/*
 * @(#)AttributeValueExp.java	4.24 04/05/18
 * 
 * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package javax.management;


// RI import
import javax.management.MBeanServer;

/**
 * Represents attributes used as arguments to relational constraints. 
 * An <CODE>AttributeValueExp</CODE> may be used anywhere a <CODE>ValueExp</CODE> is required.
 *
 * @since 1.5
 */
public class AttributeValueExp implements ValueExp  { 


    /* Serial version */
    private static final long serialVersionUID = -7768025046539163385L;

    /** 
     * @serial The name of the attribute 
     */
    private String attr;

    /**
     * An <code>AttributeValueExp</code> with a null attribute.
     * @deprecated An instance created with this constructor cannot be
     * used in a query.
     */
    @Deprecated
    public AttributeValueExp() { 
    } 
       
    /**
     * Creates a new <CODE>AttributeValueExp</CODE> representing the
     * specified object attribute, named attr.
     *
     * @param attr the name of the attribute whose value is the value
     * of this {@link ValueExp}.
     */
    public AttributeValueExp(String attr) { 
	this.attr = attr;
    } 
    
    /**
     * Returns a string representation of the name of the attribute.
     *
     * @return the attribute name.
     */
    public String getAttributeName()  { 
	return attr;
    } 

    /**
     * Applies the <CODE>AttributeValueExp</CODE> on an MBean.
     *
     * @param name The name of the MBean on which the <CODE>AttributeValueExp</CODE> will be applied.
     *
     * @return  The <CODE>ValueExp</CODE>.
     *
     * @exception BadAttributeValueExpException
     * @exception InvalidApplicationException
     * @exception BadStringOperationException
     * @exception BadBinaryOpValueExpException
     *
     */
    public ValueExp apply(ObjectName name) throws BadStringOperationException, BadBinaryOpValueExpException,
	BadAttributeValueExpException, InvalidApplicationException {
	Object result = getAttribute(name);
	
	if (result instanceof Number) {
	    return new NumericValueExp((Number)result);
	} else if (result instanceof String) {
	    return new StringValueExp((String)result);
	} else if (result instanceof Boolean) {
	    return new BooleanValueExp((Boolean)result);
	} else {
	    throw new BadAttributeValueExpException(result);
	}
    } 

    /**
     * Returns the string representing its value.
     */
    public String toString()  { 
	return attr;
    } 
    

    /**
     * Sets the MBean server on which the query is to be performed.
     *
     * @param s The MBean server on which the query is to be performed.
     */
    /* There is no need for this method, because if a query is being
       evaluted an AttributeValueExp can only appear inside a QueryExp,
       and that QueryExp will itself have done setMBeanServer.  */
    public void setMBeanServer(MBeanServer s)  { 
    }     


    /**
     * Return the value of the given attribute in the named MBean.
     * If the attempt to access the attribute generates an exception,
     * return null.
     *
     * @param name the name of the MBean whose attribute is to be returned.
     *
     * @return the value of the attribute, or null if it could not be
     * obtained.
     */
    protected Object getAttribute(ObjectName name) {
	try {
	    // Get the value from the MBeanServer

	    MBeanServer server = QueryEval.getMBeanServer();

	    return server.getAttribute(name, attr);
	} catch (Exception re) {
	    return null;
	}
    }

}