inittag.java

lucene 是java 的版的搜索引擎公共模块

package com.bitmechanic.listlib;

import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;
import javax.servlet.jsp.tagext.Tag;


public class InitTag extends TagSupport {

    public static final String TAG_KEY = "listlib_tag_";
    public static final String OFFSET_KEY = "listlib_offset";

    private String _name, _class;
    private int _max;
    private ListContainer _lc;
    private ListCreator _creator;

    public static String getTagKey(String name) {
        return TAG_KEY + name;
    }

    public static InitTag getListTag(TagSupport child, PageContext ctx, 
        String name) throws JspException {

        InitTag tag;
        if (name == null) {
            tag = (InitTag)findAncestorWithClass(child, InitTag.class);
            if (tag == null) {
                throw new JspException("No InitTag found on this page");
            }
        }
        else {
            tag = (InitTag)ctx.getAttribute(getTagKey(name));
            if (tag == null) {
                throw new JspException("No InitTag found with name: " + name);
            }
        }

        return tag;
    }

    public void setName(String name) {
        _name = name;
    }

    public void setClass(String clazz) {
        _class = clazz;
    }

    public void setListCreator(String creator) {
        _creator = (ListCreator)pageContext.getAttribute(creator);
    }

    public void setMax(int max) {
        _max = max;
    }

    public ListContainer getList() throws JspException {
        return _lc;
    }

    public int doStartTag() throws JspException {
        if (_creator == null) {
            try {
                Class c = Class.forName(_class);
                _creator = (ListCreator)c.newInstance();
            }
            catch(Exception e) {
                throw new JspException("Unable to instantiate: " + _class, e);
            }
        }

        int offset = 0;
        String offsetStr = pageContext.getRequest().getParameter(OFFSET_KEY);
        if (offsetStr != null) {
            try {
                offset = Integer.parseInt(offsetStr);
            }
            catch(Exception e) {
                // squelch.. use starting offset by default.
            }
        }

        try {
            _lc = _creator.execute(pageContext, offset, _max);
        }
        catch(Exception e) {
            _creator = null;
            throw new JspException("Unable to load list: " + e.getMessage(),e);
        }

        _lc.setMax(_max);
        _lc.setOffset(offset);

        if (_name != null) {
            pageContext.setAttribute(getTagKey(_name), this);
            pageContext.setAttribute(_name, getList());
        }

        _creator = null;

        return EVAL_BODY_INCLUDE;
    }

    public int doEndTag() throws JspException {
        return EVAL_PAGE;
    }

    public void release() {
        super.release();

        _name = _class = null;
        _lc = null;
        _max = 20;
        _creator = null;
    }

}