org.jdesktop.application

Class SessionStorage

java.lang.Object

org.jdesktop.application.SessionStorage

public class SessionStorage
extends Object

Support for storing GUI state that persists between Application sessions.

This class simplifies the common task of saving a little bit of an application's GUI "session" state when the application shuts down, and then restoring that state when the application is restarted. Session state is stored on a per component basis, and only for components with a name and for which a PropertySupport object has been defined and registeres. SessionState Properties that preserve the bounds Rectangle for Windows, the dividerLocation for JSliderPanes and the selectedIndex for JTabbedPanes are defined by default. The ApplicationContext getSessionStorage method provides a shared SessionStorage object.

A typical Application saves session state in its shutdown() method, and then restores session state in startup():

 public class MyApplication extends Application {
     @Override protected void shutdown() {
         getContext().getSessionStorage().save(mainFrame, "session.xml");
     }
     @Override protected void startup() {
         ApplicationContext appContext = getContext();
         appContext.setVendorId("Sun");
         appContext.setApplicationId("SessionStorage1");
         // ... create the GUI rooted by JFrame mainFrame
         appContext.getSessionStorage().restore(mainFrame, "session.xml");
     }
     // ...
 }
 

In this example, the bounds of mainFrame as well the session state for any of its JSliderPane or JTabbedPane will be saved when the application shuts down, and restored when the applications starts up again. Note: error handling has been omitted from the example.

Session state is stored locally, relative to the user's home directory, by the LocalStorage save and load methods. The startup method must set the ApplicationContext vendorId and applicationId properties to ensure that the correct local directory is selected on all platforms. For example, on Windows XP, the full pathname for filename "session.xml" is typically:

 ${userHome}\Application Data\${vendorId}\${applicationId}\session.xml
 

Where the value of ${userHome} is the the value of the Java System property "user.home". On Solaris or Linux the file is:

 ${userHome}/.${applicationId}/session.xml
 

and on OSX:

 ${userHome}/Library/Application Support/${applicationId}/session.xml
 

See Also:

ApplicationContext.getSessionStorage(), LocalStorage

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	SessionStorage(ApplicationContext context) Constructs a SessionStorage object.

Method Summary

Methods

Modifier and Type	Method and Description
protected ApplicationContext	getContext() Returns ApplicationContext which was used during creation of this SessionStorage object.
PropertySupport	getProperty(Class cls) Returns the PropertySupport object that was registered for the specified class or a superclass.
PropertySupport	getProperty(Component component) If a sessionState PropertySupport object exists for the specified Component return it, otherwise return null.
void	putProperty(Class cls, PropertySupport propertySupport) Register a PropertySupport for the specified class.
void	restore(Component root, String fileName) Restores each named component in the specified hierarchy from the session state loaded from a file using LocalStorage.load(fileName).
void	save(Component root, String fileName) Saves the state of each named component in the specified hierarchy to a file using LocalStorage.save(fileName).

Methods inherited from class java.lang.Object

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

Constructor Detail

SessionStorage

protected SessionStorage(ApplicationContext context)

Constructs a SessionStorage object. The following PropertySupport objects are registered by default:

Base Component Type	PropertySupport	PropertySupport Value
Window	WindowProperty	WindowState
JTabbedPane	TabbedPaneProperty	TabbedPaneState
JSplitPane	SplitPaneProperty	SplitPaneState
JTable	TableProperty	TableState

Applications typically would not create a SessionStorage object directly, they'd use the shared ApplicationContext value:

 ApplicationContext ctx = Application.getInstance(MyApplication.class).getContext();
 SessionStorage ss = ctx.getSesssionStorage();
 

Parameters:

context -

See Also:

ApplicationContext.getSessionStorage(), getProperty(Class), getProperty(Component)

Method Detail

getContext

protected final ApplicationContext getContext()

Returns ApplicationContext which was used during creation of this SessionStorage object.

Returns:

the application context for this session storage object

save

public void save(Component root,
        String fileName)
          throws IOException

Saves the state of each named component in the specified hierarchy to a file using LocalStorage.save(fileName). Each component is visited in breadth-first order: if a PropertySupport exists for that component, and the component has a name, then its state is saved.

Component names can be any string however they must be unique relative to the name's of the component's siblings. Most Swing components do not have a name by default, however there are some exceptions: JRootPane (inexplicably) assigns names to it's children (layeredPane, contentPane, glassPane); and all AWT components lazily compute a name, so JFrame, JDialog, and JWindow also have a name by default.

The type of sessionState values (i.e. the type of values returned by PropertySupport.getSessionState) must be one those supported by XMLEncoder and XMLDecoder, for example beans (null constructor, read/write properties), primitives, and Collections. Java bean classes and their properties must be public. Typically beans defined for this purpose are little more than a handful of simple properties. The JDK 6 @ConstructorProperties annotation can be used to eliminate the need for writing set methods in such beans, e.g.

 public class FooBar {
     private String foo, bar;
     // Defines the mapping from constructor params to properties
     @ConstructorProperties({"foo", "bar"})
     public FooBar(String foo, String bar) {
         this.foo = foo;
         this.bar = bar;
     }
     public String getFoo() { return foo; }  // don't need setFoo
     public String getBar() { return bar; }  // don't need setBar
 }
 

Parameters:

root - the root of the Component hierarchy to be saved.

fileName - the LocalStorage filename.

Throws:

IOException

See Also:

restore(java.awt.Component, java.lang.String), ApplicationContext.getLocalStorage(), LocalStorage.save(java.lang.Object, java.lang.String), getProperty(Component)

restore

public void restore(Component root,
           String fileName)
             throws IOException

Restores each named component in the specified hierarchy from the session state loaded from a file using LocalStorage.load(fileName). Each component is visited in breadth-first order: if a PropertySupport exists for that component, and the component has a name, then its state is restored.

Parameters:

root - the root of the Component hierarchy to be restored.

fileName - the LocalStorage filename.

Throws:

IOException

See Also:

save(java.awt.Component, java.lang.String), ApplicationContext.getLocalStorage(), LocalStorage.save(java.lang.Object, java.lang.String), getProperty(Component)

getProperty

public PropertySupport getProperty(Class cls)

Returns the PropertySupport object that was registered for the specified class or a superclass. If no PropertySupport has been registered, return null. To lookup the session state PropertySupport for a Component use getProperty(Component).

Parameters:

cls - the class to which the returned PropertySupport applies

Returns:

the PropertySupport registered with putProperty for the specified class or the first one registered for a superclass of cls.

Throws:

IllegalArgumentException - if cls is null

See Also:

getProperty(Component), putProperty(java.lang.Class, org.jdesktop.application.session.PropertySupport), save(java.awt.Component, java.lang.String), restore(java.awt.Component, java.lang.String)

putProperty

public void putProperty(Class cls,
               PropertySupport propertySupport)

Register a PropertySupport for the specified class.

One can clear the PropertySupport for a class by setting the entry to null:

 sessionStorage.putProperty(myClass.class, null);
 

Register a custom PropertySupport:

 ApplicationContext ctx = Application.getInstance(MyApplication.class).getContext();
 SessionStorage ss = ctx.getSesssionStorage();
 ctx.putProperty(JTable.class, new ExtendedTableProperty());
 

Parameters:

cls - the class to which propertySupport applies.

propertySupport - the PropertySupport object to register or null.

Throws:

IllegalArgumentException - if cls is null.

See Also:

getProperty(Component), getProperty(Class), save(java.awt.Component, java.lang.String), restore(java.awt.Component, java.lang.String)

getProperty

public final PropertySupport getProperty(Component component)

If a sessionState PropertySupport object exists for the specified Component return it, otherwise return null. This method is used by the save and restore methods to lookup the sessionState PropertySupport object for each component to whose session state is to be saved or restored.

The putProperty method registers a PropertySupport object for a class. One can specify a PropertySupport object for a single Swing component by setting the component's client property, like this:

 myJComponent.putClientProperty(PropertySupport.class, myPropertySupport);
 

One can also create components that implement the PropertySupport interface directly.

Parameters:

component - the component to retrive the PropertySupport from

Returns:

if component implements PropertySupport, then component, if component is a JComponent with a PropertySupport valued client property under (client property key) PropertySupport, then return that, otherwise return the value of getProperty(component.getClass()).

Throws:

IllegalArgumentException - if Component component is null.

See Also:

JComponent.putClientProperty(java.lang.Object, java.lang.Object), getProperty(Class), putProperty(java.lang.Class, org.jdesktop.application.session.PropertySupport), save(java.awt.Component, java.lang.String), restore(java.awt.Component, java.lang.String)