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## org.jboss.cache.loader
Interface CacheLoader

All Superinterfaces:
  org.jboss.system.Service

All Known Subinterfaces:
  CacheLoaderAop, ExtendedCacheLoader

All Known Implementing Classes:
  AsyncCacheLoader, AsyncExtendedCacheLoader, BdbjeCacheLoader, ChainingCacheLoader, ClusteredCacheLoader, DelegatingCacheLoader, FileCacheLoader, FileExtendedCacheLoader, JDBCCacheLoader, JDBCExtendedCacheLoader, JdbmCacheLoader, LocalDelegatingCacheLoader, RmiDelegatingCacheLoader, RpcDelegatingCacheLoader, SharedStoreCacheLoader, TcpDelegatingCacheLoader

    public interface CacheLoader

extends org.jboss.system.Service

A `CacheLoader` implementation persists and load keys to and from secondary storage, such as a database or filesystem. Typically, implementations store a series of keys and values (an entire `Map`) under a single `Fqn`. Loading and saving properties of an entire `Map` should be atomic.

Lifecycle: First an instance of the loader is created, then the configuration (`setConfig(java.util.Properties)` ) and cache (`setCache(TreeCache)`) are set. After this, `Service.create()` is called. Then `Service.start()` is called. When re-deployed, `Service.stop()` will be called, followed by another `Service.start()`. Finally, when shut down, `Service.destroy()` is called, after which the loader is unusable.

Version:
  $Id: CacheLoader.java,v 1.5 2006/04/02 07:33:15 genman Exp $
Author:
  Bela Ban Oct 31, 2003

Method Summary
`void` | `commit(java.lang.Object tx)` Commits the transaction.
`boolean` | `exists(Fqn name)` Returns true if the CacheLoader has a node with a `Fqn`.
`java.util.Map` | `get(Fqn name)` Returns all keys and values from the persistent store, given a fully qualified name.
`java.util.Set` | `getChildrenNames(Fqn fqn)` Returns a set of children node names as Strings.
`byte[]` | `loadEntireState()` Fetches the entire state for this cache from secondary storage (disk, DB) and returns it as a byte buffer.
`void` | `prepare(java.lang.Object tx, java.util.List modifications, boolean one_phase)` Prepares a list of modifications.
`void` | `put(Fqn name, java.util.Map attributes)` Puts all entries of the map into the existing map of the given node, overwriting existing keys, but not clearing the existing map before insertion.
`java.lang.Object` | `put(Fqn name, java.lang.Object key, java.lang.Object value)` Puts a key and value into the attribute map of a given node.
`void` | `put(java.util.List modifications)` Applies all modifications to the backend store.
`void` | `remove(Fqn name)` Removes the given node and all its subnodes.
`java.lang.Object` | `remove(Fqn name, java.lang.Object key)` Removes the given key and value from the attributes of the given node.
`void` | `removeData(Fqn name)` Removes all attributes from a given node, but doesn't delete the node itself or any subnodes.
`void` | `rollback(java.lang.Object tx)` Rolls the transaction back.
`void` | `setCache(TreeCache c)` Sets the `TreeCache` that is maintaining this CacheLoader.
`void` | `setConfig(java.util.Properties properties)` Sets the configuration.
`void` | `storeEntireState(byte[] state)` Stores the given state in secondary storage.

Methods inherited from interface org.jboss.system.Service
`create, destroy, start, stop`

Method Detail

### setConfig

    void setConfig(java.util.Properties properties)

  Sets the configuration. This is called before `Service.create()` and `Service.start()`.

  Parameters:
    `properties` - a collection of configuration properties

### setCache

    void setCache(TreeCache c)

  Sets the `TreeCache` that is maintaining this CacheLoader. This method allows this CacheLoader to invoke methods on TreeCache, including fetching additional configuration information. This method is called be called after the CacheLoader instance has been constructed.

  Parameters:
    `c` - The cache on which this loader works

### getChildrenNames

    java.util.Set getChildrenNames(Fqn fqn)
                                   throws java.lang.Exception

  Returns a set of children node names as Strings. All names are relative to this parent `Fqn`. Returns null if the named node is not found or there are no children. The returned set must not be modifiable. Implementors can use `Collections.unmodifiableSet(Set)` to make the set unmodifiable.

  Parameters:
    `fqn` - The FQN of the parent
  Returns:
    Set a set of children. Returns null if no children nodes are present, or the parent is not present
  Throws:
    `java.lang.Exception`

### get

    java.util.Map get(Fqn name)
                      throws java.lang.Exception

  Returns all keys and values from the persistent store, given a fully qualified name. NOTE that the expected return value of this method has changed from JBossCache 1.2.x and before! This will affect cache loaders written prior to JBossCache 1.3.0 and such implementations should be checked for compliance with the behaviour expected.

  Parameters:
    `name` -
  Returns:
    Map keys and values for the given node. Returns null if the node is not found. If the node is found but has no attributes, this method returns an empty Map.
  Throws:
    `java.lang.Exception`

### exists

    boolean exists(Fqn name)
                   throws java.lang.Exception

  Returns true if the CacheLoader has a node with a `Fqn`.

  Returns:
    true if node exists, false otherwise
  Throws:
    `java.lang.Exception`

### put

    java.lang.Object put(Fqn name,
                         java.lang.Object key,
                         java.lang.Object value)
                         throws java.lang.Exception

  Puts a key and value into the attribute map of a given node. If the node does not exist, all parent nodes from the root down are created automatically. Returns the old value.

  Throws:
    `java.lang.Exception`

### put

    void put(Fqn name,
             java.util.Map attributes)
             throws java.lang.Exception

  Puts all entries of the map into the existing map of the given node, overwriting existing keys, but not clearing the existing map before insertion. This is the same behavior as `Map.putAll(java.util.Map)`. If the node does not exist, all parent nodes from the root down are created automatically

  Parameters:
    `name` - The fully qualified name of the node
    `attributes` - A Map of attributes. Can be null
  Throws:
    `java.lang.Exception`

### put

    void put(java.util.List modifications)
             throws java.lang.Exception

  Applies all modifications to the backend store. Changes may be applied in a single operation.

  Parameters:
    `modifications` - A List of modifications
  Throws:
    `java.lang.Exception`

### remove

    java.lang.Object remove(Fqn name,
                            java.lang.Object key)
                            throws java.lang.Exception

  Removes the given key and value from the attributes of the given node. Does nothing if the node doesn't exist Returns the removed value.

  Throws:
    `java.lang.Exception`

### remove

    void remove(Fqn name)
                throws java.lang.Exception

  Removes the given node and all its subnodes.

  Throws:
    `java.lang.Exception`

### removeData

    void removeData(Fqn name)
                    throws java.lang.Exception

  Removes all attributes from a given node, but doesn't delete the node itself or any subnodes.

  Throws:
    `java.lang.Exception`

### prepare

    void prepare(java.lang.Object tx,
                 java.util.List modifications,
                 boolean one_phase)
                 throws java.lang.Exception

  Prepares a list of modifications. For example, for a DB-based CacheLoader:
  1. Create a local (JDBC) transaction
  2. Associate the local transaction with `tx` (tx is the key)
  3. Execute the coresponding SQL statements against the DB (statements derived from modifications)
  For non-transactional CacheLoader (e.g. file-based), this could be a null operation.

  Parameters:
    `tx` - The transaction, just used as a hashmap key
    `modifications` - List, a list of all modifications within the given transaction
    `one_phase` - Persist immediately and (for example) commit the local JDBC transaction as well. When true, we won't get a `commit(Object)` or `rollback(Object)` method call later
  Throws:
    `java.lang.Exception`

### commit

    void commit(java.lang.Object tx)
                throws java.lang.Exception

  Commits the transaction. A DB-based CacheLoader would look up the local JDBC transaction asociated with `tx` and commit that transaction. Non-transactional CacheLoaders could simply write the data that was previously saved transiently under the given `tx` key, to (for example) a file system (note this only holds if the previous prepare() did not define one_phase=true

  Parameters:
    `tx` - transaction to commit
  Throws:
    `java.lang.Exception`

### rollback

    void rollback(java.lang.Object tx)

  Rolls the transaction back. A DB-based CacheLoader would look up the local JDBC transaction asociated with `tx` and roll back that transaction.

  Parameters:
    `tx` - transaction to roll back

### loadEntireState

    byte[] loadEntireState()
                           throws java.lang.Exception

  Fetches the entire state for this cache from secondary storage (disk, DB) and returns it as a byte buffer. This is for initialization of a new cache from a remote cache. The new cache would then call `storeEntireState(byte[])`.

  Throws:
    `java.lang.Exception`

### storeEntireState

    void storeEntireState(byte[] state)
                          throws java.lang.Exception

  Stores the given state in secondary storage. Overwrites whatever is currently in storage.

  Throws:
    `java.lang.Exception`

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