EventHandler.java: Reworked documentation.

2005-04-19  Robert Schuster <thebohemian@gmx.net>

	* java/beans/EventHandler.java: Reworked documentation.
	(invoke): Fixed behavior to match spec.

From-SVN: r98372
This commit is contained in:
Robert Schuster 2005-04-19 04:50:06 +00:00 committed by Michael Koch
parent 617c100078
commit 24809ca841
2 changed files with 380 additions and 158 deletions

View File

@ -1,3 +1,8 @@
2005-04-19 Robert Schuster <thebohemian@gmx.net>
* java/beans/EventHandler.java: Reworked documentation.
(invoke): Fixed behavior to match spec.
2005-04-19 Michael Koch <konqueror@gmx.de>
* java/awt/print/PrinterJob.java

View File

@ -1,5 +1,5 @@
/* java.beans.EventHandler
Copyright (C) 2004 Free Software Foundation, Inc.
Copyright (C) 2004, 2005 Free Software Foundation, Inc.
This file is part of GNU Classpath.
@ -44,26 +44,18 @@ import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
/**
* class EventHandler
*
* EventHandler forms a bridge between dynamically created listeners and
* arbitrary properties and methods. The idea is that a Proxy that implements
* a listener class calls the EventHandler when a listener method is called.
* The Proxy calls invoke(), which dispatches the event to a method, called
* the action, in another object, called the target.
*
* The event passed to the listener method is used to access a prespecified
* property, which in turn is passed to the action method.
* <p>EventHandler forms a bridge between dynamically created listeners and
* arbitrary properties and methods.</p>
*
* Normally, call EventHandler.create(), which constructs an EventHandler and
* a Proxy for the listener interface. When the listenerMethod gets called on
* the proxy, it in turn calls invoke on the attached EventHandler. The
* invoke call extracts the bean property from the event object and passes it
* to the action method of target object.
*
* TODO: Add examples of using this thing.
* <p>You can use this class to easily create listener implementations for
* some basic interactions between an event source and its target. Using
* the three static methods named <code>create</code> you can create
* these listener implementations.</p>
*
* <p>See the documentation of each method for usage examples.</p>
*
* @author Jerry Quinn (jlquinn@optonline.net)
* @author Robert Schuster (thebohemian@gmx.net)
* @since 1.4
*/
public class EventHandler implements InvocationHandler
@ -80,6 +72,9 @@ public class EventHandler implements InvocationHandler
// The property to extract from an event passed to listenerMethod.
private String property;
// The target objects Class.
private Class targetClass;
// String class doesn't already have a capitalize routine.
private String capitalize(String s)
{
@ -89,14 +84,15 @@ public class EventHandler implements InvocationHandler
/**
* Creates a new <code>EventHandler</code> instance.
*
* Typical creation is done with the create method, not by newing an
* EventHandler.
* <p>Typical creation is done with the create method, not by knewing an
* EventHandler.</p>
*
* This constructs an EventHandler that will connect the method
* <p>This constructs an EventHandler that will connect the method
* listenerMethodName to target.action, extracting eventPropertyName from
* the first argument of listenerMethodName. and sending it to action.
*
*
* the first argument of listenerMethodName. and sending it to action.</p>
*
* <p>Throws a <code>NullPointerException</code> if the <code>target</code>
* argument is <code>null</code>.
*
* @param target Object that will perform the action.
* @param action A property or method of the target.
@ -107,14 +103,20 @@ public class EventHandler implements InvocationHandler
String listenerMethodName)
{
this.target = target;
// Retrieving the class is done for two reasons:
// 1) The class object is needed very frequently in the invoke() method.
// 2) The constructor should throw a NullPointerException if target is null.
targetClass = target.getClass();
this.action = action; // Turn this into a method or do we wait till
// runtime
// runtime
property = eventPropertyName;
listenerMethod = listenerMethodName;
}
/**
* Return the event property name.
* Returns the event property name.
*/
public String getEventPropertyName()
{
@ -122,7 +124,7 @@ public class EventHandler implements InvocationHandler
}
/**
* Return the listener's method name.
* Returns the listener's method name.
*/
public String getListenerMethodName()
{
@ -130,7 +132,7 @@ public class EventHandler implements InvocationHandler
}
/**
* Return the target object.
* Returns the target object.
*/
public Object getTarget()
{
@ -138,7 +140,7 @@ public class EventHandler implements InvocationHandler
}
/**
* Return the action method name.
* Returns the action method name.
*/
public String getAction()
{
@ -156,12 +158,7 @@ public class EventHandler implements InvocationHandler
// value will be a wrapper. If we then take the type of the wrapper and use
// it to locate the action method that takes the native type, it won't match.
private Object[] getProperty(Object o, String prop)
throws NoSuchMethodException, IllegalAccessException, InvocationTargetException
{
// Use the event object when the property name to extract is null.
if (prop == null)
return new Object[] {o, o.getClass()};
// Isolate the first property name from a.b.c.
int pos;
String rest = null;
@ -179,121 +176,287 @@ public class EventHandler implements InvocationHandler
getter = o.getClass().getMethod("is" + capitalize(prop),
null);
}
catch (NoSuchMethodException e)
catch (NoSuchMethodException nsme1)
{
// Look for regular property getter getProperty
getter = o.getClass().getMethod("get" + capitalize(prop),
try {
// Look for regular property getter getProperty
getter = o.getClass().getMethod("get" + capitalize(prop),
null);
} catch(NoSuchMethodException nsme2) {
try {
// Finally look for a method of the name prop
getter = o.getClass().getMethod(prop, null);
} catch(NoSuchMethodException nsme3) {
// Ok, give up with an intelligent hint for the user.
throw new RuntimeException("Method not called: Could not find a property or method '" + prop
+ "' in " + o.getClass() + " while following the property argument '" + property + "'.");
}
}
}
Object val = getter.invoke(o, null);
try {
Object val = getter.invoke(o, null);
if (rest != null)
return getProperty(val, rest);
if (rest != null)
return getProperty(val, rest);
return new Object[] {val, getter.getReturnType()};
return new Object[] {val, getter.getReturnType()};
} catch(InvocationTargetException ite) {
throw new RuntimeException("Method not called: Property or method '" + prop + "' has thrown an exception.", ite);
} catch(IllegalAccessException iae) {
// This cannot happen because we looked up method with Class.getMethod()
// which returns public methods only.
throw (InternalError) new InternalError("Non-public method was invoked.").initCause(iae);
}
}
/**
* Invoke the event handler.
*
* Proxy is the object that was used, method is the method that was invoked
* on object, and arguments is the set of arguments passed to this method.
* We assume that the first argument is the event to extract a property
* from.
*
* Assuming that method matches the listener method specified when creating
* this EventHandler, the desired property is extracted from this argument.
* The property is passed to target.setAction(), if possible. Otherwise
* target.action() is called, where action is the string fed to the
* constructor.
*
* For now we punt on indexed properties. Sun docs are not clear to me
* about this.
*
* @param proxy The proxy object that had method invoked on it.
* @param method The method that was invoked.
* @param arguments Arguments to method.
* @return Result of invoking target.action on the event property
* Invokes the <code>EventHandler</code>.
*
* <p>This method is normally called by the listener's proxy implementation.</p>
*
* @param proxy The listener interface that is implemented using
* the proxy mechanism.
* @param method The method that was called on the proxy instance.
* @param arguments The arguments which where given to the method.
* @throws Throwable <code>NoSuchMethodException</code> is thrown when the EventHandler's
* action method or property cannot be found.
*/
public Object invoke(Object proxy, Method method, Object[] arguments)
throws Exception
{
// Do we actually need the proxy?
if (method == null)
throw new RuntimeException("Invoking null method");
try {
// The method instance of the target object. We have to find out which
// one we have to invoke.
Method actionMethod = null;
// Listener methods that weren't specified are ignored. If listenerMethod
// is null, then all listener methods are processed.
if (listenerMethod != null && !method.getName().equals(listenerMethod))
return null;
// Extract the first arg from arguments and do getProperty on arg
if (arguments == null || arguments.length == 0)
return null;
Object event = arguments[0]; // We hope :-)
// If a property is defined we definitely need a valid object at
// arguments[0] that can be used to retrieve a value to which the
// property of the target gets set.
if(property != null) {
// Extracts the argument. We will let it fail with a NullPointerException
// the caller used a listener method that has no arguments.
Object event = arguments[0];
// Obtain the property XXX propertyType keeps showing up null - why?
// because the object inside getProperty changes, but the ref variable
// can't change this way, dolt! need a better way to get both values out
// - need method and object to do the invoke and get return type
Object v[] = getProperty(event, property);
Object val = v[0];
Class propertyType = (Class) v[1];
// Find the actual method of target to invoke. We can't do this in the
// constructor since we don't know the type of the property we extracted
// from the event then.
//
// action can be either a property or a method. Sun's docs seem to imply
// that action should be treated as a property first, and then a method,
// but don't specifically say it.
//
// XXX check what happens with native type wrappers. The better thing to
// do is look at the return type of the method
Method actionMethod;
try
// Obtains the property XXX propertyType keeps showing up null - why?
// because the object inside getProperty changes, but the ref variable
// can't change this way, dolt! need a better way to get both values out
// - need method and object to do the invoke and get return type
Object v[] = getProperty(event, property);
Object[] args = new Object[] { v[0] };
// Changes the class array that controls which method signature we are going
// to look up in the target object.
Class[] argTypes = new Class[] { initClass((Class) v[1]) };
// Tries to find a setter method to which we can apply the
while(argTypes[0] != null) {
try
{
// Look for a property setter for action.
actionMethod =
target.getClass().getMethod("set" + capitalize(action),
new Class[] {propertyType});
// Look for a property setter for action.
actionMethod = targetClass.getMethod("set" + capitalize(action), argTypes);
return actionMethod.invoke(target, args);
}
catch (NoSuchMethodException e)
{
// If action as property didn't work, try as method.
try
{
actionMethod =
target.getClass().getMethod(action, new Class[] {propertyType});
}
catch (NoSuchMethodException e1)
{
// When event property is null, we may call action with no args
if (property == null)
{
actionMethod =
target.getClass().getMethod(action, null);
return actionMethod.invoke(target, null);
}
else
throw e1;
}
// If action as property didn't work, try as method later.
}
argTypes[0] = nextClass(argTypes[0]);
}
// We could not find a suitable setter method. Now we try again interpreting
// action as the method name itself.
// Since we probably have changed the block local argTypes array
// we need to rebuild it.
argTypes = new Class[] { initClass((Class) v[1]) };
// Tries to find a setter method to which we can apply the
while(argTypes[0] != null) {
try
{
actionMethod = targetClass.getMethod(action, argTypes);
return actionMethod.invoke(target, args);
}
catch (NoSuchMethodException e)
{
}
argTypes[0] = nextClass(argTypes[0]);
}
throw new RuntimeException("Method not called: Could not find a public method named '"
+ action + "' in target " + targetClass + " which takes a '"
+ v[1] + "' argument or a property of this type.");
}
// If property was null we will search for a no-argument method here.
// Note: The ordering of method lookups is important because we want to prefer no-argument
// calls like the JDK does. This means if we have actionMethod() and actionMethod(Event) we will
// call the first *EVEN* if we have a valid argument for the second method. This is behavior compliant
// to the JDK.
// If actionMethod() is not available but there is a actionMethod(Event) we take this. That makes us
// more specification compliant than the JDK itself because this one will fail in such a case.
try
{
actionMethod = targetClass.getMethod(action, null);
}
catch(NoSuchMethodException nsme)
{
// Note: If we want to be really strict the specification says that a no-argument method should
// accept an EventObject (or subclass I guess). However since the official implementation is broken
// anyways, it's more flexible without the EventObject restriction and we are compatible on everything
// else this can stay this way.
if(arguments != null && arguments.length >= 1/* && arguments[0] instanceof EventObject*/) {
Class[] targetArgTypes = new Class[] { initClass(arguments[0].getClass()) };
while(targetArgTypes[0] != null) {
try
{
// If no property exists we expect the first element of the arguments to be
// an EventObject which is then applied to the target method.
actionMethod = targetClass.getMethod(action, targetArgTypes);
return actionMethod.invoke(target, new Object[] { arguments[0] });
}
catch(NoSuchMethodException nsme2)
{
}
targetArgTypes[0] = nextClass(targetArgTypes[0]);
}
}
}
// If we do not have a Method instance at this point this means that all our tries
// failed. The JDK throws an ArrayIndexOutOfBoundsException in this case.
if(actionMethod == null)
throw new ArrayIndexOutOfBoundsException(0);
// Invoke target.action(property)
return actionMethod.invoke(target, new Object[] {val});
return actionMethod.invoke(target, null);
} catch(InvocationTargetException ite) {
throw new RuntimeException(ite.getCause());
} catch(IllegalAccessException iae) {
// Cannot happen because we always use getMethod() which returns public
// methods only. Otherwise there is something seriously broken in
// GNU Classpath.
throw (InternalError) new InternalError("Non-public method was invoked.").initCause(iae);
}
}
/**
* <p>Returns the primitive type for every wrapper class or the
* class itself if it is no wrapper class.</p>
*
* <p>This is needed because to be able to find both kinds of methods:
* One that takes a wrapper class as the first argument and one that
* accepts a primitive instead.</p>
*/
private Class initClass(Class klass) {
if(klass == Boolean.class) {
return Boolean.TYPE;
} else if(klass == Byte.class) {
return Byte.TYPE;
} else if(klass == Short.class) {
return Short.TYPE;
} else if(klass == Integer.class) {
return Integer.TYPE;
} else if(klass == Long.class) {
return Long.TYPE;
} else if(klass == Float.class) {
return Float.TYPE;
} else if(klass == Double.class) {
return Double.TYPE;
} else {
return klass;
}
}
/**
* Construct a new object to dispatch events.
*
*
* @param klass
* @return
*/
private Class nextClass(Class klass) {
if(klass == Boolean.TYPE) {
return Boolean.class;
} else if(klass == Byte.TYPE) {
return Byte.class;
} else if(klass == Short.TYPE) {
return Short.class;
} else if(klass == Integer.TYPE) {
return Integer.class;
} else if(klass == Long.TYPE) {
return Long.class;
} else if(klass == Float.TYPE) {
return Float.class;
} else if(klass == Double.TYPE) {
return Double.class;
} else {
return klass.getSuperclass();
}
}
/**
* <p>Constructs an implementation of <code>listenerInterface</code>
* to dispatch events.</p>
*
* <p>You can use such an implementation to simply call a public
* no-argument method of an arbitrary target object or to forward
* the first argument of the listener method to the target method.</p>
*
* <p>Call this method like:</p>
* <code>
* button.addActionListener((ActionListener)
* EventHandler.create(ActionListener.class, target, "dispose"));
* </code>
*
* <p>to achieve the following behavior:</p>
* <code>
* button.addActionListener(new ActionListener() {
* public void actionPerformed(ActionEvent ae) {
* target.dispose();
* }
* });
* </code>
*
* <p>That means if you need a listener implementation that simply calls a
* a no-argument method on a given instance for <strong>each</strong>
* method of the listener interface.</p>
*
* <p>Note: The <code>action</code> is interpreted as a method name. If your target object
* has no no-argument method of the given name the EventHandler tries to find
* a method with the same name but which can accept the first argument of the
* listener method. Usually this will be an event object but any other object
* will be forwarded, too. Keep in mind that using a property name instead of a
* real method here is wrong and will throw an <code>ArrayIndexOutOfBoundsException</code>
* whenever one of the listener methods is called.<p/>
*
* Equivalent to:
* create(listenerInterface, target, action, null, null)
*
* I.e. all listenerInterface methods are mapped to
* target.action(EventObject) or target.action(), if the first doesn't
* exist.
* <p>The <code>EventHandler</code> will automatically convert primitives
* to their wrapper class and vice versa. Furthermore it will call
* a target method if it accepts a superclass of the type of the
* first argument of the listener method.</p>
*
* <p>In case that the method of the target object throws an exception
* it will be wrapped in a <code>RuntimeException</code> and thrown out
* of the listener method.</p>
*
* <p>In case that the method of the target object cannot be found an
* <code>ArrayIndexOutOfBoundsException</code> will be thrown when the
* listener method is invoked.</p>
*
* <p>A call to this method is equivalent to:
* <code>create(listenerInterface, target, action, null, null)</code></p>
*
* @param listenerInterface Listener interface to implement.
* @param target Object to invoke action on.
@ -306,14 +469,82 @@ public class EventHandler implements InvocationHandler
}
/**
* Construct a new object to dispatch events.
* <p>Constructs an implementation of <code>listenerInterface</code>
* to dispatch events.</p>
*
* Equivalent to:
* create(listenerInterface, target, action, eventPropertyName, null)
*
* I.e. all listenerInterface methods are mapped to
* target.action(event.getEventPropertyName)
* <p>Use this method if you want to create an implementation that retrieves
* a property value from the <b>first</b> argument of the listener method
* and applies it to the target's property or method. This first argument
* of the listener is usually an event object but any other object is
* valid, too.</p>
*
* <p>You can set the value of <code>eventPropertyName</code> to "prop"
* to denote the retrieval of a property named "prop" from the event
* object. In case that no such property exists the <code>EventHandler</code>
* will try to find a method with that name.</p>
*
* <p>If you set <code>eventPropertyName</code> to a value like this "a.b.c"
* <code>EventHandler</code> will recursively evaluate the properties "a", "b"
* and "c". Again if no property can be found the <code>EventHandler</code>
* tries a method name instead. This allows mixing the names, too: "a.toString"
* will retrieve the property "a" from the event object and will then call
* the method "toString" on it.</p>
*
* <p>An exception thrown in any of these methods will provoke a
* <code>RuntimeException</code> to be thrown which contains an
* <code>InvocationTargetException</code> containing the triggering exception.</p>
*
* <p>If you set <code>eventPropertyName</code> to a non-null value the
* <code>action</code> parameter will be interpreted as a property name
* or a method name of the target object.</p>
*
* <p>Any object retrieved from the event object and applied to the
* target will converted from primitives to their wrapper class or
* vice versa or applied to a method that accepts a superclass
* of the object.</p>
*
* <p>Examples:</p>
* <p>The following code:</p><code>
* button.addActionListener(
* new ActionListener() {
* public void actionPerformed(ActionEvent ae) {
* Object o = ae.getSource().getClass().getName();
* textField.setText((String) o);
* }
* });
* </code>
*
* <p>Can be expressed using the <code>EventHandler</code> like this:</p>
* <p>
* <code>button.addActionListener((ActionListener)
* EventHandler.create(ActionListener.class, textField, "text", "source.class.name");
* <code>
* </p>
*
* <p>As said above you can specify the target as a method, too:</p>
* <p>
* <code>button.addActionListener((ActionListener)
* EventHandler.create(ActionListener.class, textField, "setText", "source.class.name");
* <code>
* </p>
*
* <p>Furthermore you can use method names in the property:</p>
* <p>
* <code>button.addActionListener((ActionListener)
* EventHandler.create(ActionListener.class, textField, "setText", "getSource.getClass.getName");
* <code>
* </p>
*
* <p>Finally you can mix names:</p>
* <p>
* <code>button.addActionListener((ActionListener)
* EventHandler.create(ActionListener.class, textField, "setText", "source.getClass.name");
* <code>
* </p>
*
* <p>A call to this method is equivalent to:
* <code>create(listenerInterface, target, action, null, null)</code>
* </p>
*
* @param listenerInterface Listener interface to implement.
* @param target Object to invoke action on.
@ -327,41 +558,27 @@ public class EventHandler implements InvocationHandler
return create(listenerInterface, target, action, eventPropertyName, null);
}
/**
* Construct a new object to dispatch events.
* <p>Constructs an implementation of <code>listenerInterface</code>
* to dispatch events.</p>
*
* This creates an object that acts as a proxy for the method
* listenerMethodName in listenerInterface. When the listener method is
* activated, the object extracts eventPropertyName from the event. Then it
* passes the property to the method target.setAction, or target.action if
* action is not a property with a setter.
*
* For example, EventHandler.create(MouseListener.class, test, "pushed",
* "button", "mouseClicked") generates a proxy object that implements
* MouseListener, at least for the method mouseClicked(). The other methods
* of MouseListener are null operations. When mouseClicked is invoked, the
* generated object extracts the button property from the MouseEvent,
* i.e. event.getButton(), and calls test.setPushed() with the result. So under
* the covers the following happens:
*
* <CODE>
* object.mouseClicked(MouseEvent e) { test.setPushed(e.getButton()); }
* </CODE>
*
* The Sun spec specifies a hierarchical property naming scheme. Generally
* if the property is a.b.c, this corresponds to event.getA().getB().getC()
* or event.getA().getB().isC(). I don't see how you specify an indexed
* property, though. This may be a limitation of the Sun implementation as
* well. The spec doesn't seem to address it.
* <p>Besides the functionality described for {@link create(Class, Object, String)}
* and {@link create(Class, Object, String, String)} this method allows you
* to filter the listener method that should have an effect. Look at these
* method's documentation for more information about the <code>EventHandler</code>'s
* usage.</p>
*
* If eventPropertyName is null, EventHandler instead uses the event object
* in place of a property, i.e. it calls target.action(EventObject). If
* there is no method named action taking an EventObject argument,
* EventHandler looks for a method target.action() taking no arguments.
*
* If listenerMethodName is null, every method in listenerInterface gets
* mapped to target.action, rather than the specified listener method.
* <p>If you want to call <code>dispose</code> on a <code>JFrame</code> instance
* when the <code>WindowListener.windowClosing()</code> method was invoked use
* the following code:</p>
* <p>
* <code>
* EventHandler.create(WindowListener.class, jframeInstance, "dispose", null, "windowClosing");
* </code>
* </p>
*
* <p>A <code>NullPointerException</code> is thrown if the <code>listenerInterface</code>
* or <code>target</code> argument are <code>null</code>.
*
* @param listenerInterface Listener interface to implement.
* @param target Object to invoke action on.