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From "Mamta A. Satoor (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-1599) Clob.getSubString() throws NullPointerException when created by updatable result set
Date Tue, 30 Oct 2007 06:53:50 GMT

    [ https://issues.apache.org/jira/browse/DERBY-1599?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12538681
] 

Mamta A. Satoor commented on DERBY-1599:
----------------------------------------

I spent some time on this Jira entry and here is what I found.

When the sample program does rs.updateCharacterStream() on a Clob column, we generate a derby.client.am.Clob
object with it's dataType_ as CHARACTER_STREAM 
Thread [main] (Suspended)	
	Clob.<init>(Agent, Reader, int) line: 170	
	CrossConverters.setObject(int, Reader, int) line: 651	
	NetResultSet(ResultSet).updateCharacterStream(int, Reader, int) line: 3066	
	DERBY_1599_Repro.main(String[]) line: 56	
In other words, the resultant derby.client.am.Clob object has a character stream associated
with it but it's string_ variable is NULL. 

Later, when the sample program retrieve the Clob object using         
          Clob clob = rs.getClob(1);
we get the Clob object with character stream associated with it but no direct string value.
The return of Clob object for the call above is shown in the following call stack
Thread [main] (Suspended)	
	NetResultSet(ResultSet).getClob(int) line: 1256	
	DERBY_1599_Repro.main(String[]) line: 57	

The problem happens for the next call in the user program when we try to use substring, ie

           String string = clob.getSubString(1, (int) clob.length());
This is implemented in
	derby.client.am.Clob.getSubStringX(long, int) line: 326	
and the code for Clob.getSubStringX in derby network client looks as follows
    private String getSubStringX(long pos, int length) throws SqlException
    {
        checkForClosedConnection();
        // actual length is the lesser of the length requested
        // and the number of characters available from pos to the end
        long actualLength = Math.min(this.sqlLength() - pos + 1, (long) length);
        //Check to see if the Clob object is locator enabled.
        if (isLocator()) {
            //The Clob object is locator enabled. Hence call the stored
            //procedure CLOBGETLENGTH to determine the length of the Clob.
            return agent_.connection_.locatorProcedureCall()
                .clobGetSubString(locator_, pos, (int)actualLength);
        }
        else {
            //The Clob object is not locator enabled.
            return string_.substring
                    ((int) pos - 1, (int) (pos - 1 + actualLength));
        }
    }

Since this Clob object is not locator enabled, the code control goes to else in the code above
and since string_ is NULL, we end up getting null pointer exception. 

To fix the problem, should we be checking if string_ is null, and if yes, then check what
stream is associated with the Clob object and then materialize the string_ from the stream?
Would like to know if anyone has any thoughts on this.

BTW, I tried modifying the repro program so that we try to do 
        rs.updateCharacterStream(1, r, 3);
        rs.getCharacterStream(1);
but that didn't go very well either. It resulted in following exception
$ java org.apache.derbyTesting.functionTests.tests.lang.DERBY_1599_Repro
Exception in thread "main" java.sql.SQLException: An attempt was made to put a data value
of type 'java.sql.Clob' into a data value of type 'CHAR'.
        at org.apache.derby.client.am.SQLExceptionFactory.getSQLException(SQLExceptionFactory.java:46)
        at org.apache.derby.client.am.SqlException.getSQLException(SqlException.java:362)
        at org.apache.derby.client.am.ResultSet.getCharacterStream(ResultSet.java:1211)
        at org.apache.derbyTesting.functionTests.tests.lang.DERBY_1599_Repro.main(DERBY_1599_Repro.java:57)
Caused by: org.apache.derby.client.am.SqlException: An attempt was made to put a data value
of type 'java.sql.Clob' into a data value of type 'CHAR'.
        at org.apache.derby.client.am.CrossConverters.setObject(CrossConverters.java:810)
        at org.apache.derby.client.am.CrossConverters.setObject(CrossConverters.java:846)
        at org.apache.derby.client.am.ResultSet.getCharacterStream(ResultSet.java:1198)
        ... 1 more




> Clob.getSubString() throws NullPointerException when created by updatable result set
> ------------------------------------------------------------------------------------
>
>                 Key: DERBY-1599
>                 URL: https://issues.apache.org/jira/browse/DERBY-1599
>             Project: Derby
>          Issue Type: Bug
>          Components: JDBC, Network Client
>    Affects Versions: 10.1.3.1, 10.2.1.6
>            Reporter: Knut Anders Hatlen
>            Priority: Minor
>         Attachments: Repro.java
>
>
> If you create a clob value with one of the ResultSet.updateXXX methods that take a stream
or a reader, and retrieve that value with ResultSet.getClob(), a NullPointerException will
be thrown when getSubString() is called on the returned Clob object. This happens with the
network client driver, and it has been observed on Derby 10.1.3.1 and trunk.
> Exception in thread "main" java.lang.NullPointerException
>         at org.apache.derby.client.am.Clob.getSubStringX(Clob.java:229)
>         at org.apache.derby.client.am.Clob.getSubString(Clob.java:210)
>         at Repro.main(Repro.java:24)

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