# Package org.springframework.dao

Exception hierarchy enabling sophisticated error handling independent of the data access approach in use.

See: Description

- Exception Summary
  Exception | Description
  --- | ---
  CannotAcquireLockException | Exception thrown on failure to aquire a lock during an update, for example during a "select for update" statement.
  CannotSerializeTransactionException | Exception thrown on failure to complete a transaction in serialized mode due to update conflicts.
  CleanupFailureDataAccessException | Exception thrown when we couldn't cleanup after a data access operation, but the actual operation went OK.
  ConcurrencyFailureException | Exception thrown on concurrency failure.
  DataAccessException | Root of the hierarchy of data access exceptions discussed in Expert One-On-One J2EE Design and Development.
  DataAccessResourceFailureException | Data access exception thrown when a resource fails completely: for example, if we can't connect to a database using JDBC.
  DataIntegrityViolationException | Exception thrown when an attempt to insert or update data results in violation of an integrity constraint.
  DataRetrievalFailureException | Exception thrown if certain expected data could not be retrieved, e.g.
  DeadlockLoserDataAccessException | Generic exception thrown when the current process was a deadlock loser, and its transaction rolled back.
  DuplicateKeyException | Exception thrown when an attempt to insert or update data results in violation of an primary key or unique constraint.
  EmptyResultDataAccessException | Data access exception thrown when a result was expected to have at least one row (or element) but zero rows (or elements) were actually returned.
  IncorrectResultSizeDataAccessException | Data access exception thrown when a result was not of the expected size, for example when expecting a single row but getting 0 or more than 1 rows.
  IncorrectUpdateSemanticsDataAccessException | Data access exception thrown when something unintended appears to have happened with an update, but the transaction hasn't already been rolled back.
  InvalidDataAccessApiUsageException | Exception thrown on incorrect usage of the API, such as failing to "compile" a query object that needed compilation before execution.
  InvalidDataAccessResourceUsageException | Root for exceptions thrown when we use a data access resource incorrectly.
  NonTransientDataAccessException | Root of the hierarchy of data access exceptions that are considered non-transient - where a retry of the same operation would fail unless the cause of the Exception is corrected.
  NonTransientDataAccessResourceException | Data access exception thrown when a resource fails completely and the failure is permanent.
  OptimisticLockingFailureException | Exception thrown on an optimistic locking violation.
  PermissionDeniedDataAccessException | Exception thrown when the underlying resource denied a permission to access a specific element, such as a specific database table.
  PessimisticLockingFailureException | Exception thrown on a pessimistic locking violation.
  QueryTimeoutException | Exception to be thrown on a query timeout.
  RecoverableDataAccessException | Data access exception thrown when a previously failed operation might be able to succeed if the application performs some recovery steps and retries the entire transaction or in the case of a distributed transaction, the transaction branch.
  TransientDataAccessException | Root of the hierarchy of data access exceptions that are considered transient - where a previously failed operation might be able to succeed when the operation is retried without any intervention by application-level functionality.
  TransientDataAccessResourceException | Data access exception thrown when a resource fails temporarily and the operation can be retried.
  TypeMismatchDataAccessException | Exception thrown on mismatch between Java type and database type: for example on an attempt to set an object of the wrong type in an RDBMS column.
  UncategorizedDataAccessException | Normal superclass when we can't distinguish anything more specific than "something went wrong with the underlying resource": for example, a SQLException from JDBC we can't pinpoint more precisely.

## Package org.springframework.dao Description

Exception hierarchy enabling sophisticated error handling independent of the data access approach in use. For example, when DAOs and data access frameworks use the exceptions in this package (and custom subclasses), calling code can detect and handle common problems such as deadlocks without being tied to a particular data access strategy, such as JDBC.

All these exceptions are unchecked, meaning that calling code can leave them uncaught and treat all data access exceptions as fatal.

The classes in this package are discussed in Chapter 9 of Expert One-On-One J2EE Design and Development by Rod Johnson (Wrox, 2002).