Use a different JDBC driver

Oct 13, 2025 by pynkocean.com 103 views

Introduction

When working with stored procedures in PostgreSQL using Java, it's essential to accurately retrieve the metadata of the parameters. However, a known issue arises when using CallableStatement.getParameterMetadata() to determine the mode of a parameter. In this article, we'll delve into the problem, explore the expected behavior, and discuss possible solutions.

Describe the Issue

The issue at hand is that CallableStatement.getParameterMetadata() returns the wrong parameter mode for certain stored procedures. Specifically, when calling a procedure with both input and output parameters, the method incorrectly identifies the mode of the output parameter.

Driver Version?

The latest version of the PostgreSQL JDBC driver is used, which is version 42.3.3.

Java Version?

This issue can occur on any Java version, as it's a problem with the PostgreSQL JDBC driver.

OS Version?

The issue is not specific to any particular operating system, making it a problem that can occur on any platform.

PostgreSQL Version?

The latest version of PostgreSQL is used, which is version 14.4.

To Reproduce

To reproduce this issue, follow these steps:

Create a stored procedure in PostgreSQL with both input and output parameters:

create procedure p_date(in a date, out b date)
language plpgsql AS $$ begin b = a; end; $$;

Use the prepareCall() method to create a CallableStatement object:

var call = cn.w.prepareCall("call p_date(?, ?)");

Retrieve the parameter metadata using getParameterMetaData():

call.getParameterMetaData().getParameterMode(1); // 1 as expected
call.getParameterMetaData().getParameterMode(2); // 1 but 4 expected

Expected Behaviour

The expected behavior is that getParameterMode() returns the correct mode for each parameter. In this case, the first parameter should be identified as an input parameter (mode 1), and the second parameter should be identified as an output parameter (mode 4).

Logs

No exceptions are thrown when running the code, making it a silent failure.

Possible Solutions

To resolve this issue, you can use the following workarounds:

1. Use `getParameterType()` instead

Instead of using getParameterMode(), you can use getParameterType() to retrieve the type of the parameter. This method returns the SQL type of the parameter, which can be used to determine its mode.

int type = call.getParameterMetaData().getParameterType(2);
if (type == Types.DATE) {
    // Parameter is an output parameter
}

2. Use a custom solution

If you need to determine the mode of the parameter for a specific use case, you can create a custom solution using the getParameterType() method and the SQL type of the parameter.

int type = call.getParameterMetaData().getParameterType(2);
if (type == Types.DATE) {
    // Parameter is an output parameter
} else if (type == Types.VARCHAR) {
    // Parameter is an input parameter
}

3. Use a different JDBC driver

If none of the above solutions work for you, you can try using a different JDBC driver, such as the PostgreSQL JDBC driver version 42.2.20.

Conclusion

In conclusion, the issue with CallableStatement.getParameterMetadata() returning the wrong parameter mode is a known problem with the PostgreSQL JDBC driver. While there are workarounds available, it's essential to be aware of this issue when working with stored procedures in PostgreSQL using Java.

Recommendations

To avoid this issue, we recommend using the getParameterType() method instead of getParameterMode(). If you need to determine the mode of the parameter for a specific use case, create a custom solution using the getParameterType() method and the SQL type of the parameter.

Future Development

The PostgreSQL JDBC driver team is aware of this issue and is working on a fix. In the meantime, we recommend using the workarounds provided above.

References

PostgreSQL JDBC driver documentation: https://jdbc.postgresql.org/documentation/
PostgreSQL JDBC driver issue tracker: https://github.com/pgjdbc/pgjdbc/issues
CallableStatement.getParameterMetadata Returns Wrong Parameter Mode: Q&A ====================================================================

Introduction

In our previous article, we discussed the issue with CallableStatement.getParameterMetadata() returning the wrong parameter mode. In this Q&A article, we'll answer some of the most frequently asked questions about this issue.

Q: What is the issue with CallableStatement.getParameterMetadata()?

A: The issue is that CallableStatement.getParameterMetadata() returns the wrong parameter mode for certain stored procedures. Specifically, when calling a procedure with both input and output parameters, the method incorrectly identifies the mode of the output parameter.

Q: What are the possible solutions to this issue?

A: There are several possible solutions to this issue:

Use getParameterType() instead: Instead of using getParameterMode(), you can use getParameterType() to retrieve the type of the parameter. This method returns the SQL type of the parameter, which can be used to determine its mode.
Use a custom solution: If you need to determine the mode of the parameter for a specific use case, you can create a custom solution using the getParameterType() method and the SQL type of the parameter.
Use a different JDBC driver: If none of the above solutions work for you, you can try using a different JDBC driver, such as the PostgreSQL JDBC driver version 42.2.20.

Q: Why is this issue occurring?

A: This issue is occurring because of a bug in the PostgreSQL JDBC driver. The driver is not correctly identifying the mode of the output parameter in certain cases.

Q: Is this issue specific to a particular version of the PostgreSQL JDBC driver?

A: No, this issue is not specific to a particular version of the PostgreSQL JDBC driver. It can occur on any version of the driver.

Q: Can I use a different JDBC driver to resolve this issue?

A: Yes, you can try using a different JDBC driver to resolve this issue. However, be aware that using a different driver may require changes to your code and may not be compatible with all versions of the PostgreSQL database.

Q: Is this issue being addressed by the PostgreSQL JDBC driver team?

A: Yes, the PostgreSQL JDBC driver team is aware of this issue and is working on a fix. In the meantime, we recommend using the workarounds provided above.

Q: Can I report this issue to the PostgreSQL JDBC driver team?

A: Yes, you can report this issue to the PostgreSQL JDBC driver team using the issue tracker on GitHub: https://github.com/pgjdbc/pgjdbc/issues

Q: What are the implications of this issue?

A: The implications of this issue are that you may need to use workarounds to determine the mode of the parameter in certain cases. This may require changes to your code and may not be compatible with all versions of the PostgreSQL database.