liferoad commented on issue #35286:
URL: https://github.com/apache/beam/issues/35286#issuecomment-2973022085
I think the NullPointerException during display data population is a classic
symptom of using an anonymous inner class for a transform's logic, in this
case, the JdbcIO.RowMapper. To fix this, the RowMapper should be refactored
into a static nested class.
try this diff:
```
--- Original User Code (Problematic)
+++ Corrected Production-Quality Code
- // Anonymous inner class for RowMapper
- .withRowMapper(
- new JdbcIO.RowMapper() {
- private static final long serialVersionUID = 1L;
- public Customer1 mapRow(ResultSet rs) throws SQLException {
- Customer1 cust = new Customer1();
- cust.setCustomerId(rs.getInt("customerId"));
- cust.setName(rs.getString("name"));
- cust.setEmail(rs.getString("email"));
- cust.setAddress(rs.getString("address"));
- return cust;
- }
- })
- .withCoder(SerializableCoder.of(Customer1.class));
+ // Define the RowMapper as a static nested class elsewhere in the file
+ private static class CustomerRowMapper implements
JdbcIO.RowMapper<Customer1> {
+ @Override
+ public Customer1 mapRow(ResultSet rs) throws SQLException {
+ Customer1 cust = new Customer1();
+ cust.setCustomerId(rs.getInt("customerId"));
+ cust.setName(rs.getString("name"));
+ cust.setEmail(rs.getString("email"));
+ cust.setAddress(rs.getString("address"));
+ return cust;
+ }
+ }
+
+ // In the main pipeline construction:
+
- JdbcIO.ReadWithPartitions readTransform = JdbcIO.readWithPartitions()
+ // Parameterize the transform with the output type <Customer1>
+ JdbcIO.ReadWithPartitions<Customer1> readTransform =
JdbcIO.<Customer1>readWithPartitions()
+ // ... (DataSourceConfiguration, etc.)
+ // Use the new static nested class for the RowMapper
+ .withRowMapper(new CustomerRowMapper());
+ // The .withCoder() call is now removed as it's inferred automatically.
- pipeline.apply("ReadFromMySQL", readTransform)
- .apply("ToCSV", MapElements.via(new CustomerToCSV()))
+ pipeline.apply("ReadFromMySQL", readTransform)
+ // Add a type hint for robustness
+ .apply("ToCSV", MapElements.into(TypeDescriptors.strings()).via(new
CustomerToCSV()))
```
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