1 /*
2 * Copyright (c) 1999, 2008, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package javax.management;
27
28
29 import com.sun.jmx.mbeanserver.Introspector;
30 import java.io.IOException;
31 import java.io.ObjectInputStream;
32
33 /**
34 * <p>Represents attributes used as arguments to relational constraints.
35 * Instances of this class are usually obtained using {@link Query#attr(String)
36 * Query.attr}.</p>
37 *
38 * <p>An <CODE>AttributeValueExp</CODE> may be used anywhere a
39 * <CODE>ValueExp</CODE> is required.
40 *
41 * @since 1.5
42 */
43 public class AttributeValueExp implements ValueExp {
44
45
46 /* Serial version */
47 private static final long serialVersionUID = -7768025046539163385L;
48
49 /**
50 * @serial The name of the attribute
51 */
52 private String attr;
53
54 /**
55 * An <code>AttributeValueExp</code> with a null attribute.
56 * @deprecated An instance created with this constructor cannot be
57 * used in a query.
58 */
59 @Deprecated
60 public AttributeValueExp() {
61 }
62
63 /**
64 * Creates a new <CODE>AttributeValueExp</CODE> representing the
65 * specified object attribute, named attr.
66 *
67 * @param attr the name of the attribute whose value is the value
68 * of this {@link ValueExp}.
69 */
70 public AttributeValueExp(String attr) {
71 this.attr = attr;
72 }
73
74 /**
75 * Returns a string representation of the name of the attribute.
76 *
77 * @return the attribute name.
78 */
79 public String getAttributeName() {
80 return attr;
81 }
82
83 /**
84 * <p>Applies the <CODE>AttributeValueExp</CODE> on an MBean.
85 * This method calls {@link #getAttribute getAttribute(name)} and wraps
86 * the result as a {@code ValueExp}. The value returned by
87 * {@code getAttribute} must be a {@code Number}, {@code String},
88 * or {@code Boolean}; otherwise this method throws a
89 * {@code BadAttributeValueExpException}, which will cause
90 * the containing query to be false for this {@code name}.</p>
91 *
92 * @param name The name of the MBean on which the <CODE>AttributeValueExp</CODE> will be applied.
93 *
94 * @return The <CODE>ValueExp</CODE>.
95 *
96 * @exception BadAttributeValueExpException
97 * @exception InvalidApplicationException
98 * @exception BadStringOperationException
99 * @exception BadBinaryOpValueExpException
100 *
101 */
102 @Override
103 public ValueExp apply(ObjectName name) throws BadStringOperationException, BadBinaryOpValueExpException,
104 BadAttributeValueExpException, InvalidApplicationException {
105 Object result = getAttribute(name);
106
107 if (result instanceof Number) {
108 return new NumericValueExp((Number)result);
109 } else if (result instanceof String) {
110 return new StringValueExp((String)result);
111 } else if (result instanceof Boolean) {
112 return new BooleanValueExp((Boolean)result);
113 } else {
114 throw new BadAttributeValueExpException(result);
115 }
116 }
117
118 /**
119 * Returns the string representing its value.
120 */
121 @Override
122 public String toString() {
123 return attr;
124 }
125
126
127 /**
128 * Sets the MBean server on which the query is to be performed.
129 *
130 * @param s The MBean server on which the query is to be performed.
131 *
132 * @deprecated This method has no effect. The MBean Server used to
133 * obtain an attribute value is {@link QueryEval#getMBeanServer()}.
134 */
135 /* There is no need for this method, because if a query is being
136 evaluted an AttributeValueExp can only appear inside a QueryExp,
137 and that QueryExp will itself have done setMBeanServer. */
138 @Deprecated
139 @Override
140 public void setMBeanServer(MBeanServer s) {
141 }
142
143
144 /**
145 * <p>Return the value of the given attribute in the named MBean.
146 * If the attempt to access the attribute generates an exception,
147 * return null.</p>
148 *
149 * <p>The MBean Server used is the one returned by {@link
150 * QueryEval#getMBeanServer()}.</p>
151 *
152 * @param name the name of the MBean whose attribute is to be returned.
153 *
154 * @return the value of the attribute, or null if it could not be
155 * obtained.
156 */
157 protected Object getAttribute(ObjectName name) {
158 try {
159 // Get the value from the MBeanServer
160
161 MBeanServer server = QueryEval.getMBeanServer();
162
163 return server.getAttribute(name, attr);
164 } catch (Exception re) {
165 return null;
166 }
167 }
168 }