TagHandlerPool.java

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 * Copyright 2004 The Apache Software Foundation
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 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
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package org.apache.jasper.runtime;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.JspTag;
import javax.servlet.jsp.tagext.Tag;
import javax.servlet.ServletConfig;
import org.apache.jasper.Constants;
import org.glassfish.jsp.api.ResourceInjector;

/**
 * Pool of tag handlers that can be reused.
 *
 * @author Jan Luehe
 */
public class TagHandlerPool {

    public static final String OPTION_TAGPOOL="tagpoolClassName";
    public static final String OPTION_MAXSIZE="tagpoolMaxSize";

    private JspTag[] handlers;
    private ResourceInjector resourceInjector;

    // index of next available tag handler
    private int current;

    public static TagHandlerPool getTagHandlerPool( ServletConfig config) {
        TagHandlerPool result=null;

        String tpClassName=getOption( config, OPTION_TAGPOOL, null);
        if( tpClassName != null ) {
            try {
                Class<? extends TagHandlerPool> c =
                    Class.forName(tpClassName).asSubclass(TagHandlerPool.class);
                result = c.newInstance();
            } catch (Exception e) {
                e.printStackTrace();
                result=null;
            }
        }
        if( result==null ) result=new TagHandlerPool();
        result.init(config);

        return result;
    }

    protected void init( ServletConfig config ) {
        int maxSize=-1;
        String maxSizeS=getOption(config, OPTION_MAXSIZE, null);
        if( maxSizeS != null ) {
            try {
                maxSize=Integer.parseInt(maxSizeS);
            } catch( Exception ex) {
                maxSize=-1;
            }
        }
        if( maxSize <0  ) {
            maxSize=Constants.MAX_POOL_SIZE;
        }
        this.handlers = new JspTag[maxSize];
        this.current = -1;

        this.resourceInjector = (ResourceInjector)
            config.getServletContext().getAttribute(
                Constants.JSP_RESOURCE_INJECTOR_CONTEXT_ATTRIBUTE);
    }

    /**
     * Constructs a tag handler pool with the default capacity.
     */
    public TagHandlerPool() {
	// Nothing - jasper generated servlets call the other constructor,
        // this should be used in future + init .
    }

    /**
     * Constructs a tag handler pool with the given capacity.
     *
     * @param capacity Tag handler pool capacity
     * @deprecated Use static getTagHandlerPool
     */
    public TagHandlerPool(int capacity) {
	this.handlers = new JspTag[capacity];
	this.current = -1;
    }

    /**
     * Gets the next available tag handler from this tag handler pool,
     * instantiating one if this tag handler pool is empty.
     *
     * @param handlerClass Tag handler class
     *
     * @return Reused or newly instantiated tag handler
     *
     * @throws JspException if a tag handler cannot be instantiated
     */
    public <T extends JspTag> JspTag get(Class<T> handlerClass)
            throws JspException {
        synchronized( this ) {
            if (current >= 0) {
                return handlers[current--];
            }
        }

        // Out of sync block - there is no need for other threads to
        // wait for us to construct a tag for this thread.
        JspTag tagHandler = null;
        try {
            if (resourceInjector != null) {
                tagHandler = resourceInjector.createTagHandlerInstance(
                    handlerClass);
            } else {
                tagHandler = handlerClass.newInstance();
            }
        } catch (Exception e) {
            throw new JspException(e.getMessage(), e);
        }

        return tagHandler;
    }

    /**
     * Adds the given tag handler to this tag handler pool, unless this tag
     * handler pool has already reached its capacity, in which case the tag
     * handler's release() method is called.
     *
     * @param handler JspTag handler to add to this tag handler pool
     */
    public void reuse(JspTag handler) {
        synchronized( this ) {
            if (current < (handlers.length - 1)) {
                handlers[++current] = handler;
                return;
            }
        }
        // There is no need for other threads to wait for us to release
        if (handler instanceof Tag) {
            ((Tag)handler).release();
        }

        if (resourceInjector != null) {
            resourceInjector.preDestroy(handler);
        }
    }

    /**
     * Calls the release() method of all available tag handlers in this tag
     * handler pool.
     */
    public synchronized void release() {
	for (int i=current; i>=0; i--) {
            if (handlers[i] instanceof Tag) {
                ((Tag)handlers[i]).release();
            }
            if (resourceInjector != null) {
                resourceInjector.preDestroy(handlers[i]);
            }
	}
    }

    protected static String getOption( ServletConfig config, String name, String defaultV) {
        if( config == null ) return defaultV;

        String value=config.getInitParameter(name);
        if( value != null ) return value;
        if( config.getServletContext() ==null )
            return defaultV;
        value=config.getServletContext().getInitParameter(name);
        if( value!=null ) return value;
        return defaultV;
    }

}