org.apache.felix.cm.file

Class FilePersistenceManager

java.lang.Object

org.apache.felix.cm.file.FilePersistenceManager

All Implemented Interfaces:

PersistenceManager

public class FilePersistenceManager
extends Object
implements PersistenceManager

The FilePersistenceManager class stores configuration data in properties-like files inside a given directory. All configuration files are located in the same directory.

The configuration directory is set by either the FilePersistenceManager(String) constructor or the FilePersistenceManager(BundleContext, String) constructor. Refer to the respective JavaDocs for more information.

When this persistence manager is used by the Configuration Admin Service, the location may be configured using the org.apache.felix.cm.impl.ConfigurationManager#CM_CONFIG_DIR bundle context property. That is the Configuration Admin Service creates an instance of this class calling new FilePersistenceManager(bundleContext, bundleContext.getProperty(CM_CONFIG_DIR)).

If the location is not set, the config directory in the current working directory (as set in the user.dir system property) is used. If the the location is set but, no such directory exists, the directory and any missing parent directories are created. If a file exists at the given location, the constructor fails.

Configuration files are created in the configuration directory by appending the extension .config to the PID of the configuration. The PID is converted into a relative path name by replacing enclosed dots to slashes. Non-symbolic-name characters in the PID are encoded with their Unicode character code in hexadecimal.

Examples of PID to name conversion:
PID	Configuration File Name
sample	sample.config
org.apache.felix.log.LogService	org/apache/felix/log/LogService.config
sample.fläche	sample/fl%00e8che.config

Mulithreading Issues

In a multithreaded environment the store(String, Dictionary) and load(String) methods may be called at the the quasi-same time for the same configuration PID. It may no happen, that the store method starts writing the file and the load method might at the same time read from the file currently being written and thus loading corrupt data (if data is available at all).

To prevent this situation from happening, the methods use synchronization and temporary files as follows:

• The store(String, Dictionary) method writes a temporary file with file extension .tmp. When done, the file is renamed to actual configuration file name as implied by the PID. This last step of renaming the file is synchronized on the FilePersistenceManager instance.
• The load(String) method is completeley synchronized on the FilePersistenceManager instance such that the store(java.lang.String, java.util.Dictionary) method might inadvertantly try to replace the file while it is being read.
• Finally the Iterator returned by getDictionaries() is implemented such that any temporary configuration file is just ignored.

Field Summary

Fields

Modifier and Type	Field and Description
static String	DEFAULT_CONFIG_DIR The default configuration data directory if no location is configured (value is "config").
static String	DEFAULT_PERSISTENCE_MANAGER_NAME The name of this persistence manager when registered in the service registry.

Fields inherited from interface org.apache.felix.cm.PersistenceManager

PROPERTY_NAME

Constructor Summary

Constructors

Constructor and Description
FilePersistenceManager(org.osgi.framework.BundleContext bundleContext, String location) Creates an instance of this persistence manager using the given location as the directory to store and retrieve the configuration files.
FilePersistenceManager(String location) Creates an instance of this persistence manager using the given location as the directory to store and retrieve the configuration files.

Method Summary

Methods

Modifier and Type	Method and Description
void	delete(String pid) Deletes the file for the given identifier.
boolean	exists(String pid) Returns true if a (configuration) file exists for the given identifier.
Enumeration	getDictionaries() Loads configuration data from the configuration location and returns it as Dictionary objects.
File	getLocation() Returns the directory in which the configuration files are written as a File object.
Dictionary	load(String pid) Reads the (configuration) for the given identifier into a Dictionary object.
void	store(String pid, Dictionary props) Stores the contents of the Dictionary in a file denoted by the given identifier.

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_CONFIG_DIR

public static final String DEFAULT_CONFIG_DIR

The default configuration data directory if no location is configured (value is "config").

See Also:

Constant Field Values

DEFAULT_PERSISTENCE_MANAGER_NAME

public static final String DEFAULT_PERSISTENCE_MANAGER_NAME

The name of this persistence manager when registered in the service registry. (value is "file").

See Also:

Constant Field Values

Constructor Detail

FilePersistenceManager

public FilePersistenceManager(String location)

Creates an instance of this persistence manager using the given location as the directory to store and retrieve the configuration files.

This constructor resolves the configuration file location as follows:

• If location is null, the config directory in the current working directory as specified in the user.dir system property is assumed.
• Otherwise the named directory is used.
• If the directory name resolved in the first or second step is not an absolute path, it is resolved to an absolute path calling the File.getAbsoluteFile() method.
• If a non-directory file exists as the location found in the previous step or the named directory (including any parent directories) cannot be created, an IllegalArgumentException is thrown.

This constructor is equivalent to calling FilePersistenceManager(BundleContext, String) with a null BundleContext.

Parameters:

location - The configuration file location. If this is null the config directory below the current working directory is used.

Throws:

IllegalArgumentException - If the location exists but is not a directory or does not exist and cannot be created.

FilePersistenceManager

public FilePersistenceManager(org.osgi.framework.BundleContext bundleContext,
                      String location)

Creates an instance of this persistence manager using the given location as the directory to store and retrieve the configuration files.

This constructor resolves the configuration file location as follows:

• If location is null, the config directory in the persistent storage area of the bundle identified by bundleContext is used.
• If the framework does not support persistent storage area for bundles in the filesystem or if bundleContext is null, the config directory in the current working directory as specified in the user.dir system property is assumed.
• Otherwise the named directory is used.
• If the directory name resolved in the first, second or third step is not an absolute path and a bundleContext is provided which provides access to persistent storage area, the directory name is resolved as being inside the persistent storage area. Otherwise the directory name is resolved to an absolute path calling the File.getAbsoluteFile() method.
• If a non-directory file exists as the location found in the previous step or the named directory (including any parent directories) cannot be created, an IllegalArgumentException is thrown.

Parameters:

bundleContext - The BundleContext to optionally get the data location for the configuration files. This may be null, in which case this constructor acts exactly the same as calling FilePersistenceManager(String).

location - The configuration file location. If this is null the config directory below the current working directory is used.

Throws:

IllegalArgumentException - If the location exists but is not a directory or does not exist and cannot be created.

IllegalStateException - If the bundleContext is not valid.

Method Detail

getLocation

public File getLocation()

Returns the directory in which the configuration files are written as a File object.

Returns:

The configuration file location.

getDictionaries

public Enumeration getDictionaries()

Loads configuration data from the configuration location and returns it as Dictionary objects.

This method is a lazy implementation, which is just one configuration file ahead of the current enumeration location.

Specified by:

getDictionaries in interface PersistenceManager

Returns:

an enumeration of configuration data returned as instances of the Dictionary class.

delete

public void delete(String pid)

Deletes the file for the given identifier.

Specified by:

delete in interface PersistenceManager

Parameters:

pid - The identifier of the configuration file to delete.

exists

public boolean exists(String pid)

Returns true if a (configuration) file exists for the given identifier.

Specified by:

exists in interface PersistenceManager

Parameters:

pid - The identifier of the configuration file to check.

Returns:

true if the file exists

load

public Dictionary load(String pid)
                throws IOException

Reads the (configuration) for the given identifier into a Dictionary object.

Specified by:

load in interface PersistenceManager

Parameters:

pid - The identifier of the configuration file to delete.

Returns:

The configuration read from the file. This Dictionary may be empty if the file contains no configuration information or is not properly formatted.

Throws:

IOException - If an error occurs loading the dictionary. An IOException must also be thrown if no dictionary exists for the given identifier.

store

public void store(String pid,
         Dictionary props)
           throws IOException

Stores the contents of the Dictionary in a file denoted by the given identifier.

Specified by:

store in interface PersistenceManager

Parameters:

pid - The identifier of the configuration file to which to write the configuration contents.

props - The configuration data to write.

Throws:

IOException - If an error occurrs writing the configuration data.