Package org.apache.derby.client.am.stmtcache

Class JDBCStatementCache

  • public final class JDBCStatementCache
extends java.lang.Object
    A cache for JDBC statement objects.

    The entries in the cache contains objects implementing the java.sql.PreparedStatement interface, and they are inserted with a key object implementing the interface StatementKey. The cached objects can be either java.sql.PreparedStatement or java.sql.CallableStatement. These two should be separated by using different types of keys.

    The cache only contains free statement objects, and on a successful request for a cached statement the statement is removed from the cache. The cache is not intended to hold duplicate statements. The physical prepared statement should be (re-)inserted into the cache when close is called on the logical prepared statement using it.

    There is a maximum number of cached statements associated with the cache. If this number is exceeded, the oldest entry will be thrown out. One can always throw out an entry, because the fact that it is in the cache means it is free and not in use.

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      private static class  JDBCStatementCache.BoundedLinkedHashMap
      A LinkedHashMap with an upper bound on the number of entries.

    • Field Summary

      Fields 
      Modifier and Type Field Description
      private java.util.LinkedHashMap<StatementKey,​java.sql.PreparedStatement> statements
      Structure holding the cached prepared statement objects.

    • Constructor Summary

      Constructors 
      Constructor Description
      JDBCStatementCache​(int maxSize)
      Creates a new, empty JDBC statement cache.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      boolean cacheStatement​(StatementKey statementKey, java.sql.PreparedStatement ps)
      Cache the prepared statement if it does not already exist.
      java.sql.PreparedStatement getCached​(StatementKey statementKey)
      Retrieves a cached prepared statement if one exists.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Field Detail

      • statements

        private final java.util.LinkedHashMap<StatementKey,​java.sql.PreparedStatement> statements
        Structure holding the cached prepared statement objects.

    • Constructor Detail

      • JDBCStatementCache

        public JDBCStatementCache​(int maxSize)
        Creates a new, empty JDBC statement cache.
        Parameters:
        maxSize - maximum number of statements in the cache
        Throws:
        java.lang.IllegalArgumentException - if maxSize is less than one

    • Method Detail

      • getCached

        public java.sql.PreparedStatement getCached​(StatementKey statementKey)
        Retrieves a cached prepared statement if one exists.
        Parameters:
        statementKey - key for the prepared statement to look up
        Returns:
        A cached statement if one exists, null otherwise.

      • cacheStatement

        public boolean cacheStatement​(StatementKey statementKey,
                              java.sql.PreparedStatement ps)
        Cache the prepared statement if it does not already exist.
        Parameters:
        statementKey - key to insert prepared statement with
        ps - prepared statement to cache
        Returns:
        true if added to the cache, false if not.