examples.guestbook
Class GuestbookServiceImpl

java.lang.Object
  de.fhg.igd.semoa.service.AbstractService
      examples.guestbook.GuestbookServiceImpl

All Implemented Interfaces:

GuestbookService, Service

public class GuestbookServiceImpl

extends AbstractService

implements GuestbookService

This realizes access to a guestbook. The guestbook itself is backed by a file consisting of key-value pairs for each single entry. In SeMoA this service should be published as follows. The command may be entered on the command line or stated in file etc/rc.local (in one line!)

 java de.fhg.igd.semoa.bin.Publish 
       -class examples.GuestbookServiceImpl 
       -key ${WhatiIs:APPLICATION_SERVICE}/guestbook 
       \; -setFile myguestbook.txt
 

Version:

$Id: GuestbookServiceImpl.java 1913 2007-08-08 02:41:53Z jpeters $

Author:

U. Pinsdorf

Nested Class Summary

(package private) class	GuestbookServiceImpl.PrivilegedLoad This privileged action loads the values from a given InputStream and stores them in a Properties instance.
(package private) class	GuestbookServiceImpl.PrivilegedStore This privileged action stores the values of an Properties instance to a given OutputSteam.

Field Summary

private static String	ENTRY_KEY_PREFIX The entries in the guestbook file are represented as key-value pairs like mesg.12345="Hello dear!".
private File	file_ References the file which backs the guestbook.
private Object	lock_ This object is used for internal synchronization.
private Logger	LOG The logger instance for writing a log file.
private static String	OWNER_KEY The name of the owner entry in the guestbook.

Fields inherited from class de.fhg.igd.semoa.service.AbstractService

REV_POSTFIX, REV_PREFIX

Fields inherited from interface examples.guestbook.GuestbookService

WHATIS

Constructor Summary

GuestbookServiceImpl()

Method Summary

void	addEntry(String text) Allows to add an entry to the end of the guestbook.
String	author() Returns the name of the author of the service.
String[]	getEntries() Returns all entries from the guestbook.
String	getOwner() Returns the name of the guestbook's owner.
private String	getUniqueKey() Generates a unique key for an entry in the guestbook file.
String	info() Returns the informative string which should describe the service's essence in a sentence.
private Properties	loadGuestbook() Reads the guestbook from the file and returns it a new instance which holds all key-value-pairs from the file.
String	revision() Returns the revision number of this class as a string.
private void	saveGuestbook(Properties gb)
void	setFile(String fn) Remembers the given file name as new guestbook file.
String	toString() Pretty prints the whole guestbook.

Methods inherited from class de.fhg.igd.semoa.service.AbstractService

checkDependencies, dependencies, docs, doPrivileged, doPrivileged, getACC, getEnvironment, majorVersion, minorVersion

Methods inherited from class java.lang.Object

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

Field Detail

ENTRY_KEY_PREFIX

private static final String ENTRY_KEY_PREFIX

The entries in the guestbook file are represented as key-value pairs like mesg.12345="Hello dear!". All keys start with the string denoted in this constant. The constant is used by the method getUniqueKey().

See Also:

Constant Field Values

OWNER_KEY

private static final String OWNER_KEY

The name of the owner entry in the guestbook. All entries in the guestbook are represented as key-value pairs. An entry like owner=Snoopy states that 'Snoopy' is the name of the guestbook's owner.

See Also:

getOwner(), Constant Field Values

LOG

private final Logger LOG

The logger instance for writing a log file. For the logger's configuration refer to file etc/semoa.logging.

file_

private File file_

References the file which backs the guestbook. The file can be set by means of setFile(String).

lock_

private final Object lock_

This object is used for internal synchronization.

See Also:

loadGuestbook(), saveGuestbook(Properties)

Constructor Detail

GuestbookServiceImpl

public GuestbookServiceImpl()

Method Detail

info

public String info()

Description copied from class: AbstractService

Returns the informative string which should describe the service's essence in a sentence.

Specified by:

info in interface Service

Specified by:

info in class AbstractService

Returns:

the String with the service's short description.

See Also:

AbstractService.info()

author

public String author()

Description copied from class: AbstractService

Returns the name of the author of the service. The format to be used should be John Doe <jdoe@zilch.net>.

Specified by:

author in interface Service

Specified by:

author in class AbstractService

Returns:

the String with the author's name.

revision

public String revision()

Description copied from class: AbstractService

Returns the revision number of this class as a string. This class provides default implementations of methods majorVersion(), minorVersion based on the assumption that this method returns a revision string as generated by rcs(1) for the template "$Revision: 1.7 $/$Date: 2007-08-08 04:41:53 +0200 (Wed, 08 Aug 2007) $".

Specified by:

revision in class AbstractService

toString

public String toString()

Pretty prints the whole guestbook. This method overrides Object.toString(). It is very useful to access the service from the SeMoA shell print ${WhatiIs:APPLICATION_SERVICE}/guestbook where the path corresponds to the path where the service is actually published.

Overrides:

toString in class AbstractService

Returns:

The string representation of this instance. This default implementation returns information on the author, version, revision, and general info.

getOwner

public String getOwner()

Description copied from interface: GuestbookService

Returns the name of the guestbook's owner. The data is read from the guetsbook itself. Hence it may change only if the guestbook gets altered.

Specified by:

getOwner in interface GuestbookService

Returns:

name of the guestbook owner

See Also:

GuestbookService.getOwner()

getEntries

public String[] getEntries()

Description copied from interface: GuestbookService

Returns all entries from the guestbook. The return value is a field of strings where each field member represents one entry.

Specified by:

getEntries in interface GuestbookService

Returns:

field of all guestbook entries

See Also:

GuestbookService.getEntries()

addEntry

public void addEntry(String text)

Description copied from interface: GuestbookService

Allows to add an entry to the end of the guestbook.

Specified by:

addEntry in interface GuestbookService

Parameters:

text - the entry to be added

See Also:

GuestbookService.addEntry(java.lang.String)

setFile

public void setFile(String fn)

Remembers the given file name as new guestbook file. The file will be accessed with the next guestbook operation. Caution: it is possible that the new guestbook get overwritten instantly by an addEntry(String) operation.

Parameters:

fn - absolute file name of the guestbook file

See Also:

loadGuestbook(), saveGuestbook(Properties)

loadGuestbook

private Properties loadGuestbook()

Reads the guestbook from the file and returns it a new instance which holds all key-value-pairs from the file. The guestbook is read in a synchronized method to guarantee a thread-safe reading. Anyway, we need to synchronize the calling methods again in addEntry(String),getEntries(), and getOwner(). This is because we cannot be sure that the guestbook returned by this method is still up-to-date in the next moment.

Returns:

the guestbook as stored in the file

saveGuestbook

private void saveGuestbook(Properties gb)

getUniqueKey

private String getUniqueKey()

Generates a unique key for an entry in the guestbook file. This method is used by addEntry(String)each time a new entry has to be added.

Returns:

the unique id