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 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 }
转载于:https://www.cnblogs.com/cuizhf/archive/2011/08/23/2150235.html
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