jface databinding/PojoBindable实现对POJO对象的支持

红太狼 2022-07-13 03:19 137阅读 0赞

# POJO对象无法被监控 #

在jface databinding中，将普通的java bean(有get/set方法但没有通过PropertyChangeSupport实现属性监控)定义为POJO对象。  
我们可以对POJO对象通过`PojoProperties.value(String propertyName)`方法提供IObservableValue实例，但返回的PojoValueProperty实例并没有真正实现对POJO对象的监控(参见PojoValueProperty源码)。  
所以UI组件与POJO对象之间建立的数据绑定是单向的，UI组件的数据变化可以同步到POJO对象，但反过来不行。  
下面这个示例可以演示这个区别，  
运行程序，程序启动时，Text组件的内容被更新成POJO对象属性相同的值。  
但按”测试”按钮，修改了POJO对象的属性，但Text控件的值并没有同步变化。

package testwb;
    
    import org.eclipse.jface.dialogs.Dialog;
    import org.eclipse.jface.dialogs.IDialogConstants;
    import org.eclipse.swt.graphics.Point;
    import org.eclipse.swt.widgets.Composite;
    import org.eclipse.swt.widgets.Control;
    import org.eclipse.swt.widgets.Shell;
    import org.eclipse.swt.SWT;
    import org.eclipse.swt.widgets.Text;
    
    import org.eclipse.core.databinding.DataBindingContext;
    import org.eclipse.core.databinding.observable.value.IObservableValue;
    import org.eclipse.jface.databinding.swt.WidgetProperties;
    import org.eclipse.swt.widgets.Display;
    import org.eclipse.core.databinding.observable.Realm;
    import org.eclipse.jface.databinding.swt.DisplayRealm;
    import org.eclipse.swt.widgets.Button;
    import org.eclipse.swt.events.SelectionAdapter;
    import org.eclipse.swt.events.SelectionEvent;
    import org.eclipse.core.databinding.beans.PojoProperties;
    
    public class TestPojoBinding extends Dialog {
        
    
        /**
         * 数据对象定义
         * @author guyadong
         *
         */
        public class Configuration {
        
            private String name;
            public Configuration(String name) {
                super();
                this.name = name;
            }
    
            public String getName() {
                return name;
            }
    
            public void setName(String name) {
                this.name = name;
                System.out.printf("updated %s\n",this.name);
            }
        }
        private DataBindingContext m_bindingContext;
        /**
         * 成员变量：数据对象
         */
        protected Configuration editorConfig=new Configuration("hello!");
        private Text myNametext;
    
        /**
         * Create the dialog.
         * @param parentShell
         */
        public TestPojoBinding(Shell parentShell) {
            super(parentShell);
        }
    
        /**
         * Create contents of the dialog.
         * @param parent
         */
        @Override
        protected Control createDialogArea(Composite parent) {
            Composite container = (Composite) super.createDialogArea(parent);
            container.setLayout(null);
    
            Button btnNewButton = new Button(container, SWT.NONE);
            btnNewButton.addSelectionListener(new SelectionAdapter() {
                @Override
                public void widgetSelected(SelectionEvent e) {
                    editorConfig.setName("word");
                }
            });
            btnNewButton.setBounds(38, 154, 80, 27);
            btnNewButton.setText("测试");
    
            myNametext = new Text(container, SWT.BORDER);
            myNametext.setBounds(38, 27, 80, 23);
    
            return container;
        }
    
        /**
         * Create contents of the button bar.
         * @param parent
         */
        @Override
        protected void createButtonsForButtonBar(Composite parent) {
            createButton(parent, IDialogConstants.OK_ID, IDialogConstants.OK_LABEL, true);
            createButton(parent, IDialogConstants.CANCEL_ID, IDialogConstants.CANCEL_LABEL, false);
            m_bindingContext = initDataBindings();
        }
    
        /**
         * Return the initial size of the dialog.
         */
        @Override
        protected Point getInitialSize() {
            return new Point(362, 298);
        }
        public static void main(String[] args) {
            Display display = Display.getDefault();
            Realm.runWithDefault(DisplayRealm.getRealm(display), new Runnable() {
                public void run() {
                    try {
                        TestPojoBinding setting = new TestPojoBinding(null);
                        setting.open();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            });
        }
        protected DataBindingContext initDataBindings() {
            DataBindingContext bindingContext = new DataBindingContext();
            IObservableValue observeTextMyNametextObserveWidget = WidgetProperties.text(SWT.Modify).observe(myNametext);
            IObservableValue nameEditorConfigObserveValue = PojoProperties.value("name").observe(editorConfig);
            bindingContext.bindValue(observeTextMyNametextObserveWidget, nameEditorConfigObserveValue, null, null);
            return bindingContext;
        }
    }

# PropertyChangeSupport #

如果想要实现上面例子中数据对象属性与Text组件的内容双向同步绑定。解决方案之一就是改造数据对象Person，通过PropertyChangeSupport实现属性监控。

package testwb;
    
    import org.eclipse.jface.dialogs.Dialog;
    import org.eclipse.jface.dialogs.IDialogConstants;
    import org.eclipse.swt.graphics.Point;
    import org.eclipse.swt.widgets.Composite;
    import org.eclipse.swt.widgets.Control;
    import org.eclipse.swt.widgets.Shell;
    import org.eclipse.swt.SWT;
    import org.eclipse.swt.widgets.Text;
    
    import java.beans.PropertyChangeListener;
    import java.beans.PropertyChangeSupport;
    
    import org.eclipse.core.databinding.DataBindingContext;
    import org.eclipse.core.databinding.observable.value.IObservableValue;
    import org.eclipse.jface.databinding.swt.WidgetProperties;
    import org.eclipse.swt.widgets.Display;
    import org.eclipse.core.databinding.observable.Realm;
    import org.eclipse.jface.databinding.swt.DisplayRealm;
    import org.eclipse.swt.widgets.Button;
    import org.eclipse.swt.events.SelectionAdapter;
    import org.eclipse.swt.events.SelectionEvent;
    import org.eclipse.core.databinding.beans.BeanProperties;
    
    public class TestPojoBinding2 extends Dialog {
        
        public class ModelObject {
        
            private final PropertyChangeSupport changeSupport =
                    new PropertyChangeSupport(this);
    
            public void addPropertyChangeListener(PropertyChangeListener
                    listener) {
                changeSupport.addPropertyChangeListener(listener);
            }
    
            public void removePropertyChangeListener(PropertyChangeListener
                    listener) {
                changeSupport.removePropertyChangeListener(listener);
            }
    
            protected void firePropertyChange(String propertyName, Object oldValue,
                    Object newValue) {
                changeSupport.firePropertyChange(propertyName, oldValue, newValue);
            }
        }
        /**
         * 数据对象定义，继承ModelObject类，获取属性改变时被监控能力
         * @author guyadong
         *
         */
        public class Person extends ModelObject {
        
            private String name;
            public Person(String name) {
                super();
                this.name = name;
            }
    
            public String getName() {
                return name;
            }
    
            public void setName(String name) {
                // 修改set方法，在修改属性的同时，调用firePropertyChange通知所有侦听器属性已经改变
                firePropertyChange("name", this.name, this.name = name);
                System.out.printf("updated %s\n",this.name);
            }
        }
        private DataBindingContext m_bindingContext;
        /**
         * 成员变量：数据对象
         */
        protected Person editorConfig=new Person("hello!");
        private Text myNametext;
    
        /**
         * Create the dialog.
         * @param parentShell
         */
        public TestPojoBinding2(Shell parentShell) {
            super(parentShell);
        }
    
        /**
         * Create contents of the dialog.
         * @param parent
         */
        @Override
        protected Control createDialogArea(Composite parent) {
            Composite container = (Composite) super.createDialogArea(parent);
            container.setLayout(null);
    
            Button btnNewButton = new Button(container, SWT.NONE);
            btnNewButton.addSelectionListener(new SelectionAdapter() {
                @Override
                public void widgetSelected(SelectionEvent e) {
                    editorConfig.setName("word");
                }
            });
            btnNewButton.setBounds(38, 154, 80, 27);
            btnNewButton.setText("测试");
    
            myNametext = new Text(container, SWT.BORDER);
            myNametext.setBounds(38, 27, 80, 23);
    
            return container;
        }
    
        /**
         * Create contents of the button bar.
         * @param parent
         */
        @Override
        protected void createButtonsForButtonBar(Composite parent) {
            createButton(parent, IDialogConstants.OK_ID, IDialogConstants.OK_LABEL, true);
            createButton(parent, IDialogConstants.CANCEL_ID, IDialogConstants.CANCEL_LABEL, false);
            m_bindingContext = initDataBindings();
        }
    
        /**
         * Return the initial size of the dialog.
         */
        @Override
        protected Point getInitialSize() {
            return new Point(362, 298);
        }
        public static void main(String[] args) {
            Display display = Display.getDefault();
            Realm.runWithDefault(DisplayRealm.getRealm(display), new Runnable() {
                public void run() {
                    try {
                        TestPojoBinding2 setting = new TestPojoBinding2(null);
                        setting.open();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            });
        }
        protected DataBindingContext initDataBindings() {
            DataBindingContext bindingContext = new DataBindingContext();
            // 为Text组件创建观察对象
            IObservableValue observeTextMyNametextObserveWidget = WidgetProperties.text(SWT.Modify).observe(myNametext);
            // 为数据对象属性创建观察对象
            IObservableValue nameEditorConfigObserveValue = BeanProperties.value("name").observe(editorConfig);
            // 数据绑定
            bindingContext.bindValue(observeTextMyNametextObserveWidget, nameEditorConfigObserveValue, null, null);
            //
            return bindingContext;
        }
    }

再运行程序，点击”测试”按钮，Text的值随着数据对象的属性同步改变了。

# PojoBindable #

上面这个方案已经实现了数据对象和UI组件的双向同步更新，但缺点就是需要对POJO对象进行改造，当项目中有多个POJO对象需要实现与UI组件的双同步更新时，这个工作量也是挺大的。  
有没有办法在不改变现有POJO对象的代码的情况下，实现双向同步的目标呢？  
有，解决方案就是本文的标题[jface databinding/PojoBindable][jface databinding_PojoBindable]。\[注意：这还是个实验项目，使用需谨慎\]  
PojoBindable利用ASM代码动态修改的技术，通过在运行时为POJO对象添加PropertyChangeSupport 的方法并修改setter方法，提供了一个途径让开发者在不修改自己的POJO类代码的情况下让POJO对象拥有完整的数据绑定能力。  
凡事都有代价，使用PojoBindable想不修改POJO对象代码就拥有PropertyChangeSupport能力的话，代价是什么呢？

## 要修改JVM的运行参数 ##

Pojo Bindable是一个Java Agent，所以为了使用PojoBindable，必须在java程序启动时指定jvm参数，用`-javaagent`参数指定使用PojoBindable

-javaagent:<your path>/org.eclipse.core.databinding.pojo.bindable_1.0.0.jar

需要`-Dbindable.packages`指定对哪些pojo对象进行修改java代码

-Dbindable.packages=org.eclipse.core.examples.databinding.pojo.bindable.model

## 需要 ASM支持 ##

必须将 [ObjectWeb ASM][]加入classpath

关于Pojo Bindable配置的更详细说明参见其官网原文：

[https://wiki.eclipse.org/JFace\_Data\_Binding/PojoBindable\#With\_Pojo\_Bindable][jface databinding_PojoBindable]

参考资料  
[《JFace Data Binding/PojoBindable》][JFace Data Binding_PojoBindable]  
[《AJFace Data Binding - Tutorial》][AJFace Data Binding - Tutorial]

[jface databinding_PojoBindable]: https://wiki.eclipse.org/JFace_Data_Binding/PojoBindable#With_Pojo_Bindable
[ObjectWeb ASM]: http://asm.ow2.org/
[JFace Data Binding_PojoBindable]: https://wiki.eclipse.org/JFace_Data_Binding/PojoBindable
[AJFace Data Binding - Tutorial]: http://www.vogella.com/tutorials/EclipseDataBinding/article.html#using-jface-data-binding