Java Doc for JDBCPersistentMap.java in  » Workflow-Engines » wfmopen-2.1.1 » de » danet » an » util » persistentmaps » Java Source Code / Java DocumentationJava Source Code and Java Documentation

The class uses an abstract SQL table model. The table consists of a column for the map id, the entry key and two value entries.

All columns except the second value entry are of type string, with lengths as appropriate for the application. The second value field is of type BLOB (binary large object) and is used if either the value to be stored is not of type java.lang.String String or longer than a given limit. The map id enables storing of several jdbc persistent maps in a single table. It is passed as paramter to all constructors of this class. Only a single instance for a map id may be created as creating two instances may corrupt caching.

The SQL statements used to retrieve and save data are configurable. Thus any table or view may be used as a base for a jdbc persistent map.

Note that this implementation is not synchronized. If multiple threads access this map concurrently, and at least one of the threads modifies the map structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more mappings; merely changing the value associated with a key that an instance already contains is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the map. This can be done at creation time, to prevent accidental unsynchronized access to the map: JDBCPersistentMap pm = new JDBCPersistentMap(...); Map m = Collections.synchronizedMap(pm); Since only the methods defined by Map are synchronized by this mechanism, all supplemented methods (like 'load' or 'store' have to be synchronized on the map object 'm', created above, e.g.: synchronized(m) { pm.load(); // Must be in the synchronized block }

The class is serializable. Note, however, that the database connection is transient.

DELETE FROM table WHERE MAPID=?

NOTE: The statement must declare semantically corresponding columns for all the restriction values described in the example above!

DELETE FROM table WHERE MAPID=? AND ITEM=?

NOTE: The statement must declare semantically corresponding columns for all the restriction values described in the example above!

INSERT INTO table (MAPID, ITEM, SVALUE, BVALUE) 
 VALUES (?, ?, ?, ?)

NOTE: The statement must declare semantically corresponding columns for all the values described in the example above!

SELECT ITEM, SVALUE, BVALUE FROM table WHERE MAPID = ?

NOTE: The statement must declare semantically corresponding columns for all the selection and restriction values described in the example above!

UPDATE table SET
 SVALUE = ?, BVALUE = ? WHERE MAPID=? AND ITEM=?

NOTE: The statement must declare semantically corresponding columns for all the data and restriction values described in the example above! The names of the key columns in the restriction phrase have to be in the same order as above (first: map-ident, second: item-ident)