/*
 * Copyright (c) 1999, 2008, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package javax.management;


import com.sun.jmx.mbeanserver.Introspector;
import java.io.IOException;
import java.io.ObjectInputStream;

/**
 * <p>Represents attributes used as arguments to relational constraints.
 * Instances of this class are usually obtained using {@link Query#attr(String)
 * Query.attr}.</p>
 *
 * <p>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;
 }

 /**
 * <p>Applies the <CODE>AttributeValueExp</CODE> on an MBean.
 * This method calls {@link #getAttribute getAttribute(name)} and wraps
 * the result as a {@code ValueExp}. The value returned by
 * {@code getAttribute} must be a {@code Number}, {@code String},
 * or {@code Boolean}; otherwise this method throws a
 * {@code BadAttributeValueExpException}, which will cause
 * the containing query to be false for this {@code name}.</p>
 *
 * @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
 *
 */
 @Override
 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.
 */
 @Override
 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.
 *
 * @deprecated This method has no effect. The MBean Server used to
 * obtain an attribute value is {@link QueryEval#getMBeanServer()}.
 */
 /* 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. */
 @Deprecated
 @Override
 public void setMBeanServer(MBeanServer s) {
 }


 /**
 * <p>Return the value of the given attribute in the named MBean.
 * If the attempt to access the attribute generates an exception,
 * return null.</p>
 *
 * <p>The MBean Server used is the one returned by {@link
 * QueryEval#getMBeanServer()}.</p>
 *
 * @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;
 }
 }
}