|
1 <html> |
|
2 <head> |
|
3 <title>javax.management.relation package</title> |
|
4 <!-- |
|
5 Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved. |
|
6 DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
|
7 |
|
8 This code is free software; you can redistribute it and/or modify it |
|
9 under the terms of the GNU General Public License version 2 only, as |
|
10 published by the Free Software Foundation. Oracle designates this |
|
11 particular file as subject to the "Classpath" exception as provided |
|
12 by Oracle in the LICENSE file that accompanied this code. |
|
13 |
|
14 This code is distributed in the hope that it will be useful, but WITHOUT |
|
15 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
|
16 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
|
17 version 2 for more details (a copy is included in the LICENSE file that |
|
18 accompanied this code). |
|
19 |
|
20 You should have received a copy of the GNU General Public License version |
|
21 2 along with this work; if not, write to the Free Software Foundation, |
|
22 Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
|
23 |
|
24 Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
|
25 or visit www.oracle.com if you need additional information or have any |
|
26 questions. |
|
27 --> |
|
28 </head> |
|
29 <body bgcolor="white"> |
|
30 <p>Provides the definition of the Relation Service. The |
|
31 Relation Service is used to record relationships between |
|
32 MBeans in an MBean Server. The Relation Service is itself an |
|
33 MBean. More than one instance of a {@link |
|
34 javax.management.relation.RelationService RelationService} |
|
35 MBean can be registered in an MBean Server.</p> |
|
36 |
|
37 <p>A <em>relation type</em> defines a relationship between MBeans. |
|
38 It contains <em>roles</em> that the MBeans play in the |
|
39 relationship. Usually there are at least two roles in a |
|
40 relation type.</p> |
|
41 |
|
42 <p>A <em>relation</em> is a named instance of a relation type, |
|
43 where specific MBeans appear in the roles, represented by |
|
44 their {@link javax.management.ObjectName ObjectName}s.</p> |
|
45 |
|
46 <p>For example, suppose there are <code>Module</code> MBeans, |
|
47 representing modules within an application. A |
|
48 <code>DependsOn</code> relation type could express the |
|
49 relationship that some modules depend on others, which could |
|
50 be used to determine the order in which the modules are |
|
51 started or stopped. The <code>DependsOn</code> relation type |
|
52 would have two roles, <code>dependent</code> and |
|
53 <code>dependedOn</code>.</p> |
|
54 |
|
55 <p>Every role is <em>typed</em>, meaning that an MBean that |
|
56 appears in that role must be an instance of the role's type. |
|
57 In the <code>DependsOn</code> example, both roles would be of |
|
58 type <code>Module</code>.</p> |
|
59 |
|
60 <p>Every role has a <em>cardinality</em>, which provides lower |
|
61 and upper bounds on the number of MBeans that can appear in |
|
62 that role in a given relation instance. Usually, the lower |
|
63 and upper bounds are both 1, with exactly one MBean appearing |
|
64 in the role. The cardinality only limits the number of MBeans |
|
65 in the role per relation instance. The same MBean can appear |
|
66 in the same role in any number of instances of a relation |
|
67 type. In the <code>DependsOn</code> example, a given module |
|
68 can depend on many other modules, and be depended on by many |
|
69 others, but any given relation instance links exactly one |
|
70 <code>dependent</code> module with exactly one |
|
71 <code>dependedOn</code> module.</p> |
|
72 |
|
73 <p>A relation type can be created explicitly, as an object |
|
74 implementing the {@link javax.management.relation.RelationType |
|
75 RelationType} interface, typically a {@link |
|
76 javax.management.relation.RelationTypeSupport |
|
77 RelationTypeSupport}. Alternatively, it can be created |
|
78 implicitly using the Relation Service's {@link |
|
79 javax.management.relation.RelationServiceMBean#createRelationType(String, |
|
80 RoleInfo[]) createRelationType} method.</p> |
|
81 |
|
82 <p>A relation instance can be created explicitly, as an object |
|
83 implementing the {@link javax.management.relation.Relation |
|
84 Relation} interface, typically a {@link |
|
85 javax.management.relation.RelationSupport RelationSupport}. |
|
86 (A <code>RelationSupport</code> is itself a valid MBean, so it |
|
87 can be registered in the MBean Server, though this is not |
|
88 required.) Alternatively, a relation instance can be created |
|
89 implicitly using the Relation Service's {@link |
|
90 javax.management.relation.RelationServiceMBean#createRelation(String, |
|
91 String, RoleList) createRelation} method.</p> |
|
92 |
|
93 <p>The <code>DependsOn</code> example might be coded as follows.</p> |
|
94 |
|
95 <pre> |
|
96 import java.util.*; |
|
97 import javax.management.*; |
|
98 import javax.management.relation.*; |
|
99 |
|
100 // ... |
|
101 MBeanServer mbs = ...; |
|
102 |
|
103 // Create the Relation Service MBean |
|
104 ObjectName relSvcName = new ObjectName(":type=RelationService"); |
|
105 RelationService relSvcObject = new RelationService(true); |
|
106 mbs.registerMBean(relSvcObject, relSvcName); |
|
107 |
|
108 // Create an MBean proxy for easier access to the Relation Service |
|
109 RelationServiceMBean relSvc = |
|
110 MBeanServerInvocationHandler.newProxyInstance(mbs, relSvcName, |
|
111 RelationServiceMBean.class, |
|
112 false); |
|
113 |
|
114 // Define the DependsOn relation type |
|
115 RoleInfo[] dependsOnRoles = { |
|
116 new RoleInfo("dependent", Module.class.getName()), |
|
117 new RoleInfo("dependedOn", Module.class.getName()) |
|
118 }; |
|
119 relSvc.createRelationType("DependsOn", dependsOnRoles); |
|
120 |
|
121 // Now define a relation instance "moduleA DependsOn moduleB" |
|
122 |
|
123 ObjectName moduleA = new ObjectName(":type=Module,name=A"); |
|
124 ObjectName moduleB = new ObjectName(":type=Module,name=B"); |
|
125 |
|
126 Role dependent = new Role("dependent", Collections.singletonList(moduleA)); |
|
127 Role dependedOn = new Role("dependedOn", Collections.singletonList(moduleB)); |
|
128 Role[] roleArray = {dependent, dependedOn}; |
|
129 RoleList roles = new RoleList(Arrays.asList(roleArray)); |
|
130 relSvc.createRelation("A-DependsOn-B", "DependsOn", roles); |
|
131 |
|
132 // Query the Relation Service to find what modules moduleA depends on |
|
133 Map<ObjectName,List<String>> dependentAMap = |
|
134 relSvc.findAssociatedMBeans(moduleA, "DependsOn", "dependent"); |
|
135 Set<ObjectName> dependentASet = dependentAMap.keySet(); |
|
136 // Set of ObjectName containing moduleB |
|
137 </pre> |
|
138 |
|
139 @see <a href="https://jcp.org/aboutJava/communityprocess/mrel/jsr160/index2.html"> |
|
140 JMX Specification, version 1.4</a> |
|
141 |
|
142 @since 1.5 |
|
143 |
|
144 </BODY> |
|
145 </HTML> |