Escape non-printable characters in WSO2 Data Services Server

  • By Chanika Geeganage
  • 28 Sep, 2013

WSO2 Data Services Server (DSS) can be used to expose data from different data sources (ex: MYSQL, ORACLE) as a web service. Escaping non printable characters is a feature introduced from WSO2 DSS 3.1.0 onward.

Lets say in your database there are characters which cannot be printed. But you cannot replace or delete them as those are the data you have. But if you want to retrieve those data through a web service it will not allow to do so as they cannot be represented. For an example when you are invoking a data service (using soap-ui or try-it) and do a select query for a data contains characters which are not in printable format it will throw the following exception.

ERROR {org.wso2.carbon.dataservices.core.description.query.SQLQuery} -  DS Fault Message: Error in XML generation at StaticOutputElement.execute
DS Code: UNKNOWN_ERROR
Nested Exception:-
com.ctc.wstx.exc.WstxIOException: Invalid white space character (0x5) in text to output
 {org.wso2.carbon.dataservices.core.description.query.SQLQuery}
DS Fault Message: Error in XML generation at StaticOutputElement.execute
DS Code: UNKNOWN_ERROR
Nested Exception:-
com.ctc.wstx.exc.WstxIOException: Invalid white space character (0x5) in text to output

 at org.wso2.carbon.dataservices.core.engine.StaticOutputElement.execute(StaticOutputElement.java:232)
 at org.wso2.carbon.dataservices.core.engine.OutputElementGroup.execute(OutputElementGroup.java:121)
 at org.wso2.carbon.dataservices.core.description.query.Query.writeResultEntry(Query.java:339)
 at org.wso2.carbon.dataservices.core.description.query.SQLQuery.processNormalQuery(SQLQuery.java:822)
 at org.wso2.carbon.dataservices.core.description.query.SQLQuery.runQuery(SQLQuery.java:2034)
 at org.wso2.carbon.dataservices.core.description.query.Query.execute(Query.java:254)
 at org.wso2.carbon.dataservices.core.engine.CallQuery.execute(CallQuery.java:161)
 at org.wso2.carbon.dataservices.core.engine.CallQueryGroup.execute(CallQueryGroup.java:118)
 at org.wso2.carbon.dataservices.core.description.operation.Operation.execute(Operation.java:73)
 at org.wso2.carbon.dataservices.core.engine.DataService.invoke(DataService.java:598)
 at org.wso2.carbon.dataservices.core.engine.DSOMDataSource.execute(DSOMDataSource.java:135)
 at org.wso2.carbon.dataservices.core.engine.DSOMDataSource.serialize(DSOMDataSource.java:147)
 at org.apache.axiom.om.impl.llom.OMSourcedElementImpl.internalSerialize(OMSourcedElementImpl.java:691)

This happened as those characters cannot be serialized to xml when they are going to be printed. But with this newly added feature you can define to escape the those characters with '?' when you define output mapping in the process of creating the data service. You can select "Escape Non Printable Characters" from the UI.

If it is selected the corresponding characters will be replaced by ? and if it is not, then it will throw the above exception.

Source:https://chanikageeganage.blogspot.com/2013/09/escape-non-printable-characters-in-wso2.html