" [line ").append(getLine())
            .append(", column ").append(getColumn()).append("])");

        if (!context.getCurrentTemplateName().equals(definingTemplate))
        {
            str.append(" used in ").append(context.getCurrentTemplateName());
        }

        return str.toString();
    }
    
    /**
     * actual class placed in the context, holds the context and writer
     * being used for the render, as well as the parent (which already holds
     * everything else we need).
     */
    public static class Block implements Renderable
    {
        private InternalContextAdapter context;
        private Define parent;
        private int depth;
        
        public Block(InternalContextAdapter context, Define parent)
        {
            this.context = context;
            this.parent = parent;
        }
        
        /**
         *
         */
        public boolean render(InternalContextAdapter context, Writer writer)
        {
            try
            {
                depth++;
                if (depth > parent.maxDepth)
                {
                    /* this is only a debug message, as recursion can
                     * happen in quasi-innocent situations and is relatively
                     * harmless due to how we handle it here.
                     * this is more to help anyone nuts enough to intentionally
                     * use recursive block definitions and having problems
                     * pulling it off properly.
                     */
                    parent.log.debug("Max recursion depth reached for "+parent.id(context));
                    depth--;
                    return false;
                }
                else
                {
                    parent.block.render(context, writer);
                    depth--;
                    return true;
                }
            }
            catch (IOException e)
            {
                String msg = "Failed to render "+parent.id(context)+" to writer";
                parent.log.error(msg, e);
                throw new RuntimeException(msg, e);
            }
            catch (VelocityException ve)
            {
                String msg = "Failed to render "+parent.id(context)+" due to "+ve;
                parent.log.error(msg, ve);
                throw ve;
            }
        }

        public String toString()
        {
            Writer stringwriter = new StringWriter();
            if(render(context,stringwriter))
            {
                return stringwriter.toString();
            }
            else
            {
                return null;
            }
        }
    }
}