R2DBC Proxy is a framework that provides callbacks to the R2DBC interactions. It consists of a thin layer on top of the R2DBC drivers to implement cross-cutting concerns, such as query loggings, observability instrumentation, or your own actions.

R2DBC Proxy Tips is a series of mini blog posts. I will introduce typical usage of the R2DBC proxy and sample implementations with tips.

This first post explains the prime use case of the R2DBC Proxy: “how to log queries”.


In R2DBC Proxy, a callback is implemented as ProxyExecutionListener.

This listener interface defines beforeQuery and afterQuery callback methods. As the names suggest, they are invoked when queries get executed.

To log the executed queries, you can create a listener that performs logging in beforeQuery or afterQuery. (Note, some of the values, such as the time the query took to run, are available only on the afterQuery.)

The following example shows a listener implementation that logs queries after each query:

public class LoggingListener implements ProxyExecutionListener {

  private static final Logger logger = LoggerFactory.getLogger(LoggingListener.class);

  private final QueryExecutionInfoFormatter formatter = QueryExecutionInfoFormatter.showAll();

  public void afterQuery(QueryExecutionInfo execInfo) {


Instead of creating a dedicated LoggingListener class, you can also register a listener for this purpose while creating a proxy ConnectionFactory.

QueryExecutionInfoFormatter formatter = QueryExecutionInfoFormatter.showAll();

ConnectionFactory original = ...;

// create a proxy ConnectionFactory
ConnectionFactory connectionFactory = ProxyConnectionFactory.builder(original)
    .onAfterQuery(queryInfo -> {  // listener

Sample Output (multiline for display purpose)

Thread:http-nio-8080-exec-3(38) Connection:3 Transaction:{Create:1 Rollback:0 Commit:0}
Success:True Time:5 Type:Statement BatchSize:0 BindingsSize:1
Query:["INSERT INTO test VALUES ($1)"] Bindings:[($1=100)]

Customizing a Formatter

QueryExecutionInfoFormatter is a utility class that converts QueryExecutionInfo to a String for logging. The default static method, showAll(), creates a formatter that converts all information available in the query execution.

However, it may be too long for your logging or you may want to customize the format.

QueryExecutionInfoFormatter provides show... methods to selectively choose the information you want to include, or you can use addConsumer to add your own conversion logic. The following example uses showQuery() and showBinding() with new lines for nicer formatting:

QueryExecutionInfoFormatter custom = new QueryExecutionInfoFormatter()
    .addConsumer((info, sb) -> {
      // custom conversion

Sample output:

Query:["SELECT * FROM employee WHERE id=$1"]