Learning Apache Apex

The exactly-once output to JDBC

The JDBC output for this example extends the base transactional JDBC output operator from the Apex library. This operator contains all the plumbing for JDBC connection and transaction handling, so that we can focus on what's required to update the counts:

public static class CountStoreOperator  extends AbstractJdbcTransactionableOutputOperator<KeyValPair<String,     Integer>>  {    public static final String SQL =        "MERGE INTO words USING (VALUES ?, ?) I (word, wcount)"        + " ON (words.word=I.word)"        + " WHEN MATCHED THEN UPDATE SET words.wcount = words.wcount + I.wcount"        + " WHEN NOT MATCHED THEN INSERT (word, wcount) VALUES (I.word,           I.wcount)";    @Override    protected String getUpdateCommand()    {      return SQL;    } @Override ...