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29 </head> |
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30 |
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31 |
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32 |
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33 <body bgcolor="white"> |
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34 |
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35 Provides the API for server side data source access and processing from |
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36 the Java™ programming language. |
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37 This package supplements the <code>java.sql</code> |
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38 package and, as of the version 1.4 release, is included in the |
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39 Java Platform, Standard Edition (Java SE™). |
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40 It remains an essential part of the Java Platform, Enterprise Edition |
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41 (Java EE™). |
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42 <P> |
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43 The <code>javax.sql</code> package provides for the following: |
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44 <OL> |
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45 <LI>The <code>DataSource</code> interface as an alternative to the |
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46 <code>DriverManager</code> for establishing a |
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47 connection with a data source |
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48 <LI>Connection pooling and Statement pooling |
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49 <LI>Distributed transactions |
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50 <LI>Rowsets |
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51 </OL> |
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52 <P> |
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53 Applications use the <code>DataSource</code> and <code>RowSet</code> |
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54 APIs directly, but the connection pooling and distributed transaction |
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55 APIs are used internally by the middle-tier infrastructure. |
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56 |
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57 <H2>Using a <code>DataSource</code> Object to Make a Connection</H2> |
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58 |
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59 The <code>javax.sql</code> package provides the preferred |
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60 way to make a connection with a data source. The <code>DriverManager</code> |
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61 class, the original mechanism, is still valid, and code using it will |
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62 continue to run. However, the newer <code>DataSource</code> mechanism |
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63 is preferred because it offers many advantages over the |
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64 <code>DriverManager</code> mechanism. |
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65 <P> |
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66 These are the main advantages of using a <code>DataSource</code> object to |
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67 make a connection: |
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68 <UL> |
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69 |
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70 <LI>Changes can be made to a data source's properties, which means |
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71 that it is not necessary to make changes in application code when |
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72 something about the data source or driver changes. |
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73 <LI>Connection and Statement pooling and distributed transactions are available |
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74 through a <code>DataSource</code> object that is |
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75 implemented to work with the middle-tier infrastructure. |
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76 Connections made through the <code>DriverManager</code> |
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77 do not have connection and statement pooling or distributed transaction |
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78 capabilities. |
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79 </UL> |
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80 <P> |
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81 Driver vendors provide <code>DataSource</code> implementations. A |
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82 particular <code>DataSource</code> object represents a particular |
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83 physical data source, and each connection the <code>DataSource</code> object |
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84 creates is a connection to that physical data source. |
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85 <P> |
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86 A logical name for the data source is registered with a naming service that |
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87 uses the Java Naming and Directory Interface™ |
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88 (JNDI) API, usually by a system administrator or someone performing the |
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89 duties of a system administrator. An application can retrieve the |
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90 <code>DataSource</code> object it wants by doing a lookup on the logical |
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91 name that has been registered for it. The application can then use the |
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92 <code>DataSource</code> object to create a connection to the physical data |
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93 source it represents. |
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94 <P> |
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95 A <code>DataSource</code> object can be implemented to work with the |
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96 middle tier infrastructure so that the connections it produces will be |
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97 pooled for reuse. An application that uses such a <code>DataSource</code> |
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98 implementation will automatically get a connection that participates in |
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99 connection pooling. |
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100 A <code>DataSource</code> object can also be implemented to work with the |
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101 middle tier infrastructure so that the connections it produces can be |
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102 used for distributed transactions without any special coding. |
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103 |
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104 <H2>Connection Pooling and Statement Pooling</H2> |
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105 |
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106 Connections made via a <code>DataSource</code> |
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107 object that is implemented to work with a middle tier connection pool manager |
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108 will participate in connection pooling. This can improve performance |
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109 dramatically because creating new connections is very expensive. |
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110 Connection pooling allows a connection to be used and reused, |
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111 thus cutting down substantially on the number of new connections |
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112 that need to be created. |
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113 <P> |
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114 Connection pooling is totally transparent. It is done automatically |
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115 in the middle tier of a Java EE configuration, so from an application's |
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116 viewpoint, no change in code is required. An application simply uses |
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117 the <code>DataSource.getConnection</code> method to get the pooled |
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118 connection and uses it the same way it uses any <code>Connection</code> |
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119 object. |
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120 <P> |
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121 The classes and interfaces used for connection pooling are: |
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122 <UL> |
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123 <LI><code>ConnectionPoolDataSource</code> |
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124 <LI><code>PooledConnection</code> |
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125 <LI><code>ConnectionEvent</code> |
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126 <LI><code>ConnectionEventListener</code> |
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127 <LI><code>StatementEvent</code> |
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128 <LI><code>StatementEventListener</code> |
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129 </UL> |
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130 The connection pool manager, a facility in the middle tier of |
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131 a three-tier architecture, uses these classes and interfaces |
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132 behind the scenes. When a <code>ConnectionPoolDataSource</code> object |
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133 is called on to create a <code>PooledConnection</code> object, the |
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134 connection pool manager will register as a <code>ConnectionEventListener</code> |
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135 object with the new <code>PooledConnection</code> object. When the connection |
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136 is closed or there is an error, the connection pool manager (being a listener) |
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137 gets a notification that includes a <code>ConnectionEvent</code> object. |
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138 <p> |
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139 If the connection pool manager supports <code>Statement</code> pooling, for |
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140 <code>PreparedStatements</code>, which can be determined by invoking the method |
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141 <code>DatabaseMetaData.supportsStatementPooling</code>, the |
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142 connection pool manager will register as a <code>StatementEventListener</code> |
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143 object with the new <code>PooledConnection</code> object. When the |
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144 <code>PreparedStatement</code> is closed or there is an error, the connection |
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145 pool manager (being a listener) |
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146 gets a notification that includes a <code>StatementEvent</code> object. |
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147 |
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148 <H2>Distributed Transactions</H2> |
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149 |
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150 As with pooled connections, connections made via a <code>DataSource</code> |
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151 object that is implemented to work with the middle tier infrastructure |
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152 may participate in distributed transactions. This gives an application |
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153 the ability to involve data sources on multiple servers in a single |
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154 transaction. |
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155 <P> |
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156 The classes and interfaces used for distributed transactions are: |
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157 <UL> |
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158 <LI><code>XADataSource</code> |
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159 <LI><code>XAConnection</code> |
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160 </UL> |
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161 These interfaces are used by the transaction manager; an application does |
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162 not use them directly. |
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163 <P> |
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164 The <code>XAConnection</code> interface is derived from the |
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165 <code>PooledConnection</code> interface, so what applies to a pooled connection |
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166 also applies to a connection that is part of a distributed transaction. |
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167 A transaction manager in the middle tier handles everything transparently. |
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168 The only change in application code is that an application cannot do anything |
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169 that would interfere with the transaction manager's handling of the transaction. |
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170 Specifically, an application cannot call the methods <code>Connection.commit</code> |
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171 or <code>Connection.rollback</code>, and it cannot set the connection to be in |
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172 auto-commit mode (that is, it cannot call |
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173 <code>Connection.setAutoCommit(true)</code>). |
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174 <P> |
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175 An application does not need to do anything special to participate in a |
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176 distributed transaction. |
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177 It simply creates connections to the data sources it wants to use via |
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178 the <code>DataSource.getConnection</code> method, just as it normally does. |
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179 The transaction manager manages the transaction behind the scenes. The |
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180 <code>XADataSource</code> interface creates <code>XAConnection</code> objects, and |
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181 each <code>XAConnection</code> object creates an <code>XAResource</code> object |
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182 that the transaction manager uses to manage the connection. |
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183 |
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184 |
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185 <H2>Rowsets</H2> |
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186 The <code>RowSet</code> interface works with various other classes and |
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187 interfaces behind the scenes. These can be grouped into three categories. |
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188 <OL> |
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189 <LI>Event Notification |
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190 <UL> |
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191 <LI><code>RowSetListener</code><br> |
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192 A <code>RowSet</code> object is a JavaBeans™ |
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193 component because it has properties and participates in the JavaBeans |
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194 event notification mechanism. The <code>RowSetListener</code> interface |
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195 is implemented by a component that wants to be notified about events that |
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196 occur to a particular <code>RowSet</code> object. Such a component registers |
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197 itself as a listener with a rowset via the <code>RowSet.addRowSetListener</code> |
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198 method. |
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199 <P> |
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200 When the <code>RowSet</code> object changes one of its rows, changes all of |
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201 it rows, or moves its cursor, it also notifies each listener that is registered |
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202 with it. The listener reacts by carrying out its implementation of the |
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203 notification method called on it. |
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204 <LI><code>RowSetEvent</code><br> |
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205 As part of its internal notification process, a <code>RowSet</code> object |
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206 creates an instance of <code>RowSetEvent</code> and passes it to the listener. |
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207 The listener can use this <code>RowSetEvent</code> object to find out which rowset |
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208 had the event. |
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209 </UL> |
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210 <LI>Metadata |
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211 <UL> |
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212 <LI><code>RowSetMetaData</code><br> |
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213 This interface, derived from the |
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214 <code>ResultSetMetaData</code> interface, provides information about |
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215 the columns in a <code>RowSet</code> object. An application can use |
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216 <code>RowSetMetaData</code> methods to find out how many columns the |
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217 rowset contains and what kind of data each column can contain. |
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218 <P> |
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219 The <code>RowSetMetaData</code> interface provides methods for |
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220 setting the information about columns, but an application would not |
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221 normally use these methods. When an application calls the <code>RowSet</code> |
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222 method <code>execute</code>, the <code>RowSet</code> object will contain |
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223 a new set of rows, and its <code>RowSetMetaData</code> object will have been |
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224 internally updated to contain information about the new columns. |
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225 </UL> |
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226 <LI>The Reader/Writer Facility<br> |
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227 A <code>RowSet</code> object that implements the <code>RowSetInternal</code> |
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228 interface can call on the <code>RowSetReader</code> object associated with it |
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229 to populate itself with data. It can also call on the <code>RowSetWriter</code> |
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230 object associated with it to write any changes to its rows back to the |
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231 data source from which it originally got the rows. |
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232 A rowset that remains connected to its data source does not need to use a |
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233 reader and writer because it can simply operate on the data source directly. |
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234 |
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235 <UL> |
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236 <LI><code>RowSetInternal</code><br> |
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237 By implementing the <code>RowSetInternal</code> interface, a |
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238 <code>RowSet</code> object gets access to |
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239 its internal state and is able to call on its reader and writer. A rowset |
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240 keeps track of the values in its current rows and of the values that immediately |
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241 preceded the current ones, referred to as the <i>original</i> values. A rowset |
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242 also keeps track of (1) the parameters that have been set for its command and |
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243 (2) the connection that was passed to it, if any. A rowset uses the |
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244 <code>RowSetInternal</code> methods behind the scenes to get access to |
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245 this information. An application does not normally invoke these methods directly. |
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246 |
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247 <LI><code>RowSetReader</code><br> |
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248 A disconnected <code>RowSet</code> object that has implemented the |
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249 <code>RowSetInternal</code> interface can call on its reader (the |
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250 <code>RowSetReader</code> object associated with it) to populate it with |
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251 data. When an application calls the <code>RowSet.execute</code> method, |
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252 that method calls on the rowset's reader to do much of the work. Implementations |
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253 can vary widely, but generally a reader makes a connection to the data source, |
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254 reads data from the data source and populates the rowset with it, and closes |
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255 the connection. A reader may also update the <code>RowSetMetaData</code> object |
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256 for its rowset. The rowset's internal state is also updated, either by the |
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257 reader or directly by the method <code>RowSet.execute</code>. |
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258 |
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259 |
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260 <LI><code>RowSetWriter</code><br> |
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261 A disconnected <code>RowSet</code> object that has implemented the |
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262 <code>RowSetInternal</code> interface can call on its writer (the |
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263 <code>RowSetWriter</code> object associated with it) to write changes |
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264 back to the underlying data source. Implementations may vary widely, but |
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265 generally, a writer will do the following: |
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266 |
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267 <UL> |
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268 <LI>Make a connection to the data source |
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269 <LI>Check to see whether there is a conflict, that is, whether |
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270 a value that has been changed in the rowset has also been changed |
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271 in the data source |
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272 <LI>Write the new values to the data source if there is no conflict |
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273 <LI>Close the connection |
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274 </UL> |
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275 |
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276 |
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277 </UL> |
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278 </OL> |
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279 <P> |
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280 The <code>RowSet</code> interface may be implemented in any number of |
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281 ways, and anyone may write an implementation. Developers are encouraged |
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282 to use their imaginations in coming up with new ways to use rowsets. |
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283 |
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284 |
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285 <h2>Package Specification</h2> |
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286 |
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287 <ul> |
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288 <li><a href="https://jcp.org/en/jsr/detail?id=221">JDBC 4.3 Specification</a> |
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289 </ul> |
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290 |
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291 <h2>Related Documentation</h2> |
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292 |
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293 The Java Series book published by Addison-Wesley Longman provides detailed |
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294 information about the classes and interfaces in the <code>javax.sql</code> |
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295 package: |
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296 |
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297 <ul> |
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298 <li><a href="http://www.oracle.com/technetwork/java/index-142838.html"> |
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299 <i>JDBC™API Tutorial and Reference, Third Edition</i></a> |
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300 </ul> |
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301 </body> |
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302 </html> |
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