/*
 * @(#)ClassAttributeValueExp.java	4.21 03/12/19
 * 
 * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package javax.management;

import java.security.AccessController;
import java.security.PrivilegedAction;

import com.sun.jmx.mbeanserver.GetPropertyAction;

/**
 * This class represents the name of the Java implementation class of
 * the MBean. It is used for performing queries based on the class of
 * the MBean.
 * @serial include
 *
 * @since 1.5
 */
class ClassAttributeValueExp extends AttributeValueExp   { 

    // Serialization compatibility stuff:
    // Two serial forms are supported in this class. The selected form depends
    // on system property "jmx.serial.form":
    //  - "1.0" for JMX 1.0
    //  - any other value for JMX 1.1 and higher
    //
    // Serial version for old serial form 
    private static final long oldSerialVersionUID = -2212731951078526753L;
    //
    // Serial version for new serial form 
    private static final long newSerialVersionUID = -1081892073854801359L;

    private static final long serialVersionUID;
    static {
	boolean compat = false;
	try {
	    PrivilegedAction act = new GetPropertyAction("jmx.serial.form");
	    String form = (String) AccessController.doPrivileged(act);
	    compat = (form != null && form.equals("1.0"));
	} catch (Exception e) {
	    // OK: exception means no compat with 1.0, too bad
	}
	if (compat)
	    serialVersionUID = oldSerialVersionUID;
	else 
	    serialVersionUID = newSerialVersionUID;
    }

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

    /**
     * Basic Constructor.
     */    
    public ClassAttributeValueExp() { 
	attr = "Class";
    } 


    /**
     * Applies the ClassAttributeValueExp on an MBean. Returns the name of
     * the Java implementation class of the MBean.
     *
     * @param name The name of the MBean on which the ClassAttributeValueExp will be applied.
     *
     * @return  The ValueExp.
     *
     * @exception BadAttributeValueExpException 
     * @exception InvalidApplicationException
     */
    public ValueExp apply(ObjectName name) throws BadStringOperationException, BadBinaryOpValueExpException,
	BadAttributeValueExpException, InvalidApplicationException  { 
	getAttribute(name);
	Object result = getValue(name);   
	if  (result instanceof String) {
	    return new StringValueExp((String)result);
	} else {
	    throw new BadAttributeValueExpException(result);
	}
    } 
    
    /**
     * Returns the string "Class" representing its value
     */
    public String toString()  { 
	return attr;
    } 
    

    protected Object getValue(ObjectName name) {
	try {       
	    // Get the class of the object          
	    MBeanServer server = QueryEval.getMBeanServer();
	    return server.getObjectInstance(name).getClassName();
	} catch (Exception re) {
	    return null;
	    /* In principle the MBean does exist because otherwise we
	       wouldn't be evaluating the query on it.  But it could
	       potentially have disappeared in between the time we
	       discovered it and the time the query is evaluated.

	       Also, the exception could be a SecurityException.
	    
	       Returning null from here will cause
	       BadAttributeValueExpException, which will in turn cause
	       this MBean to be omitted from the query result.  */
	}
    }   

 }
