jsp标签缓存池分析

  之前的分页标签写完了，放到线上没出现问题，之后由于要支持wml和html版本，并且要支持form表单，所以改了一下，在TagSupport加了一些变量，没一会写完了，后测试的时候发现好像有缓存，把之前复制的值存下来了，不是每次都new吗？好吧！google，原来确实如此，反编译jsp生成的class文件，发现一下代码。

 

 

public void _jspInit() {
    this._005fjspx_005ftagPool_005fc_005fchoose = TagHandlerPool.getTagHandlerPool(getServletConfig());
    this._005fjspx_005ftagPool_005fc_005fwhen_0026_005ftest = TagHandlerPool.getTagHandlerPool(getServletConfig());
    this._005fjspx_005ftagPool_005fc_005fif_0026_005ftest = TagHandlerPool.getTagHandlerPool(getServletConfig());
    this._005fjspx_005ftagPool_005fc_005fforEach_0026_005fvar_005fitems = TagHandlerPool.getTagHandlerPool(getServletConfig());
    this._el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
    this._jsp_annotationprocessor = ((AnnotationProcessor)getServletConfig().getServletContext().getAttribute(AnnotationProcessor.class.getName()));
  }

  public void _jspDestroy() {
    this._005fjspx_005ftagPool_005fc_005fout_0026_005fvalue_005fnobody.release();
    this._005fjspx_005ftagPool_005fc_005fchoose.release();
    this._005fjspx_005ftagPool_005fc_005fwhen_0026_005ftest.release();
    this._005fjspx_005ftagPool_005fc_005fif_0026_005ftest.release();
    this._005fjspx_005ftagPool_005fc_005fforEach_0026_005fvar_005fitems.release();
  }

 

 

这里面有个缓存池-TagHandlerPool，看源码。

 

 

public class TagHandlerPool {

    private Tag[] handlers;

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

    // 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 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;
    }

    /**
     * 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 {
            return (Tag) handlerClass.newInstance();
        } catch (Exception e) {
Rate            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();
    }

    /**
     * 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();
    }
    }

    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;
    }

}

 

      原来每个jsp生成的servlet都有个TagHandlerPool，每次初始化的时候创建各个标签的连接池，然后想用就从缓存池里面获取，由于此缓存标签用完还要放到缓存池中，所以每次标签里面的变量要重新复制，不然会出现数据不一致的问题。