在实现自定义服务时，我们很可能会依赖其它服务或核心服务，在这种情况下，要求自定义服务的启动必须在依赖服务启动之后。例如我们在ResolverService服务之上实现自己的服务，就是说我们的服务要使用ResolverService来实现自己的功能。
那么在自定义服务的
java 代码
那么在自定义服务的
java 代码
public int startApp(String[] args) {
// Now that the service is being started, set the ResolverService
// object to use handle our queries and send responses.
resolver = peerGroup.getResolverService();
if(resolver == null) {
return Module.START_AGAIN_PROGRESS;
}
// Add ourselves as a handler using the uniquely constructed
// handler name.
resolver.registerHandler(handlerName, this);
return Module.START_OK;
}
// Now that the service is being started, set the ResolverService
// object to use handle our queries and send responses.
resolver = peerGroup.getResolverService();
if(resolver == null) {
return Module.START_AGAIN_PROGRESS;
}
// Add ourselves as a handler using the uniquely constructed
// handler name.
resolver.registerHandler(handlerName, this);
return Module.START_OK;
}
通过上述代码判断，如果resolver的值为null,那么说明ResolverService还没有初始化，我们返回Module.START_AGAIN_PROGRESS，表示我们的服务还需要再次初始化。如果resolver的值不为null,那么说明ResolverService已经初始化，我们返回Module.START_OK,即可。其它依赖服务与此类似。
下面的Module接口中对几个常量进行了说明，可以看出Module.START_AGAIN_PROGRESS与Module.START_AGAIN_STALLED的含义基本相同。
java 代码
下面的Module接口中对几个常量进行了说明，可以看出Module.START_AGAIN_PROGRESS与Module.START_AGAIN_STALLED的含义基本相同。
java 代码
1 /*
2 * Copyright (c) 2001-2007 Sun Microsystems, Inc. All rights reserved.
3 *
4 * The Sun Project JXTA(TM) Software License
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions are met:
8 *
9 * 1. Redistributions of source code must retain the above copyright notice,
10 * this list of conditions and the following disclaimer.
11 *
12 * 2. Redistributions in binary form must reproduce the above copyright notice,
13 * this list of conditions and the following disclaimer in the documentation
14 * and/or other materials provided with the distribution.
15 *
16 * 3. The end-user documentation included with the redistribution, if any, must
17 * include the following acknowledgment: "This product includes software
18 * developed by Sun Microsystems, Inc. for JXTA(TM) technology."
19 * Alternately, this acknowledgment may appear in the software itself, if
20 * and wherever such third-party acknowledgments normally appear.
21 *
22 * 4. The names "Sun", "Sun Microsystems, Inc.", "JXTA" and "Project JXTA" must
23 * not be used to endorse or promote products derived from this software
24 * without prior written permission. For written permission, please contact
25 * Project JXTA at http://www.jxta.org.
26 *
27 * 5. Products derived from this software may not be called "JXTA", nor may
28 * "JXTA" appear in their name, without prior written permission of Sun.
29 *
30 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES,
31 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
32 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL SUN
33 * MICROSYSTEMS OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
34 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
35 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
36 * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
37 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
38 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
39 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
40 *
41 * JXTA is a registered trademark of Sun Microsystems, Inc. in the United
42 * States and other countries.
43 *
44 * Please see the license information page at :
45 * <http://www.jxta.org/project/www/license.html> for instructions on use of
46 * the license in source files.
47 *
48 * ====================================================================
49 *
50 * This software consists of voluntary contributions made by many individuals
51 * on behalf of Project JXTA. For more information on Project JXTA, please see
52 * http://www.jxta.org.
53 *
54 * This license is based on the BSD license adopted by the Apache Foundation.
55 */
56
57 package net.jxta.platform;
58
59
60 import net.jxta.peergroup.PeerGroup;
61 import net.jxta.document.Advertisement;
62 import net.jxta.id.ID;
63 import net.jxta.exception.PeerGroupException;
64
65
66 /**
67 * Defines the interface for modules loaded by PeerGroups. Message transports,
68 * services and applications need to implement this interface if they are
69 * to be loaded and started by a PeerGroup. Service and Application extend
70 * Module, PeerGroup implements Service and ShellApp implements Application, as
71 * a result both implement Module.
72 *
73 * <p/>Jxta Modules are given their initialization parameters via the init()
74 * method rather than a non-default constructor.
75 *
76 * <p/>Modules are passed the peer group within which they are created.
77 * From the peergroup object, Modules can access all the peer group
78 * services. The PeerGroup within which a PeerGroup runs is known as its
79 * parent.
80 *
81 * <p/>The initial root peer group is known as the World Peer Group and is
82 * implemented by an object of class Platform, a subclass of PeerGroup.
83 * The "parent" PeerGroup of the World Peer Group is null.
84 *
85 * @see net.jxta.protocol.ModuleImplAdvertisement
86 * @see net.jxta.platform.ModuleClassID
87 * @see net.jxta.peergroup.PeerGroup
88 * @see net.jxta.document.Advertisement
89 * @see net.jxta.id.ID
90 * @see net.jxta.platform.Application
91 * @see net.jxta.service.Service
92 **/
93 public interface Module {
94
95 /**
96 * <code>startApp()</code> completed successfully. This module claims to now
97 * be fully functional and no further invocation of startApp is required.
98 **/
99 public static final int START_OK = 0;
100
101 /**
102 * This is to be used mostly by co-dependent services when started as
103 * a set (such as {@link PeerGroup} services) so that their
104 * <code>startApp()</code> method may be invoked multiple times.
105 *
106 * <p/>This value indicates that startApp must be retried later in order for
107 * this module to become fully functional. However, some progress in
108 * functionality was accomplished.
109 *
110 * <p/>This is a strong indication that some other modules may be able
111 * to advance or complete their initialization if their
112 * <code>startApp()</code> method is invoked again.
113 *
114 * <p/>The distinction between START_AGAIN_STALLED and START_AGAIN_PROGRESS
115 * is only a hint. Each module makes an arbitrary judgment in this
116 * respect. It is up to the invoker of startApp to ensure that the
117 * starting of a set of modules eventually succeeds or fails.
118 **/
119 public static final int START_AGAIN_PROGRESS = 1;
120
121 /**
122 * This is to be used mostly by co-dependent services when started as
123 * a set (such as {@link PeerGroup} services) so that their startApp
124 * method may be invoked multiple times.
125 *
126 * <p/>This value indicates that startApp must be retried later in order for
127 * this module to become fully functional. However, some progress in
128 * functionality was accomplished.
129 *
130 * <p/>If all modules in a set return this value, it is a strong indication
131 * that the modules co-dependency is such that it prevents them
132 * collectively from starting.
133 *
134 * <p/>The distinction between START_AGAIN_STALLED and START_AGAIN_PROGRESS
135 * is only a hint. Each module makes an arbitrary judgment in this
136 * respect. It is up to the invoker of startApp to ensure that the
137 * starting of a set of modules eventually succeeds or fails.
138 **/
139 public static final int START_AGAIN_STALLED = 2;
140
141 /**
142 * This return result is used to indicate that the module refuses to start
143 * because it has been configured to be disabled or otherwise cannot run
144 * (missing hardware, missing system resources, etc.) The module will not be
145 * functional and should be discarded but the failure to load may be ignored
146 * by the loader at it's discretion.
147 */
148 public static final int START_DISABLED = Integer.MIN_VALUE + 100;
149
150 /**
151 * Initialize the module, passing it its peer group and advertisement.
152 *
153 * <p/>Note: when subclassing one of the existing PeerGroup implementations
154 * (which implement Module), it may not be recommended to overload the init
155 * method. See the documentation of the PeerGroup class being subclassed.
156 *
157 * @param group The PeerGroup from which this Module can obtain services.
158 * If this module is a Service, this is also the PeerGroup of which this
159 * module is a service.
160 *
161 * @param assignedID Identity of Module within group.
162 * modules can use it as a the root of their namespace to create
163 * names that are unique within the group but predictable by the
164 * same module on another peer. This is normally the ModuleClassID
165 * which is also the name under which the module is known by other
166 * modules. For a group it is the PeerGroupID itself.
167 * The parameters of a service, in the Peer configuration, are indexed
168 * by the assignedID of that service, and a Service must publish its
169 * run-time parameters in the Peer Advertisement under its assigned ID.
170 *
171 * @param implAdv The implementation advertisement for this
172 * Module. It is permissible to pass null if no implementation
173 * advertisement is available. This may happen if the
174 * implementation was selected by explicit class name rather than
175 * by following an implementation advertisement. Modules are not
176 * required to support that style of loading, but if they do, then
177 * their documentation should mention it.
178 *
179 * @exception PeerGroupException This module failed to initialize.
180 **/
181 public void init(PeerGroup group, ID assignedID, Advertisement implAdv) throws PeerGroupException;
182
183 /**
184 * Complete any remaining initialization of the module. The module should
185 * be fully functional after <code>startApp()</code> is completed. That is
186 * also the opportunity to supply arbitrary arguments (mostly to
187 * applications).
188 *
189 * <p/>If this module is a {@link PeerGroup} service, it may be invoked
190 * several times depending on its return value.
191 *
192 * @param args An array of Strings forming the parameters for this
193 * Module.
194 *
195 * @return int A status indication which may be one of
196 * {@link #START_OK}, {@link #START_AGAIN_PROGRESS},
197 * {@link #START_AGAIN_STALLED}, which indicates partial or complete
198 * success, or any other value (negative values are
199 * recommended for future compatibility), which indicates failure.
200 **/
201 public int startApp(String[] args);
202
203 /**
204 * Stop a module. This may be called any time after <code>init()</code>
205 * completes and should not assume that <code>startApp()</code> has been
206 * called or completed.
207 *
208 * <p/>The Module cannot be forced to comply, but in the future
209 * we might be able to deny it access to anything after some timeout.
210 **/
211 public void stopApp();
212 }
2 * Copyright (c) 2001-2007 Sun Microsystems, Inc. All rights reserved.
3 *
4 * The Sun Project JXTA(TM) Software License
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions are met:
8 *
9 * 1. Redistributions of source code must retain the above copyright notice,
10 * this list of conditions and the following disclaimer.
11 *
12 * 2. Redistributions in binary form must reproduce the above copyright notice,
13 * this list of conditions and the following disclaimer in the documentation
14 * and/or other materials provided with the distribution.
15 *
16 * 3. The end-user documentation included with the redistribution, if any, must
17 * include the following acknowledgment: "This product includes software
18 * developed by Sun Microsystems, Inc. for JXTA(TM) technology."
19 * Alternately, this acknowledgment may appear in the software itself, if
20 * and wherever such third-party acknowledgments normally appear.
21 *
22 * 4. The names "Sun", "Sun Microsystems, Inc.", "JXTA" and "Project JXTA" must
23 * not be used to endorse or promote products derived from this software
24 * without prior written permission. For written permission, please contact
25 * Project JXTA at http://www.jxta.org.
26 *
27 * 5. Products derived from this software may not be called "JXTA", nor may
28 * "JXTA" appear in their name, without prior written permission of Sun.
29 *
30 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES,
31 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
32 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL SUN
33 * MICROSYSTEMS OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
34 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
35 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
36 * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
37 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
38 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
39 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
40 *
41 * JXTA is a registered trademark of Sun Microsystems, Inc. in the United
42 * States and other countries.
43 *
44 * Please see the license information page at :
45 * <http://www.jxta.org/project/www/license.html> for instructions on use of
46 * the license in source files.
47 *
48 * ====================================================================
49 *
50 * This software consists of voluntary contributions made by many individuals
51 * on behalf of Project JXTA. For more information on Project JXTA, please see
52 * http://www.jxta.org.
53 *
54 * This license is based on the BSD license adopted by the Apache Foundation.
55 */
56
57 package net.jxta.platform;
58
59
60 import net.jxta.peergroup.PeerGroup;
61 import net.jxta.document.Advertisement;
62 import net.jxta.id.ID;
63 import net.jxta.exception.PeerGroupException;
64
65
66 /**
67 * Defines the interface for modules loaded by PeerGroups. Message transports,
68 * services and applications need to implement this interface if they are
69 * to be loaded and started by a PeerGroup. Service and Application extend
70 * Module, PeerGroup implements Service and ShellApp implements Application, as
71 * a result both implement Module.
72 *
73 * <p/>Jxta Modules are given their initialization parameters via the init()
74 * method rather than a non-default constructor.
75 *
76 * <p/>Modules are passed the peer group within which they are created.
77 * From the peergroup object, Modules can access all the peer group
78 * services. The PeerGroup within which a PeerGroup runs is known as its
79 * parent.
80 *
81 * <p/>The initial root peer group is known as the World Peer Group and is
82 * implemented by an object of class Platform, a subclass of PeerGroup.
83 * The "parent" PeerGroup of the World Peer Group is null.
84 *
85 * @see net.jxta.protocol.ModuleImplAdvertisement
86 * @see net.jxta.platform.ModuleClassID
87 * @see net.jxta.peergroup.PeerGroup
88 * @see net.jxta.document.Advertisement
89 * @see net.jxta.id.ID
90 * @see net.jxta.platform.Application
91 * @see net.jxta.service.Service
92 **/
93 public interface Module {
94
95 /**
96 * <code>startApp()</code> completed successfully. This module claims to now
97 * be fully functional and no further invocation of startApp is required.
98 **/
99 public static final int START_OK = 0;
100
101 /**
102 * This is to be used mostly by co-dependent services when started as
103 * a set (such as {@link PeerGroup} services) so that their
104 * <code>startApp()</code> method may be invoked multiple times.
105 *
106 * <p/>This value indicates that startApp must be retried later in order for
107 * this module to become fully functional. However, some progress in
108 * functionality was accomplished.
109 *
110 * <p/>This is a strong indication that some other modules may be able
111 * to advance or complete their initialization if their
112 * <code>startApp()</code> method is invoked again.
113 *
114 * <p/>The distinction between START_AGAIN_STALLED and START_AGAIN_PROGRESS
115 * is only a hint. Each module makes an arbitrary judgment in this
116 * respect. It is up to the invoker of startApp to ensure that the
117 * starting of a set of modules eventually succeeds or fails.
118 **/
119 public static final int START_AGAIN_PROGRESS = 1;
120
121 /**
122 * This is to be used mostly by co-dependent services when started as
123 * a set (such as {@link PeerGroup} services) so that their startApp
124 * method may be invoked multiple times.
125 *
126 * <p/>This value indicates that startApp must be retried later in order for
127 * this module to become fully functional. However, some progress in
128 * functionality was accomplished.
129 *
130 * <p/>If all modules in a set return this value, it is a strong indication
131 * that the modules co-dependency is such that it prevents them
132 * collectively from starting.
133 *
134 * <p/>The distinction between START_AGAIN_STALLED and START_AGAIN_PROGRESS
135 * is only a hint. Each module makes an arbitrary judgment in this
136 * respect. It is up to the invoker of startApp to ensure that the
137 * starting of a set of modules eventually succeeds or fails.
138 **/
139 public static final int START_AGAIN_STALLED = 2;
140
141 /**
142 * This return result is used to indicate that the module refuses to start
143 * because it has been configured to be disabled or otherwise cannot run
144 * (missing hardware, missing system resources, etc.) The module will not be
145 * functional and should be discarded but the failure to load may be ignored
146 * by the loader at it's discretion.
147 */
148 public static final int START_DISABLED = Integer.MIN_VALUE + 100;
149
150 /**
151 * Initialize the module, passing it its peer group and advertisement.
152 *
153 * <p/>Note: when subclassing one of the existing PeerGroup implementations
154 * (which implement Module), it may not be recommended to overload the init
155 * method. See the documentation of the PeerGroup class being subclassed.
156 *
157 * @param group The PeerGroup from which this Module can obtain services.
158 * If this module is a Service, this is also the PeerGroup of which this
159 * module is a service.
160 *
161 * @param assignedID Identity of Module within group.
162 * modules can use it as a the root of their namespace to create
163 * names that are unique within the group but predictable by the
164 * same module on another peer. This is normally the ModuleClassID
165 * which is also the name under which the module is known by other
166 * modules. For a group it is the PeerGroupID itself.
167 * The parameters of a service, in the Peer configuration, are indexed
168 * by the assignedID of that service, and a Service must publish its
169 * run-time parameters in the Peer Advertisement under its assigned ID.
170 *
171 * @param implAdv The implementation advertisement for this
172 * Module. It is permissible to pass null if no implementation
173 * advertisement is available. This may happen if the
174 * implementation was selected by explicit class name rather than
175 * by following an implementation advertisement. Modules are not
176 * required to support that style of loading, but if they do, then
177 * their documentation should mention it.
178 *
179 * @exception PeerGroupException This module failed to initialize.
180 **/
181 public void init(PeerGroup group, ID assignedID, Advertisement implAdv) throws PeerGroupException;
182
183 /**
184 * Complete any remaining initialization of the module. The module should
185 * be fully functional after <code>startApp()</code> is completed. That is
186 * also the opportunity to supply arbitrary arguments (mostly to
187 * applications).
188 *
189 * <p/>If this module is a {@link PeerGroup} service, it may be invoked
190 * several times depending on its return value.
191 *
192 * @param args An array of Strings forming the parameters for this
193 * Module.
194 *
195 * @return int A status indication which may be one of
196 * {@link #START_OK}, {@link #START_AGAIN_PROGRESS},
197 * {@link #START_AGAIN_STALLED}, which indicates partial or complete
198 * success, or any other value (negative values are
199 * recommended for future compatibility), which indicates failure.
200 **/
201 public int startApp(String[] args);
202
203 /**
204 * Stop a module. This may be called any time after <code>init()</code>
205 * completes and should not assume that <code>startApp()</code> has been
206 * called or completed.
207 *
208 * <p/>The Module cannot be forced to comply, but in the future
209 * we might be able to deny it access to anything after some timeout.
210 **/
211 public void stopApp();
212 }