[FLINK-35916] AbstractJdbcRowConverter: type conversion to string (ClassCastException)

• Type: Bug
• Status: Open
• Priority: Critical
• Resolution: Unresolved
• Affects Version/s: jdbc-3.2.0
• Fix Version/s: jdbc-3.2.0, jdbc-3.1.2
• Component/s: Connectors / JDBC
• Assignee: Unassigned
• Reporter: Evgeniy
• Created: 29/Jul/24 07:52
• Updated: 30/Jul/24 15:53

Description

Problem: When converting a type to a string, Java types are explicitly cast, which generates a ClassCastException.

 

Effects: Most Java types, one way or another, have the ability to be converted to a String type. However, not all types with this capability inherit a class of type String or similar, where the type can be cast to type String. As java suggests, any object can be cast to the String: Object#toString type if its implementation does not imply the opposite. However, explicit casting to the String type makes this impossible for 99% of custom Java objects.

 

Goals: Calling the Object#toString method for all objects that are supposed to be converted to a string.

 

 

Solution:

To begin with, I suggest you pay attention to the class that deals with type conversion - AbstractJdbcRowConverter. Pay attention to the method that deals with type conversion - createInternalConverter, and specifically to the lambda expression that deals with converting a type to a String type (CHAR, VARCHAR).

switch (type.getTypeRoot()) {
  ...
  case CHAR:
  case VARCHAR:
    return val -> StringData.fromString((String) val);
  ...
} 

You can observe (String) val, which is problematic.

My intended solution is the following change.

return val -> StringData.fromString(val.toString()); 

val.toString() can give a chance for a new life to most objects that cannot be processed by Flink by default, and this is very cool because it solves at least 1 problem.

 

 

For further research:

For example, pay attention to the type that is used in the podtgres driver to package PostgreSQL types other than primitive ones - PGobject.

public class PGobject implements Serializable, Cloneable {

  protected @Nullable String type;
  protected @Nullable String value;

  ...
  ...

  public String toString() {
    return this.getValue();
  }

  ...
} 

As you may have noticed, PostgreSQL itself is engaged in converting types to a string, which is an excellent argument for using val.toString().

Perhaps in the future, you can add PGobject type processing, as was done for PGarray, but it seems to me that the solution described above is the fastest and most optimal. Thanks!