javax.jnlp

Interface PersistenceService

public interface PersistenceService

PersistenceService provides methods for storing data locally on the client system, even for applications that are running in the untrusted execution environment. The service is somewhat similar to that which the cookie mechanism provides to HTML-based applications.

Each entry in the persistence data store is named with a URL. This provides a similar hierarchical structure as a traditional file system.

An application is only allowed to access data stored with a URL that is based on its codebase. For example, given the codebase http://www.mysite.com/apps/App1/, the application would be allowed to access the data at the associated URLs:

• http://www.mysite.com/apps/App1/
• http://www.mysite.com/apps/
• http://www.mysite.com/

This scheme allows sharing of data between different applications from the same host. For example, if another application is located at http://www.mysite.com/apps/App2/, then they can share data between them in the http://www.mysite.com/ and http://www.mysite.com/apps/ directories.

A JNLP client should track the amount of storage that a given application uses. A PersistenceService implementation provides methods to get the current storage usage and limits and to request more storage. Storage is allocated on a per file basis, but a JNLP Client will typically grant or deny the request based on the total storage is use by an application.

Data stored using this mechanism is intended to be a local copy of data stored on a remote server. The individual entries can be tagged as either cached, meaning the server has an up-to-date copy, dirty, meaning the server does not have an up-to-date copy, or temporary, meaning that the file can always be recreated.

Since:

1.4.2

Field Summary

Fields

Modifier and Type	Field and Description
static int	CACHED
static int	DIRTY
static int	TEMPORARY

Method Summary

Modifier and Type	Method and Description
long	create(java.net.URL url, long maxsize) Creates a new persistent storage entry on the client side named with the given URL.
void	delete(java.net.URL url) Removes the stream associated with the given URL from the client-side date persistence store.
FileContents	get(java.net.URL url) Returns a FileContents object representing the contents of this file.
java.lang.String[]	getNames(java.net.URL url) Returns an array of Strings containing the names of all the entries for a given URL.
int	getTag(java.net.URL url) Returns an int corresponding to the current value of the tag for the persistent data store entry associated with the given URL.
void	setTag(java.net.URL url, int tag) Tags the persistent data store entry associated with the given URL with the given tag value.

Field Detail

CACHED

static final int CACHED

See Also:

Constant Field Values

TEMPORARY

static final int TEMPORARY

See Also:

Constant Field Values

DIRTY

static final int DIRTY

See Also:

Constant Field Values

Method Detail

create

long create(java.net.URL url,
            long maxsize)
     throws java.net.MalformedURLException,
            java.io.IOException

Creates a new persistent storage entry on the client side named with the given URL.

Parameters:

url - the URL representing the name of the entry in the persistent data store.

maxsize - maximum size of storage that can be written to this entry.

Returns:

the maximum size of storage that got granted, in bytes.

Throws:

java.net.MalformedURLException - if the application is denied access to the persistent data store represented by the given URL or the URL is null.

java.io.IOException - if an I/O exception occurs, or the entry already exists.

get

FileContents get(java.net.URL url)
          throws java.net.MalformedURLException,
                 java.io.IOException,
                 java.io.FileNotFoundException

Returns a FileContents object representing the contents of this file.

Parameters:

url - the URL representing the persistent data store entry.

Returns:

the file contents as a FileContents.

Throws:

java.io.IOException - if an I/O error occurs.

java.net.MalformedURLException - if the application is denied access to the persistent data store represented by the given URL or the URL is null.

java.io.FileNotFoundException - if a persistence store for the given URL is not found.

delete

void delete(java.net.URL url)
     throws java.net.MalformedURLException,
            java.io.IOException

Removes the stream associated with the given URL from the client-side date persistence store.

Parameters:

url - the URL representing the entry to delete from the persistent data store.

Throws:

java.net.MalformedURLException - if the application is denied access to the persistent data store represented by the given URL or the URL is null.

java.io.IOException - if an I/O exception occurs.

getNames

java.lang.String[] getNames(java.net.URL url)
                     throws java.net.MalformedURLException,
                            java.io.IOException

Returns an array of Strings containing the names of all the entries for a given URL.

Parameters:

url - the URL representing the root directory to search for entry names.

Returns:

a String array containing the entries names.

Throws:

java.net.MalformedURLException - if the application is denied access to the persistent data store represented by the given URL or the URL is null.

java.io.IOException - if an I/O exception occurs.

getTag

int getTag(java.net.URL url)
    throws java.net.MalformedURLException,
           java.io.IOException

Returns an int corresponding to the current value of the tag for the persistent data store entry associated with the given URL.

Parameters:

url - the URL representing the persistent data store entry for which the tag value is requested.

Returns:

an int containing one of the following tag values:

• CACHED
• TEMPORARY
• DIRTY

Throws:

java.net.MalformedURLException - if the application is denied access to the persistent data store represented by the given URL or the URL is null.

java.io.IOException - if an I/O exception occurs.

setTag

void setTag(java.net.URL url,
            int tag)
     throws java.net.MalformedURLException,
            java.io.IOException

Tags the persistent data store entry associated with the given URL with the given tag value.

Parameters:

url - the URL representing the persistent data store entry for which to set the tag value.

tag - the tag value to set.

Throws:

java.net.MalformedURLException - if the application is denied access to the persistent data store represented by the given URL or the URL is null.

java.io.IOException - if an I/O exception occurs.