libjava/java/beans/PropertyDescriptor.java

/* java.beans.PropertyDescriptor
   Copyright (C) 1998, 2001 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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any later version.
 
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

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02111-1307 USA.

Linking this library statically or dynamically with other modules is
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permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
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this exception to your version of the library, but you are not
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exception statement from your version. */


package java.beans;

import java.lang.reflect.Method;

/**
 ** PropertyDescriptor describes information about a JavaBean property,
 ** by which we mean a property that has been exposed via a pair of
 ** get and set methods.  (There may be no get method, which means
 ** the property is write-only, or no set method, which means the
 ** the property is read-only.)<P>
 **
 ** The constraints put on get and set methods are:<P>
 ** <OL>
 ** <LI>A get method must have signature
 **     <CODE>&lt;propertyType&gt; &lt;getMethodName&gt;()</CODE></LI>
 ** <LI>A set method must have signature
 **     <CODE>void &lt;setMethodName&gt;(&lt;propertyType&gt;)</CODE></LI>
 ** <LI>Either method type may throw any exception.</LI>
 ** <LI>Both methods must be public.</LI>
 ** </OL>
 **
 ** @author John Keiser
 ** @since JDK1.1
 ** @version 1.1.0, 26 Jul 1998
 **/

public class PropertyDescriptor extends FeatureDescriptor {
  Class propertyType;
  Method getMethod;
  Method setMethod;
  
  Class propertyEditorClass;
  boolean bound;
  boolean constrained;
  
  PropertyDescriptor(String name) {
    setName(name);
  }
  
  /** Create a new PropertyDescriptor by introspection.
   ** This form of constructor creates the PropertyDescriptor by
   ** looking for a getter method named <CODE>get&lt;name&gt;()</CODE>
   ** (or, optionally, if the property is boolean,
   ** <CODE>is&lt;name&gt;()</CODE>) and
   ** <CODE>set&lt;name&gt;()</CODE> in class
   ** <CODE>&lt;beanClass&gt;</CODE>, where &lt;name&gt; has its
   ** first letter capitalized by the constructor.<P>
   **
   ** <B>Implementation note:</B> If there is both are both isXXX and
   ** getXXX methods, the former is used in preference to the latter.
   ** We do not check that an isXXX method returns a boolean. In both
   ** cases, this matches the behaviour of JDK 1.4<P>
   **
   ** @param name the programmatic name of the property, usually
   **             starting with a lowercase letter (e.g. fooManChu
   **             instead of FooManChu).
   ** @param beanClass the class the get and set methods live in.
   ** @exception IntrospectionException if the methods are not found 
   **            or invalid.
   **/
  public PropertyDescriptor(String name, Class beanClass) 
    throws IntrospectionException 
  {
    setName(name);
    if (name.length() == 0) {
      throw new IntrospectionException("empty property name");
    }
    String caps = Character.toUpperCase(name.charAt(0)) + name.substring(1);
    findMethods(beanClass, "is" + caps, "get" + caps, "set" + caps);
    if (getMethod == null) {
      throw new IntrospectionException("Cannot find an is" + caps + 
				       " or get" + caps + " method");
    }
    if (setMethod == null) {
      throw new IntrospectionException("Cannot find a " + caps + " method");
    }
    checkMethods();
  }
  
  /** Create a new PropertyDescriptor by introspection.
   ** This form of constructor allows you to specify the
   ** names of the get and set methods to search for.<P>
   **
   ** <B>Implementation note:</B> If there is a get method (or
   ** boolean isXXX() method), then the return type of that method
   ** is used to find the set method.  If there is no get method,
   ** then the set method is searched for exhaustively.<P>
   **
   ** <B>Spec note:</B>
   ** If there is no get method and multiple set methods with
   ** the same name and a single parameter (different type of course),
   ** then an IntrospectionException is thrown.  While Sun's spec
   ** does not state this, it can make Bean behavior different on
   ** different systems (since method order is not guaranteed) and as
   ** such, can be treated as a bug in the spec.  I am not aware of
   ** whether Sun's implementation catches this.
   **
   ** @param name the programmatic name of the property, usually
   **             starting with a lowercase letter (e.g. fooManChu
   **             instead of FooManChu).
   ** @param beanClass the class the get and set methods live in.
   ** @param getMethodName the name of the get method.
   ** @param setMethodName the name of the set method.
   ** @exception IntrospectionException if the methods are not found 
   **            or invalid.
   **/
  public PropertyDescriptor(String name, Class beanClass, 
			    String getMethodName, String setMethodName) 
    throws IntrospectionException 
  {
    setName(name);
    findMethods(beanClass, getMethodName, null, setMethodName);
    if (getMethod == null && getMethodName != null) {
      throw new IntrospectionException("Cannot find a getter method called " + 
				       getMethodName);
    }
    if (setMethod == null && setMethodName != null) {
      throw new IntrospectionException("Cannot find a setter method called " + 
				       setMethodName);
    }
    checkMethods();
  }
  
  /** Create a new PropertyDescriptor using explicit Methods.
   ** Note that the methods will be checked for conformance to standard
   ** Property method rules, as described above at the top of this class.
   ** 
   ** @param name the programmatic name of the property, usually
   **             starting with a lowercase letter (e.g. fooManChu
   **             instead of FooManChu).
   ** @param getMethod the get method.
   ** @param setMethod the set method.
   ** @exception IntrospectionException if the methods are not found 
   **            or invalid.
   **/
  public PropertyDescriptor(String name, Method getMethod, Method setMethod)
    throws IntrospectionException 
  {
    setName(name);
    this.getMethod = getMethod;
    this.setMethod = setMethod;
    if (getMethod != null) {
      this.propertyType = getMethod.getReturnType();
    } 
    else if (setMethod != null) {
      this.propertyType = setMethod.getParameterTypes()[0];
    }
    checkMethods();
  }
  
  /** Get the property type.
   ** This is the type the get method returns and the set method
   ** takes in.
   **/
  public Class getPropertyType() {
    return propertyType;
  }
  
  /** Get the get method.  Why they call it readMethod here and
   ** get everywhere else is beyond me.
   **/
  public Method getReadMethod() {
    return getMethod;
  }
  
  /** Get the set method.  Why they call it writeMethod here and
   ** set everywhere else is beyond me.
   **/
  public Method getWriteMethod() {
    return setMethod;
  }
  
  /** Get whether the property is bound.  Defaults to false. **/
  public boolean isBound() {
    return bound;
  }
  
  /** Set whether the property is bound.
   ** As long as the the bean implements addPropertyChangeListener() and
   ** removePropertyChangeListener(), setBound(true) may safely be called.<P>
   ** If these things are not true, then the behavior of the system
   ** will be undefined.<P>
   **
   ** When a property is bound, its set method is required to fire the
   ** <CODE>PropertyChangeListener.propertyChange())</CODE> event
   ** after the value has changed.
   ** @param bound whether the property is bound or not.
   **/
  public void setBound(boolean bound) {
    this.bound = bound;
  }
  
  /** Get whether the property is constrained.  Defaults to false. **/
  public boolean isConstrained() {
    return constrained;
  }
  
  /** Set whether the property is constrained.
   ** If the set method throws <CODE>java.beans.PropertyVetoException</CODE>
   ** (or subclass thereof) and the bean implements addVetoableChangeListener()
   ** and removeVetoableChangeListener(), then setConstrained(true) may safely
   ** be called.  Otherwise, the system behavior is undefined.
   ** <B>Spec note:</B> given those strict parameters, it would be nice if it
   ** got set automatically by detection, but oh well.<P>
   ** When a property is constrained, its set method is required to:<P>
   ** <OL>
   ** <LI>Fire the <CODE>VetoableChangeListener.vetoableChange()</CODE>
   **     event notifying others of the change and allowing them a chance to
   **     say it is a bad thing.</LI>
   ** <LI>If any of the listeners throws a PropertyVetoException, then
   **     it must fire another vetoableChange() event notifying the others
   **     of a reversion to the old value (though, of course, the change
   **     was never made).  Then it rethrows the PropertyVetoException and
   **     exits.</LI>
   ** <LI>If all has gone well to this point, the value may be changed.</LI>
   ** </OL>
   ** @param constrained whether the property is constrained or not.
   **/
  public void setConstrained(boolean constrained) {
    this.constrained = constrained;
  }
  
  /** Get the PropertyEditor class.  Defaults to null. **/
  public Class getPropertyEditorClass() {
    return propertyEditorClass;
  }
  
  /** Set the PropertyEditor class.  If the class does not implement
   ** the PropertyEditor interface, you will likely get an exception
   ** late in the game.
   ** @param propertyEditorClass the PropertyEditor class for this 
   **        class to use.
   **/
  public void setPropertyEditorClass(Class propertyEditorClass) {
    this.propertyEditorClass = propertyEditorClass;
  }
  
  private void findMethods(Class beanClass, String getMethodName1, 
			   String getMethodName2, String setMethodName) 
    throws IntrospectionException 
  {
    try {
      // Try the first get method name
      if (getMethodName1 != null) {
	try {
	  getMethod = beanClass.getMethod(getMethodName1, new Class[0]);
	} 
	catch (NoSuchMethodException e) {
	}
      }

      // Fall back to the second get method name
      if (getMethod == null && getMethodName2 != null) {
	try {
	  getMethod = beanClass.getMethod(getMethodName2, new Class[0]);
	} 
	catch (NoSuchMethodException e) {
	}
      }

      // Try the set method name
      if (setMethodName != null) {
	if (getMethod != null) {
	  // If there is a get method, use its return type to help
	  // select the corresponding set method.
	  Class propertyType = getMethod.getReturnType();
	  if (propertyType == Void.TYPE) {
	    String msg = "The property's read method has return type 'void'";
	    throw new IntrospectionException(msg);
	  }
	  
	  Class[] setArgs = new Class[]{propertyType};
	  try {
	    setMethod = beanClass.getMethod(setMethodName, setArgs);
	  } 
	  catch (NoSuchMethodException e) {
	  }
	}
	else if (getMethodName1 == null && getMethodName2 == null) {
	  // If this is a write-only property, choose the first set method
	  // with the required name, one parameter and return type 'void'
	  Method[] methods = beanClass.getMethods();
	  for (int i = 0; i < methods.length; i++) {
	    if (methods[i].getName().equals(setMethodName) &&
		methods[i].getParameterTypes().length == 1 &&
		methods[i].getReturnType() == Void.TYPE) {
	      setMethod = methods[i];
	      break;
	    }
	  }
	}
      }
    } 
    catch (SecurityException e) {
      // FIXME -- shouldn't we just allow SecurityException to propagate?
      String msg = "SecurityException thrown on attempt to access methods.";
      throw new IntrospectionException(msg);
    }
  }

  private void checkMethods() 
    throws IntrospectionException
  {
    if (getMethod != null) {
      if (getMethod.getParameterTypes().length > 0) {
	throw new IntrospectionException("get method has parameters");
      }
      this.propertyType = getMethod.getReturnType();
      if (propertyType == Void.TYPE) {
	throw new IntrospectionException("get method has void return type");
      }
    }
    if (setMethod != null) {
      if (setMethod.getParameterTypes().length != 1) {
	String msg = "set method does not have exactly one parameter"; 
	throw new IntrospectionException(msg);
      }
      if (getMethod == null) {
	propertyType = setMethod.getParameterTypes()[0];
      }
      else {
	if (!propertyType.equals(setMethod.getParameterTypes()[0])) {
	  String msg = "set and get methods do not share the same type";
	  throw new IntrospectionException(msg);
	}
	if ((!getMethod.getDeclaringClass().
	     isAssignableFrom(setMethod.getDeclaringClass())) &&
	    (!setMethod.getDeclaringClass().
	     isAssignableFrom(getMethod.getDeclaringClass()))) {
	  String msg = "set and get methods are not in the same class.";
	  throw new IntrospectionException(msg);
	}
      }
    }
  }
}