definetag.java

这是Java学习的一些常用的例子

/* ====================================================================
 * Copyright (c) 2004 Guillermo Meyer.                                    
 * Project: Providers                                                      
 * (#)DefineTag.java                  
 *                                         
 * Permission is granted to copy, distribute and/or modify this document  
 * under the terms of the GNU Free Documentation License, Version 1.1 or  
 * any later version published by the Free Software Foundation; with no   
 * Invariant Sections, with no Front-Cover Texts.                     
 * A copy of the license is included in the section entitled 
 * "GNU Free Documentation License".                                 
 * ====================================================================
 */            
package ar.com.koalas.providers.taglibs;

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

import ar.com.koalas.providers.Provider;
import ar.com.koalas.providers.ProviderFactory;

/**
 * This tag defines a new bean in a given scope and sets there the collection returned from the provider
 *
 * @author Guillermo Meyer
 */
public class DefineTag
        extends TagSupport {
    //~ Instance fields ----------------------------------------------------------------------------

    protected String id = null;
    protected String toScope = null;
	protected String provider = null;
    //~ Methods ------------------------------------------------------------------------------------

    /**
     * DOCUMENT ME!
     *
     * @param id DOCUMENT ME!
     */
    public void setId(String id) {
        this.id = id;
    }

    /**
     * DOCUMENT ME!
     *
     * @return DOCUMENT ME!
     */
    public String getId() {
        return (this.id);
    }

    /**
     * DOCUMENT ME!
     *
     * @param toScope DOCUMENT ME!
     */
    public void setToScope(String toScope) {
        this.toScope = toScope;
    }

    /**
     * DOCUMENT ME!
     *
     * @return DOCUMENT ME!
     */
    public String getToScope() {
        return (this.toScope);
    }

    /**
     * Retrieve the required property and expose it as a scripting variable.
     *
     * @exception JspException if a JSP exception has occurred
     */
    public int doEndTag()
            throws JspException {

        Object value = null;
		try {
			ProviderFactory factory = ProviderFactory.getInstance();
			Provider prov = factory.getProvider(this.getProvider());
			if(prov==null) throw new NullPointerException("provider not found: " + this.getProvider());
			value=prov.getCollection();			
		} catch (Exception e) {
			throw new JspException("Error en el provider " + this.getProvider() + ". en DefineTag: " + e.getMessage());
		}

        int targetScope = PageContext.PAGE_SCOPE;
        if (toScope != null) {
            targetScope = this.getScope(toScope);
        }

        pageContext.setAttribute(id, value, targetScope);

        // Continue processing this page
        return (EVAL_PAGE);
    }

    /**
     * DOCUMENT ME!
     *
     * @return DOCUMENT ME!
     *
     * @throws JspException DOCUMENT ME!
     */
    public int doStartTag()
            throws JspException {
        return (SKIP_BODY);
    }

    /**
     * Release all allocated resources.
     */
    public void release() {
        super.release();
        id = null;
        toScope = "page";
    }

    private int getScope(String toScope) {
        if ("request".equalsIgnoreCase(this.toScope)) {
            return PageContext.SESSION_SCOPE;
        }
        if ("session".equalsIgnoreCase(this.toScope)) {
            return PageContext.REQUEST_SCOPE;
        }
        if ("application".equalsIgnoreCase(this.toScope)) {
            return PageContext.APPLICATION_SCOPE;
        }

        return PageContext.PAGE_SCOPE;
    }
	/**
	 * @return
	 */
	public String getProvider() {
		return provider;
	}

	/**
	 * @param string
	 */
	public void setProvider(String string) {
		provider = string;
	}

}