Pojos中Javafx属性的全部支持

Question

关于在现有POJO类中添加Javafx属性支持有很多问题。可以通过在Javafx.beans.property.adapter软件包中使用适配器创建这些类的属性。但是，以这种方式创建的属性不会反映使用POJO类的设置方法进行的更改，除非将propertyChangeSupport添加到POJO类中。

。

有时不可能更改现有类，即使是，如果您有很多类，添加属性changeSupport也可能非常乏味。因此，我想分享一种不需要更改现有类的方法。

Answer 1

该解决方案的灵感来自Ben Galbraith的一篇文章，并使用了FactextJ。它绝对不需要对现有模型类的更改。安装extactj超出了本教程的范围，足以说所有主要的IDE支持它（将其安装在Eclipse中是微不足道的）。

此示例假定您的所有模型类都扩展了一个基类，在这种情况下称为基数。如果您的实施与此不同，那么您当然需要调整各个方面。

首先，我们将创建一个界面，该接口定义属性changeSupport所需的方法。

package com.mycompany.myapp;
import java.beans.PropertyChangeListener;
public interface ChangeSupport {
    // Add listener for all properties
    public void addPropertyChangeListener(PropertyChangeListener listener);
    // Remove listener for all properties
    public void removePropertyChangeListener(PropertyChangeListener listener);
    // Add listener for specific property
    public void addPropertyChangeListener(String propertyName, PropertyChangeListener listener);
    // Remove listener for specific property
    public void removePropertyChangeListener(String propertyName, PropertyChangeListener listener);
    // Fire change event for specific property
    public void firePropertyChange(String propertyName, Object oldValue, Object newValue);
    // Check if property has any listeners attached
    public boolean hasListeners(String propertyName);
}

接下来，我们将创建该接口的实现。

package com.mycompany.myapp;
import com.mycompany.myapp.model.BaseEntity;
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;
public class ChangeSupportImpl implements ChangeSupport {
    // Declared transient as there is no need to serialize these fields
    private transient PropertyChangeSupport propertyChangeSupport;
    private final transient Object source;
    public ChangeSupportImpl() {
        super();
        this.source = this;
    }
    // Needed for annotation-style aspect
    public ChangeSupportImpl(final BaseEntity baseEntity) {
        super();
        this.source = baseEntity;
    }
    @Override
    public void addPropertyChangeListener(final PropertyChangeListener listener) {
        // PropertyChangeSupport is loaded lazily
        if (this.propertyChangeSupport == null)
            this.propertyChangeSupport = new PropertyChangeSupport(this.source);
        this.propertyChangeSupport.addPropertyChangeListener(listener);
    }
    @Override
    public void removePropertyChangeListener(final PropertyChangeListener listener) {
        if (this.propertyChangeSupport != null)
            this.propertyChangeSupport.removePropertyChangeListener(listener);
    }
    @Override
    public void addPropertyChangeListener(final String propertyName, final PropertyChangeListener listener) {
        // PropertyChangeSupport is loaded lazily
        if (this.propertyChangeSupport == null)
            this.propertyChangeSupport = new PropertyChangeSupport(this.source);
        this.propertyChangeSupport.addPropertyChangeListener(propertyName, listener);
    }
    @Override
    public void removePropertyChangeListener(final String propertyName, final PropertyChangeListener listener) {
        if (this.propertyChangeSupport != null)
            this.propertyChangeSupport.removePropertyChangeListener(propertyName, listener);
    }
    @Override
    public void firePropertyChange(final String propertyName, final Object oldValue, final Object newValue) {
        if (this.propertyChangeSupport != null)
            this.propertyChangeSupport.firePropertyChange(propertyName, oldValue, newValue);
    }
    @Override
    public boolean hasListeners(final String propertyName) {
        return this.propertyChangeSupport != null && (this.propertyChangeSupport.hasListeners(propertyName)
                || this.propertyChangeSupport.hasListeners(null));
    }
}

最后，我们将创建一个方面，将属性changeSupport添加到基数类中。该方面使用自定义类反射仪来获取属性的旧值。您可以使用自己喜欢的任何实用程序或普通的旧Java反射（尽管可能会影响性能）。

package com.mycompany.myapp;
import com.mycompany.myapp.model.BaseEntity;
import com.mycompany.myapp.util.ReflectUtils;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.DeclareMixin;
import java.util.Objects;
@Aspect
public class BaseEntityObservabilityAspect {
    @DeclareMixin("com.mycompany.myapp.model.BaseEntity")
    public static ChangeSupport createChangeSupportImplementation(final BaseEntity baseEntity) {
        return new ChangeSupportImpl(baseEntity);
    }
    // Intercept setters in all BaseEntity objects in order to notify about property change
    @Around("this(baseEntity) && execution(public void set*(*))")
    public void firePropertyChange(final BaseEntity baseEntity,
            final ProceedingJoinPoint joinPoint) throws Throwable {
        // Get property name from method name
        final String setterName = joinPoint.getSignature().getName();
        final String property = setterName.substring(3, 4).toLowerCase() + setterName.substring(4);
        final ChangeSupport support = (ChangeSupport)baseEntity;
        if (support.hasListeners(property)) {
            // Get old value via reflection
            final Object oldValue = ReflectUtils.invokeGetter(baseEntity, property);
            // Proceed with the invocation of the method
            joinPoint.proceed();
            // New value is the first (and only) argument of this method
            final Object newValue = joinPoint.getArgs()[0];
            // Fire only if value actually changed
            if (!Objects.equals(oldValue, newValue))
                support.firePropertyChange(property, oldValue, newValue);
        } else {
            // No listeners have been registered with BaseEntity, so there is no need to fire property change event
            joinPoint.proceed();
        }
    }
}

如果您由于某种原因无法使用注释样式，则使用ActectJ Code样式是相同的。

package com.mycompany.myapp;
import java.util.Objects;
import com.mycompany.myapp.model.BaseEntity;
import com.mycompany.myapp.util.ReflectUtils;
public aspect BaseEntityObservabilityAspect {
    declare parents: BaseEntity extends ChangeSupportImpl;
    // Intercept setters in all BaseEntity objects in order to notify about property change
    void around(final BaseEntity entity, final ChangeSupport support):
            this(entity) && this(support) && execution(public void BaseEntity+.set*(*)) {
        // Get property name from method name
        final String setterName = thisJoinPoint.getSignature().getName();
        final String property = setterName.substring(3, 4).toLowerCase() + setterName.substring(4);
        if (support.hasListeners(property)) {
            final Object oldValue;
            try {
                // Get old value via reflection
                oldValue = ReflectUtils.invokeGetter(entity, property);
            } catch (final Throwable e) {
                // Should not happen
                proceed(entity, support);
                return;
            }
            // Proceed with the invocation of the method
            proceed(entity, support);
            // New value is the first (and only) argument of this method
            final Object newValue = thisJoinPoint.getArgs()[0];
            // Fire only if value actually changed
            if (!Objects.equals(oldValue, newValue))
                support.firePropertyChange(property, oldValue, newValue);
        } else {
            // No listeners have been registered with BaseEntity, so there is no need to fire property change event
            proceed(entity, support);
        }
    }
}