Constants in BPEL - best practice?

Question

Hello,
In our workflows we use a lot of constant values. Constants can be of course hardcoded to the bpel process, but it is not very nice solution for viewing or editing them later. What would be the best practice for handling constants in BPEL? Could the constants be defined in a xml schema and use them in bpel process? I couldn't get this work with a quick try.
Best regards,
Tommi

Answer 1

This should work as well. Thanks!
I made a customXPath function for reading the constants from a table. Here is the how-to if somebody is interested:
1. I created a table "bpel_constants" with two colums "key" and "Value"
2. I created a customXPath function for reading a "value" from the "bpel_constants" based on the "key"
public class ReadConstant implements IXPathFunction
private String dbName = "jdbc/BPELSamplesDataSource";
public Object call(IXPathContext context,
List args) throws XPathFunctionException
if (args.size() == 1)
if (args.get(0) instanceof String)
return readConstant((String)args.get(0));
throw new XPathFunctionException( "readConstant() requires string argument." );
private String readConstant(String key) throws XPathFunctionException
Connection conn = null;
String result = "";
Statement stmt = null;
try
conn = makeConnection();
stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("select " + "value " + "from " + "bpel_constants " + "where " + "key = '" + key + "'");
if (rs.next())
result = rs.getString(1);
else
throw new XPathFunctionException("Value not found for " + key);
} catch (SQLException se)
throw new XPathFunctionException(se.getMessage(), se);
} catch (NamingException ne)
throw new XPathFunctionException(ne.getMessage(), ne);
} finally
try
if (stmt != null)
stmt.close();
if (conn != null)
conn.close();
} catch (SQLException se)
throw new XPathFunctionException(se.getMessage(), se);
return result;
private Connection makeConnection() throws NamingException, SQLException
InitialContext ic = new InitialContext();
DataSource ds = (DataSource) ic.lookup(dbName);
return ds.getConnection();
- makeConnection uses a JNDI to lookup the same datasource that the BPEL Engine uses (this requires a jndi.properties file to be in a BPEL Engine classpath to work).
3. I put the ReadConnection class to the BPEL Engine classpath and defined the function in the xpath-functions.xml config file:
<function id="readConstant">
<classname>asdf.xpath.function.ReadConstant</classname>
<comment>
<![CDATA[Reads constant from bpel_constants table based on the key. The signature of this function is <i>asdf:readConstant(string)</i>.]]>
</comment>
<property id="namespace-uri">
<value>http://asdf.com/xpath/CustomXpathFunction</value>
<comment>Namespace URI for this function</comment>
</property>
<property id="namespace-prefix">
<value>asdf</value>
<comment>Namespace prefix for this function</comment>
</property>
</function>
4. Then the function can be called in the bpel like for example:
<assign name="Assign_2">
<copy>
<from expression="asdf:readConstant(string(bpws:getVariableData('inputVariable','payload','/client:customXPathtestProcessRequest/client:input')))"/>
<to variable="outputVariable" part="payload" query="/client:customXPathtestProcessResponse/client:result"/>
</copy>
</assign>