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1 <html> |
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2 <head> |
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3 <title>RMI connector</title> |
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4 <!-- |
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28 </head> |
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29 <body bgcolor="white"> |
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30 <p>The RMI connector is a connector for the JMX Remote API that |
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31 uses RMI to transmit client requests to a remote MBean server. |
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32 This package defines the classes that the user of an RMI |
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33 connector needs to reference directly, for both the client and |
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34 server sides. It also defines certain classes that the user |
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35 will not usually reference directly, but that must be defined so |
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36 that different implementations of the RMI connector can |
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37 interoperate.</p> |
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38 |
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39 <p>The RMI connector supports the JRMP transport for RMI.</p> |
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40 |
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41 <p>Like most connectors in the JMX Remote API, an RMI connector |
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42 usually has an address, which |
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43 is a {@link javax.management.remote.JMXServiceURL |
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44 JMXServiceURL}. The protocol part of this address is |
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45 <code>rmi</code> for a connector that uses the default RMI |
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46 transport (JRMP).</p> |
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47 |
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48 <p>There are two forms for RMI connector addresses:</p> |
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49 |
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50 <ul> |
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51 <li> |
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52 In the <em>JNDI form</em>, the URL indicates <em>where to find |
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53 an RMI stub for the connector</em>. This RMI stub is a Java |
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54 object of type {@link javax.management.remote.rmi.RMIServer |
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55 RMIServer} that gives remote access to the connector server. |
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56 With this address form, the RMI stub is obtained from an |
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57 external directory entry included in the URL. An external |
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58 directory is any directory recognized by {@link javax.naming |
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59 JNDI}, typically the RMI registry, LDAP, or COS Naming. |
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60 |
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61 <li> |
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62 In the <em>encoded form</em>, the URL directly includes the |
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63 information needed to connect to the connector server. When |
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64 using RMI/JRMP, the encoded form is the serialized RMI stub |
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65 for the server object, encoded using BASE64 without embedded |
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66 newlines. |
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67 </ul> |
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68 |
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69 <p>Addresses are covered in more detail below.</p> |
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70 |
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71 |
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72 <h3>Creating an RMI connector server</h3> |
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73 |
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74 <p>The usual way to create an RMI connector server is to supply an |
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75 RMI connector address to the method {@link |
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76 javax.management.remote.JMXConnectorServerFactory#newJMXConnectorServer |
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77 JMXConnectorServerFactory.newJMXConnectorServer}. The MBean |
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78 server to which the connector server is attached can be |
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79 specified as a parameter to that method. Alternatively, the |
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80 connector server can be registered as an MBean in that MBean |
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81 server.</p> |
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82 |
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83 <p>An RMI connector server can also be created by constructing an |
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84 instance of {@link |
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85 javax.management.remote.rmi.RMIConnectorServer |
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86 RMIConnectorServer}, explicitly or through the MBean server's |
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87 <code>createMBean</code> method.</p> |
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88 |
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89 <h4>Choosing the RMI transport</h4> |
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90 |
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91 <p>You can choose the RMI transport by specifying |
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92 <code>rmi</code> in the <code><em>protocol</em></code> part of the |
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93 <code>serviceURL</code> when creating the connector server. You |
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94 can also create specialized connector servers by instantiating |
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95 an appropriate subclass of {@link |
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96 javax.management.remote.rmi.RMIServerImpl RMIServerImpl} and |
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97 supplying it to the <code>RMIConnectorServer</code> |
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98 constructor.</p> |
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99 |
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100 |
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101 <h4><a name="servergen">Connector addresses generated by the |
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102 server</a></h4> |
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103 |
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104 <p>If the <code>serviceURL</code> you specify has an empty URL |
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105 path (after the optional host and port), or if you do not |
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106 specify a <code>serviceURL</code>, then the connector server |
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107 will fabricate a new <code>JMXServiceURL</code> that clients can |
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108 use to connect:</p> |
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109 |
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110 <ul> |
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111 |
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112 <li><p>If the <code>serviceURL</code> looks like:</p> |
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113 |
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114 <pre> |
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115 <code>service:jmx:rmi://<em>host</em>:<em>port</em></code> |
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116 </pre> |
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117 |
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118 <p>then the connector server will generate an {@link |
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119 javax.management.remote.rmi.RMIJRMPServerImpl |
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120 RMIJRMPServerImpl} and the returned <code>JMXServiceURL</code> |
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121 looks like:</p> |
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122 |
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123 <pre> |
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124 <code>service:jmx:rmi://<em>host</em>:<em>port</em>/stub/<em>XXXX</em></code> |
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125 </pre> |
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126 |
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127 <p>where <code><em>XXXX</em></code> is the serialized form of the |
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128 stub for the generated object, encoded in BASE64 without |
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129 newlines.</p> |
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130 |
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131 <li><p>If there is no <code>serviceURL</code>, there must be a |
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132 user-provided <code>RMIServerImpl</code>. The connector server |
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133 will generate a <code>JMXServiceURL</code> using the <code>rmi</code> |
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134 form.</p> |
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135 |
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136 </ul> |
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137 |
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138 <p>The <code><em>host</em></code> in a user-provided |
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139 <code>serviceURL</code> is optional. If present, it is copied |
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140 into the generated <code>JMXServiceURL</code> but otherwise |
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141 ignored. If absent, the generated <code>JXMServiceURL</code> |
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142 will have the local host name.</p> |
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143 |
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144 <p>The <code><em>port</em></code> in a user-provided |
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145 <code>serviceURL</code> is also optional. If present, it is |
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146 also copied into the generated <code>JMXServiceURL</code>; |
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147 otherwise, the generated <code>JMXServiceURL</code> has no port. |
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148 For an <code>serviceURL</code> using the <code>rmi</code> |
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149 protocol, the <code><em>port</em></code>, if present, indicates |
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150 what port the generated remote object should be exported on. It |
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151 has no other effect.</p> |
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152 |
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153 <p>If the user provides an <code>RMIServerImpl</code> rather than a |
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154 <code>JMXServiceURL</code>, then the generated |
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155 <code>JMXServiceURL</code> will have the local host name in its |
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156 <code><em>host</em></code> part and no |
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157 <code><em>port</em></code>.</p> |
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158 |
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159 |
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160 <h4><a name="directory">Connector addresses based on directory |
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161 entries</a></h4> |
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162 |
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163 <p>As an alternative to the generated addresses just described, |
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164 the <code>serviceURL</code> address supplied when creating a |
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165 connector server can specify a <em>directory address</em> in |
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166 which to store the provided or generated <code>RMIServer</code> |
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167 stub. This directory address is then used by both client and |
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168 server.</p> |
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169 |
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170 <p>In this case, the <code>serviceURL</code> has the following form:</p> |
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171 |
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172 <pre> |
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173 <code>service:jmx:rmi://<em>host</em>:<em>port</em>/jndi/<em>jndi-name</em></code> |
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174 </pre> |
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175 |
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176 <p>Here, <code><em>jndi-name</em></code> is a string that can be |
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177 supplied to {@link javax.naming.InitialContext#bind |
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178 javax.naming.InitialContext.bind}.</p> |
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179 |
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180 <p>As usual, the <code><em>host</em></code> and |
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181 <code>:<em>port</em></code> can be omitted.</p> |
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182 |
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183 <p>The connector server will generate an |
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184 <code>RMIServerImpl</code> based on the protocol |
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185 (<code>rmi</code>) and the <code><em>port</em></code> if any. When |
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186 the connector server is started, it will derive a stub from this |
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187 object using its {@link |
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188 javax.management.remote.rmi.RMIServerImpl#toStub toStub} method |
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189 and store the object using the given |
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190 <code><em>jndi-name</em></code>. The properties defined by the |
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191 JNDI API are consulted as usual.</p> |
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192 |
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193 <p>For example, if the <code>JMXServiceURL</code> is: |
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194 |
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195 <pre> |
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196 <code>service:jmx:rmi://ignoredhost/jndi/rmi://myhost/myname</code> |
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197 </pre> |
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198 |
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199 then the connector server will generate an |
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200 <code>RMIJRMPServerImpl</code> and store its stub using the JNDI |
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201 name |
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202 |
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203 <pre> |
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204 <code>rmi://myhost/myname</code> |
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205 </pre> |
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206 |
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207 which means entry <code>myname</code> in the RMI registry |
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208 running on the default port of host <code>myhost</code>. Note |
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209 that the RMI registry only allows registration from the local |
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210 host. So, in this case, <code>myhost</code> must be the name |
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211 (or a name) of the host that the connector server is running |
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212 on. |
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213 |
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214 <p>In this <code>JMXServiceURL</code>, the first <code>rmi:</code> |
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215 specifies the RMI |
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216 connector, while the second <code>rmi:</code> specifies the RMI |
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217 registry. |
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218 |
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219 <p>As another example, if the <code>JMXServiceURL</code> is: |
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220 |
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221 <pre> |
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222 <code>service:jmx:rmi://ignoredhost/jndi/ldap://dirhost:9999/cn=this,ou=that</code> |
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223 </pre> |
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224 |
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225 then the connector server will generate an |
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226 <code>RMIJRMPServerImpl</code> and store its stub using the JNDI |
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227 name |
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228 |
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229 <pre> |
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230 <code>ldap://dirhost:9999/cn=this,ou=that</code> |
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231 </pre> |
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232 |
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233 which means entry <code>cn=this,ou=that</code> in the LDAP |
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234 directory running on port 9999 of host <code>dirhost</code>. |
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235 |
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236 <p>If the <code>JMXServiceURL</code> is: |
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237 |
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238 <pre> |
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239 <code>service:jmx:rmi://ignoredhost/jndi/cn=this,ou=that</code> |
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240 </pre> |
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241 |
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242 then the connector server will generate an |
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243 <code>RMIJRMPServerImpl</code> and store its stub using the JNDI |
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244 name |
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245 |
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246 <pre> |
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247 <code>cn=this,ou=that</code> |
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248 </pre> |
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249 |
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250 For this case to work, the JNDI API must have been configured |
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251 appropriately to supply the information about what directory to |
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252 use. |
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253 |
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254 <p>In these examples, the host name <code>ignoredhost</code> is |
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255 not used by the connector server or its clients. It can be |
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256 omitted, for example:</p> |
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257 |
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258 <pre> |
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259 <code>service:jmx:rmi:///jndi/cn=this,ou=that</code> |
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260 </pre> |
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261 |
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262 <p>However, it is good practice to use the name of the host |
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263 where the connector server is running. This is often different |
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264 from the name of the directory host.</p> |
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265 |
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266 |
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267 <h4>Connector server attributes</h4> |
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268 |
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269 <p>When using the default JRMP transport, RMI socket factories can |
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270 be specified using the attributes |
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271 <code>jmx.remote.rmi.client.socket.factory</code> and |
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272 <code>jmx.remote.rmi.server.socket.factory</code> in the |
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273 <code>environment</code> given to the |
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274 <code>RMIConnectorServer</code> constructor. The values of these |
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275 attributes must be of type {@link |
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276 java.rmi.server.RMIClientSocketFactory} and {@link |
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277 java.rmi.server.RMIServerSocketFactory}, respectively. These |
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278 factories are used when creating the RMI objects associated with |
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279 the connector.</p> |
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280 |
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281 <h3>Creating an RMI connector client</h3> |
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282 |
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283 <p>An RMI connector client is usually constructed using {@link |
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284 javax.management.remote.JMXConnectorFactory}, with a |
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285 <code>JMXServiceURL</code> that has <code>rmi</code> as its protocol.</p> |
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286 |
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287 <p>If the <code>JMXServiceURL</code> was generated by the server, |
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288 as described above under <a href="#servergen">"connector |
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289 addresses generated by the server"</a>, then the client will |
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290 need to obtain it directly or indirectly from the server. |
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291 Typically, the server makes the <code>JMXServiceURL</code> |
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292 available by storing it in a file or a lookup service.</p> |
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293 |
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294 <p>If the <code>JMXServiceURL</code> uses the directory syntax, as |
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295 described above under <a href="#directory">"connector addresses |
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296 based on directory entries"</a>, then the client may obtain it |
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297 as just explained, or client and server may both know the |
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298 appropriate directory entry to use. For example, if the |
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299 connector server for the Whatsit agent uses the entry |
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300 <code>whatsit-agent-connector</code> in the RMI registry on host |
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301 <code>myhost</code>, then client and server can both know |
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302 that the appropriate <code>JMXServiceURL</code> is:</p> |
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303 |
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304 <pre> |
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305 <code>service:jmx:rmi:///jndi/rmi://myhost/whatsit-agent-connector</code> |
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306 </pre> |
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307 |
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308 <p>If you have an RMI stub of type {@link |
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309 javax.management.remote.rmi.RMIServer RMIServer}, you can |
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310 construct an RMI connection directly by using the appropriate |
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311 constructor of {@link javax.management.remote.rmi.RMIConnector |
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312 RMIConnector}.</p> |
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313 |
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314 <h3>Dynamic code downloading</h3> |
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315 |
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316 <p>If an RMI connector client or server receives from its peer an |
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317 instance of a class that it does not know, and if dynamic code |
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318 downloading is active for the RMI connection, then the class can |
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319 be downloaded from a codebase specified by the peer. The |
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320 article <a |
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321 href="{@docRoot}/../technotes/guides/rmi/codebase.html"><em>Dynamic |
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322 code downloading using Java RMI</em></a> explains this in more |
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323 detail.</p> |
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324 |
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325 |
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326 @see <a href="{@docRoot}/../technotes/guides/rmi/index.html"> |
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327 Java™ Remote Method |
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328 Invocation (RMI)</a> |
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329 |
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330 @see <a href="{@docRoot}/../technotes/guides/jndi/index.html"> |
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331 Java Naming and Directory Interface™ (JNDI)</a> |
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332 |
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333 @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045, |
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334 section 6.8, "Base64 Content-Transfer-Encoding"</a> |
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335 |
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336 |
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337 @since 1.5 |
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338 |
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339 </body> |
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340 </html> |