200a40b332
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231 lines
13 KiB
HTML
231 lines
13 KiB
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<DIV class="wiki-content">
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<H1><A name="WorkingWithColumnConverters-WorkingWithColumnConverters"></A>WorkingWithColumnConverters</H1>
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<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>
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<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>
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<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
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<PRE class="code-java">
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<SPAN class="code-keyword">package</SPAN> org.apache.tuscany.das.rdb;
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/**
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* A lightweight Table-column <--> DataObject-property converter framework. Converters allow a user to
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* insert a transformation between a column value and is destination DataObject property value. For example,
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* 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.
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* 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
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* although the column returns character data, the DataObject property will be an <SPAN class="code-object">Integer</SPAN>
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*/
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<SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">interface</SPAN> Converter {
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/**
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* 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
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* operation of #getColumnValue
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*
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* @param columnData
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* The column value to transorm
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* @<SPAN class="code-keyword">return</SPAN> Returns the transformed value
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*/
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<SPAN class="code-object">Object</SPAN> getPropertyValue(<SPAN class="code-object">Object</SPAN> columnData);
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/**
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* 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
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* operation of #getPropertyValue
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*
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* @param propertyData
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* The property value to transform
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* @<SPAN class="code-keyword">return</SPAN> Returns the transformed value
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*/
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<SPAN class="code-object">Object</SPAN> getColumnValue(<SPAN class="code-object">Object</SPAN> propertyData);
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}
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</PRE>
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</DIV></DIV>
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<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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<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
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<PRE class="code-java">
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DAS das = DAS.FACTORY.createDAS(getConfig(<SPAN class="code-quote">"CustomerConfig.xml"</SPAN>), getConnection());
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<SPAN class="code-comment">// Create and initialize command to read customers
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</SPAN> Command read = das.getCommand(<SPAN class="code-quote">"getFirstCustomer"</SPAN>);
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<SPAN class="code-comment">// Read
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</SPAN> DataObject root = read.executeQuery();
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<SPAN class="code-comment">//Modify
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</SPAN> root.setString(<SPAN class="code-quote">"CUSTOMER[1]/LASTNAME"</SPAN>, <SPAN class="code-quote">"Some <SPAN class="code-keyword">new</SPAN> name"</SPAN>);
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das.applyChanges(root);
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</PRE>
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</DIV></DIV>
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<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>
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<P>Converters are specified in the configuration, usually as part of a config.xml file. Here is the config file for the example:</P>
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<DIV class="preformatted panel" style="border-width: 1px;"><DIV class="preformattedContent panelContent">
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<PRE><Config xsi:noNamespaceSchemaLocation="http:///org.apache.tuscany.das.rdb/config.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
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<Command name="getFirstCustomer" SQL="Select * from CUSTOMER where ID = 1" kind="Select"/>
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<Table tableName="CUSTOMER">
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<Column columnName="ID" primaryKey="true"/>
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<Column columnName="LASTNAME" converterClassName="org.apache.tuscany.das.rdb.test.mappings.StringObfuscationConverter"/>
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</Table>
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</Config>
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</PRE>
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</DIV></DIV>
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<P>Here is the user-defined converter class:</P>
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<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
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<PRE class="code-java">
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<SPAN class="code-keyword">public</SPAN> class StringObfuscationConverter <SPAN class="code-keyword">implements</SPAN> Converter {
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<SPAN class="code-keyword">public</SPAN> StringObfuscationConverter() {
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<SPAN class="code-keyword">super</SPAN>();
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}
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<SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">Object</SPAN> getPropertyValue(<SPAN class="code-object">Object</SPAN> columnData) {
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<SPAN class="code-keyword">return</SPAN> toRot13((<SPAN class="code-object">String</SPAN>) columnData);
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}
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<SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">Object</SPAN> getColumnValue(<SPAN class="code-object">Object</SPAN> propertyData) {
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<SPAN class="code-keyword">return</SPAN> toRot13((<SPAN class="code-object">String</SPAN>) propertyData);
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}
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<SPAN class="code-comment">// Utilities
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</SPAN>
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<SPAN class="code-comment">// A simple, reversible, obfuscation algorithm using a ROT13 implementation
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</SPAN> <SPAN class="code-keyword">private</SPAN> <SPAN class="code-object">String</SPAN> toRot13(<SPAN class="code-object">String</SPAN> original) {
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<SPAN class="code-object">int</SPAN> abyte = 0;
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<SPAN class="code-object">byte</SPAN>[] buffer = {};
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<SPAN class="code-keyword">try</SPAN> {
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buffer = original.getBytes(<SPAN class="code-quote">"ISO-8859-1"</SPAN>);
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} <SPAN class="code-keyword">catch</SPAN> (UnsupportedEncodingException e) {
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<SPAN class="code-keyword">throw</SPAN> <SPAN class="code-keyword">new</SPAN> Error(e);
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}
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<SPAN class="code-keyword">for</SPAN> (<SPAN class="code-object">int</SPAN> i = 0; i < buffer.length; i++) {
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abyte = buffer[i];
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<SPAN class="code-object">int</SPAN> cap = abyte & 32;
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abyte &= ~cap;
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abyte = ((abyte >= 'A') && (abyte <= 'Z') ? ((abyte - 'A' + 13) % 26 + 'A') : abyte) | cap;
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buffer[i] = (<SPAN class="code-object">byte</SPAN>) abyte;
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}
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<SPAN class="code-keyword">try</SPAN> {
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<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>);
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} <SPAN class="code-keyword">catch</SPAN> (UnsupportedEncodingException e) {
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<SPAN class="code-keyword">throw</SPAN> <SPAN class="code-keyword">new</SPAN> Error(e);
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}
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}
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}
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</PRE>
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</DIV></DIV>
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</DIV>
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</DIV>
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