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34 <title>javax.sql.rowset.spi</title> |
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35 |
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36 </head> |
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37 <body> |
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38 |
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39 The standard classes and interfaces that a third party vendor has to |
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40 use in its implementation of a synchronization provider. These classes and |
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41 interfaces are referred to as the Service Provider Interface (SPI). To make it possible |
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42 for a <code>RowSet</code> object to use an implementation, the vendor must register |
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43 it with the <code>SyncFactory</code> singleton. (See the class comment for |
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44 <code>SyncProvider</code> for a full explanation of the registration process and |
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45 the naming convention to be used.) |
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46 |
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47 <h2>Table of Contents</h2> |
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48 <ul> |
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49 <li><a href="#pkgspec">1.0 Package Specification</a> |
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50 <li><a href="#arch">2.0 Service Provider Architecture</a> |
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51 <li><a href="#impl">3.0 Implementer's Guide</a> |
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52 <li><a href="#resolving">4.0 Resolving Synchronization Conflicts</a> |
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53 <li><a href="#relspec">5.0 Related Specifications</a> |
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54 <li><a href="#reldocs">6.0 Related Documentation</a> |
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55 </ul> |
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56 |
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57 <h3><a id="pkgspec">1.0 Package Specification</a></h3> |
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58 <P> |
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59 The following classes and interfaces make up the <code>javax.sql.rowset.spi</code> |
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60 package: |
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61 <UL> |
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62 <LI><code>SyncFactory</code> |
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63 <LI><code>SyncProvider</code> |
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64 <LI><code>SyncFactoryException</code> |
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65 <LI><code>SyncProviderException</code> |
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66 <LI><code>SyncResolver</code> |
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67 <LI><code>XmlReader</code> |
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68 <LI><code>XmlWriter</code> |
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69 <LI><code>TransactionalWriter</code> |
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70 </UL> |
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71 The following interfaces, in the <code>javax.sql</code> package, are also part of the SPI: |
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72 <UL> |
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73 <LI><code>RowSetReader</code> |
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74 <LI><code>RowSetWriter</code> |
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75 </UL> |
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76 <P> |
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77 A <code>SyncProvider</code> implementation provides a disconnected <code>RowSet</code> |
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78 object with the mechanisms for reading data into it and for writing data that has been |
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79 modified in it |
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80 back to the underlying data source. A <i>reader</i>, a <code>RowSetReader</code> or |
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81 <code>XMLReader</code> object, reads data into a <code>RowSet</code> object when the |
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82 <code>CachedRowSet</code> methods <code>execute</code> or <code>populate</code> |
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83 are called. A <i>writer</i>, a <code>RowSetWriter</code> or <code>XMLWriter</code> |
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84 object, writes changes back to the underlying data source when the |
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85 <code>CachedRowSet</code> method <code>acceptChanges</code> is called. |
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86 <P> |
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87 The process of writing changes in a <code>RowSet</code> object to its data source |
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88 is known as <i>synchronization</i>. The <code>SyncProvider</code> implementation that a |
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89 <code>RowSet</code> object is using determines the level of synchronization that the |
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90 <code>RowSet</code> object's writer uses. The various levels of synchronization are |
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91 referred to as <i>grades</i>. |
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92 <P> |
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93 The lower grades of synchronization are |
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94 known as <i>optimistic</i> concurrency levels because they optimistically |
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95 assume that there will be no conflicts or very few conflicts. A conflict exists when |
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96 the same data modified in the <code>RowSet</code> object has also been modified |
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97 in the data source. Using the optimistic concurrency model means that if there |
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98 is a conflict, modifications to either the data source or the <code>RowSet</code> |
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99 object will be lost. |
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100 <P> |
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101 Higher grades of synchronization are called <i>pessimistic</i> because they assume |
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102 that others will be accessing the data source and making modifications. These |
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103 grades set varying levels of locks to increase the chances that no conflicts |
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104 occur. |
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105 <P> |
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106 The lowest level of synchronization is simply writing any changes made to the |
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107 <code>RowSet</code> object to its underlying data source. The writer does |
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108 nothing to check for conflicts. |
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109 If there is a conflict and the data |
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110 source values are overwritten, the changes other parties have made by to the data |
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111 source are lost. |
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112 <P> |
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113 The <code>RIXMLProvider</code> implementation uses the lowest level |
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114 of synchronization and just writes <code>RowSet</code> changes to the data source. |
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115 |
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116 <P> |
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117 For the next level up, the |
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118 writer checks to see if there are any conflicts, and if there are, |
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119 it does not write anything to the data source. The problem with this concurrency |
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120 level is that if another party has modified the corresponding data in the data source |
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121 since the <code>RowSet</code> object got its data, |
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122 the changes made to the <code>RowSet</code> object are lost. The |
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123 <code>RIOptimisticProvider</code> implementation uses this level of synchronization. |
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124 <P> |
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125 At higher levels of synchronization, referred to as pessimistic concurrency, |
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126 the writer take steps to avoid conflicts by setting locks. Setting locks |
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127 can vary from setting a lock on a single row to setting a lock on a table |
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128 or the entire data source. The level of synchronization is therefore a tradeoff |
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129 between the ability of users to access the data source concurrently and the ability |
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130 of the writer to keep the data in the <code>RowSet</code> object and its data source |
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131 synchronized. |
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132 <P> |
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133 It is a requirement that all disconnected <code>RowSet</code> objects |
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134 (<code>CachedRowSet</code>, <code>FilteredRowSet</code>, <code>JoinRowSet</code>, |
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135 and <code>WebRowSet</code> objects) obtain their <code>SyncProvider</code> objects |
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136 from the <code>SyncFactory</code> mechanism. |
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137 <P> |
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138 The reference implementation (RI) provides two synchronization providers. |
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139 <UL> |
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140 <LI><b><code>RIOptimisticProvider</code></b> <br> |
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141 The default provider that the <code>SyncFactory</code> instance will |
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142 supply to a disconnected <code>RowSet</code> object when no provider |
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143 implementation is specified.<BR> |
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144 This synchronization provider uses an optimistic concurrency model, |
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145 assuming that there will be few conflicts among users |
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146 who are accessing the same data in a database. It avoids |
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147 using locks; rather, it checks to see if there is a conflict |
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148 before trying to synchronize the <code>RowSet</code> object and the |
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149 data source. If there is a conflict, it does nothing, meaning that |
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150 changes to the <code>RowSet</code> object are not persisted to the data |
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151 source. |
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152 <LI><B><code>RIXMLProvider</code></B> <BR> |
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153 A synchronization provider that can be used with a |
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154 <code>WebRowSet</code> object, which is a rowset that can be written |
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155 in XML format or read from XML format. The |
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156 <code>RIXMLProvider</code> implementation does no checking at all for |
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157 conflicts and simply writes any updated data in the |
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158 <code>WebRowSet</code> object to the underlying data source. |
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159 <code>WebRowSet</code> objects use this provider when they are |
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160 dealing with XML data. |
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161 </UL> |
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162 |
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163 These <code>SyncProvider</code> implementations |
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164 are bundled with the reference implementation, which makes them always available to |
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165 <code>RowSet</code> implementations. |
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166 <code>SyncProvider</code> implementations make themselves available by being |
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167 registered with the <code>SyncFactory</code> singleton. When a <code>RowSet</code> |
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168 object requests a provider, by specifying it in the constructor or as an argument to the |
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169 <code>CachedRowSet</code> method <code>setSyncProvider</code>, |
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170 the <code>SyncFactory</code> singleton |
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171 checks to see if the requested provider has been registered with it. |
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172 If it has, the <code>SyncFactory</code> creates an instance of it and passes it to the |
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173 requesting <code>RowSet</code> object. |
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174 If the <code>SyncProvider</code> implementation that is specified has not been registered, |
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175 the <code>SyncFactory</code> singleton causes a <code>SyncFactoryException</code> object |
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176 to be thrown. If no provider is specified, |
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177 the <code>SyncFactory</code> singleton will create an instance of the default |
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178 provider implementation, <code>RIOptimisticProvider</code>, |
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179 and pass it to the requesting <code>RowSet</code> object. |
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180 |
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181 <P> |
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182 If a <code>WebRowSet</code> object does not specify a provider in its constructor, the |
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183 <code>SyncFactory</code> will give it an instance of <code>RIOptimisticProvider</code>. |
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184 However, the constructor for <code>WebRowSet</code> is implemented to set the provider |
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185 to the <code>RIXMLProvider</code>, which reads and writes a <code>RowSet</code> object |
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186 in XML format. |
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187 <P> |
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188 See the <a href="SyncProvider.html">SyncProvider</a> class |
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189 specification for further details. |
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190 <p> |
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191 Vendors may develop a <code>SyncProvider</code> implementation with any one of the possible |
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192 levels of synchronization, thus giving <code>RowSet</code> objects a choice of |
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193 synchronization mechanisms. |
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194 |
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195 <h3><a id="arch">2.0 Service Provider Interface Architecture</a></h3> |
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196 <b>2.1 Overview</b> |
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197 <p> |
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198 The Service Provider Interface provides a pluggable mechanism by which |
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199 <code>SyncProvider</code> implementations can be registered and then generated when |
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200 required. The lazy reference mechanism employed by the <code>SyncFactory</code> limits |
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201 unnecessary resource consumption by not creating an instance until it is |
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202 required by a disconnected |
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203 <code>RowSet</code> object. The <code>SyncFactory</code> class also provides |
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204 a standard API to configure logging options and streams that <b>may</b> be provided |
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205 by a particular <code>SyncProvider</code> implementation. |
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206 <p> |
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207 <b>2.2 Registering with the <code>SyncFactory</code></b> |
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208 <p> |
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209 A third party <code>SyncProvider</code> implementation must be registered with the |
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210 <code>SyncFactory</code> in order for a disconnected <code>RowSet</code> object |
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211 to obtain it and thereby use its <code>javax.sql.RowSetReader</code> and |
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212 <code>javax.sql.RowSetWriter</code> |
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213 implementations. The following registration mechanisms are available to all |
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214 <code>SyncProvider</code> implementations: |
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215 <ul> |
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216 <li><b>System properties</b> - Properties set at the command line. These |
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217 properties are set at run time and apply system-wide per invocation of the Java |
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218 application. See the section <a href="#reldocs">"Related Documentation"</a> |
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219 further related information. |
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220 |
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221 <li><b>Property Files</b> - Properties specified in a standard property file. |
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222 This can be specified using a System Property or by modifying a standard |
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223 property file located in the platform run-time. The |
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224 reference implementation of this technology includes a standard property |
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225 file than can be edited to add additional <code>SyncProvider</code> objects. |
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226 |
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227 <li><b>JNDI Context</b> - Available providers can be registered on a JNDI |
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228 context. The <code>SyncFactory</code> will attempt to load <code>SyncProvider</code> |
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229 objects bound to the context and register them with the factory. This |
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230 context must be supplied to the <code>SyncFactory</code> for the mechanism to |
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231 function correctly. |
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232 </ul> |
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233 <p> |
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234 Details on how to specify the system properties or properties in a property file |
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235 and how to configure the JNDI Context are explained in detail in the |
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236 <a href="SyncFactory.html"><code>SyncFactory</code></a> class description. |
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237 <p> |
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238 <b>2.3 SyncFactory Provider Instance Generation Policies</b> |
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239 <p> |
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240 The <code>SyncFactory</code> generates a requested <code>SyncProvider</code> |
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241 object if the provider has been correctly registered. The |
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242 following policies are adhered to when either a disconnected <code>RowSet</code> object |
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243 is instantiated with a specified <code>SyncProvider</code> implementation or is |
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244 reconfigured at runtime with an alternative <code>SyncProvider</code> object. |
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245 <ul> |
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246 <li> If a <code>SyncProvider</code> object is specified and the <code>SyncFactory</code> |
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247 contains <i>no</i> reference to the provider, a <code>SyncFactoryException</code> is |
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248 thrown. |
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249 |
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250 <li> If a <code>SyncProvider</code> object is specified and the <code>SyncFactory</code> |
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251 contains a reference to the provider, the requested provider is supplied. |
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252 |
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253 <li> If no <code>SyncProvider</code> object is specified, the reference |
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254 implementation provider <code>RIOptimisticProvider</code> is supplied. |
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255 </ul> |
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256 <p> |
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257 These policies are explored in more detail in the <a href="SyncFactory.html"> |
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258 <code>SyncFactory</code></a> class. |
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259 |
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260 <h3><a id="impl">3.0 SyncProvider Implementer's Guide</a></h3> |
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261 |
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262 <b>3.1 Requirements</b> |
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263 <p> |
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264 A compliant <code>SyncProvider</code> implementation that is fully pluggable |
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265 into the <code>SyncFactory</code> <b>must</b> extend and implement all |
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266 abstract methods in the <a href="SyncProvider.html"><code>SyncProvider</code></a> |
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267 class. In addition, an implementation <b>must</b> determine the |
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268 grade, locking and updatable view capabilities defined in the |
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269 <code>SyncProvider</code> class definition. One or more of the |
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270 <code>SyncProvider</code> description criteria <b>must</b> be supported. It |
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271 is expected that vendor implementations will offer a range of grade, locking, and |
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272 updatable view capabilities. |
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273 <p> |
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274 Furthermore, the <code>SyncProvider</code> naming convention <b>must</b> be followed as |
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275 detailed in the <a href="SyncProvider.html"><code>SyncProvider</code></a> class |
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276 description. |
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277 <p> |
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278 <b>3.2 Grades</b> |
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279 <p> |
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280 JSR 114 defines a set of grades to describe the quality of synchronization |
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281 a <code>SyncProvider</code> object can offer a disconnected <code>RowSet</code> |
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282 object. These grades are listed from the lowest quality of service to the highest. |
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283 <ul> |
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284 <li><b>GRADE_NONE</b> - No synchronization with the originating data source is |
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285 provided. A <code>SyncProvider</code> implementation returning this grade will simply |
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286 attempt to write any data that has changed in the <code>RowSet</code> object to the |
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287 underlying data source, overwriting whatever is there. No attempt is made to compare |
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288 original values with current values to see if there is a conflict. The |
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289 <code>RIXMLProvider</code> is implemented with this grade. |
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290 |
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291 <li><b>GRADE_CHECK_MODIFIED_AT_COMMIT</b> - A low grade of optimistic synchronization. |
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292 A <code>SyncProvider</code> implementation returning this grade |
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293 will check for conflicts in rows that have changed between the last synchronization |
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294 and the current synchronization under way. Any changes in the originating data source |
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295 that have been modified will not be reflected in the disconnected <code>RowSet</code> |
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296 object. If there are no conflicts, changes in the <code>RowSet</code> object will be |
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297 written to the data source. If there are conflicts, no changes are written. |
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298 The <code>RIOptimisticProvider</code> implementation uses this grade. |
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299 |
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300 <li><b>GRADE_CHECK_ALL_AT_COMMIT</b> - A high grade of optimistic synchronization. |
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301 A <code>SyncProvider</code> implementation returning this grade |
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302 will check all rows, including rows that have not changed in the disconnected |
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303 <code>RowSet</code> object. In this way, any changes to rows in the underlying |
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304 data source will be reflected in the disconnected <code>RowSet</code> object |
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305 when the synchronization finishes successfully. |
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306 |
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307 <li><b>GRADE_LOCK_WHEN_MODIFIED</b> - A pessimistic grade of synchronization. |
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308 <code>SyncProvider</code> implementations returning this grade will lock |
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309 the row in the originating data source that corresponds to the row being changed |
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310 in the <code>RowSet</code> object to reduce the possibility of other |
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311 processes modifying the same data in the data source. |
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312 |
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313 <li><b>GRADE_LOCK_WHEN_LOADED</b> - A higher pessimistic synchronization grade. |
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314 A <code>SyncProvider</code> implementation returning this grade will lock |
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315 the entire view and/or table affected by the original query used to |
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316 populate a <code>RowSet</code> object. |
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317 </ul> |
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318 <p> |
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319 <b>3.3 Locks</b> |
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320 <p> |
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321 JSR 114 defines a set of constants that specify whether any locks have been |
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322 placed on a <code>RowSet</code> object's underlying data source and, if so, |
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323 on which constructs the locks are placed. These locks will remain on the data |
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324 source while the <code>RowSet</code> object is disconnected from the data source. |
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325 <P> |
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326 These constants <b>should</b> be considered complementary to the |
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327 grade constants. The default setting for the majority of grade settings requires |
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328 that no data source locks remain when a <code>RowSet</code> object is disconnected |
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329 from its data source. |
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330 The grades <code>GRADE_LOCK_WHEN_MODIFIED</code> and |
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331 <code>GRADE_LOCK_WHEN_LOADED</code> allow a disconnected <code>RowSet</code> object |
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332 to have a fine-grained control over the degree of locking. |
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333 <ul> |
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334 <li><b>DATASOURCE_NO_LOCK</b> - No locks remain on the originating data source. |
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335 This is the default lock setting for all <code>SyncProvider</code> implementations |
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336 unless otherwise directed by a <code>RowSet</code> object. |
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337 |
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338 <li><b>DATASOURCE_ROW_LOCK</b> - A lock is placed on the rows that are touched by |
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339 the original SQL query used to populate the <code>RowSet</code> object. |
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340 |
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341 <li><b>DATASOURCE_TABLE_LOCK</b> - A lock is placed on all tables that are touched |
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342 by the query that was used to populate the <code>RowSet</code> object. |
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343 |
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344 <li><b>DATASOURCE_DB_LOCK</b> |
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345 A lock is placed on the entire data source that is used by the <code>RowSet</code> |
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346 object. |
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347 </ul> |
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348 <p> |
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349 <b>3.4 Updatable Views</b> |
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350 <p> |
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351 A <code>RowSet</code> object may be populated with data from an SQL <code>VIEW</code>. |
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352 The following constants indicate whether a <code>SyncProvider</code> object can |
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353 update data in the table or tables from which the <code>VIEW</code> was derived. |
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354 <ul> |
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355 <li><b>UPDATABLE_VIEW_SYNC</b> |
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356 Indicates that a <code>SyncProvider</code> implementation supports synchronization |
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357 to the table or tables from which the SQL <code>VIEW</code> used to populate |
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358 a <code>RowSet</code> object is derived. |
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359 |
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360 <li><b>NONUPDATABLE_VIEW_SYNC</b> |
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361 Indicates that a <code>SyncProvider</code> implementation does <b>not</b> support |
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362 synchronization to the table or tables from which the SQL <code>VIEW</code> |
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363 used to populate a <code>RowSet</code> object is derived. |
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364 </ul> |
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365 <p> |
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366 <b>3.5 Usage of <code>SyncProvider</code> Grading and Locking</b> |
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367 <p> |
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368 In the example below, the reference <code>CachedRowSetImpl</code> implementation |
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369 reconfigures its current <code>SyncProvider</code> object by calling the |
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370 <code>setSyncProvider</code> method.<br> |
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371 |
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372 <PRE> |
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373 CachedRowSetImpl crs = new CachedRowSetImpl(); |
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374 crs.setSyncProvider("com.foo.bar.HASyncProvider"); |
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375 </PRE> |
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376 An application can retrieve the <code>SyncProvider</code> object currently in use |
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377 by a disconnected <code>RowSet</code> object. It can also retrieve the |
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378 grade of synchronization with which the provider was implemented and the degree of |
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379 locking currently in use. In addition, an application has the flexibility to set |
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380 the degree of locking to be used, which can increase the possibilities for successful |
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381 synchronization. These operation are shown in the following code fragment. |
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382 <PRE> |
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383 SyncProvider sync = crs.getSyncProvider(); |
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384 |
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385 switch (sync.getProviderGrade()) { |
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386 case: SyncProvider.GRADE_CHECK_ALL_AT_COMMIT |
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387 //A high grade of optimistic synchronization |
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388 break; |
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389 case: SyncProvider.GRADE_CHECK_MODIFIED_AT_COMMIT |
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390 //A low grade of optimistic synchronization |
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391 break; |
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392 case: SyncProvider.GRADE_LOCK_WHEN_LOADED |
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393 // A pessimistic synchronization grade |
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394 break; |
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395 case: SyncProvider.GRADE_LOCK_WHEN_MODIFIED |
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396 // A pessimistic synchronization grade |
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397 break; |
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398 case: SyncProvider.GRADE_NONE |
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399 // No synchronization with the originating data source provided |
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400 break; |
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401 } |
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402 |
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403 switch (sync.getDataSourcLock() { |
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404 case: SyncProvider.DATASOURCE_DB_LOCK |
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405 // A lock is placed on the entire datasource that is used by the |
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406 // <code>RowSet</code> object |
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407 break; |
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408 |
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409 case: SyncProvider.DATASOURCE_NO_LOCK |
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410 // No locks remain on the originating data source. |
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411 break; |
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412 |
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413 case: SyncProvider.DATASOURCE_ROW_LOCK |
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414 // A lock is placed on the rows that are touched by the original |
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415 // SQL statement used to populate |
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416 // the RowSet object that is using the SyncProvider |
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417 break; |
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418 |
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419 case: DATASOURCE_TABLE_LOCK |
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420 // A lock is placed on all tables that are touched by the original |
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421 // SQL statement used to populated |
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422 // the RowSet object that is using the SyncProvider |
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423 break; |
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424 |
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425 </PRE> |
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426 It is also possible using the static utility method in the |
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427 <code>SyncFactory</code> class to determine the list of <code>SyncProvider</code> |
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428 implementations currently registered with the <code>SyncFactory</code>. |
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429 |
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430 <pre> |
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431 Enumeration e = SyncFactory.getRegisteredProviders(); |
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432 </pre> |
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433 |
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434 |
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435 <h3><a id="resolving">4.0 Resolving Synchronization Conflicts</a></h3> |
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436 |
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437 The interface <code>SyncResolver</code> provides a way for an application to |
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438 decide manually what to do when a conflict occurs. When the <code>CachedRowSet</code> |
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439 method <code>acceptChanges</code> finishes and has detected one or more conflicts, |
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440 it throws a <code>SyncProviderException</code> object. An application can |
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441 catch the exception and |
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442 have it retrieve a <code>SyncResolver</code> object by calling the method |
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443 <code>SyncProviderException.getSyncResolver()</code>. |
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444 <P> |
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445 A <code>SyncResolver</code> object, which is a special kind of |
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446 <code>CachedRowSet</code> object or |
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447 a <code>JdbcRowSet</code> object that has implemented the <code>SyncResolver</code> |
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448 interface, examines the conflicts row by row. It is a duplicate of the |
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449 <code>RowSet</code> object being synchronized except that it contains only the data |
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450 from the data source this is causing a conflict. All of the other column values are |
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451 set to <code>null</code>. To navigate from one conflict value to another, a |
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452 <code>SyncResolver</code> object provides the methods <code>nextConflict</code> and |
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453 <code>previousConflict</code>. |
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454 <P> |
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455 The <code>SyncResolver</code> interface also |
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456 provides methods for doing the following: |
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457 <UL> |
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458 <LI>finding out whether the conflict involved an update, a delete, or an insert |
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459 <LI>getting the value in the data source that caused the conflict |
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460 <LI>setting the value that should be in the data source if it needs to be changed |
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461 or setting the value that should be in the <code>RowSet</code> object if it needs |
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462 to be changed |
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463 </UL> |
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464 <P> |
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465 When the <code>CachedRowSet</code> method <code>acceptChanges</code> is called, it |
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466 delegates to the <code>RowSet</code> object's <code>SyncProvider</code> object. |
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467 How the writer provided by that <code>SyncProvider</code> object is implemented |
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468 determines what level (grade) of checking for conflicts will be done. After all |
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469 checking for conflicts is completed and one or more conflicts has been found, the method |
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470 <code>acceptChanges</code> throws a <code>SyncProviderException</code> object. The |
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471 application can catch the exception and use it to obtain a <code>SyncResolver</code> object. |
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472 <P> |
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473 The application can then use <code>SyncResolver</code> methods to get information |
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474 about each conflict and decide what to do. If the application logic or the user |
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475 decides that a value in the <code>RowSet</code> object should be the one to |
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476 persist, the application or user can overwrite the data source value with it. |
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477 <P> |
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478 The comment for the <code>SyncResolver</code> interface has more detail. |
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479 |
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480 <h3><a id="relspec">5.0 Related Specifications</a></h3> |
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481 <ul> |
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482 <li><a href="http://docs.oracle.com/javase/jndi/tutorial/index.html">JNDI</a> |
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483 <li><a href="{@docRoot}/java/util/logging/package-summary.html">Java Logging |
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484 APIs</a> |
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485 </ul> |
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486 <h3><a id="reldocs">6.0 Related Documentation</a></h3> |
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487 <ul> |
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488 <li><a href="http://docs.oracle.com/javase/tutorial/jdbc/">DataSource for JDBC |
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489 Connections</a> |
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490 </ul> |
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491 |
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492 </body> |
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493 </html> |
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