frl-coding-standard

---

name: frl-coding-standard description: Coding standards for all Java code in fdb-record-layer. Apply when writing or reviewing any Java code. Some example usages: "Review this class for coding standards" "Write a new implementation of RecordCursor"

All Java, Gradle, and property files MUST end with a newline character.

Target Java 17 language level, compiled with JDK 21.

Exceptions

The two layers use different exception systems. Know which layer you are in.

fdb-record-layer-* (record layer)

Exceptions extend RecordCoreException, which extends LoggableException (unchecked).

• The exception message MUST be a static string — no string interpolation or variables.
• Use .addLogInfo(LogMessageKeys.KEY, value) to attach context. Include as much as needed to diagnose the error: subspace, primary key, record type, index name, etc.

// Wrong
throw new RecordCoreException("Found corrupt record: " + record.getPrimaryKey());

// Correct
throw new RecordCoreException("Found corrupt record")
    .addLogInfo(LogMessageKeys.PRIMARY_KEY, record.getPrimaryKey())
    .addLogInfo(LogMessageKeys.RECORD_TYPE, record.getRecordType());

fdb-relational-* (relational / SQL layer)

Exceptions are RelationalException (checked, extends Exception). Always pair with an ErrorCode, which maps to a SQLSTATE-standard 5-digit code.

• Message must still be a static string.
• Attach context with .addContext("key", value) — this travels with the exception for logging and is preserved when converting to SQLException.

// Minimal form
throw new RelationalException("Transaction rolled back", ErrorCode.SERIALIZATION_FAILURE);

// With context
throw new RelationalException("Unsupported type in column", ErrorCode.CANNOT_CONVERT_TYPE)
    .addContext("columnName", colName)
    .addContext("typeName", typeName);

At JDBC interface boundaries (where the signature throws SQLException), convert via .toSqlException(), which produces a ContextualSQLException carrying the ErrorCode as the SQLState and the context map for logging:

throw new RelationalException("Element is not of STRUCT type", ErrorCode.CANNOT_CONVERT_TYPE)
    .toSqlException();

Specialized subclasses (InvalidColumnReferenceException, InvalidTypeException) exist for common error cases — prefer them when they fit. InternalErrorException is deprecated; use new RelationalException("...", ErrorCode.INTERNAL_ERROR) directly.

UncheckedRelationalException wraps a RelationalException as a RuntimeException for contexts where checked exceptions cannot be thrown (e.g., inside lambdas). Unwrap with .unwrap() to recover the original RelationalException.

Logging

Same principle as exceptions — structured, static messages:

• Always use KeyValueLogMessage.of("static message", key, value, ...).
• The message text must be a static string. Variables go in key/value pairs.

// Wrong
LOGGER.info("Unable to open file: " + filename);

// Correct
LOGGER.info(KeyValueLogMessage.of("Unable to open file", LogMessageKeys.FILENAME, filename));

Futures (async code)

The fdb-record-layer-* and lower-level parts of fdb-relational-core are fully asynchronous via CompletableFuture. The JDBC-facing relational API presents a synchronous surface, but async code is common in the implementation beneath it.

• Never call join() or get() in production code. Use context.asyncToSync() or database.asyncToSync() instead — they enforce timeouts, record wait timers, and handle error wrapping.
• Never call any blocking method from inside a CompletableFuture completion lambda. The thread pool is finite; blocking inside a future can deadlock the entire system.
• Avoid thenApplyAsync() / thenComposeAsync() unless the lambda does significant CPU work. These enqueue a new task on the executor for no benefit in the common case. When you do need them, always pass an explicit Executor.
• Always pass an Executor to any AsyncUtil or MoreAsyncUtil method that accepts one (e.g. AsyncUtil.whileTrue()). Never use the overload without an executor.

Checkstyle-banned imports

The authoritative list is in gradle/check.gradle (BANNED_IMPORTS).

Inline comments

Describe intent, not mechanics. Explain the why — a hidden constraint, a non-obvious invariant, a workaround for a specific FDB behavior. If removing the comment would not confuse a future reader, don't write it.

Javadoc

Add Javadoc for public APIs. It is not necessary for private methods unless the logic is genuinely non-obvious.