expressionevaluator.java

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package net.sf.navigator.taglib.el;

import org.apache.taglibs.standard.lang.support.ExpressionEvaluatorManager;

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


/**
 * Utility class to help with the evaluation of JSTL Expression Language.  It
 * mainly encapsulates the calls to ExpressionEvaluationManager to ease the
 * use of this class.
 */
public class ExpressionEvaluator {
    //~ Instance fields ========================================================

    private PageContext context;
    private Tag tag;

    //~ Constructors ===========================================================

    public ExpressionEvaluator(Tag tag, PageContext context) {
        this.tag = tag;
        this.context = context;
    }

    //~ Methods ================================================================

    /**
     * Evaluate expression in attrValue.
     *
     * @return evaluate expression of attrValue, null if attrValue is null.
     */
    public Object eval(String attrName, String attrValue, Class returnClass)
    throws JspException {
        Object result = null;

        if (attrValue != null) {
            result =
                ExpressionEvaluatorManager.evaluate(attrName, attrValue,
                                                    returnClass, tag, context);
        }

        return result;
    }

    public String evalString(String attrName, String attrValue)
    throws JspException {
        return (String) eval(attrName, attrValue, String.class);
    }

    public boolean evalBoolean(String attrName, String attrValue)
    throws JspException {
        Boolean rtn = (Boolean) eval(attrName, attrValue, Boolean.class);

        if (rtn != null) {
            return rtn.booleanValue();
        } else {
            return false;
        }
    }

    public long evalLong(String attrName, String attrValue)
    throws JspException {
        Long rtn = (Long) eval(attrName, attrValue, Long.class);

        if (rtn != null) {
            return rtn.longValue();
        } else {
            return -1L;
        }
    }

    public int evalInt(String attrName, String attrValue)
    throws JspException {
        Integer rtn = (Integer) eval(attrName, attrValue, Integer.class);

        if (rtn != null) {
            return rtn.intValue();
        } else {
            return -1;
        }
    }
}