How do I listen for a constrained JavaBean prop...

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The constrained property change is fired when a bean's value is about to change. When aVetoableChangeListener veto the value change the bean's value will be rolled-back to the previous value. In this example we have a constrained property called interest.

package org.kodejava.example.bean;

import java.beans.VetoableChangeSupport;
import java.beans.PropertyVetoException;

public class VetoBean {
    private double interest;

    private VetoableChangeSupport vcs = new VetoableChangeSupport(this);

    public VetoBean() {
        vcs.addVetoableChangeListener(new VetoChangeListener());
    }

    public double getInterest() {
        return interest;
    }

    public void setInterest(double interest) {
        try {
            vcs.fireVetoableChange("interest", new Double(this.interest), new Double(interest));

            this.interest = interest;
        } catch (PropertyVetoException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        VetoBean bean = new VetoBean();
        bean.setInterest(10.99);
        bean.setInterest(15.99);
        
        //
        // PropertyVetoException will be thrown beacuse the interest value 
        // should not exceed 20.00.
        //
        bean.setInterest(20.99);
    }
}

package org.kodejava.example.bean;

import java.beans.VetoableChangeListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyVetoException;

public class VetoChangeListener implements VetoableChangeListener {
    /**
     * This method gets called when a constrained property is changed.
     *
     * @param evt a <code>PropertyChangeEvent</code> object describing the
     *            event source and the property that has changed.
     * @throws java.beans.PropertyVetoException
     *          if the recipient wishes the property
     *          change to be rolled back.
     */
    public void vetoableChange(PropertyChangeEvent evt) throws PropertyVetoException {
        String eventName = evt.getPropertyName();
        if (eventName.equalsIgnoreCase("interest")) {
            double interest = ((Double) evt.getNewValue()).doubleValue();
            if (interest > 20.00) {
                throw new PropertyVetoException("Interest must be below 20.00", evt);                
            }
            System.out.println("Interest applied = " + interest);
        }
    }
}

转载于:https://my.oschina.net/jsan/blog/57638