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<H1><A name="WorkingWithColumnConverters-WorkingWithColumnConverters"></A>WorkingWithColumnConverters</H1>
<P>Sometimes it is desireable to modify a column value retreived from a database column <B>before</B> it is stored into a DataObject property. One example might be a database column with possible values '0' or '1' but the desired DataObject property is 'false' or 'true'. Another example might be a String property that should be obfuscated or encryted before it is stored into a column.</P>
<P>The RDB DAS provides a simple "converter" framework that can be used for these cases and others. To use this framework the application developer must provide a new Converter class to provide the desired transformations from column to property and from property back to column. The provided converter must implement the following interface:</P>
<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
<PRE class="code-java">
<SPAN class="code-keyword">package</SPAN> org.apache.tuscany.das.rdb;
/**
* A lightweight Table-column <--> DataObject-property converter framework. Converters allow a user to
* insert a transformation between a column value and is destination DataObject property value. For example,
* by <SPAN class="code-keyword">default</SPAN>, a VARCHAR column will be represented as a <SPAN class="code-object">String</SPAN> in its corresponding DataObject property.
* A user could insert a converter that transforms the the VARCHAR value to an <SPAN class="code-object">Integer</SPAN>. If <SPAN class="code-keyword">this</SPAN> is done then
* although the column returns character data, the DataObject property will be an <SPAN class="code-object">Integer</SPAN>
*/
<SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">interface</SPAN> Converter {
/**
* Transform the columnData object to a <SPAN class="code-keyword">new</SPAN> value and possibly <SPAN class="code-keyword">new</SPAN> type. This should be the inverse
* operation of #getColumnValue
*
* @param columnData
* The column value to transorm
* @<SPAN class="code-keyword">return</SPAN> Returns the transformed value
*/
<SPAN class="code-object">Object</SPAN> getPropertyValue(<SPAN class="code-object">Object</SPAN> columnData);
/**
* Transform the columnData object to a <SPAN class="code-keyword">new</SPAN> value and possibly <SPAN class="code-keyword">new</SPAN> type. This should be the inverse
* operation of #getPropertyValue
*
* @param propertyData
* The property value to transform
* @<SPAN class="code-keyword">return</SPAN> Returns the transformed value
*/
<SPAN class="code-object">Object</SPAN> getColumnValue(<SPAN class="code-object">Object</SPAN> propertyData);
}
</PRE>
</DIV></DIV>
<P>The following example illustrates the use of the converter framework to obfuscate a String value before it is stored to the database and deobfuscate it on read.</P>
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<PRE class="code-java">
DAS das = DAS.FACTORY.createDAS(getConfig(<SPAN class="code-quote">"CustomerConfig.xml"</SPAN>), getConnection());
<SPAN class="code-comment">// Create and initialize command to read customers
</SPAN> Command read = das.getCommand(<SPAN class="code-quote">"getFirstCustomer"</SPAN>);
<SPAN class="code-comment">// Read
</SPAN> DataObject root = read.executeQuery();
<SPAN class="code-comment">//Modify
</SPAN> root.setString(<SPAN class="code-quote">"CUSTOMER[1]/LASTNAME"</SPAN>, <SPAN class="code-quote">"Some <SPAN class="code-keyword">new</SPAN> name"</SPAN>);
das.applyChanges(root);
</PRE>
</DIV></DIV>
<P>This example just shows a simple read of a customer DataObject followed setting the last name to some new value. You will have to take my word for it that the value is not written as-is but is instead obfuscated. The actual value written to the database table column is "Fbzr arj anzr" based on the ROT13 algorithm used in the converter.</P>
<P>Converters are specified in the configuration, usually as part of a config.xml file. Here is the config file for the example:</P>
<DIV class="preformatted panel" style="border-width: 1px;"><DIV class="preformattedContent panelContent">
<PRE><Config xsi:noNamespaceSchemaLocation="http:///org.apache.tuscany.das.rdb/config.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<Command name="getFirstCustomer" SQL="Select * from CUSTOMER where ID = 1" kind="Select"/>
<Table tableName="CUSTOMER">
<Column columnName="ID" primaryKey="true"/>
<Column columnName="LASTNAME" converterClassName="org.apache.tuscany.das.rdb.test.mappings.StringObfuscationConverter"/>
</Table>
</Config>
</PRE>
</DIV></DIV>
<P>Here is the user-defined converter class:</P>
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<PRE class="code-java">
<SPAN class="code-keyword">public</SPAN> class StringObfuscationConverter <SPAN class="code-keyword">implements</SPAN> Converter {
<SPAN class="code-keyword">public</SPAN> StringObfuscationConverter() {
<SPAN class="code-keyword">super</SPAN>();
}
<SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">Object</SPAN> getPropertyValue(<SPAN class="code-object">Object</SPAN> columnData) {
<SPAN class="code-keyword">return</SPAN> toRot13((<SPAN class="code-object">String</SPAN>) columnData);
}
<SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">Object</SPAN> getColumnValue(<SPAN class="code-object">Object</SPAN> propertyData) {
<SPAN class="code-keyword">return</SPAN> toRot13((<SPAN class="code-object">String</SPAN>) propertyData);
}
<SPAN class="code-comment">// Utilities
</SPAN>
<SPAN class="code-comment">// A simple, reversible, obfuscation algorithm using a ROT13 implementation
</SPAN> <SPAN class="code-keyword">private</SPAN> <SPAN class="code-object">String</SPAN> toRot13(<SPAN class="code-object">String</SPAN> original) {
<SPAN class="code-object">int</SPAN> abyte = 0;
<SPAN class="code-object">byte</SPAN>[] buffer = {};
<SPAN class="code-keyword">try</SPAN> {
buffer = original.getBytes(<SPAN class="code-quote">"ISO-8859-1"</SPAN>);
} <SPAN class="code-keyword">catch</SPAN> (UnsupportedEncodingException e) {
<SPAN class="code-keyword">throw</SPAN> <SPAN class="code-keyword">new</SPAN> Error(e);
}
<SPAN class="code-keyword">for</SPAN> (<SPAN class="code-object">int</SPAN> i = 0; i < buffer.length; i++) {
abyte = buffer[i];
<SPAN class="code-object">int</SPAN> cap = abyte & 32;
abyte &= ~cap;
abyte = ((abyte >= 'A') && (abyte <= 'Z') ? ((abyte - 'A' + 13) % 26 + 'A') : abyte) | cap;
buffer[i] = (<SPAN class="code-object">byte</SPAN>) abyte;
}
<SPAN class="code-keyword">try</SPAN> {
<SPAN class="code-keyword">return</SPAN> <SPAN class="code-keyword">new</SPAN> <SPAN class="code-object">String</SPAN>(buffer, <SPAN class="code-quote">"ISO-8859-1"</SPAN>);
} <SPAN class="code-keyword">catch</SPAN> (UnsupportedEncodingException e) {
<SPAN class="code-keyword">throw</SPAN> <SPAN class="code-keyword">new</SPAN> Error(e);
}
}
}
</PRE>
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