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Struts example source code file (TagHandlerPool.java)

This example Struts source code file (TagHandlerPool.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Struts tags/keywords

annotationprocessor, error, exception, exception, http, jsp, jspexception, option_maxsize, option_tagpool, servlet, servletconfig, string, string, tag, tag, taghandlerpool, taghandlerpool

The Struts TagHandlerPool.java source code

/*
 * 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.struts2.jasper.runtime;

import javax.servlet.ServletConfig;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.Tag;

import org.apache.AnnotationProcessor;
import org.apache.struts2.jasper.Constants;
import org.apache.juli.logging.Log;
import org.apache.juli.logging.LogFactory;

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

    private Tag[] handlers;

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

    private Log log = LogFactory.getLog(TagHandlerPool.class);
    
    // index of next available tag handler
    private int current;
    protected AnnotationProcessor annotationProcessor = null;

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

        String tpClassName=getOption( config, OPTION_TAGPOOL, null);
        if( tpClassName != null ) {
            try {
                Class c=Class.forName( tpClassName );
                result=(TagHandlerPool)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 Tag[maxSize];
        this.current = -1;
        this.annotationProcessor = 
            (AnnotationProcessor) config.getServletContext().getAttribute(AnnotationProcessor.class.getName());
    }

    /**
     * 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 Tag[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 Tag get(Class handlerClass) throws JspException {
	Tag handler = null;
        synchronized( this ) {
            if (current >= 0) {
                handler = handlers[current--];
                return handler;
            }
        }

        // Out of sync block - there is no need for other threads to
        // wait for us to construct a tag for this thread.
        try {
            Tag instance = (Tag) handlerClass.newInstance();
            AnnotationHelper.postConstruct(annotationProcessor, instance);
            return instance;
        } catch (Exception e) {
            throw new JspException(e.getMessage(), e);
        }
    }

    /**
     * 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 Tag handler to add to this tag handler pool
     */
    public void reuse(Tag 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
        handler.release();
        if (annotationProcessor != null) {
            try {
                AnnotationHelper.preDestroy(annotationProcessor, handler);
            } catch (Exception e) {
                log.warn("Error processing preDestroy on tag instance of " 
                        + handler.getClass().getName(), e);
            }
        }
    }

    /**
     * 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--) {
            handlers[i].release();
            if (annotationProcessor != null) {
                try {
                    AnnotationHelper.preDestroy(annotationProcessor, handlers[i]);
                } catch (Exception e) {
                    log.warn("Error processing preDestroy on tag instance of " 
                            + handlers[i].getClass().getName(), e);
                }
            }
        }
    }

    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;
    }

}

Other Struts examples (source code examples)

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